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  Subjects -> EARTH SCIENCES (Total: 652 journals)
    - EARTH SCIENCES (470 journals)
    - GEOLOGY (71 journals)
    - GEOPHYSICS (27 journals)
    - HYDROLOGY (21 journals)
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EARTH SCIENCES (470 journals)                  1 2 3 | Last

Showing 1 - 200 of 371 Journals sorted alphabetically
Acta Geochimica     Hybrid Journal   (Followers: 3)
Acta Geodaetica et Geophysica     Hybrid Journal   (Followers: 1)
Acta Geodaetica et Geophysica Hungarica     Full-text available via subscription   (Followers: 2)
Acta Geophysica     Open Access   (Followers: 6)
Acta Geotechnica     Hybrid Journal   (Followers: 6)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 3)
Advances in High Energy Physics     Open Access   (Followers: 21)
Advances In Physics     Hybrid Journal   (Followers: 18)
Aeolian Research     Hybrid Journal   (Followers: 5)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 12)
Algological Studies     Full-text available via subscription   (Followers: 2)
Alpine Botany     Hybrid Journal   (Followers: 3)
AMBIO     Hybrid Journal   (Followers: 13)
Anadolu University Journal of Science and Technology     Open Access  
Anales del Instituto de la Patagonia     Open Access   (Followers: 1)
Andean geology     Open Access   (Followers: 13)
Annales Henri Poincaré     Hybrid Journal   (Followers: 3)
Annales UMCS, Geographia, Geologia, Mineralogia et Petrographia     Open Access  
Annals of Geophysics     Full-text available via subscription   (Followers: 12)
Annals of GIS     Hybrid Journal   (Followers: 19)
Annals of Glaciology     Full-text available via subscription   (Followers: 3)
Annual Review of Marine Science     Full-text available via subscription   (Followers: 10)
Anthropocene     Hybrid Journal   (Followers: 3)
Anthropocene Review     Hybrid Journal   (Followers: 4)
Applied Clay Science     Hybrid Journal   (Followers: 4)
Applied Geochemistry     Hybrid Journal   (Followers: 11)
Applied Geomatics     Hybrid Journal   (Followers: 3)
Applied Geophysics     Hybrid Journal   (Followers: 7)
Applied Ocean Research     Hybrid Journal   (Followers: 4)
Applied Petrochemical Research     Open Access   (Followers: 2)
Applied Remote Sensing Journal     Open Access   (Followers: 33)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 34)
Arctic Science     Open Access   (Followers: 6)
Arctic, Antarctic, and Alpine Research     Full-text available via subscription   (Followers: 10)
Artificial Satellites : The Journal of Space Research Centre of Polish Academy of Sciences     Open Access   (Followers: 16)
Asia-Pacific Journal of Atmospheric Sciences     Hybrid Journal   (Followers: 20)
Asian Journal of Earth Sciences     Open Access   (Followers: 20)
Asian Review of Environmental and Earth Sciences     Open Access   (Followers: 1)
Atlantic Geology : Journal of the Atlantic Geoscience Society / Atlantic Geology : revue de la Société Géoscientifique de l'Atlantique     Full-text available via subscription   (Followers: 10)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 12)
Atmospheric and Climate Sciences     Open Access   (Followers: 25)
Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia     Hybrid Journal   (Followers: 11)
Boletim de Ciências Geodésicas     Open Access  
Boletín de Ciencias de la Tierra     Open Access   (Followers: 1)
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 10)
Bragantia     Open Access   (Followers: 2)
Bulletin of Earthquake Engineering     Hybrid Journal   (Followers: 10)
Bulletin of Geosciences     Open Access   (Followers: 8)
Bulletin of the Lebedev Physics Institute     Hybrid Journal   (Followers: 1)
Bulletin of the Seismological Society of America     Full-text available via subscription   (Followers: 21)
Bulletin of Volcanology     Hybrid Journal   (Followers: 17)
Cadernos de Geociências     Open Access  
Canadian Journal of Plant Science     Full-text available via subscription   (Followers: 15)
Canadian Mineralogist     Full-text available via subscription   (Followers: 3)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 20)
Carbonates and Evaporites     Hybrid Journal   (Followers: 3)
CATENA     Hybrid Journal   (Followers: 4)
Chemical Geology     Hybrid Journal   (Followers: 15)
Chemie der Erde - Geochemistry     Hybrid Journal   (Followers: 4)
Chinese Geographical Science     Hybrid Journal   (Followers: 5)
Chinese Journal of Oceanology and Limnology     Hybrid Journal   (Followers: 3)
Ciencias Espaciales     Open Access  
Climate and Development     Hybrid Journal   (Followers: 12)
Coastal Management     Hybrid Journal   (Followers: 24)
Cogent Geoscience     Open Access  
Comptes Rendus Geoscience     Full-text available via subscription   (Followers: 8)
Computational Geosciences     Hybrid Journal   (Followers: 12)
Computational Mathematics and Mathematical Physics     Hybrid Journal   (Followers: 1)
Computers and Geotechnics     Hybrid Journal   (Followers: 8)
Contemporary Trends in Geoscience     Open Access   (Followers: 3)
Continental Shelf Research     Hybrid Journal   (Followers: 8)
Contributions to Mineralogy and Petrology     Hybrid Journal   (Followers: 9)
Contributions to Plasma Physics     Hybrid Journal   (Followers: 3)
Coral Reefs     Hybrid Journal   (Followers: 16)
Cretaceous Research     Hybrid Journal   (Followers: 6)
Cybergeo : European Journal of Geography     Open Access   (Followers: 5)
Depositional Record     Open Access  
Developments in Geotectonics     Full-text available via subscription   (Followers: 3)
Developments in Quaternary Science     Full-text available via subscription   (Followers: 3)
Développement durable et territoires     Open Access   (Followers: 3)
Diatom Research     Hybrid Journal   (Followers: 1)
Doklady Physics     Hybrid Journal   (Followers: 1)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 10)
E&S Engineering and Science     Open Access  
E3S Web of Conferences     Open Access  
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 98)
Earth and Space Science     Open Access   (Followers: 10)
Earth Interactions     Full-text available via subscription   (Followers: 11)
Earth Science Research     Open Access   (Followers: 6)
Earth Sciences Research Journal     Open Access  
Earth Surface Dynamics (ESurf)     Open Access   (Followers: 4)
Earth Surface Processes and Landforms     Hybrid Journal   (Followers: 19)
Earth System Dynamics     Open Access   (Followers: 6)
Earth System Dynamics Discussions     Open Access   (Followers: 4)
Earth's Future     Open Access   (Followers: 1)
Earth, Planets and Space     Open Access   (Followers: 68)
Earthquake Engineering and Engineering Vibration     Hybrid Journal   (Followers: 6)
Earthquake Science     Hybrid Journal   (Followers: 9)
Earthquake Spectra     Full-text available via subscription   (Followers: 17)
Ecohydrology     Hybrid Journal   (Followers: 10)
Ecological Questions     Open Access   (Followers: 7)
Electromagnetics     Hybrid Journal   (Followers: 4)
Energy Efficiency     Hybrid Journal   (Followers: 11)
Energy Exploration & Exploitation     Full-text available via subscription   (Followers: 4)
Environmental Earth Sciences     Hybrid Journal   (Followers: 22)
Environmental Geology     Hybrid Journal   (Followers: 20)
Environmental Geosciences     Full-text available via subscription   (Followers: 3)
Environmental Geotechnics     Hybrid Journal   (Followers: 3)
Erwerbs-Obstbau     Hybrid Journal  
Estuaries and Coasts     Hybrid Journal   (Followers: 17)
Estuarine, Coastal and Shelf Science     Hybrid Journal   (Followers: 34)
Estudios Geográficos     Open Access  
European Journal of Mineralogy     Full-text available via subscription   (Followers: 12)
Exploration Geophysics     Hybrid Journal   (Followers: 4)
Facies     Hybrid Journal   (Followers: 9)
Fieldiana Life and Earth Sciences     Full-text available via subscription   (Followers: 1)
Física de la Tierra     Open Access  
Folia Musei rerum naturalium Bohemiae occidentalis. Geologica et Paleobiologica     Open Access  
Folia Quaternaria     Open Access  
Forestry Chronicle     Full-text available via subscription   (Followers: 10)
Frontiers in Earth Science     Open Access   (Followers: 5)
Frontiers in Geotechnical Engineering     Open Access   (Followers: 2)
Frontiers of Earth Science     Hybrid Journal   (Followers: 8)
Fundamental and Applied Limnology / Archiv für Hydrobiologie     Full-text available via subscription   (Followers: 4)
GEM - International Journal on Geomathematics     Hybrid Journal   (Followers: 1)
Geo-Marine Letters     Hybrid Journal   (Followers: 7)
Geoacta     Open Access   (Followers: 4)
Geobiology     Hybrid Journal   (Followers: 8)
Geocarto International     Hybrid Journal   (Followers: 22)
Geochemical Perspectives     Hybrid Journal  
Geochemistry : Exploration, Environment, Analysis     Hybrid Journal   (Followers: 7)
Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 25)
Geochimica et Cosmochimica Acta     Hybrid Journal   (Followers: 42)
Geochronometria     Hybrid Journal   (Followers: 3)
Geoderma Regional : The International Journal for Regional Soil Research     Full-text available via subscription   (Followers: 3)
Geodinamica Acta     Hybrid Journal   (Followers: 3)
Geodynamics & Tectonophysics     Open Access   (Followers: 1)
Geoenvironmental Disasters     Open Access   (Followers: 3)
Geofluids     Hybrid Journal   (Followers: 4)
Geoforum     Hybrid Journal   (Followers: 21)
Géographie physique et Quaternaire     Full-text available via subscription   (Followers: 1)
Geography and Natural Resources     Hybrid Journal   (Followers: 5)
Geoheritage     Hybrid Journal   (Followers: 1)
Geoinformatica Polonica : The Journal of Polish Academy of Arts and Sciences     Open Access  
Geoinformatics & Geostatistics     Hybrid Journal   (Followers: 8)
Geological Journal     Hybrid Journal   (Followers: 14)
Geology Today     Hybrid Journal   (Followers: 24)
Geomagnetism and Aeronomy     Hybrid Journal   (Followers: 3)
Geomatics, Natural Hazards and Risk     Hybrid Journal   (Followers: 9)
Geomechanics for Energy and the Environment     Full-text available via subscription  
GEOmedia     Open Access   (Followers: 1)
Geomorphology     Hybrid Journal   (Followers: 25)
Geophysical & Astrophysical Fluid Dynamics     Hybrid Journal   (Followers: 2)
Geophysical Journal International     Hybrid Journal   (Followers: 31)
Geophysical Prospecting     Hybrid Journal   (Followers: 7)
Geophysics     Full-text available via subscription   (Followers: 18)
GeoResJ     Hybrid Journal  
Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards     Hybrid Journal   (Followers: 8)
Geoscience Canada : Journal of the Geological Association of Canada / Geoscience Canada : journal de l'Association Géologique du Canada     Full-text available via subscription   (Followers: 3)
Geoscience Data Journal     Open Access   (Followers: 2)
Geoscience Frontiers     Open Access   (Followers: 9)
Geoscience Letters     Open Access   (Followers: 1)
Geoscience Records     Open Access  
Geosciences     Open Access   (Followers: 2)
Geosciences Journal     Hybrid Journal   (Followers: 9)
Geoscientific Instrumentation, Methods and Data Systems     Open Access   (Followers: 4)
Geoscientific Model Development     Open Access   (Followers: 2)
Geostandards and Geoanalytical Research     Hybrid Journal   (Followers: 2)
Geosystem Engineering     Hybrid Journal   (Followers: 1)
Geotectonic Research     Full-text available via subscription   (Followers: 4)
Geotectonics     Hybrid Journal   (Followers: 7)
GISAP : Earth and Space Sciences     Open Access   (Followers: 2)
Glass Physics and Chemistry     Hybrid Journal   (Followers: 3)
Global and Planetary Change     Hybrid Journal   (Followers: 16)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 12)
Gondwana Research     Hybrid Journal   (Followers: 6)
Grassland Science     Hybrid Journal   (Followers: 1)
Ground Water     Hybrid Journal   (Followers: 30)
Ground Water Monitoring & Remediation     Hybrid Journal   (Followers: 17)
Groundwater for Sustainable Development     Full-text available via subscription  
GSA Today     Partially Free  
Helgoland Marine Research     Open Access   (Followers: 3)
History of Geo- and Space Sciences     Open Access   (Followers: 4)
Hydrobiologia     Hybrid Journal   (Followers: 18)
Hydrogeology Journal     Hybrid Journal   (Followers: 16)
Hydrological Processes     Hybrid Journal   (Followers: 23)
Hydrology and Earth System Sciences     Open Access   (Followers: 26)
ICES Journal of Marine Science: Journal du Conseil     Hybrid Journal   (Followers: 53)
IEEE Journal of Oceanic Engineering     Hybrid Journal   (Followers: 11)
Indian Geotechnical Journal     Hybrid Journal   (Followers: 2)
Indonesian Journal on Geoscience     Open Access   (Followers: 2)
Interdisciplinary Environmental Review     Hybrid Journal   (Followers: 3)
International Geology Review     Hybrid Journal   (Followers: 12)
International Journal of Advanced Geosciences     Open Access  
International Journal of Advanced Remote Sensing and GIS     Open Access   (Followers: 33)
International Journal of Advancement in Earth and Enviromental Sciences     Open Access   (Followers: 3)
International Journal of Advancement in Remote Sensing, GIS, and Geography     Open Access   (Followers: 27)
International Journal of Applied Earth Observation and Geoinformation     Hybrid Journal   (Followers: 35)
International Journal of Coal Geology     Hybrid Journal   (Followers: 2)
International Journal of Disaster Risk Reduction     Hybrid Journal   (Followers: 11)

