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  Subjects -> EARTH SCIENCES (Total: 645 journals)
    - EARTH SCIENCES (466 journals)
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EARTH SCIENCES (466 journals)                  1 2 3 4 5 | Last

Acta Geodaetica et Geophysica     Hybrid Journal  
Acta Geodaetica et Geophysica Hungarica     Full-text available via subscription   (Followers: 2)
Acta Geophysica     Open Access   (Followers: 7)
Acta Geotechnica     Hybrid Journal   (Followers: 8)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 4)
Advances in High Energy Physics     Open Access   (Followers: 16)
Advances In Physics     Hybrid Journal   (Followers: 9)
Aeolian Research     Hybrid Journal   (Followers: 3)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 12)
Algological Studies     Full-text available via subscription   (Followers: 2)
Alpine Botany     Hybrid Journal   (Followers: 5)
AMBIO     Hybrid Journal   (Followers: 13)
Anales del Instituto de la Patagonia     Open Access   (Followers: 1)
Andean geology     Open Access   (Followers: 4)
Annales Henri Poincaré     Hybrid Journal   (Followers: 2)
Annales UMCS, Geographia, Geologia, Mineralogia et Petrographia     Open Access   (Followers: 2)
Annals of Geophysics     Full-text available via subscription   (Followers: 9)
Annals of GIS     Hybrid Journal   (Followers: 17)
Annals of Glaciology     Full-text available via subscription   (Followers: 2)
Annual Review of Marine Science     Full-text available via subscription   (Followers: 12)
Anthropocene     Hybrid Journal  
Anthropocene Review     Hybrid Journal   (Followers: 3)
Applied Clay Science     Hybrid Journal   (Followers: 3)
Applied Geochemistry     Hybrid Journal   (Followers: 8)
Applied Geomatics     Hybrid Journal   (Followers: 5)
Applied Geophysics     Hybrid Journal   (Followers: 8)
Applied Ocean Research     Hybrid Journal   (Followers: 6)
Applied Petrochemical Research     Open Access   (Followers: 3)
Applied Remote Sensing Journal     Open Access   (Followers: 12)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 35)
Arctic Science     Open Access   (Followers: 6)
Arctic, Antarctic, and Alpine Research     Full-text available via subscription   (Followers: 9)
Artificial Satellites : The Journal of Space Research Centre of Polish Academy of Sciences     Open Access   (Followers: 14)
Asia-Pacific Journal of Atmospheric Sciences     Hybrid Journal   (Followers: 2)
Asian Journal of Earth Sciences     Open Access   (Followers: 21)
Asian Review of Environmental and Earth Sciences     Open Access  
Atlantic Geology : Journal of the Atlantic Geoscience Society / Atlantic Geology : revue de la Société Géoscientifique de l'Atlantique     Full-text available via subscription   (Followers: 3)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 6)
Atmospheric and Climate Sciences     Open Access   (Followers: 15)
Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia     Hybrid Journal   (Followers: 12)
Boletim de Ciências Geodésicas     Open Access  
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 11)
Bragantia     Open Access   (Followers: 2)
Bulletin of Earthquake Engineering     Hybrid Journal   (Followers: 10)
Bulletin of Geosciences     Open Access   (Followers: 10)
Bulletin of the Lebedev Physics Institute     Hybrid Journal   (Followers: 1)
Bulletin of the Seismological Society of America     Full-text available via subscription   (Followers: 17)
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: 2)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 18)
Carbonates and Evaporites     Hybrid Journal   (Followers: 4)
CATENA     Hybrid Journal   (Followers: 4)
Chemical Geology     Hybrid Journal   (Followers: 11)
Chemie der Erde - Geochemistry     Hybrid Journal   (Followers: 4)
Chinese Geographical Science     Hybrid Journal   (Followers: 5)
Chinese Journal of Geochemistry     Hybrid Journal   (Followers: 3)
Chinese Journal of Oceanology and Limnology     Hybrid Journal   (Followers: 2)
Ciencia del suelo     Open Access   (Followers: 2)
Ciencias Espaciales     Open Access  
Climate and Development     Hybrid Journal   (Followers: 12)
Coastal Management     Hybrid Journal   (Followers: 23)
Cogent Geoscience     Open Access  
Comptes Rendus Geoscience     Full-text available via subscription   (Followers: 7)
Computational Geosciences     Hybrid Journal   (Followers: 13)
Computational Mathematics and Mathematical Physics     Hybrid Journal   (Followers: 1)
Computers and Geotechnics     Hybrid Journal   (Followers: 8)
Contemporary Trends in Geoscience     Open Access   (Followers: 2)
Continental Shelf Research     Hybrid Journal   (Followers: 8)
Contributions to Mineralogy and Petrology     Hybrid Journal   (Followers: 8)
Contributions to Plasma Physics     Hybrid Journal   (Followers: 2)
Coral Reefs     Hybrid Journal   (Followers: 16)
Cretaceous Research     Hybrid Journal   (Followers: 6)
Cybergeo : European Journal of Geography     Open Access   (Followers: 3)
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: 1)
Diatom Research     Hybrid Journal  
Doklady Physics     Hybrid Journal   (Followers: 1)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 2)
E&S Engineering and Science     Open Access  
E3S Web of Conferences     Open Access  
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 73)
Earth and Space Science     Open Access   (Followers: 1)
Earth Interactions     Full-text available via subscription   (Followers: 11)
Earth Science Research     Open Access   (Followers: 7)
Earth Surface Dynamics (ESurf)     Open Access   (Followers: 3)
Earth Surface Processes and Landforms     Hybrid Journal   (Followers: 19)
Earth System Dynamics     Open Access   (Followers: 7)
Earth System Dynamics Discussions     Open Access   (Followers: 4)
Earth's Future     Open Access   (Followers: 1)
Earth, Planets and Space     Open Access   (Followers: 4)
Earthquake Engineering and Engineering Vibration     Hybrid Journal   (Followers: 7)
Earthquake Science     Hybrid Journal   (Followers: 8)
Earthquake Spectra     Full-text available via subscription   (Followers: 13)
Ecohydrology     Hybrid Journal   (Followers: 9)
Ecological Questions     Open Access   (Followers: 6)
Electromagnetics     Hybrid Journal   (Followers: 2)