        1 2 3 | Last

Journal Cover Chemie der Erde - Geochemistry
  [SJR: 0.881]   [H-I: 34]   [4 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0009-2819
   Published by Elsevier Homepage  [3038 journals]
  • Editorial board members
    • Abstract: Publication date: December 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 4


      PubDate: 2016-11-30T07:52:46Z
       
  • Combined bulk-rock Hf- and Nd-isotope compositions of Mesoarchaean
           metavolcanic rocks from the Ivisaartoq Supracrustal Belt, SW Greenland:
           Deviations from the mantle array caused by crustal recycling
    • Abstract: Publication date: December 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 4
      Author(s): Kristoffer Szilas, J. Elis Hoffmann, Toni Schulz, Christina Hansmeier, Ali Polat, Sebastian Viehmann, Haino Uwe Kasper, Carsten Münker
      Bulk-rock Lu-Hf and Sm-Nd isotope compositions, as well as major and trace element data are presented for metavolcanic rocks from the Mesoarchaean (ca. 3075 Ma) Ivisaartoq Supracrustal Belt in the Nuuk region of southern West Greenland. The εHft calculated at 3075 Ma range from +0.8 to +3.1 and the corresponding εNdt values range from +0.7 to +3.6, which forms an array that is displaced off the mantle array for these two isotopic systems. Primitive mantle normalized trace element plots of the metabasalts display negative Nb- and Ti-anomalies in combination with the elevated Th abundances, which is consistent with a subduction zone affinity as proposed by previous studies of this metavolcanic belt. No significant correlations are observed between the isotope compositions and proxies of shallow crustal contamination in the Ivisaartoq rocks, despite clear evidence for inherited Eoarchaean zircon [Polat et al. (2009a) Chemical Geology 268, 248-271], which would have dominated the bulk-rock Hf-isotope budget. Furthermore, the measured samples are less radiogenic than the estimate for the depleted mantle composition at 3075 Ma. The lack of isotope and trace element correlation suggests incomplete equilibration between the crustal contaminant and the parental Ivisaartoq melts. We prefer a petrogenetic model with some combination of slab-derived metasomatism of the mantle source region for the Ivisaartoq magmas, which homogenized their trace element contents, in combination with the incorporation of granitoid residue with unradiogenic Hf-isotope composition at higher degrees of partial melting and finally the eruption of mechanically entrained Eoarchaean crust without significant chemical equilibration. The geochemical arc-affinity and lower than depleted mantle (DM) isotope compositions of these metavolcanic rocks support the notion that crustal recycling and plate tectonics has been operating on Earth since at least the Mesoarchaean Eon.

      PubDate: 2016-11-30T07:52:46Z
       
  • In–situ LA–ICP–MS trace elemental analyzes of magnetite: The Tieshan
           skarn Fe–Cu deposit, Eastern China
    • Abstract: Publication date: Available online 29 November 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Minfang Wang, Wei Wang, Kun Liu, Przemysław P. Michalak, Ketao Wei, Mingyue Hu
      The Tieshan Fe–Cu deposit is located in the Edong district, which represents the westernmost and largest region within the Middle–Lower Yangtze River Metallogenic Belt (YRMB), Eastern China. Skarn Fe–Cu mineralization is spatially associated with the Tieshan pluton, which intruded carbonates of the Lower Triassic Daye Formation. Ore bodies are predominantly located along the contact between the diorite or quartz diorite and marbles/dolomitic marbles. This study investigates the mineral chemistry of magnetite in different skarn ore bodies. The contrasting composition of magnetite obtained are used to suggest different mechanisms of formation for magnetite in the western and eastern part of the Tieshan Fe–Cu deposit. A total of 178 grains of magnetite from four magnetite ore samples are analyzed by LA–ICP–MS, indicating a wide range of trace element contents, such as V (13.61–542.36ppm), Cr (0.003–383.96ppm), Co (11.12–187.55ppm) and Ni (0.19–147.41ppm), etc. The Ti/V ratio of magnetite from the Xiangbishan (western part of the Tieshan deposit) and Jianshan ore body (eastern part of the Tieshan deposit) ranges from 1.32 to 5.24, and 1.31 to 10.34, respectively, indicating a relatively reduced depositional environment in the Xiangbishan ore body. Incorporation of Ti and Al in magnetite are temperature dependent, which hence propose that the temperature of hydrothermal fluid from the Jianshan ore body (Al=3747–9648ppm, with 6381ppm as an average; Ti=381.7–952.0ppm, with 628.2ppm as an average) was higher than the Xiangbishan ore body (Al=2011–11122ppm, with 5997ppm as an average, Ti=302.5–734.8, with 530.8ppm as an average), indicating a down–temperature precipitation trend from the Jianshan ore body to the Xiangbishan ore body. In addition, in the Ca+Al+Mn versus Ti+V diagram, magnetite is plotted in the skarn field, consideration with the ternary diagram of TiO2–Al2O3–MgO, proposing that the magnetite ores are formed by replacement, instead of directly crystallized from iron oxide melts, which provide a better understanding regarding the composition of ore fluids and processes responsible for Fe mineralization in the Tieshan Fe–Cu deposit.

      PubDate: 2016-11-30T07:52:46Z
       
  • Petrogenesis and geochemical characteristics of plagiogranites from Naga
           Ophiolite Belt, northeast India: Fractional crystallization of MORB-type
           magma
    • Abstract: Publication date: Available online 29 November 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Ranjit Nayak, B.V. Rao
      The Naga Ophiolite Belt is a part of the Naga-Arakan-Yoma flysch trough that occurs along the Indo-Myanmar border. It is represented by peridotites, mafic-ultramafic cumulates, mafic volcanics, mafic dykes, plagiogranites, pelagic sediments and minor felsic to intermediate intrusives. Minor plagiogranites, gabbros and thin serpentinite bands occur juxtaposed near Luthur, with the slate-phyllite-metagreywacke sequence (Phokpur Formation) adjacent to the contact. The development of tonalites, trondhjemites and diorites in the oceanic crust, which is grouped as plagiogranites, offers an opportunity to study the process of formation of silicic melts from mafic crust. Plagiogranites from Naga Ophiolite Belt contains moderate SiO2 (51.81–56.71wt.%), low K2O (0.08–1.65wt.%) and high Na2O (4.3–5.03wt.%). The Naga Ophiolite Belt plagiogranites like ocean-ridge granites contain low K2O, high Na2O and CaO. The rocks investigated from Naga Ophiolite Belt contain TiO2 concentrations above the lower limit for fractionated Mid Oceanic Ridge Basalt which is above 1wt% of TiO2 and the ternary plots of A (Na2O+K2O) F(FeOT) M(MgO) and TiO2-K2O-SiO2/50 indicate that the plagiogranite are tholeiitic in character and gabbro samples are calc-alkaline in nature. The plagiogranites are enriched in Rb, Ba, Th, U, Nb and Sm against chondrite with negative anomalies on Sr and Zr whereas Y and Yb are depleted to Mid Oceanic Ridge Basalt. The chondrite normalized REE patterns of the plagiogranite display enrichments in LREE (LaN/SmN: 2.37–3.62) and flat HREE (Eu/Eu*: 0.90–1.06). The Mid Oceanic Ridge Basalt normalization of gabbro is characterized by strong enrichment of LILE like Ba and Th. The REE pattern is about 50–100 times chondrite with slight enrichment of LREE (LaN/SmN =2.21–3.13) and flat HREE (Eu/Eu*: 0.94–1.19). The major-element and trace element data of the NOB plagiogranites and their intrusive nature with host gabbroic rock suggest that the plagiogranites were produced by fractional crystallization of basaltic parental magmas at Mid Oceanic Ridge.

      PubDate: 2016-11-30T07:52:46Z
       
  • Cobalt sorption–desorption behavior of calcareous soils from some
           Iranian soils
    • Abstract: Publication date: March 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 1
      Author(s): Mohsen Jalali, Mahin Majeri
      Little research has been done to study the role of soil parameters in cobalt (Co) retention, release and the processes involved in calcareous soils of arid and semi-arid regions. We studied the Co sorption and desorption capacity of various calcareous soils using batch technique. The sorption and desorption behavior of Co varied greatly among the studied soils. The sorbed fraction ranged from 92.3% to 97.2% and from 51.0% to 71.8%, when 5 and 200mg Col−1, was added to the soil samples, respectively. Cobalt sorption curves were well fitted with Langmuir, Freundlich, and linear equations. The values of the distribution coefficients obtained from linear equation ranged from 9.5lkg−1 to 23.4lkg−1. Desorption experiments resulted in a Co recovery ranged from 3.6% to 11.4%, indicating a low desorption of Co from soils. The results of the geochemical modeling indicated that under low Co addition, the solutions were undersaturated with respect to Co(OH)2(am), Co(OH)2(c), Co3(PO4)2(s), CoCl2(s), CoHPO4(s), CoCl2·6H2O(s), and CoO(s), whereas under higher Co addition, the solutions were undersaturated with respect to Co(OH)2(am), CoCl2(s), CoCl2·6H2O(s), CoO(s), CoHPO4(s), and saturated with respect to Co3(PO4)2(s), and CoCO3(s). The hysteresis indices indicated that desorption of freshly sorbed Co with 0.01M CaCl2 was hysteretic in all soils and low mobility and leaching potential of freshly sorbed Co can be expected from these calcareous soils. Statistical correlations revealed that Co sorption and desorption onto the soils were influenced by the presence of CaCO3 in soils. These findings suggested that calcareous soils are able to retain strongly Co in which the movement of Co in the soil profile would be negligible. Thus, little risk of groundwater contamination can be expected with Co in these calcareous soils.

      PubDate: 2016-11-17T15:41:10Z
       
  • Petrogenesis of Miocene alkaline volcanic suites from western Bohemia:
           whole rock geochemistry and Sr–Nd–Pb isotopic signatures
    • Abstract: Publication date: March 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 1
      Author(s): Jaromír Ulrych, Lukáš Krmíček, Čestmír Tomek, Felicity E. Lloyd, Anna Ladenberger, Lukáš Ackerman, Kadosa Balogh
      The Mid to Late Miocene intraplate alkaline volcanic suites of western Bohemia are relict of the intensive voluminous volcanism accompanied by large-scale uplift and doming. The association with the uplift of the NE flank of the Cheb–Domažlice Graben (CDG) is uncertain in view of the mostly transpressional tectonics of the graben. The volcanism is most probably of the Ohře/Eger Rift off-rift settings. Two cogenetic volcanic suites have been recognised: (i) silica-saturated to oversaturated consisting of olivine basalt–trachybasalt-(basaltic) trachyandesite–trachyte–rhyolite (13.5 to 10.2Ma) and (ii) silica-undersaturated (significantly Ne-normative) (melilite-bearing) olivine nephelinite–basanite–tephrite (18.3 to 6.25Ma). A common mantle source is suggested by similar primitive mantle-normalised incompatible element patterns and Sr–Nd–Pb isotopic compositions for the assumed near-primary mantle-derived compositions of both suites, i.e., olivine basalt and olivine nephelinite. Apparently, they were generated by different degrees of partial melting of a common mantle source, with garnet, olivine and clinopyroxene in the residuum. Negative Rb and K anomalies indicate a residual K-phase (amphibole/phlogopite) and melting of partly metasomatised mantle lithosphere. The evolution of the basanite–olivine basalt–trachybasalt-(basaltic) trachyandesite–trachyte–rhyolite suite suggests the presence of an assimilation–fractional crystallization process (AFC). Substantial fractionation of olivine, clinopyroxene, Fe–Ti oxide, plagioclase/alkali feldspar and apatite accompanied by a significant assimilation of magma en route by crustal material is most evident in evolved member, namely, trachytes and rhyolites. The magmas were probably sourced by both sub-lithospheric and lithospheric partly metasomatised mantle. The evolution of the (melilite-bearing) olivine nephelinite–basanite–tephrite suite is less clear because of its limited extent. Parental magma of both these rock suites is inferred to have originated by low-degree melting of the mantle source initiated at ca. 18Ma and reflects mixing of asthenosphere-derived melts with isotopically enriched lithospheric melts. The older Oligocene alkaline rocks (29–26Ma) occur within the Cheb–Domažlice Graben (CDG) locally but are significant in the closely adjacent neighbouring western Ohře Rift. The Sr–Nd–Pb isotopic composition of primitive volcanic rocks of both suites is similar to that of the European Asthenospheric Reservoir (EAR). Initial Pb isotopic data plot partly above the northern hemisphere reference line at radiogenic 206Pb/204Pb ratios of ∼19 to 20, and indicate the presence of a Variscan crustal component in the source.