        1 2 3 4 5 | Last

Journal Cover Chemie der Erde - Geochemistry
  [SJR: 0.701]   [H-I: 26]   [4 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0009-2819
   Published by Elsevier Homepage  [2801 journals]
  • Petrography and classification of NWA 7402: A new sulfide-rich
           unequilibrated ordinary chondrite
    • Abstract: Publication date: Available online 23 January 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Christine E. Jilly-Rehak, Gary R. Huss, Lydie Bonal, Eric Twelker
      We classify a new chondritic find Northwest Africa (NWA) 7402. This meteorite is highly unequilibrated, and is therefore potentially significant for the study of primitive Solar System materials. Mineralogy, mineral chemistry, and modal abundances of minerals indicate that NWA 7402 is most likely an L chondrite. However, the specimen contains a higher abundance of sulfide than commonly seen in ordinary chondrites. The structural order of organic matter in the matrix and the chromium content of Fe-rich olivine grains indicate a petrologic type of 3.1. NWA 7402 largely escaped thermal metamorphism, and secondary phases formed by aqueous alteration are rare to absent. Minor planar fractures and undulatory extinction of olivine grains suggest that NWA 7402 experienced shock up to stage 2 or 3. Terrestrial weathering is heterogeneous in the specimen; much of the stone's exterior shows substantial Fe oxidation (weathering grade 2), while some parts of the interior remain relatively fresh (weathering grade 1). NWA 7402 has some unusual features that should be investigated further. The sulfide abundance is higher than reported sulfide contents for other L chondrites, and the chromium content of the olivines does not fall on the trend established for unequilibrated ordinary chondrites by Grossman and Brearley (2005).


      PubDate: 2016-01-28T05:45:05Z
       
  • Elemental and organic geochemistry of Gondwana sediments from the
           Krishna–Godavari Basin, India
    • Abstract: Publication date: Available online 22 January 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Devleena Mani, B. Ratnam, M.S. Kalpana, D.J. Patil, A.M. Dayal
      Elemental and organic geochemical studies have been carried out on the Gondwana sediments, collected from the outcrops of Permian and Jurassic–Cretaceous rocks in the Krishna–Godavari basin on the eastern coast of India, to understand their paleo and depositional environment and its implications for hydrocarbon generation in the basin. Amongst the studied formations, the Raghavapuram, Gollapalli and Tirupati form a dominant Cretaceous Petroleum System in the west of the basin. Raghavapuram shales and its stratigraphic equivalents are the source rock and Gollapalli and Tirupati sandstones form the reservoirs, along with basaltic Razole formation as the caprock. Major element systematics and X-ray diffraction study of the sandstones indicate them to be variably enriched with SiO2 relative to Al2O3 and CaO, which is associated, inherently with the deposition and diagenesis of the Gondwana sediments. Post-Archean Average Shale normalized rare earth elements in shales show enrichment in most of the samples due to the increasing clay mineral and organic matter assemblage. A negative europium and cerium anomaly is exhibited by the REE's in majority of rocks. Composed primarily of quartz grains and silica cement, the Gollapalli and Tirupati sandstones have characteristics of high quality reservoirs. The shales show a significant increase in the concentration of redox sensitive trace elements, Ni, V, Cr, Ba and Zn. The total organic carbon content of the shales ranges between 0.1 and 0.5wt%. Programmed pyrolysis of selected samples show the Tmax values to range between 352–497°C and that of hydrogen index to be between 57–460mgHC/gTOC. The organic matter is characterized by, mainly, gas prone Type III kerogen. The n-alkane composition is dominated by n-C11–C18 and acyclic isoprenoid, phytane. The aromatic fraction shows the presence of naphthalene, anthracene, phenanthrene, chrysene and their derivatives, resulting largely from the diagenetic alteration of precursor terpenoids. The organic geochemical proxies indicate the input of organic matter from near-shore terrestrial sources and its deposition in strongly reducing, low oxygen conditions. The organic matter richness and maturity derived from a favorable depositional setting has its bearing upon the Gondwana sediments globally, and also provides promising exploration opportunities, particularly in the Raghavapuram sequence of the KG basin.


      PubDate: 2016-01-22T11:54:03Z
       
  • U–Pb dating of zircons from tuff layer, sandstone and tillite
           samples in the uppermost Liantuo Formation and the lowermost Nantuo
           Formation in Three Gorges area, South China
    • Abstract: Publication date: Available online 21 January 2016
      Source:Chemie der Erde - Geochemistry
      Author(s): Dao-Hui Pi, Shao-Yong Jiang
      Uranium-lead (U–Pb) dating was conducted on zircons in tuff layers and sandstone samples from the uppermost Liantuo Formation and in a tillite sample from the lowermost Nantuo Formation in Three Gorges area, South China, using SHRIMP and LA-ICP-MS techniques. Zircons from these samples yielded age spectrum (within 1000Ma) of ∼890, ∼830, ∼780, ∼730, and 646Ma. Zircons from the Liantuo tuffs have a weighted mean 206Pb/238U age of 734.1±8.1Ma (2σ, n =7, MSWD=0.48), which was regarded as the best estimation of the upper boundary age of the Liantuo Formation. Combining with previous geochronologic data, the Liantuo Formation was proposed to be a pre-Chang′an glaciation unit, and it is comparable to the middle-upper Banxi/Danzhou Group in South China.


      PubDate: 2016-01-22T11:54:03Z
       
  • Advances in determining asteroid chemistries and mineralogies
    • Abstract: Publication date: Available online 23 December 2015
      Source:Chemie der Erde - Geochemistry
      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: 2015-12-25T07:37:38Z
       
  • Geochemical mapping based on geological units: a case study from the
           Marnoso-arenacea formation (Northern Apennines, Italy)
    • Abstract: Publication date: Available online 18 December 2015
      Source:Chemie der Erde - Geochemistry
      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: 2015-12-21T11:23:53Z
       
  • Petrogenesis of Miocene alkaline volcanic suites from western Bohemia:
           whole rock geochemistry and Sr–Nd–Pb isotopic signatures
    • Abstract: Publication date: Available online 7 December 2015
      Source:Chemie der Erde - Geochemistry
      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: 2015-12-09T03:06:37Z
       
  • Chondrule size and related physical properties: A compilation and
           evaluation of current data across all meteorite groups
    • Abstract: Publication date: December 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 4
      Author(s): Jon M. Friedrich, Michael K. Weisberg, Denton S. Ebel, Alison E. Biltz, Bernadette M. Corbett, Ivan V. Iotzov, Wajiha S. Khan, Matthew D. Wolman
      The examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. Among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. Knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. To examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data. We include all chondrite chemical groups as well as the acapulcoite primitive achondrites, some of which contain relict chondrules. We also compile and review current literature data for other astrophysically-relevant physical properties (chondrule mass and density). Finally, we briefly examine some additional physical aspects of chondrules such as the frequencies of compound and “cratered” chondrules. A purpose of this compilation is to provide a useful resource for meteoriticists and astrophysicists alike.