      PubDate: 2016-11-17T15:41:10Z
       
  • Geochemical constraint on origin and evolution of solutes in geothermal
           springs in western Yunnan, China
    • Abstract: Publication date: March 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 1
      Author(s): Yanfei Zhang, Hongbing Tan, Wenjie Zhang, Haizhen Wei, Tao Dong
      Geothermal resources are very rich in Yunnan, China. However, source of dissolved solutes in geothermal water and chemical evolution processes remain unclear. Geochemical and isotopic studies on geothermal springs and river waters were conducted in different petrological-tectonic units of western Yunnan, China. Geothermal waters contain Ca–HCO3, Na–HCO3, and Na (Ca)–SO4 type, and demonstrate strong rock-related trace elemental distributions. Enhanced water–rock interaction increases the concentration of major and trace elements of geothermal waters. The chemical compositions of geothermal waters in the Rehai geothermal field are very complicated and different because of the magma chamber developed at the shallow depth in this area. In this geothermal field, neutral-alkaline geothermal waters with high Cl, B, Li, Rb Cs, As, Sb, and Tl contents and acid–sulfate waters with high Al, Mn, Fe, and Pb contents are both controlled by magma degassing and water–rock interaction. Geothermal waters from metamorphic, granite, and sedimentary regions (except in the Rehai area) exhibit varying B contents ranging from 3.31mg/L to 4.49mg/L, 0.23mg/L to 1.24mg/L, and <0.07mg/L, respectively, and their corresponding δ11B values range from −4.95‰ to −9.45‰, −2.57‰ to −8.85‰, and −4.02‰ to +0.06‰. The B contents of these geothermal waters are mainly controlled by leaching host rocks in the reservoir, and their δ11B values usually decrease and achieve further equilibrium with its surrounding rocks, which can also be proven by the positive δ18O-shift. In addition to fluid–rock reactions, the geothermal waters from Rehai hot springs exhibit higher δ11B values (−3.43‰ to +1.54‰) than those yielded from other areas because mixing with the magmatic fluids from the shallow magma. The highest δ11B of steam–heated waters (pH 3.25) from the Zhenzhu spring in Rehai is caused by the fractionation induced by pH and the phase separation of coexisting steam and fluids. Given the strong water–rock interaction, some geothermal springs in western Yunnan show reservoir temperatures higher than 180°C, which demonstrate potential for electricity generation and direct-use applications. The most potential geothermal field in western Yunnan is located in the Rehai area because of the heat transfer from the shallow magma chamber.

      PubDate: 2016-11-17T15:41:10Z
       
  • Geochemical mapping based on geological units: a case study from the
           Marnoso-arenacea formation (Northern Apennines, Italy)
    • Abstract: Publication date: March 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 1
      Author(s): Valerio Lancianese, Enrico Dinelli
      Geochemical maps can provide us with much information on geology, earth surface processes and anthropogenic pressure and are valuable tools for ore prospecting and land management. Stream sediments represent an integral of the various possible sources of sediments upstream from the sampling point therefore there can be multiple signal sources but generally the prevailing signal source is the one related to bedrock geology. Stream sediments collected from active second-order channels including singular geological units, were selected in order to determine the geochemical characteristics of each unit. The aim of this study was to analyze their potential for using them to integrate geological interpretation and produce a geologically-oriented geochemical map. From the 770 samples collected for a regional geochemical mapping program, we selected 149 samples whose catchment basin included only one of the members recognized within the Marnoso-arenacea formation. This middle–upper Miocene (Langhian–Tortonian) turbiditic unit forms the backbone of the Romagna Apennines and has been subdivided into 14 members according to age and lithostratigraphic criteria. The results indicate that there are marked differences in the composition of the members of the Marnoso arenecea formation which indicate the provenance of the sediment and the palaeogeographic evolution of the units. By means of univariate and multivariate statistical analyses (Factor analyzes) two main types of sediment compositions are identified: Tortonian members are characterized by sialic coarse grain-sediments while the Langhian–Serravallian members are richer in carbonate fraction, slightly enriched in a mafic contribution. This study elaborated the geochemical data from a geological point of view by integrating the information available in literature to spatially extend the interpretation based on limited site observation as for petrographic studies. In general, the geochemical map based on a geological unit could be a useful tool for carrying out the geological reconstruction of a complex area.

      PubDate: 2016-11-17T15:41:10Z
       
  • Mineralogical and geochemical investigations of the Mombi bauxite deposit,
           Zagros Mountains, Iran
    • Abstract: Publication date: March 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 1
      Author(s): Hassan Zamanian, Farhad Ahmadnejad, Alireza Zarasvandi
      The Mombi bauxite deposit is located in 165km northwest of Dehdasht city, southwestern Iran. The deposit is situated in the Zagros Simply Fold Belt and developed as discontinuous stratified layers in Upper Cretaceous carbonates (Sarvak Formation). Outcrops of the bauxitic horizons occur in NW-SE trending Bangestan anticline and are situated between the marine neritic limestones of the Ilam and Sarvak Formations. From the bottom to top, the deposit is generally consisting of brown, gray, pink, pisolitic, red, and yellow bauxite horizons. Boehmite, diaspore, kaolinite, and hematite are the major mineral components, while gibbsite, goethite, anatase, rutile, pyrite, chlorite, quartz, as well as feldspar occur to a lesser extent. The Eh–pH conditions during bauxitization in the Mombi bauxite deposit show oxidizing to reducing conditions during the Upper Cretaceous. This feature seems to be general and had a significant effect on the mineral composition of Cretaceous bauxite deposits in the Zagros fold belt. Geochemical data show that Al2O3, SiO2, Fe2O3 and TiO2 are the main components in the bauxite ores at Mombi and immobile elements like Al, Ti, Nb, Zr, Hf, Cr, Ta, Y, and Th were enriched while Rb, Ba, K, Sr, and P were depleted during the bauxitization process. Chondrite-normalized REE pattern in the bauxite ores indicate REE enrichment (ΣREE=162.8–755.28ppm, ave. ∼399.36ppm) relative to argillic limestone (ΣREE=76.26–84.03ppm, ave. ∼80.145ppm) and Sarvak Formation (ΣREE=40.15ppm). The REE patterns also reflect enrichment in LREE relative to HREE. Both positive and negative Ce anomalies (0.48–2.0) are observed in the Mombi bauxite horizons. These anomalies are related to the change of oxidation state of Ce (from Ce3+ to Ce4+), ionic potential, and complexation of Ce4+ with carbonate compounds in the studied horizons. It seems that the variations in the chemistry of ore-forming solutions (e.g., Eh and pH), function of carbonate host rock as a geochemical barrier, and leaching degree of lanthanide-bearing minerals are the most important controlling factors in the distribution and concentration of REEs. Several lines of evidences such as Zr/Hf and Nb/Ta ratios as well as similarity in REE patterns indicate that the underlying marly limestone (Sarvak Formation) could be considered as the source of bauxite horizons. Based on mineralogical and geochemical data, it could be inferred that the Mombi deposit has been formed in a karstic environment during karstification and weathering of the Sarvak limy Formation.

      PubDate: 2016-11-17T15:41:10Z
       
  • Geochemical fractionation of Ni, Cu and Pb in the deep sea sediments from
           the Central Indian Ocean Basin: An insight into the mechanism of metal
           enrichment in sediment
    • Abstract: Publication date: March 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 1
      Author(s): Simontini Sensarma, Parthasarathi Chakraborty, Ranadip Banerjee, Subir Mukhopadhyay
      Metal speciation study in combination with major element chemistry of deep sea sediments provided possible metal enrichment pathways in sediments collected from environmentally different locations of Central Indian Ocean Basin (CIB). Metal speciation study suggests that Fe–Mn oxyhydroxide phase was the major binding phase for Ni, Cu and Pb in the sediments. The second highest concentrations of all these metals were present within the structure of the sediments. Easily reducible oxide phase (within the Fe–Mn oxyhydroxide binding phases) was the major host for all the three metals in the studied sediments. Major element chemistry of these sediments revealed that there was an increased tendency of Cu and Ni to get incorporated into the deep sea sediment via the non-terrigenous Mn-oxyhydroxide fraction, whereas, Pb gets incorporated mostly via amorphous Fe-hydroxides into the sediment from the CIB. This is the first attempt to provide an insight into the mechanism of metal enrichment in sediment that host vast manganese nodule.

      PubDate: 2016-11-17T15:41:10Z
       
  • Geochemistry and U-Pb zircon dating constraints of some plutonic rocks
           along Bir Tawilah shear zone, central Saudi Arabia: Implication for magma
           peterogenesis and age of gold mineralization
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2
      Author(s): Hesham M. Harbi, Kamal A. Ali, Abdelmonem A. Eldougdoug, Nasir S. Al-Jahdli
      The study area covered by this work is located along the Bir Tawilah fault zone which encompasses the Arabian Shield between Afif terrane and western oceanic terranes. The rocks are dominantly ophiolite assemblages, island arc metavolcanic and metasedimentary rocks, and dioritic to granitic intrusions. The diorite and granodiorite rocks are I-type granitoids, calk-alkaline, metaluminous to peraluminous, formed in a volcanic arc setting, whereas the monzogranite is classified as A-type granite, alkaline and highly fractionated calc-alkaline, generated in within-plate tectonic setting. Nb and Y relationships indicated that the diorites and granodiorites were generated by a mafic parental magma contaminated with crustal materials, and controlled by fractional crystallization, whereas the monzogranites were generated from a magma characterized by an enriched mantle (EM) source. Mineralization including gold is hosted by the carbonatized serpentinite (listvenite) and the syn-tectonic granodiorite along Bir Tawilah thrust zone. U-Pb zircon geochronology indicates that the granodiorite at Jabal Ghadarah is emplaced at ca. 630±12Ma, probably suggests that the metallic minerals associated with the granodiorite along Bir Tawilah thurst zone are the result of remobilization of pre-existing gold mineralization associated with listevenite that is related to arc accretion.

      PubDate: 2016-11-17T15:41:10Z
       
  • Editorial board members
    • Abstract: Publication date: March 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 1


      PubDate: 2016-11-17T15:41:10Z
       
  • Great new insights from failed experiments, unanticipated results and
           embracing controversial observations
    • Abstract: Publication date: March 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 1
      Author(s): Joseph A. Nuth, Natasha M. Johnson, Frank T. Ferguson, Frans J.M. Rietmeijer, Hugh G.M. Hill
      Experimental data and observations, whether telescopic or analytical, are never wrong, though data derived from such sources can be misinterpreted or applied inappropriately to derive conclusions that are incorrect. Given that nature always behaves according to the laws of physics and chemistry, rather than according to currently popular models and theories, experimental results should always be considered correct even when the results are far from those that one might initially expect. We discuss a number of cases where the results of experiments, even one carried out as a simple calibration measure, produced wildly different results that generally required many years of effort or contemplation to understand. On the positive side, exploration of the circumstances that produced the “errant” results often led to new and interesting insights concerning processes that might occur in natural environments and that were well worth the effort involved. Specifically, we show how an experiment that “failed” due to a broken conductor led to experiments that made the first refractory oxide solids containing mass independently fractionated oxygen isotopes and to 1998 predictions of the oxygen isotopic composition of the sun that were confirmed by the analysis of Genesis samples in 2011. We describe a calibration experiment that unexpectedly produced single magnetic domain iron particles. We discuss how tracking down a persistent source of “contamination” in experiments intended to produce amorphous iron and magnesium silicate smokes led to a series of studies on the synthesis of carbonaceous grain coatings that turn out to be very efficient Fischer–Tropsch catalysts and have great potential for trapping the planetary noble gases found in meteorites. We describe how models predicting the instability of silicate grains in circumstellar environments spurred new measurements of the vapor pressure of SiO partially based on previous experiments showing unexpected but systematic non-equilibrium behavior instead of the anticipated equilibrium products resembling meteoritic minerals. We trace the process that led from observations of the presence of crystalline minerals detected in the comae of some comets to the 1999 prediction of large-scale circulation of materials from the hot, innermost regions of the solar nebula out to the cold dark nebular environments where comets form. This large-scale circulation was ultimately confirmed by analyses of highly refractory Stardust samples collected from the Kuiper Belt Comet Wild 2. Finally we discuss a modern and still unresolved conflict between the assumptions built into three well known processes: the CO Self Shielding Model for mass independent isotopic fractionation of oxygen in solar system solids, rapid and thorough mixing within the solar nebula, and the efficient conversion of CO into organic coatings and volatiles on the surfaces of nebular grains via Fischer–Tropsch-type processes.

      PubDate: 2016-11-17T15:41:10Z
       
  • Sediment characteristics and mineralogy of salt mounds linked to
           underground spring activity in the Lop Nor playa, Western China
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): Lichun Ma, Qingfeng Tang, Baoguo Li, Yufei Hu, Wenjun Shang
      Salt mounds are commonly distributed along playa margins and typically comprise alternating layers of loose fine sand and slightly hard halite-rich sediments as a result of long-term underground spring activity. A model of salt mound development was constructed for this study. It suggests that wind-blown sand supply and upward recharge of underground springs are two important factors in salt mound construction. Furthermore, it proposes that salt mound height is mainly controlled by the vertical transport range of underground springs and the thickness of the capillary fringe. A 1.5m representative profile dug from the center of salt mound LP1 in the Lop Nor playa revealed a fairly complicated mineral assemblage including halite, gypsum, anhydrite, glauberite, epsomite, anhydrite, calcite, bischofite, polyhalite, schoenite, kieserite and carnallite. This matches closely with the assemblage predicted by the EQL/EVP model. The groundwater in the area is highly concentrated brine rich in Cl− and Na+ and poor in Ca2+, displaying low alkalinity, and containing considerable amounts of SO4 2−, Mg2+ and K+. Chemical analysis of groundwater revealed considerable variation in the salinity and chemical composition of groundwater over time. The Cs-137 technique was used to measure the accumulated ages of the salt mounds. This method may prove useful in the research of relatively young playa environments where carbon dating techniques are unworkable because of an absence of carbon-rich materials in recent saline sediments.