      PubDate: 2015-12-05T08:00:37Z
       
  • Editorial board members
    • Abstract: Publication date: December 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 4




      PubDate: 2015-12-05T08:00:37Z
       
  • Cobalt sorption–desorption behavior of calcareous soils from some
           Iranian soils
    • Abstract: Publication date: Available online 28 November 2015
      Source:Chemie der Erde - Geochemistry
      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: 2015-12-01T07:39:33Z
       
  • Geochemical constraint on origin and evolution of solutes in geothermal
           springs in western Yunnan, China
    • Abstract: Publication date: Available online 25 November 2015
      Source:Chemie der Erde - Geochemistry
      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: 2015-11-26T23:36:32Z
       
  • Mineralogical and geochemical investigations of the Mombi bauxite deposit,
           Zagros Mountains, Iran
    • Abstract: Publication date: Available online 25 November 2015
      Source:Chemie der Erde - Geochemistry
      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: 2015-11-26T23:36:32Z
       
  • 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: Available online 19 November 2015
      Source:Chemie der Erde - Geochemistry
      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: 2015-11-22T23:07:31Z
       
  • Influence of a CO2 long term exposure on the mobilisation and speciation
           of metals in soils
    • Abstract: Publication date: Available online 10 November 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Yang Wei, Patricia Córdoba, Giorgio Caramanna, Mercedes Maroto-Valer, Paul Nathaniel, Michael D Steven
      This study investigates the potential risks associated with high levels and long term exposure of carbon dioxide (CO2) on the mobility and speciation of exchangeable metals in soils. CO2 incubation batch experiments at high pressure and temperature coupled with geochemical modelling were carried out to elucidate the behaviour and mobilisation of metals and the response of soil chemical parameters as a result of long term CO2 exposure. A t-Student analysis was performed to ascertain whether differences in the mean concentration of exchangeable metals in soils before and after CO2-incubations are attributable to increase of metal molibilisation because of the long term CO2 exposure. The t-Student revealed the CO2 long term incubation was statistically significant (p <0.05) for the exchangeable concentration of Ni, Zn, and Pb. The CO2-soil incubation induces the acidification of the pore water of soils via CO2 hydrolysis and as a consequence, it increases the exchangeable concentration of Ni, Zn, and Pb in the soils. As, Al, Cr, Cu, and Fe show a different mobilisation pattern depending on the moisture content in soils. Al3+, Fe2+, Cr3+, and Cu2+ as free cations, As as HAsO2, Pb2+and PbHCO3 −, Zn2+ and ZnHCO3 −, are predicted to be the predominant aqueous complexes in the pore water of the incubated soils.
      Graphical abstract image

      PubDate: 2015-11-10T21:20:23Z
       
  • Estimation of carbon dioxide flux degassing from percolating waters in a
           karst cave: Case study from Bijambare cave, Bosnia and Herzegovina
    • Abstract: Publication date: Available online 4 November 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Simone Milanolo, Franci Gabrovšek
      Drip water, collected above three actively forming stalagmites, has been analyzed and the results discussed using a calcite saturation index versus equilibrium carbon dioxide partial pressure theoretical relationship. Percolating water appears to have been originated from a parent solution in equilibrium with a carbon dioxide rich gas phase having a minimum concentration varying between 15,000ppmv and 26,000ppmv while large part of the variability recorded in the cave can be explained by different stage of degassing. Similarly, analyses performed at several cave pools confirm that drip water rapidly achieves equilibrium with the cave atmosphere after impact on the stalagmite apex, while oversaturation is retained longer. Using these boundary conditions, the changes in inorganic carbon concentration in the percolating water have been calculated and converted into fluxes using an average effective infiltration flow estimated from the annual water balance. The predicted flux of carbon dioxide degassing from drip water is in the range of 0.03–0.06μmolm−2 s−1. This flux has been found to be one of the major sources of carbon dioxide in the cave atmosphere during low ventilation periods.


      PubDate: 2015-11-06T19:33:15Z
       
  • Physils and organic matter-base palaeoenvironmental records of the K/Pg
           boundary transition from the late Cretaceous-early Palaeogene succession
           of the Um-Sohryngkew River section of Meghalaya, India
    • Abstract: Publication date: Available online 20 October 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Sucharita Pal, J.P. Shrivastava, Sanjay K. Mukhopadhyay
      A continuous, shallow marine succession of the Um-Sohryngkew River section is distinct as it contains late Maastrichtian-early Danian planktonic foraminiferal zones and the K/Pg boundary, although K/Pg transition events remain inconclusive. Physils divide entire succession in to lower, middle and upper sub-divisions and represent anomalous values of redox-sensitive elements (δCe, La/Yb and Gd/Yb) in biozone CF3. Organic matter when analyzed show TOC and C spikes in biozone CF3. Illite thermometry also revealed sudden increase in the palaeo-temperature (>140°C) for yellowish brown 1–2mm thick organic rich clay layer in biozone CF3. Interestingly, conspicuous increase in the short chain n-alkanes and fatty acids is observed in the biozone CF3, although, long chain n-alkanes (C27–C33) derived from terrestrial plants show low abundance throughout the succession. High amount of combustion derived fluoranthene, pyrene, chrysene, benzo(a) anthracene PAH compounds found in the biozone CF3 are analogous to those reported from the K/T boundary sections of Stevns Klint, Gubbio, Woodside Creek and Arroyo el Mimbral. The pyrolitic signatures of these organic macro-molecules reflect global fire, caused distress to biota (during the deposition of biozone CF3 layer) which is coincidental with the well documented Ce anomaly layer, but, preceded by planktonic foraminiferal change in biozone P0 and PGE anomaly bearing layer in the biozone CF2. These organic macro-molecules reflect global fire, induced by the heat supplied by the late Cretaceous Abor and/or Deccan extrusions perhaps linked with the K/T transition events as later initiated prior to the K/Pg boundary, however, the main episode of Deccan volcanic activity occurred ∼300ky earlier or at the K/Pg boundary itself. The deposition of 1–2mm thick, yellowish brown, smooth (with conchoidal fracture) pyrite nodules and micro-spherules bearing organic rich clay layer marked with the decrease in the carbonate content (2.43%) that lies at the contact between the silty mudstone and grey calcareous shale located in the biozone CF3 of this succession coincides with the first appearance of Pseudoguembelina hariaensis representing age of 66.83–65.45Ma is also related to the India’s collision with the Eurasia and Burma andextrusion of Abor volcanic.These events also endorse succeeding events such as anomalous concentration of platinum group of elements and concentration of spherules during biozone CF2, which are other end Cretaceous events before the advent of the K/Pg boundary.


      PubDate: 2015-10-22T16:36:27Z
       
  • Editorial board members
    • Abstract: Publication date: October 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 3




      PubDate: 2015-10-17T16:06:29Z
       
  • Chemical and strontium isotopic characteristics of shallow groundwater in
           the Ordos Desert Plateau, North China: Implications for the dissolved Sr
           source and water–rock interactions
    • Abstract: Publication date: October 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 3
      Author(s): Wenbo Rao, Ke Jin, Sanyuan Jiang, Hongbing Tan, Liangfeng Han, Quanyong Tang
      In this study, the chemical and Sr isotopic compositions of shallow groundwater and rainwater in the Ordos Desert Plateau, North China, and river water from the nearby Yellow River, are investigated to determine the dissolved Sr source and water–rock interactions, and quantify the relative Sr contribution from each end-member. Three groundwater systems have been identified, namely, GWS-1, GWS-2 and GWS-3 according to the watershed distribution in the Ordos Desert Plateau. Ca2+ and Mg2+ are the most dominant cations in GWS-1, while Na+ is dominant in GWS-3. In addition, there is more SO4 2− and less Cl− in GWS-1 than in GWS-3. The shallow groundwater in GWS-2 seems to be geochemically between that in GWS-1 and GWS-3. The 87Sr/86Sr ratios of the shallow groundwater are high in GWS-1 and GWS-2 and are low in GWS-3. By geochemically comparing the nearby Yellow River, local precipitation and deep groundwater, the shallow groundwater is recharged only by local precipitation. The ionic and isotopic ratios indicate that carbonate dissolution is an important process controlling the chemistry of the shallow groundwater. The intensity of the water–rock interactions varies among the three groundwater systems and even within each groundwater system. Three end-members controlling the groundwater chemistry are isotopically identified: (1) precipitation infiltration, (2) carbonate dissolution and (3) silicate weathering. The relative Sr contributions of the three end-members show that precipitation infiltration and carbonate dissolution are the primary sources of the shallow groundwater Sr in GWS-3 whereas only carbonate dissolution is responsible for the shallow groundwater Sr in GWS-1 and GWS-2. Silicate weathering seems insignificant towards the shallow groundwater's chemistry in the Ordos Desert Plateau. This study is helpful for understanding groundwater chemistry and managing water resources.