      PubDate: 2016-11-17T15:41:10Z
       
  • Melt impregnation phases in the mantle section of the Ślęża
           ophiolite (SW Poland)
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2
      Author(s): Piotr Marian Wojtulek, Jacek Puziewicz, Theodoros Ntaflos
      The ultramafic member of the Variscan Ślęża Ophiolite (SW Poland) consists of heavily serpentinised, refractory harzburgites. Those located down to 1.5km below paleo-Moho contain scarce grains or aggregates of olivine, clinopyroxene and spinel. Non-serpentine phases occur in various assemblages: M1—olivine (Fo 90.2–91.0%, NiO 0.38–0.47wt.%) and rounded or amaeboidal aluminous chromite, rimmed by Al poor chromite and magnetite; M2—olivine (Fo 90.5–91.5, NiO 0.32–0.44wt.%), olivine with magnetite inclusions (Fo 87.1–92.5, NiO 0.01–0.68wt.%), rounded, cleavaged clinopyroxene I (Mg# 91.1–93.2, Al2O3 3.00–4.00wt.%, Cr2O3 1.00–1.40wt.%) and elongated clinopyroxene II and clinopyroxene from symplectites with magnetite (Mg#=92.2–94.1, Al2O3 2.20–3.20wt.% and Cr2O3 0.80–1.20wt.%). Clinopyroxene is depleted in REEs relative to chondrite. The M3 assemblage consists of intergrown olivine (Fo 90.8–92.7, NiO 0.20–0.38wt.%) and clinopyroxene (Mg#=96.0–98.1, Al2O3 0.00–1.00wt.% and Cr2O3 0.20–0.60wt.%). The M1 assemblage contains chromite which records greenschist-facies metamorphism. Textural relationships and chemical composition of clinopyroxene occurring in the M2 assemblage are similar to those formed in oceanic spreading centres by LREE depleted basaltic melt percolation. Olivine occurring in M1 assemblage and part of that from M2 have composition typical of residual olivine from the abyssal harzburgites and of olivine formed in those rocks by melt percolation. The olivine with magnetite inclusions (M2 assemblage) and that from M3 record later deserpentinization event, which supposedly produced also M3 clinopyroxene. The non-serpentine phases from the Ślęża ophiolite mantle member, albeit very poorly preserved, document depleted basaltic melt percolation in the Variscan oceanic spreading centre.

      PubDate: 2016-11-17T15:41:10Z
       
  • Chemical, isotopic and mineralogical characteristics of volcanogenic
           epithermal fluorite deposits on the Permo-Mesozoic foreland of the Andean
           volcanic arc in Patagonia (Argentina)
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2
      Author(s): Harald G. Dill, Liliana I. Luna, Nicole Nolte, Bent T. Hansen
      Epithermal deposits mined for fluorite in Patagonia, Argentina, are closely related to late Triassic through Jurassic magmatic activity which brought about felsic to intermediate magmatic rocks. The fluorite mineralization in the Patagonian epithermal system resulted from gaseous F-and CO2-enriched magmas which lead to an explosive phreatomagmatic volcanism, when getting in contact with groundwater near the surface. As a result of these hydrothermal processes, rapid cooling took place in the epithermal mineralization. Changes in the viscosity along with the cooling down of mineralizing fluids caused mottled mineral colors blurring the boundaries between the stages and ore textures. The fluids accountable for the main constituents fluorite, quartz, barite and silica were operative over a vertical extension of roughly 600m. Their temperature of formation dropped from 379°C through 64°C, while the pH decreased from the heat center towards the paleosurface under oxidizing conditions. This steep temperature gradient conducive to the telescoping of mineral associations into each other was accompanied by a rapid loss in CO2, and a mixing of meteoric and magmatic fluids. Even the boundary between the hypogene and supergene alteration cannot be drawn precisely within the assemblage of Mn oxides, which bridge the gap between hypogene and supergen mineralization. The physical-chemical parameters of the fluids, particularly, the redox conditions did not allow sulfides to be preserved. A classification of the epithermal system as to its degree of sulfidation is based on K-feldspar and kaolinite which are present in significant amounts, whereas APS (aluminum-phosphate-sulfate) minerals are absent. Therefore a categorization as an epithermal fluorite deposit of low- to intermediate sulfidation is justified, because the only mineral of economic interest in the system is fluorite. The data obtained during this joint study render the Patagonian fluorite district a reference type of fluorite in an epithermal system of low- to intermediate sulfidation which are widespread in Argentina, e.g., Sierras Pampeanas, and evolved on part of the stable craton, called Gondwana and which grade into epithermal Au, Ag, In, Pb and Zn deposits.

      PubDate: 2016-11-17T15:41:10Z
       
  • Geochronology and geochemistry of the major host rock of the Dong’an
           gold deposit, Lesser Khingan Range: Implications for petrogenesis and
           metallogenic setting during the Early–Middle Jurassic in northeast China
           
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2
      Author(s): Yubo Zhi, Bile Li, Aihua Xi, Qinglin Xu, Liang Zhang, Yonggang Sun, Jingjuan Chang, Bo Peng
      The Dong’an gold deposit is a large-sized epithermal gold deposit recently discovered in the Lesser Khingan Range, NE China. Here, we present a detailed study of the petrogenesis, magma source, and tectonic setting of a medium–coarse grained alkali-feldspar granite, the major host rock of the Dong’an gold deposit. The LA–ICP–MS zircon U–Pb dating of the medium–coarse grained alkali-feldspar granite yields an early Jurassic age of 176.3±1.1Ma (MSWD=0.62). The whole-rock geochemical data indicate that the samples are felsic, ferroan, alkali-calcic and peraluminous with relatively high alkali (K2O+Na2O) content. They are enriched in LREEs and LILEs (e.g., Rb, Ba, K), but are depleted in HFSEs (e.g., Nb, Ta, P, Ti), especially in P and Ti, showing characteristics of volcanic arc magmas and similarities with the Early–Middle Jurassic granitic rocks in Xing’an Mongolian orogenic belt. Meanwhile, the negative Eu, Nb, Ta, Ti, and P anomalies are consistent with fractional crystallization of plagioclase, Ti-bearing phases (rutile, ilmenite, titanite, etc.) and apatite during magma evolution. The samples have low Nb/Ta ratios (8.65–14.91) and low Mg# values (18–36), which are indicative of crustal derived magmas and no interaction between source magmas and the mantle. In-situ Hf isotopic analyses of the zircons from the medium–coarse grained alkali-feldspar granite yield εHf(t) values of +3.38–+5.68 and two-stage model ages (TDM2) of 772–900 Ma, indicating the magmas formed this intrusion were generated by partial melting of Neoproterozoic basaltic materials in the young lower crust, and the magma source could be derived from a depleted mantle. The medium–coarse grained alkali-feldspar granite most likely formed in the late stage of Toarcian subduction of the Pacific plate, which can be identified on the tectonic setting discrimination diagrams, and the formation of this intrusion was associated with underplating of mantle-derived magmas, which provided heat for crustal partial melting. Similar to the medium–coarse grained alkali-feldspar granite, large amounts of granitic rocks and a series of nonferrous metal hydrothermal deposits (Mo, Cu, Au) formed in northeast China as results of magmatic activities triggered by subduction of the Pacific plate during the Early–Middle Jurassic.

      PubDate: 2016-11-17T15:41:10Z
       
  • Isotopic and geochemical identifications of groundwater salinisation
           processes in Salalah coastal plain, Sultanate of Oman
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2
      Author(s): Brahim Askri, Abdelkader T. Ahmed, Razan Ali Al-Shanfari, Rachida Bouhlila, Khater Ben Khamis Al-Farisi
      A detail investigation was carried out to improve the current knowledge of groundwater salinisation processes in coastal aquifers using hydrochemical and isotopic parameters. Data of major ions for 40 wells located in the Salalah plain aquifer, Sultanate of Oman, were collected during pre-monsoon 2004 and analysed. The groundwater changes along the general flow path towards the coast from fresh (EC<1500μS/cm), brackish (EC: 1500–3000μS/cm) and saline (EC>3000μS/cm). Results of inverse modeling simulations using PHREEQC show that dissolution of halite may be the main source of Cl and Na in the study area. Ionic delta calculation indicates that the depletion of Na and K and enrichment of Ca and Mg in groundwater were probably attributed to reverse ion exchange reactions. During a sampling campaign conducted in October 2015, 11 groundwater samples were collected for Cl, Br and isotopic analysis (2H/18O). Molar Cl/Br ratios in fresh groundwater were higher than those of seawater, indicating the impact of halite dissolution on the groundwater quality. For saline groundwater, these ratios were less than those of seawater, showing the influence of anthropogenic input from agriculture on the same. Relatively depleted isotopic signature of all groundwater samples show that the monsoon precipitation is the main source of groundwater recharge in the study area.

      PubDate: 2016-11-17T15:41:10Z
       
  • Assessment of groundwater quantity and quality and saltwater intrusion in
           the Damghan basin, Iran
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2
      Author(s): Milad Ebrahimi, Hamidreza Kazemi, Majid Ehtashemi, Thomas D. Rockaway
      This study describes the groundwater quantity and quality conditions in the Damghan aquifer in Iran. The quantitative analysis of data obtained from observation wells indicates overexploitation of groundwater during recent years, which has resulted in deterioration of water quality. The mean water level has declined about 7.4m between years of 1966 and 2010. The hydrochemical facies of water collected from sampling wells were investigated though Piper and Chadha diagrams, and the general dominant type of water in the study area was determined as Na-Cl. The quality assessment examined the suitability of groundwater for drinking and irrigation purposes. Compared to the World Health Organization (WHO) guidelines for drinking water, all regions were found to have unpotable groundwater. Furthermore, unsuitability of groundwater for agricultural applications due to high salinity was observed through analysis of major quality indicators. The saltwater intrusion was investigated by ionic ratio analyses and was determined to be the main factor contributing to high salinity and deterioration of the groundwater quality in the Damghan basin.

      PubDate: 2016-11-17T15:41:10Z
       
  • Geochemical mapping based on geological units: A case study from the
           Marnoso-arenacea formation (Northern Apennines, Italy)
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2
      Author(s): Valerio Lancianese, Enrico Dinelli
      Geochemical maps can provide us with much information on geology, earth surface processes and anthropogenic pressure and are valuable tools for ore prospecting and land management. Stream sediments represent an integral of the various possible sources of sediments upstream from the sampling point therefore there can be multiple signal sources but generally the prevailing signal source is the one related to bedrock geology. Stream sediments collected from active second-order channels including singular geological units, were selected in order to determine the geochemical characteristics of each unit. The aim of this study was to analyse their potential for using them to integrate geological interpretation and produce a geologically-oriented geochemical map. From the 770 samples collected for a regional geochemical mapping program, we selected 149 samples whose catchment basin included only one of the members recognized within the Marnoso–Arenacea formation. This Middle-Upper Miocene (Langhian–Tortonian) turbiditic unit forms the backbone of the Romagna Apennines and has been subdivided into 14 members according to age and lithostratigraphic criteria. The results indicate that there are marked differences in the composition of the members of the Marnoso Arenecea formation which indicate the provenance of the sediment and the palaeogeographic evolution of the units. By means of univariate and multivariate statistical analyses (Factor analyses) two main types of sediment compositions are identified: Tortonian members are characterized by sialic coarse grain- sediments while the Langhian–Serravallian members are richer in carbonate fraction, slightly enriched in a mafic contribution. This study elaborated the geochemical data from a geological point of view by integrating the information available in literature to spatially extend the interpretation based on limited site observation as for petrographic studies. In general, the geochemical map based on a geological unit could be a useful tool for carrying out the geological reconstruction of a complex area.

      PubDate: 2016-11-17T15:41:10Z
       
  • Preservation of coal-waste geochemical markers in vegetation and soil on
           self-heating coal-waste dumps in Silesia, Poland
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2
      Author(s): Monika J. Fabiańska, Justyna Ciesielczuk, Magdalena Misz-Kennan, Łukasz Kruszewski, Adam Kowalski
      Occurrence and distributions of geochemical markers on vegetation and in soils covering two self-heating coal waste dumps were investigated with gas chromatography-mass spectrometry (GC–MS) and compared with those of bitumen expelled on the coal waste dump surface. Presence of biomarkers, alkyl aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and such polar compounds as phenols indicate that components of self-heating coal wastes indeed migrate to soils and plants surface and their characteristic fingerprints can be applied in passive monitoring to investigate migration of contaminants from self-heating coal wastes. Moreover, results allow to discriminate between the Upper- and Lower Silesian coal basins, notwithstanding value shifts caused by heating. Mechanisms enabling the migration of geochemical compounds into soils include mixing with weathered coal-waste material, transport in gases emitted due to self-heating and, indirectly, by deposition of biomass containing geochemical substances. Transport in gases involves mostly lighter compounds such as phenols, methylnaphthalenes, methylbiphenyls, etc. Distributions and values of geochemical ratios are related to differences in their boiling temperatures in the case of lighter compounds but preserve geochemical features in the case of heavier compounds such as pentacyclic trierpanes.