      PubDate: 2015-10-17T16:06:29Z
       
  • Great new insights from failed experiments, unanticipated results and
           embracing controversial observations
    • Abstract: Publication date: Available online 9 October 2015
      Source:Chemie der Erde - Geochemistry
      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: 2015-10-09T19:19:11Z
       
  • Petrology and geochemistry of the banded iron-formations from Ntem complex
           greenstones belt, Elom area, Southern Cameroon: Implications for the
           origin and depositional environment
    • Abstract: Publication date: Available online 17 August 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Ganno Sylvestre, Ngnotue Timoleon, Kouankap Nono Gus Djibril, Nzenti Jean Paul, Notsa Fokeng Marianne
      Banded iron-formations (BIFs) form an important part of the Archaean to Proterozoic greenstone belts in the Southern Cameroon. In this study, major, trace and REE chemistry of the banded iron-formation are utilized to explore the source of metals and to constraint the origin and depositional environment of these BIFs. The studied BIF belongs to the oxide facies iron formations composed mainly of iron oxide (mainly magnetite) mesobands alternating with quartz mesobands. The mineralogy of the BIF sample consists of magnetite and quartz with lesser amount of secondary martite, goethite and trace of gibbsite and smectite. The major element chemistry of these iron-formations is remarkably simple with the main constituents being SiO2 and Fe2O3 which constitute 95.6–99.5% of the bulk rock. Low Al2O3, TiO2, and HFSE concentrations show that they are relatively detritus-free chemical sediments. The Pearson’s correlation matrix of major element reveals that there is a strong positive correlation (r =0.99) of Al with Ti and no to weak negative correlation of Ti with Mn, Ca and weak positive correlation of Si with Ca, suggesting the null to very minor contribution of detrital material to chemical sediment. The trace elements with minor enrichments are transition metals such as Zn, Cr, Sr, V and Pb. This is an indicator of direct volcanogenic hydrothermal input in chemical precipitates. The studied BIF have a low ΣREE content, ranging between 0.41 and 3.22ppm with an average of 0.87ppm, similar to that of pure chemical sediments. The shale-normalized patterns show depletion in light REE, slightly enrichment in heavy REE and exhibit weak positive europium anomalies. These geochemical characteristics indicate that the source of Fe and Si was the result of deep ocean hydrothermal activity admixed with sea water. The absence of a large positive Eu anomaly in the studied BIF indicates an important role of low-temperature hydrothermal solutions. The chondrite-normalized REE patterns are characterized by LREE-enriched (Mean LaCN/YbCN =8.01) and HREE depletion (Mean TbCN/YbCN =1.61) patterns and show positive Ce anomalies. With the exception of one sample (LBR133), all of the BIF samples analyzed during this study have positive Ce anomalies on both chondrite- and PASS-normalized plots. This may indicate that the BIFs within the Elom area were formed within a redox stratified ocean. The positive Ce anomalies in the studied samples likely suggest that the basin in which Fe formations were deposited was reducing with respect to Ce, probably in the suboxic or anoxic seawaters.