      PubDate: 2016-11-17T15:41:10Z
       
  • Editorial board members
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2


      PubDate: 2016-11-17T15:41:10Z
       
  • Advances in determining asteroid chemistries and mineralogies
    • Abstract: Publication date: June 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 2
      Author(s): Thomas H. Burbine
      Considerable progress has been made in the last few years in determining asteroid chemistries and mineralogies. Dedicated spacecraft missions have allowed mineralogical predictions based on ground-based data to be confirmed or refuted. These missions include NEAR-Shoemaker to (253) Mathilde and (433) Eros, Hayabusa to (25143) Itokawa, and Dawn to (4) Vesta and (1) Ceres, the upcoming Hayabusa2 to (162173) Ryugu, and the upcoming OSIRIS-Rex to (101955) Bennu. All of these missions have or will make significant advances that could not have been made through just Earth-based observations. The recovery of Almahata Sitta from 2008 TC3 was a rare opportunity to recover meteorite samples from a spectrally observed body from a naturally occurring event. This review will discuss the importance of spacecraft missions to asteroids.

      PubDate: 2016-11-17T15:41:10Z
       
  • Do lunar and meteoritic archives record temporal variations in the
           composition of solar wind noble gases and nitrogen? A reassessment in the
           light of Genesis data
    • Abstract: Publication date: Available online 12 July 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Rainer Wieler
      Since about half a century samples from the lunar and asteroidal regoliths been used to derive information about elemental and isotopic composition and other properties of the present and past solar wind, predominantly for the noble gases and nitrogen. Secular changes of several important compositional parameters in the solar wind were proposed, as was a likely secular decrease of the solar wind flux. In 2004 NASA’s Genesis mission returned samples which had been exposed to the solar wind for almost 2.5 years. Their analyses resulted in an unprecendented accuracy for the isotopic and elemental composition of several elements in the solar wind, including noble gases, O and N. The Genesis data therefore also allow to re-evaluate the lunar and meteorite data, which is done here. In particular, claims for long-term changes of solar wind composition are reviewed. Outermost grain layers from relatively recently irradiated lunar regolith samples conserve the true isotopic ratios of implanted solar wind species. This conclusion had been made before Genesis based on the agreement of He and Ne isotopic data measured in the aluminum foils exposed to the solar wind on the Moon during the Apollo missions with data obtained in the first gas release fractions of stepwise in-vacuo etch experiments. Genesis data allowed to strengthen this conclusion and to extend it to all five noble gases. Minor variations in the isotopic compositions of implanted solar noble gases between relatively recently irradiated samples (<100Ma) and samples irradiated billions of years ago are very likely the result of isotopic fractionation processes that happened after trapping of the gases rather than indicative of true secular changes in the solar wind composition. This is particularly important for the 3He/4He ratio, whose constancy over billions of years indicates that hardly any 3He produced as transient product of the pp-chains has been mixed from the solar interior into its outer convective zone. The He isotopic composition measured in the present-day solar wind therefore is identical to the (D+ 3He)/4He ratio at the start of the suns’s main sequence phase and hence can be used to determine the protosolar D/H ratio. Genesis settled the long-standing controversy on the isotopic composition of nitrogen in lunar regolith samples. The 15N/14N ratio in the solar wind as measured by Genesis is lower than in any lunar sample. This proves that nitrogen in regolith samples is dominated by non-solar sources. A postulated secular increase of 15N/14N by some 30% over the past few Ga is not tenable any longer. Genesis also provided accurate data on the isotopic composition of oxygen in the solar wind, invaluable for cosmochemisty. These data superseded but essentially confirmed one value – and disproved a second one – derived from lunar regolith samples shortly prior to Genesis. Genesis also confirmed prior conclusions that lunar regolith samples essentially conserve the true elemental ratios of the heavy noble gases in the solar wind (Ar/Kr, Kr/Xe). Several secular changes of elemental abundances of noble gases in the solar wind had been proposed based on lunar and meteoritic data. I argue here that lunar data – in concert with Genesis – provide convincing evidence only for a long-term decrease of the Kr/Xe ratio by almost a factor of two over the past several Ga. It appears that the enhancement of abundances of elements with a low first ionisation potential in the solar wind (FIP effect) changed with time. Finally, Genesis allows a somewhat improved comparison of the present-day flux of solar wind Kr and Xe with the total amount of heavy solar wind noble gases in the lunar regolith. It remains unclear whether the past solar wind flux has been several times higher on average than it is today.

      PubDate: 2016-11-17T15:41:10Z
       
  • Spatial variability of soils and stream sediments and the remediation
           effects in a Portuguese uranium mine area
    • Abstract: Publication date: Available online 28 August 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Ana Margarida Ribeiro Neiva, Paula Cristina Simões de Carvalho, Isabel Margarida Horta Ribeiro Antunes, Marina Marques da Silva Cabral Pinto, António Carlos Tavares dos Santos, Pedro P. Cunha, Maria Mafalda Costa
      The old Senhora das Fontes uranium mine, located in central Portugal, was closed down in 1971. The treatment of ores from this mine and other mines by heap-leach ended in 1982. Seven dumps partially covered by vegetation were left in the area. Soil and stream sediment samples were collected in December 2009. The remediation was carried out from May 2010 to January 2011. Stream sediment samples were collected again in October 2013. Before the remediation, soils from inside the mine influence area have higher Al, As, Co, Cr, Cu, Fe, Ni, Sr, Th, U and Zn concentrations than soils from outside this area, due to radionuclides, metals and metalloid released from the mine dumps. The principal component analysis (PCA) shows a distinction between soils from inside and outside the mine influence area. The U(VI), As(V) and metals from soils can be adsorbed to Fe-oxyhydroxides and the humic acid can increase the U uptake. Soils must not be used for public or private green and residential areas, because they are contaminated in U, As, Co, Cd and Ni. Before the remediation, downstream sediments have higher Al, As, Cu, Mn, Ni, Pb, U and Zn than upstream sediments, due to erosion and percolation of water through the mine dumps. The PCA shows a distinction between downstream and upstream sediments. The U(VI), Th and As(V) can be adsorbed to Fe-oxyhydroxides. The stream sediments are contaminated in As, Mn, Th and U. Downstream sediments are the most contaminated in U and As. After the remediation, upstream and downstream sediments have generally higher Al, Fe, As, Cr, Ni, Th, U and Zn concentrations than before the remediation, attributed to the relocation of dumps. Radionuclides, metals and metalloids were transported by surface water. Consequently downstream sediments have higher Al, As, Cu, Mn, Ni, Th, U and Zn concentrations than upstream sediments. The U(VI), Th and As(V) can be adsorbed to Fe-oxyhydroxides. Stream sediments became more contaminated in U, Th and As than before the remediation, but more intensively downstream.

      PubDate: 2016-11-17T15:41:10Z
       
  • Combination of single and sequential chemical extractions to study the
           mobility and host phases of potentially toxic elements in airborne
           particulate matter
    • Abstract: Publication date: Available online 30 August 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Péter Sipos, Chung Choi, Zoltán May
      Risk assessment of metals associated to airborne particulate matter (PM) has usually been based on the analysis of their total concentrations, which is a poor indicator of metal mobility. Chemical fractionation processes may provide an additional level of information, however, chemical complexity and small sample sizes do not allow to combine several extraction methods. Additionally, analysing the metal concentrations during the extractions exceptionally provides restricted information about metals’ speciation. To overcome these limitations we collected total suspended particulate matter (TSP) samples from the air filters placed in the air supply channel of methane-heated turbines of thermal power stations which allows collecting large amounts of TSP materials. Additionally, we combined single and sequential chemical extractions in which not only the concentrations of potentially toxic elements (PTE) (Cd, Cr, Cu, Ni, Pb, Zn) but also that of the major chemical components (Al, Ca, Fe, K, Mg, Mn, Na, P, S, Ti) were analysed. Our aims were to study these metals’ mobility and speciation through the study of their association to major chemical components. Accumulation of the studied PTEs in the TSP material suggests moderate contamination for Ni, Cd and Cr whereas a heavy one for Cu, Zn and Pb. Three groups of these PTEs could be distinguished based on their mobility. The highly mobile Zn and Cd (large ratios of water and weak acid soluble fractions) can be considered as especially harmful elements to environment. The moderately mobile Pb and Cu (large ratios of reducible and oxidizable fractions, respectively) may potentially have a negative effect on the environment, whereas the immobile Cr and Ni cannot be expected to pose a serious risk. Based on the statistical evaluation of extraction data, the potential phases for Zn and Cu are presented by metal-sulphates, -nitrates, -chlorides, -carbonates and -hydroxides, as well as sorbed forms. Lead primarily hosted by metal-carbonates and sorbed forms, as well as by -hydroxides, whereas Cu by organic matter. Finally, Cr and Ni are mostly incorporated into very resistant phases, most probably by magnetite or other resistant metal-oxides. Combination of single and sequential extractions, as well as that of the analysis of not only the target elements but also the major chemical components were found to be a very effective tool to study the host phases of PTEs in the TSP material. The necessity for relatively large sample amounts for such analyses could be fulfilled using special sampling methodology; however, obvious disadvantages of this kind of sampling must be taken into account when resulted data are evaluated.

      PubDate: 2016-11-17T15:41:10Z
       
  • Strongly peraluminous leucogranite (Ebrahim-Attar granite) as evidence for
           extensional tectonic regime in the Cretaceous, Sanandaj Sirjan zone,
           northwest Iran
    • Abstract: Publication date: Available online 1 September 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Hossein Azizi, Keivan Mohammadi, Yoshihiro Asahara, Motohiro Tsuboi, Narges Daneshvar, Behzad Mehrabi
      The Ebrahim-Attar (EBAT) leucogranite body is intruded within the Jurassic metamorphic complex of the Ghorveh area, located in the northern part of the Sanandaj Sirjan zone (SaSZ) of northwest Iran. The granite comprises alkali feldspar, quartz, Na-rich plagioclase and to a lesser extent, muscovite and biotite. Garnet and beryl are also observed as accessory minerals. Additionally, high SiO2 (71.4–81.0wt%) and Rb (145–440ppm) content; low MgO (<0.12wt%), Fe2O3 (<0.68wt.%), Sr (mainly<20ppm), Ba (<57ppm), Zr (10–53ppm) and rare earth elements (REEs) low content (3.88–94.9ppm with an average=21.2ppm); and flat REE patterns with a negative Eu anomaly characterize these rocks. The chemical composition and mineral paragenesis indicate that the rocks were formed by the partial melting of siliciclastic to pelitic rocks and can be classified as per-aluminous leucogranite or strongly per-aluminous (SP) granite. The Rb-Sr whole rock and mineral isochrons confirm that crystallization of the body occurred at 102.5±6.1 Ma in Albian. The 87Sr/86Sr(i) and 143Nd/144Nd(i) ratios are 0.7081±0.009 and 0.51220±0.00005, respectively, and εNd(t) values range from −5.8 to −1.6. These values verify that the source of this body is continental crust. The Nd model ages (TDM2) vary between 1.0 and 1.3 Ga and are more consistent with the juvenile basement of Pan African crust. Based on these results, we suggest that the upwelling of the hot asthenospheric mantle in the SaSZ (likely during the Neo-Tethys rollback activity) occurred after the late Cimmerian orogeny. Consequently, we suggest that this process was responsible for a thinning and heating of the continental crust, from which the SP granite was produced by the partial melting of muscovite rich in pelitic or felsic-metapelitic rocks in the northern SaSZ.

      PubDate: 2016-11-17T15:41:10Z
       
  • Petrogenesis and geodynamic evolution of the Kajan Neogene subvolcanic
           rocks, Nain, Central Iran
    • Abstract: Publication date: Available online 3 September 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Shirin Golkaram, Nematollah Rashidnejad–Omran, Hossein Azizi, Yoshihiro Asahara, David M. Buchs, Iain McDonald, José Francisco Santos
      Kajan subvolcanic rocks in the Urumieh–Dokhtar magmatic arc (UDMA), Central Iran, form a Late Miocene-Pliocene shallow-level intrusion. These subvolcanics correspond to a variety of intermediate and felsic rocks, comprising quartz diorite, quartz monzodiorite, tonalite and granite. These lithologies are medium-K calc-alkaline, with SiO2 (wt.%) varying from 52% (wt.%) to 75 (wt.%). The major element chemical data also show that MgO, CaO, TiO2, P2O5, MnO, Al2O3 and Fe2O3 define linear trends with negative slopes against SiO2, whilst Na2O and K2O are positively correlated with silica. Contents of incompatible trace elements (e.g. Ba, Rb, Nb, La and Zr) become higher with increasing SiO2, whereas Sr shows an opposite behaviour. Chondrite-normalized multi-element patterns show enrichment in LILE relative to HFSE and troughs in Nb, P and Ti. These observations are typical of subduction related magmas that formed in an active continental margin. The Kajan rocks show a strong affinity with calc-alkaline arc magmas, confirmed by REE fractionation (LaN/YbN =4.5–6.4) with moderate HREE fractionation (SmN/YbN =1.08–1.57). The negative Eu anomaly (Eu/Eu* <1), the low to moderate Sr content (<400ppm) and the Dy/Yb values reflect plagioclase and hornblende (+- clinopyroxene) fractionation from a calc-alkaline melt Whole–rock Sr and Nd isotope analyses show that the 87Sr/86Sr initial ratios vary from 0.704432 to 0.705989, and the 143Nd/144Nd initial ratios go from 0.512722 to 0.512813. All the studied samples have similar Sr-Nd isotopes, indicating an origin from a similar source, with granite samples that has more radiogenic Sr and low radiogenic Nd isotopes, suggesting a minor interaction with upper crust during magma ascent. The Kajan subvolcanic rocks plot within the depleted mantle quadrant of the conventional Sr-Nd isotope diagram, a compositional region corresponding to mantle-derived igneous rocks.

      PubDate: 2016-11-17T15:41:10Z
       
  • Separation of a geochemical anomaly from background by fractal and
           U-statistic methods, a case study: Khooni district, Central Iran
    • Abstract: Publication date: Available online 16 September 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Neda Mahvash Mohammadi, Ardeshir Hezarkhani, Bashir Shokouh Saljooghi
      Separation of geochemical anomalies from background are one of the important steps in mineral exploration. The Khooni mineral district (Central Iran) has complex geochemical surface expression due to a complex geological background. This region was chosen as a study area for recognition of the spatial distribution of geochemical elements and separating anomalies from background using stream sediment geochemical data. In the past decades, geochemical anomalies have been identified by means of various methods. Some of these separation methods include: statistical analysis methods, spatial statistical methods and fractal and multi-fractal methods. In this article, two efficient methods, i.e. U-statistics and the fractal concentration-area for separation and detection of anomalous areas of the background were used. The U spatial statistic method is a weighted mean, which considers sampling point positions and their spatial relation in the estimation of anomaly location. Also, fractal and multi-fractal models have also been applied to separate anomalies from background values. In this paper, the concentration–area model (C–A) was suggested to separate the anomaly of background. For this purpose, about 256 stream sediment samples were collected and analyzed. Then anomaly maps of elements were generated based on U spatial statistics and the C-A fractal methods for Au, As and Sb elements. According to obtained results, the U-statistics method performed better than C-A method. Because the comparisons of the known deposits and occurrences against the anomalous area created using thresholds from U-statistics and C-A method show that the spatial U-statistics method hits all of 3 known deposits and occurrences, the C-A fractal method hits 1 and fails 2. In addition, the results showed that these methods with regard to spatial distribution and variability within neighboring samples, in addition to concentration value frequency distributions and correlation coefficients, have more accurate results than the traditional approaches.

      PubDate: 2016-11-17T15:41:10Z
       
  • Data analysis of a revisited exploration geochemical dataset of quartz
           porphyrites from SW Jordan using GIS techniques
    • Abstract: Publication date: Available online 19 September 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Ghazi Saffarini, Ghaleb H. Jarrar, Harald. G. Dill, Hind Ghanem, Najel Yaseen
      The spatial distribution of Cu and its pathfinder elements in quartz porphyrites along Wadi Araba was studied in order to gain an insight about the geologic framework of Cu mineralization in the area. A geochemical exploration data set of 242 samples was revisited. Multivariate statistical and geostatistical analysis were performed on the data set. The objectives of the study were to define Cu relationships with its possible pathfinder elements and to figure out whether geostatistical treatment of exploration data would help telescoping already existing Cu mineralization in Wadi Araba, SW Jordan. Factor analysis and hierarchical cluster analysis were performed on the data set. The results of which indicate that seven elements, namely, Ba, Cr, Mn, Ni, Sc, Sr and V can be considered as pathfinder elements for Cu. Significant correlations do exist between Cu and these elements. The encountered experimental semivariograms of the defined pathfinders were fit to exponential models with varying nugget effects with the exception of Mn which was fit to the spherical model. Ordinary kriging was found to be most appropriate to generate geochemical exploration maps. The applied methods succeeded in deriving valuable information and visualizing the already existing Cu mineralization in Wadi Abu Khusheiba area.

      PubDate: 2016-11-17T15:41:10Z
       
  • Evidence of Mid-ocean ridge and shallow subduction forearc magmatism in
           the Nagaland-Manipur ophiolites, northeast India: constraints from
           mineralogy and geochemistry of gabbros and associated mafic dykes
    • Abstract: Publication date: Available online 19 September 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): A. Krishnakanta Singh, S. Khogenkumar, L. Romendro Singh, R.K. Bikramaditya, Ch. Mangi Khuman, S.S. Thakur
      We discuss here the mineralogical and geochemical characteristics of mafic intrusive rocks from the Nagaland-Manipur Ophiolites (NMO) of Indo-Myanmar Orogenic Belt, northeast India to define their mantle source and tectonic environment. Mafic intrusive sequence in the NMO is characterized by hornblende-free (type-I) and hornblende-bearing (type-II) rocks. The type-I is further categorized as mafic dykes (type-Ia) of tholeiitic N-MORB composition, having TiO2 (0.72–1.93wt.%) and flat REE patterns (LaN/YbN =0.76–1.51) and as massive gabbros (type-Ib) that show alkaline E-MORB affinity, having moderate to high Ti content (TiO2 =1.18 to 1.45wt.%) with strong LREE-HREE fractionations (LaN/YbN =4.54–7.47). Such geochemical enrichment from N-MORB to E-MORB composition indicates mixing of melts derived from a depleted mantle and a fertile mantle/plume source at the spreading center. On the other hand, type-II mafic intrusives are hornblende bearing gabbros of SSZ-type tholeiitic composition with low Ti content (TiO2 =0.54wt.%–0.86wt.%) and depleted LREE pattern with respect to HREE (LaN/YbN =0.37–0.49). They also have high Ba/Zr (1.13–2.82), Ba/Nb (45.56–151.66) and Ba/Th (84.58–744.19) and U/Th ratios (0.37–0.67) relative to the primitive mantle, which strongly represents the melt composition generated by partial melting of depleted lithospheric mantle wedge contaminated by hydrous fluids derived from subducting oceanic lithosphere in a forearc setting. Their subduction related origin is also supported by presence of calcium-rich plagioclase (An16.6–32.3). Geothermometry calculation shows that the hornblende bearing (type-II) mafic rocks crystallized at temperature in range of 565°–625°C±50 (at 10kbar). Based on these available mineralogical and geochemical evidences, we conclude that mid ocean ridge (MOR) type mafic intrusive rocks from the NMO represent the section of older oceanic crust which was generated during the divergent process of the Indian plate from the Australian plate during Cretaceous period. Conversely, the hornblende-bearing gabbros (type-II) represent the younger oceanic crust which was formed at the forearc region by partial melting of the depleted mantle wedge slightly modified by the hydrous fluids released from the subducting oceanic slab during the initial stage of subduction of Indian plate beneath the Myanmar plate.

      PubDate: 2016-11-17T15:41:10Z
       
  • Natural iron oxalates and their analogous synthetic counterparts: A review
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): Enrique J. Baran
      Four iron-containing natural oxalates, usually classified as organic minerals, are known (humboldtine, minguzzite, stepanovite and zhemchuzhnikovite). Their occurrences and general properties are presented and briefly discussed. The subsequent part of the review is devoted to the discussion of synthetic oxalato-complexes, analogous to these natural species, including usual synthetic procedures and a thorough analysis of their crystallographic and structural peculiarities. The thermal, spectroscopic and magnetic properties of these complexes are also analyzed in detail and comparisons with other closely related complexes are also included in the discussions.

      PubDate: 2016-11-17T15:41:10Z
       
  • Geochronology and magma oxygen fugacity of Ehu S-type granitic pluton in
           Zhe-Gan-Wan region, SE China
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): Jun-Ting Qiu, Liang Qiu
      In this paper, we determined the U-Pb isotopic and trace element compositions of zircons from the Ehu S-type granite in the Zhe-Gan-Wan region, SE China, using in-situ laser ablation (LA) ICP-MS. The weighted mean 206Pb/238U age of 132.0±0.6Ma for the Ehu granite indicates that the pluton was formed in the Early Cretaceous and during the Late Mesozoic Cu-Mo mineralization quiescence in Zhe-Gan-Wan region. The calculated logarithmic magma oxygen fugacities for Ehu granite range from −19.19 to −11.43 with an average magma oxidation state of FMQ-0.29, which is much lower than those of Cu-Mo bearing granites in the Zhe-Gan-Wan region. Since Ehu granite was derived from partial melting of metasedimentary basement without fractional crystallization and mantle-derived magma contamination, the low oxidation state of this granite suggests that the assimilation of metasedimentary basement component may not significantly increase the oxidation state of reduced melts from asthenospheric mantle and could not generate oxidized magmas that are favorable for Cu-Mo mineralization.

      PubDate: 2016-11-17T15:41:10Z
       
  • Petrogenesis of a late-Variscan rhyodacite at the Ossa Morena-Central
           Iberian zones boundary, Iberian Massif, Central Portugal: Evidence for the
           involvement of lithospheric mantle and meta-igneous lower crust
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): S.B.A. Henriques, A.M.R. Neiva, G.R. Dunning
      A late-Variscan rhyodacite is exposed at the contact between the Ossa Morena Zone and the Central Iberian Zone of the Iberian Massif, Central Portugal. Dykes of rhyodacite intruded the Série Negra Unit and the Sardoal Complex that are part of the Cadomian basement. The igneous crystallization age of the rhyodacite (308±1 Ma) was obtained on igneous monazite by the ID-TIMS U-Pb method. It is broadly coeval with the emplacement of late-Variscan granitoids during the last deformation phase of the Variscan Orogeny (ca. 304–314 Ma) and with the development of the large late-Variscan strike-slip shear zones (ca. 307 Ma). The rhyodacite samples are calc-alkaline, show identical composition and belong to the same magmatic sequence. The rhyodacite isotopic signatures (Sm-Nd and δ18O) are consistent with depleted-mantle juvenile sources and the contribution of the meta-igneous lower crust. The input of mantle juvenile sources is related to Variscan reactivation of lithospheric fractures. The inherited Neoproterozoic (ca. 619 Ma) and Mesoproterozoic (ca. 1054 Ma) zircon ages, are similar to those of the Central Iberian Zone. This suggests that lower crust of the Central Iberian Zone was involved in the magma generation of the rhyodacite. Coeval late-Variscan magmatic rocks display a larger contribution from ancient crustal components, which may be attributed to the smaller volume and faster cooling rate of the rhyodacite and consequent lower melting of the crust. Mixing of juvenile mantle-derived melts with melts from the lower continental crust was followed by fractional crystallization of garnet and amphibole that remained in the source. Fractional crystallization of plagioclase, biotite, quartz and zircon occurred in shallower magma chambers. Fractional crystallization of zircon was not significant.

      PubDate: 2016-11-17T15:41:10Z
       
  • Thermodynamic properties of tooeleite, Fe63+(As3+O3)4(SO4)(OH)4·4H2O
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): Juraj Majzlan, Edgar Dachs, Artur Benisek, Christian Bender Koch, Ralph Bolanz, Jörg Göttlicher, Ralph Steininger
      Tooeleite, nominally Fe6 3+(As3+O3)4(SO4)(OH)4·4H2O, is a relatively uncommon mineral of some acid-mine drainage systems. Yet, if it does occur, it does so in large quantities, indicating that some specific conditions favor the formation of this mineral in the system Fe-As-S-O-H. In this contribution, we report the thermodynamic properties of synthetic tooeleite. The sample was characterized by powder X-ray diffraction, scanning electron microscopy, extended X-ray absorption fine-structure spectroscopy, and Mössbauer spectroscopy. These methods confirmed that the sample is pure, devoid of amorphous impurities of iron oxides, and that the oxidation state of arsenic is 3+. Using acid-solution calorimetry, the enthalpy of formation of this mineral from the elements at the standard conditions was determined as −6196.6±8.6kJmol−1. The entropy of tooeleite, calculated from low-temperature heat capacity data measured by relaxation calorimetry, is 899.0±10.8Jmol−1 K−1. The calculated standard Gibbs free energy of formation is −5396.3±9.3kJmol−1. The log K sp value, calculated for the reaction Fe6(AsO3)4(SO4)(OH)4·4H2O+16H+ =6Fe3+ +4H3AsO3 +SO4 2− +8H2O, is −17.25±1.80. Tooeleite has stability field only at very high activities of aqueous sulfate and arsenate. As such, it does not appear to be a good candidate for arsenic immobilization at polluted sites. An inspection of speciation diagrams shows that the predominance field of Fe3+ and As3+ overlap only at strongly basic conditions. The formation of tooeleite, therefore, requires strictly selective oxidation of Fe2+ to Fe3+ and, at the same time, firm conservation of the trivalent oxidation state of arsenic. Such conditions can be realized only by biological systems (microorganisms) which can selectively oxidize one redox-active element but leave the other ones untouched. Hence, tooeleite is the first example of an “obligatory” biomineral under the conditions prevailing at or near the Earth's surface because its formation under these conditions necessitates the action of microorganisms.

      PubDate: 2016-11-17T15:41:10Z
       
  • The synorogenic pegmatitic quartz veins of the Guacha Corral Shear zone
           (Sierra de Comechingones, Argentina): A textural, chemical, isotopic,
           cathodoluminescence and fluid inclusion study
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): G. Morteani, F. Eichinger, A. Tarantola, A. Müller, J. Götze, J.A. Sfragulla
      The quartz veins and pegmatites of the Sierra de Comechingones (Sierras de Córdoba, NE Argentina) belong to the Comechingones Pegmatite field (CPF). For the quartz veins and the zoned pegmatites related parental granites are missing. The country rock of the quartz veins are mylonitic augengneisses in granulite to upper amphibolite facies. Field relations, microscopy, cathodoluminescence, radiometric age data, fluid inclusion, chemical and isotopic composition and literature define the quartz veins as synorogenic formed during the high-temperature phase of the Famatinian (480–460Ma) event. During the Famatinian up to the Achalian (382–366Ma) event the synorogenic quartz veins were subjected to high temperature ductile deformation documented by folding, boudinage and finally brittle shearing. K-Ar ages of illite from the shear zones of about 166Ma document the final cooling of the Sierras Pampeanas below 100°C. The long lasting thermal and deformational history of the study area is reflected by very different populations of fluid inclusions in vein quartz with remarkably high contents of thermogenic hydrocarbons in the early-formed fluid inclusions. LA–ICP–MS analysis reveals very low lattice-bound trace element contents, i.e. high purity quartz.