      PubDate: 2015-08-18T07:34:33Z
       
  • Patterns of rare earth and other trace elements in Paleogene and Miocene
           clayey sediments from the Mondego platform (Central Portugal)
    • Abstract: Publication date: Available online 1 August 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): J.V. Lisboa, D.P.S. de Oliveira, F. Rocha, A. Oliveira, J. Carvalho
      In the present study the origin of clay deposits occurring in an inland platform, in central Portugal, was investigated by their mineralogical and chemical composition. The clay deposits, exploited for ceramic industry are composed of silt-clay facies, the Monteira Member and the Arroça Member, which are assigned to the Coja Formation (Paleogene) and the Campelo Formation (Miocene), respectively. These clayey facies show almost compositional homogeneity, especially concerning texture. The mineralogical composition of the Monteira Member displays slightly higher content in smectite and interstratified clay minerals, which is supported by the chemical composition of samples analyzed. Both members present similar REE patterns, displaying an intense weathering record and little variation in the source area composition. Minor element geochemistry suggests low content in heavy minerals and transition metals. REE patterns and ratios of geochemical parameters support the dominant metasedimentary provenance, with a granite source contribution and also mature recycled sediments of continental origin. The study results’ suggest that the clays of these two members have the same source in terms of lithology and recycled sediments from the Hesperian massif. During the deposition of the Arroça Member, a major remobilization of the Monteira Member is suggested, explaining the geochemical similarity of both facies.


      PubDate: 2015-08-05T05:12:05Z
       
  • Geochemistry of trace and rare earth elements during weathering of black
           shale profiles in Northeast Chongqing, Southwestern China: Their
           mobilization, redistribution, and fractionation
    • Abstract: Publication date: Available online 29 July 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Sixiang Ling, Xiyong Wu, Yong Ren, Chunwei Sun, Xin Liao, Xiaoning Li, Baolong Zhu
      In this study, the mobilization, redistribution, and fractionation of trace and rare earth elements (REE) during chemical weathering in mid-ridge (A), near mountaintop (B), and valley (C) profiles (weak, weak to moderate, and moderate to intense chemical weathering stage, respectively), are characterized. Among the trace elements, U and V were depleted in the regolith in all three profiles, Sr, Nb, Ta, Zr, and Hf displayed slight gains or losses, and Th, Rb, Cs, and Sc remained immobile. Mn, Ba, Zn, Cu, and Cr were enriched at the regolith in profiles A and B, but depleted in profile C. Mn, Pb, and Co were also depleted in the saprock and fractured shale zones in profiles A and B and enriched in profile C. REEs were enriched in the regolith and depleted at the saprock zone in profiles A and B and depleted along profile C. Mobility of trace and REEs increased with increasing weathering intensity. Normalized REE patterns based on the parent shale revealed light REE (LREE) enrichment, middle REE (MREE), and heavy REE (HREE) depletion patterns. LREEs were less mobile compared with MREEs and HREEs, and this differentiation increased with increasing weathering degree. Positive Ce anomalies were higher in profile C than in profiles A and B. The Ce fractionated from other REE showed that Ce changed from trivalent to tetravalent (as CeO2) under oxidizing conditions. Minimal REE fractionation was observed in the saprock zone in profiles A and B. In contrast, more intense weathering in profile C resulted in preferential retention of LREE (especially Ce), leading to considerable LREE/MREE and LREE/HREE fractionation. (La/Yb)N and (La/Sm)N ratios displayed maximum values in the saprock zone within low pH values. Findings demonstrate that acidic solutions can mobilize REEs and result in leaching of REEs out of the highly acidic portions of the saprock material and transport downward into fractured shale. The overall behavior of elements in the three profiles suggests that solution pH, as well as the presence of primary and secondary minerals, play important roles in the mobilization and redistribution of trace elements and REEs during black shale chemical weathering.