      PubDate: 2016-11-17T15:41:10Z
       
  • A comparison of black claystones, lignites and dump materials from the
           Maritsa Iztok Coal Basin, Bulgaria, using organic geochemical proxies
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): K. Markova, M. Stefanova, Z. Milakovska, S.P. Marinov
      Geochemical analysis of dump materials from the opencast Maritsa Iztok mines, Bulgaria, was carried out based on biomarker assemblages of hydrocarbon fractions. Organic matter (OM) and secondary transformations in three representative samples (massive black claystones and materials from the Iztok and Staroselets dump sites) were studied using geochemical proxies. A number of differences were recognised in the respective OM compositions of the samples compared to both published data and between the individual dump samples themselves. The ОM of the studied samples was found to be polar, but also contains some apolar compounds. It consists mainly of resins and asphalthenes. Claystone OM is of the dispersed type, with intense oxidative-reductive interactions in a lacustrine environment resulting in its transformation into an inert material. Dump sample kerogen is of Type II and mixed Type II/III. In all samples, “odd” numbered n-alkanes are found in higher amounts. Diterpenoids (С19, С20) with pimarane, abietane and phyllocladane skeletons are preponderant. Tri- and tetracyclic terpenoids and steranes have been identified in the black claystones OM only. Hopanes are present in low amounts in extractable OM from all three samples. Biomarkers indicate that black claystone OM is formed from aqueous flora, with a minor supply of gymnosperms (mainly G. Sequoia). Iztok Dump OM is structured by higher plants with an aqueous vegetation input. The Staroselets Dump OM formation is assigned to an active microbial reworking of aqueous vegetation and bacteria with a minor coniferous supply. Different geochemical parameters admit anoxic stratified bottom waters for the black claystones with an addition of deep water stagnation for Staroselets sample in a Maritsa Iztok Basin (MIB) aqueous environment. An attempt was also made to track the effect of secondary processes (oxidation, destruction, dearomatisation), temperature, water drainage and wash-out on dump materials. Leaching and weak degradation processes in the MIB dump environment are likely for a time span of ca. 40–50 years, considering the low percentage of short-chain n-alkanes, long-chain prevalence and low Pr/nC17 and Ph/nC18 ratios, with the Iztok Dump sample experiencing more advanced transformations.

      PubDate: 2016-11-17T15:41:10Z
       
  • Geology, mineralogy, and geochemistry of low grade Ni-lateritic soil (Oman
           Mountains, Oman)
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): Salah A. Al-Khirbash
      The laterite profiles investigated in the present study developed after the emplacement of a slab of oceanic crust and upper mantle sequence (the Semail ophiolite) onto the East Arabian margin during the late Cretaceous. The laterites formed as a result of prolonged weathering of the ophiolite assemblage under tropical to subtropical conditions. Nine laterite profiles have been examined for their Ni potential along a NW-SE segment of the Oman Mountains. The preserved laterite profile shows variations in thickness, mineralogy, and chemical composition. The profiles show a vertical succession from bedrock protolith through saprolite, oxide laterite, to clay laterite. The laterite profiles are unconformably capped either by clastics rocks of the Late Cretaceous Qahlah Formation or by Palaeogene carbonates of the Jafnayn or Abat Formations. The protolith corresponds either to a fine-grained, blackish to greenish serpentinized peridotite or to a coarse-grained dark green altered layered gabbro. The bulk geochemistry of the studied profiles indicates a typical low Ni-laterite pattern in which magnesium (Mg) and silica (Si) become depleted towards the top of the profile, whereas iron (Fe) and aluminum (Al) increase. A significant enrichment in Ni and Co occurred as a result of the laterization process. Ni concentrations average 0.63% (Ibra), 0.72% (East Ibra), 0.67% (Al-Russayl), and 0.33% (Tiwi). Other elements such as Cr, V, Pb, TiO2, Zr, Ba, and Zn were also remobilized across the profiles during the laterization processes.

      PubDate: 2016-11-17T15:41:10Z
       
  • Editorial board members
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3


      PubDate: 2016-11-17T15:41:10Z
       
  • Greenhouse gas emissions from soils—A review
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): Cornelius Oertel, Jörg Matschullat, Kamal Zurba, Frank Zimmermann, Stefan Erasmi
      Soils act as sources and sinks for greenhouse gases (GHG) such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Since both storage and emission capacities may be large, precise quantifications are needed to obtain reliable global budgets that are necessary for land-use management (agriculture, forestry), global change and for climate research. This paper discusses exclusively the soil emission-related processes and their influencing parameters. It reviews soil emission studies involving the most important land-cover types and climate zones and introduces important measuring systems for soil emissions. It addresses current shortcomings and the obvious bias towards northern hemispheric data. When using a conservative average of 300mg CO2e m−2 h−1 (based on our literature review), this leads to global annual net soil emissions of ≥350Pg CO2e (CO2e=CO2 equivalents=total effect of all GHG normalized to CO2). This corresponds to roughly 21% of the global soil C and N pools. For comparison, 33.4 Pg CO2 are being emitted annually by fossil fuel combustion and the cement industry.

      PubDate: 2016-11-17T15:41:10Z
       
  • Assessment of trace metal and rare earth elements contamination in rivers
           around abandoned and active mine areas. The case of Lubumbashi River and
           Tshamilemba Canal, Katanga, Democratic Republic of the Congo
    • Abstract: Publication date: October 2016
      Source:Chemie der Erde - Geochemistry, Volume 76, Issue 3
      Author(s): Emmanuel K. Atibu, Naresh Devarajan, Amandine Laffite, Gregory Giuliani, Joseph A. Salumu, Richard C. Muteb, Crispin K. Mulaji, Jean-Paul Otamonga, Vicky Elongo, Pius T. Mpiana, John Poté
      Active and abandoned mine activities constitute the sources of deterioration of water and soil quality in many parts of the world, particularly in the African Copperbelt regions. The accumulation in soils and the release of toxic substances into the aquatic ecosystem can lead to water resources pollution and may place aquatic organisms and human health at risk. In this study, the impact of past mining activity (i.e., abandoned mine) on aquatic ecosystems has been studied using ICP-MS analysis for trace metals and Rare Earth Elements (REE) in sediment samples from Lubumbashi River (RL) and Tshamilemba Canal (CT), Katanga, Democratic Republic of the Congo (DRC). Soil samples from surrounding CT were collected to evaluate trace metal and REE concentrations and their spatial distribution. The extent of trace metal contamination compared to the background area was assessed by Enrichment Factor (EF) and Geoaccumulation Index (Igeo ). Additionally, the trace metal concentrations probable effect levels (PELs) for their potential environmental impact was achieved by comparing the trace metal concentrations in the sediment/soil samples with the Sediment Quality Guidelines (SQGs). Spearman's Rank-order correlation was used to identify the source and origin of contaminants. The results highlighted high concentrations of trace metals in surface sediments of CT reaching the values of 40152, 15586, 610, 10322, 60704 and 15152mgkg−1 for Cu, Co, Zn, Pb, Fe and Mn, respectively. In the RL, the concentrations reached the values of 24093, 2046, 5463, 3340, 68290 and 769mgkg−1 for Cu, Co, Zn, Pb, Fe and Mn, respectively. The ΣREE varied from 66 to 218 and 142–331mgkg−1 for CT and RL, respectively. The soil samples are characterized by variable levels of trace metals. The EF analysis showed “extremely severe enrichment” for Cu and Co. However, no enrichment was observed for REE. Except for Mo, Th, U, Eu, Mo, Ho and Tm for which Igeo is classified as “moderately polluted and/or unpolluted”, all elements in different sites are classified in the class 6, “extremely polluted”. The trace metal concentrations in all sampling sites largely exceeded the SQGs and the PELs for the Protection of Aquatic Life recommendation. Cu and Co had positive correlation coefficient values (r=0.741, P<0.05, n=14). This research presents useful tools for the evaluation of water contamination in abandoned and active mining areas.

      PubDate: 2016-11-17T15:41:10Z
       
  • Alteration processes of cement induced by CO2-saturated water and its
           effect on physical properties: Experimental and geochemical modeling study
           
    • Abstract: Publication date: Available online 4 October 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Byoung-Young Choi, Hikweon Lee, Gi-Tak Chae, Taehee Kim, Jeong-Chan Kim
      The objective of this study is to understand cement alteration processes with the evolution of porosity and hardness under geologic CO2 storage conditions. For this study, the cylindrical cement cores (class G) were reacted with CO2–saturated water in a vessel (40°C and 8MPa) for 10 and 100 days. After the experiment, the CO2 concentration and Vickers hardness were measured in the hydrated cement core to estimate the carbonation depth and to identify the change in hardness, respectively. Diffusive-reactive transport modeling was also performed to trace the alteration processes and subsequent porosity changes. The results show that cement alteration mainly results from carbonation. With alteration processes, four different reaction zones are developed: degradation zone, carbonation zone, portlandite depletion zone, and unreacted zone. In the degradation zone, the re-dissolution of calcite formed in the carbonation zone leads to the increase of porosity. In contrast, the carbonation zone is characterized by calcite formation resulting mainly from the dissolution of portlandite. The carbonation zone acts as a barrier to CO2 intrusion by consuming dissolved CO2. Especially in this zone, although the porosity decreases, the Vickers hardness increases. Our results show that cement alteration processes can affect the physical and hydrological properties of the hydrated cement under CO2-saturated conditions. Further long-term observation is required to confirm our results under in-situ fluid chemistry of a CO2 storage reservoir. Nonetheless, this study would be helpful to understand alteration processes of wellbore cements under CO2 storage conditions.

      PubDate: 2016-11-17T15:41:10Z
       
  • Dissolution kinetics of selected natural minerals relevant to potential
           CO2-injection sites − Part 1: A review
    • Abstract: Publication date: Available online 7 October 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Astrid Holzheid
      This publication provides a literature review on experimental studies of dissolution kinetics of mainly carbonates and feldspar group minerals, i.e. most common minerals at potential CO2-injection and/or storage sites. Geochemical interaction processes between injected CO2 and coexisting phases, namely reservoir and cap rock minerals and formation fluids close to the CO2-injection site can be simulated by flow-through or mixed flow reactors, while processes far from the injection site and long-term processes after termination actual CO2-injection can be mimicked by batch reactors. At sufficient small stirring rates or fluid flow rates as well as low solute concentrations flow-through reactors are also able to simulate processes far from the injection site. The experimental parameter temperature not only intensifies the dissolution process, the dominant dissolution mechanisms are also influenced by temperature. The dissolution mechanisms change from incongruent and surface controlled mechanisms at lower temperatures to congruent and transport controlled mechanisms at higher temperatures. The CO2 partial pressure has only a second order influence on dissolution behavior compared to the influence of pH-value and ionic strength of the CO2-bearing brine. Minerals exposed to CO2-bearing brines at elevated temperatures and pressures are subject of alteration, leading to severe changes of reactive surfaces and potential precipitation of secondary minerals. Computational simulations of mineral reactions at potential CO2 storage sites have therefore to include not only the time-resolved changes of dissolution behavior and hence kinetics of mineral dissolution, but also the influence of secondary minerals on the interaction of the minerals with CO2-enriched brines.

      PubDate: 2016-11-17T15:41:10Z
       
  • Dissolution kinetics of selected natural minerals relevant to potential
           CO2-injection sites – Part 2: Dissolution and alteration of carbonates
           and feldspars in CO2-bearing brines
    • Abstract: Publication date: Available online 13 October 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Astrid Holzheid
      Chemical interaction processes among injected CO2, saline fluids and potential reservoir materials are experimentally simulated to derive dissolution rates of natural materials (minerals) that can be used as input parameters for modeling of CO2 storage in deep saline formations and risk analyses. In order to study dissolution processes, mineral aliquots were exposed to CO2-bearing brines at elevated temperature (60, 100, 150°C) and pressure (85bar) and at various run durations. Several potential reservoir rocks include carbonates as cement. Calcite and dolomite grains were therefore mainly used as solid starting material. Experiments with the two feldspar varieties alkali feldspar and almost pure anorthite were performed in addition. Grain sizes of the mineral starting materials varied between <63μm and 500μm with most experiments performed at grain size fractions of 160 – 250μm and 250 – 500μm. All experiments run with a complex synthetic brine (total dissolved solids: ∼156g/l) according to a natural upper cretaceous formation water. Dry ice was used as CO2-source. All experiments were done in closed batch reactors. These reactors allow mimicking reservoir conditions far from the injection site as well as reservoir conditions after finishing the CO2 injection. The concentration changes during the experiment were monitored by ICP-OES measurements of the initial and the post-run fluids. Dissolution rates were derived based on the concentration changes of the brine. Most of the studied experimental variables and parameters (temperature, run duration, grain size, brine composition – expressed as pH-value and ionic strength) impact alteration of the reacting agents, i.e. they change the chemical composition of the brine, change the surfaces of the mineral aliquots exposed to the CO2-bearing brine, and induce formation of secondary minerals. Hence, all influencing parameters on dissolution processes have to be considered and time-resolved changes of the dissolution behavior have to be implemented in numerical simulations of processes at CO2 injection sites and CO2 storage reservoirs.

      PubDate: 2016-11-17T15:41:10Z
       
  • Geochronological, geochemical and mineralogical constraints on the
           petrogenesis of appinites from the Laoniushan complex, eastern Qinling,
           central China
    • Abstract: Publication date: Available online 18 October 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Lixue Ding, Changqian Ma, Jianwei Li, Lianxun Wang
      Appinites are commonly derived from a mantle source and are potentially significant in constraining the tectonic nature and evolution of ancient orogens, yet they have received little attention because of their limited outcrop. Here we investigate the newly identified appinitic rocks from the Laoniushan complex in the eastern Qinling Orogen. The appinites are composed of coarse-grained hornblendite, medium- and fine-grained hornblende-gabbro, and diorite porphyrite in the field occurrence. Winthin the appinitic rocks, the hornblendite displays features of cumulates. This study presents LA-ICP-MS zircon U-Pb data, mineral chemistry and whole rock geochemistry of the appinites. Zircons in the mafic to ultramafic rocks yield a U-Pb age of 152±1Ma. The geochemistry of the rocks displays: lower SiO2, higher Fe2O3 T and MgO contents, relatively flat chondrite normalized REE patterns with slight enrichment in light REE and a minor negative Eu anomaly; enrichment in large-ion lithophile elements(LILE, e.g. Rb, Ba, Sr and P), and depletion in high field strength elements(HFSE, e.g. Nb, Zr, Hf and Ti). Such geochemical features, together with crust-like bulk Sr-Nd isotopic compositions(initial 87Sr/86Sr ratios of 0.7057–0.7072, εNd(t)=−17.2 to −9), suggest that the Laoniushan appinites likely originated from an ancient metasomatised mantle, followed by fractional crystallization in the petrogenetic process. The studied appinites were most likely generated in an intracontinental extensional environment in the Late Mesozoic.

      PubDate: 2016-11-17T15:41:10Z
       
  • Mixing geochemistry of cold water around non-volcanic thermal springs in
           high-grade metamorphic terrain, Sri Lanka
    • Abstract: Publication date: Available online 21 October 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): D.T. Jayawardana, D.T. Udagedara, A.A.M.P. Silva, H.M.T.G.A. Pitawala, W.K.P. Jayathilaka, A.M.N.M. Adikaram
      A geochemical survey was conducted on thermal water and cold water around non-volcanic geothermal fields at Mahaoya and Marangala in Sri Lanka. One hundred forty-two samples were analyzed for fifteen selected irons to investigate geochemical relationships resulting from water-rock interactions and mixing. Based on measurements using a Na-K-Mg geothermometer, the maximum temperatures of thermal reservoirs were estimated to be 148°C in Mahaoya and 191°C in Marangala, which were higher values than those obtained using Na-Li and Li-Mg geothermometers. This suggests that the reservoirs extend from intermediate to deep levels. Hydrogeochemistry of thermal waters is distinct from that of cold water; higher contents of Na, K, Cl, F, SO4, and TDS in thermal water are most likely due to the dissolution of feldspar, mica, and sulfide minerals in the granitic rocks. Conversely, lower values of Fe, Mg, Cu, Zn, and Pb imply less ferromagnesian minerals in the basement. Classification based on major ions reveals a Na-K-SO4 type of thermal water for Mahaoya and Marangala. Cold water is dominated by the Na-K-HCO3 type, which indicates deep groundwater influence by iron exchange. Non-mixing cold water indicates a Ca-HCO3 type. In general, chemistry of cold water wells (<400m) close to the thermal water changes significantly due to direct mixing of thermal water and cold water. In comparison, a contrasting action occurs with increasing distance from the geothermal field. Gradual decline of SO4 with increasing distance from thermal water may indicate a trend of clear oxidation. However, the chemistry of more distant wells demarcates deep circulations through fractures and faults in the basement.

      PubDate: 2016-11-17T15:41:10Z
       
  • Paleofluids circulation associated with the Gerês late-orogenic granitic
           massif, northern Portugal
    • Abstract: Publication date: Available online 2 November 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): L. Jaques, F. Noronha, N. Liewig, I. Bobos
      The Hercynian late-orogenic granites from the Gerês massif, northern Portugal, underwent intense hydrothermal activity along tectonic structures striking N-S and NE-SW. The first hydrothermal stage is characterized by the albitization of feldspars (primary K-feldspar and plagioclase) followed by the dissolution of magmatic quartz, the chloritization of biotite, and the muscovitization of magmatic biotite and feldspars and occasionally of authigenic albite. Whole-rock geochemistry shows a decrease of SiO2, K2O and Rb and an increase of Na2O, Al2O3 and Sr amounts during the albitization. The second hydrothermal stage is characterized by a mineral assemblage consisting of secondary quartz, albite, chlorite, hematite, apatite, muscovite, epidote, sphene and carbonates, which infilled the cavities produced by the early quartz leaching. Mass balance calculations demonstrate a noticeable element mobilization during the granite alteration. The average ∑REE of the Gerês granite is nearly constant at 154ppm, but ranges from 91 to 163ppm in the altered rocks. A relative LREE depletion and a slight HREE enrichment associated with a negative Eu anomaly characterize the feldspathization process of Gerês granite. The average ∑REE of the Carris granite is at 159ppm but in the altered epidote+chlorite+hematite assemblage it reaches about 201ppm with a slight HREE increase. Two different fluids were involved in the hydrothermal alteration. A first aqueous fluid (Lw1), with a low to intermediate salinity (<10wt.% eq. NaCl) circulated along the main structures (N-S, NE-SW and NW-SE), characterized by entrapment temperature lower than 350°C and maximum pressure of 115MPa followed by a later colder and more saline fluid (Lw2) under a temperature of 220°C and a pressure of about 27MPa. Oxygen isotope data obtained on magmatic quartz indicate δ18Oquartz of+9.3 and+11.0‰, pointing to an interaction of magmatic fluids with others of meteoric origin. For the secondary quartz, δ18Owater of +0.5 and +0.7‰ were calculated for a temperature of 250°C, suggesting a meteoric fluid with a possible seawater signature. The K-Ar data of K-feldspar from the altered rocks confirm an age of 273.6±11.7 Ma, attributed to the first alteration process. Younger K-Ar ages between 155.8±6.7 Ma and 124±5.3 Ma were also obtained in the feldspathized rocks, confirming the late hydrothermal activity. Albitization and quartz dissolution of granitic rocks from the Gerês massif occurred at depths shallower than 5km, induced by the circulation of fluids along brittle structures, during the orogenic uplift and extensional tectonics which affected the Iberian Massif in the Early Permian. A second major event is attributed to late hydrothermal circulations of aqueous brines until a depth of about 3km, presumably derived from interaction with sub-surface evaporites throughout Late Jurassic to Early Cretaceous. These late hydrothermal events probably reflect the rifting episodes and the rising of geothermal gradient, associated with the opening of the Atlantic Ocean and Gulf of Biscay, respectively.

      PubDate: 2016-11-17T15:41:10Z
       
  • Melting and differentiation of early-formed asteroids: The perspective
           from high precision oxygen isotope studies
    • Abstract: Publication date: Available online 14 November 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Richard C. Greenwood, Thomas H. Burbine, Martin F. Miller, Ian. A. Franchi
      A number of distinct methodologies are available for determining the oxygen isotope composition of minerals and rocks, these include laser-assisted fluorination, secondary ion mass spectrometry (SIMS) and UV laser ablation. In this review we focus on laser-assisted fluorination, which currently achieves the highest levels of precision available for oxygen isotope analysis. In particular, we examine how results using this method have furthered our understanding of early-formed differentiated meteorites. Due to its rapid reaction times and low blank levels, laser-assisted fluorination has now largely superseded the conventional externally-heated Ni “bomb” technique for bulk analysis. Unlike UV laser ablation and SIMS analysis, laser-assisted fluorination is not capable of focused spot analysis. While laser fluorination is now a mature technology, further analytical improvements are possible via refinements to the construction of sample chambers, clean-up lines and the use of ultra-high resolution mass spectrometers. High-precision oxygen isotope analysis has proved to be a particularly powerful technique for investigating the formation and evolution of early-formed differentiated asteroids and has provided unique insights into the interrelationships between various groups of achondrites. A clear example of this is seen in samples that lie close to the terrestrial fractionation line (TFL). Based on the data from conventional oxygen isotope analysis, it was suggested that the main-group pallasites, the howardite eucrite diogenite suite (HEDs) and mesosiderites could all be derived from a single common parent body. However, high precision analysis demonstrates that main-group pallasites have a Δ17O composition that is fully resolvable from that of the HEDs and mesosiderites, indicating the involvement of at least two parent bodies. The range of Δ17O values exhibited by an achondrite group provides a useful means of assessing the extent to which their parent body underwent melting and isotopic homogenization. Oxygen isotope analysis can also highlight relationships between ungrouped achondrites and the more well-populated groups. A clear example of this is the proposed link between the evolved GRA 06128/9 meteorites and the brachinites. The evidence from oxygen isotopes, in conjunction with that from other techniques, indicates that we have samples from approximately 110 asteroidal parent bodies (∼60 irons, ∼35 achondrites and stony-iron, and  ∼15 chondrites) in our global meteorite collection. However, compared to the likely size of the original protoplanetary asteroid population, this is an extremely low value. In addition, almost all of the differentiated samples (achondrites, stony-iron and irons) are derived from parent bodies that were highly disrupted early in their evolution. High-precision oxygen isotope analysis of achondrites provides some important insights into the origin of mass-independent variation in the early Solar System. In particular, the evidence from various primitive achondrite groups indicates that both the slope 1 (Y&R) and CCAM lines are of primordial significance. Δ17O differences between water ice and silicate-rich solids were probably the initial source of the slope 1 anomaly. These phases most likely acquired their isotopic composition as a result of UV photo-dissociation of CO that took place either in the early solar nebula or precursor giant molecular cloud. Such small-scale isotopic heterogeneities were propagated into larger-sized bodies, such as asteroids and planets, as a result of early Solar System processes, including dehydration, aqueous alteration, melting and collisional interactions. There is increasing evidence that chondritic parent bodies accreted relatively late compared to achondritic asteroids. This may account for the fact that apart from a few notable exceptions’ such as the aubrite-enstatite chondrite association, known chondrite groups could not have been the parents to the main achondrite groups.

      PubDate: 2016-11-17T15:41:10Z
       
  • The Braunschweig meteorite − a recent L6 chondrite fall in Germany
    • Abstract: Publication date: Available online 15 November 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Rainer Bartoschewitz, Peter Appel, Jean-Alix Barrat, Addi Bischoff, Marc W. Caffee, Ian A. Franchi, Zelimir Gabelica, Richard C. Greenwood, Mourad Harir, Dennis Harries, Rupert Hochleitner, Jens Hopp, Matthias Laubenstein, Barbara Mader, Rosa Marques, Andreas Morlok, Gert Nolze, Maria Isabel Prudêncio, Pierre Rochette, Alexander Ruf, Philippe Schmitt-Kopplin, Erhard Seemann, Marian Szurgot, Roald Tagle, Radosław A. Wach, Kees C. Welten, Mona Weyrauch, Karl Wimmer
      On April 23rd 2013 at 2:07a.m., a 1.3kg meteorite fell in the Braunschweig suburb Melverode (52° 13′ 32.19″ N. 10° 31′ 11.60″ E). Its estimated velocity was 250km/h and it formed an impact pit in the concrete fall site with a diameter of 7cm and a depth of 3cm. Radial dust striae are present around the impact pit. As a result of the impact, the meteorite disintegrated into several hundred fragments with masses up to 214g. The meteorite is a typical L6 chondrite, moderately shocked (S4) – but with a remarkably high porosity (up to 20vol%). The meteorite was ejected from its parent body as an object with a radius of about 10–15cm (15–50kg). The U,Th-He gas retention age of ∼550 Ma overlaps with the main impact event on the L-chondrite parent body ∼470 Ma ago that is recorded by many shocked L chondrites. The preferred cosmic-ray exposure age derived from production of radionuclides and noble gas isotopes is (6.0±1.3) Ma.

      PubDate: 2016-11-17T15:41:10Z
       
  • Cordierite from a high-temperature low-pressure shear zone of the
           south-western Bohemian Massif (Moldanubian terrain, Austria)
    • Abstract: Publication date: Available online 15 November 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Robert Sturm
      A medium-scale shear zone exposed in the gneiss rocks of the South-western Bohemian Massif (Moldanubian Zone) contains cordierite, whose Na p.f.u. is subject to a significant increase from the centre to the edge of the deformation area, whilst other elements only show negligible variations. Coexisting mineral phases of cordierite include garnet, biotite, and sillimanite. According to the results obtained from the garnet-cordierite Fe2+/Mg2+-exchange thermometer a decrease of peak temperature from 639°C in the central mylonite to 593°C in the marginal mylonite can be observed, which indicates significant shear heating. Lithological pressures were estimated by considering the position of cordierite-forming reactions in the P-T field and the stability of coexisting sillimanite. They are subject to a reduction from 0.35GPa in the highest deformed mylonite to 0.31GPa at the margin of the shear zone. According to the results of comprehensive petrographic and mineralogical studies the investigated shear zone underwent a Variscan HT-LP metamorphic event implying the formation of cordierite and an Alpine MT-LP event entailing the rotation and decomposition of the cordierite phase.

      PubDate: 2016-11-17T15:41:10Z
       
 
 
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