      PubDate: 2015-07-31T22:01:32Z
       
  • Multiple, isotopically heterogeneous plagioclase populations in the
           Bushveld Complex suggest mush intrusion
    • Abstract: Publication date: Available online 23 July 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Frederick Roelofse, Lewis D. Ashwal, Rolf L. Romer
      The Bushveld Complex and other layered intrusions show significant initial isotopic heterogeneity, both between and within co-existing cumulate minerals. Various processes have been proposed to account for this, including (i) intrusion of variably contaminated crystal mushes from deeper staging chambers, (ii) blending of semi-consolidated crystal mushes as a result of subsidence during cooling, (iii) variable infiltration of contaminants into a partially solidified crystal mush, (iv) density-driven mixing of minerals from isotopically distinct magma pulses, (v) contamination of crystals at the roof of the intrusion and mechanical incorporation of such contaminated crystals into the lower crystallisation front as a result of gravitational instability at the upper crystallisation front, and (vi) late-stage metasomatic processes. In order to assess the likely process(es) responsible for initial isotopic heterogeneities within the Bushveld Complex, we analysed core and rim domains of 12 plagioclase crystals from the Main and Upper zones of the Bushveld Complex for their Sr-isotopic compositions. The data show the presence of multiple, isotopically heterogeneous populations of plagioclase occurring within the same rocks. The data presented here are best explained through the intrusion of variably contaminated crystal mushes derived from a sub-compartmentalized, sub-Bushveld staging chamber that underwent different degrees of contamination with crustal rocks of the Kaapvaal craton.


      PubDate: 2015-07-23T22:27:18Z
       
  • Distribution and partitioning of major and trace elements in
           pyrite-bearing sediments of a Mediterranean coastal lagoon
    • Abstract: Publication date: June 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 2
      Author(s): F. Botsou , A. Godelitsas , H. Kaberi , T.J. Mertzimekis , J. Goettlicher , R. Steininger , M. Scoullos
      The formation of iron sulphide minerals exerts significant control on the behaviour of trace elements in sediments. In this study, three short sediment cores, retrieved from the remote Antinioti lagoon (N. Kerkyra Island, NW Greece), are investigated concerning the solid phase composition, distribution, and partitioning of major (Al, Fe) and trace elements (Cd, Cu, Mn, Pb, and Zn). According to 210Pb, the sediments sampled correspond to depositions of the last 120 years. The high amounts of organic carbon (4.1–27.5%) result in the formation of Fe sulphides, predominantly pyrite, already at the surface sediment layers. Pyrite morphologies include monocrystals, polyframboids, and complex FeS–FeS2 aggregates. According to synchrotron-generated micro X-ray fluorescence and X-ray absorption near-edge structure spectra, authigenically formed, Mn-containing, Fe(III) oxyhydroxides (goethite type) co-exist with pyrite in the sediments studied. Microscopic techniques evidence the formation of galena, sphalerite and CuS, whereas sequential extractions show that carbonates are important hosts for Mn, Cd, and Zn. However, significant percentages of non-lattice held elements are bound to Fe/Mn oxyhydroxides that resist reductive dissolution (on average 60% of Pb, 46% of Cd, 43% of Zn and 9% of Cu). The partitioning pattern changes drastically in the deeper part of the core that is influenced by freshwater inputs. In these sediments, the post-depositional pyritization mechanism, illustrated by overgrowths of Fe monosulphides on pre-existing pyrite grains, results in relatively high degree of pyritization that reaches 49% for Cd, 66% for Cu, 32% for Zn and 7% for Pb.


      PubDate: 2015-07-06T19:15:26Z
       
  • Petrology, geochemistry and zircon U–Pb dating of Band-e-Hezarchah
           metabasites (NE Iran): An evidence for back-arc magmatism along the
           northern active margin of Gondwana
    • Abstract: Publication date: June 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 2
      Author(s): Seyed Hossein Hosseini , Mahmoud Sadeghian , Minggou Zhai , Habibollah Ghasemi
      The Band-e-Hezarchah granitoids (BHG) is located in the northern margin of the central Iran, where the very old continental crust of Iran is found. The BHG mainly include granodiorite, granite and leucogranite. Small meta-gabbroic stocks and dykes are associated with BHG. U–Pb zircon dating of the BHG granites and metabasites yield 238U/206Pb crystallization ages of ca. 553.6 and 533.5Ma respectively (Ediacaran–early Cambrian). The metabasites have calc-alkaline signature and their magmas seem to have originated from a mantle wedge above a subduction zone. These rocks are thought to be formed in a continental back-arc setting, related to the oblique subduction of Proto-Tethys oceanic lithosphere beneath the northern margin of Gondwanan supercontinent during Ediacaran–Cambrian time. The initial 87Sr/86Sr ratios and ɛNd (t) values for metabasites are change from 0.705 to 0.706 and −3.5 to −3.6 respectively. Sr–Nd isotope composition of metabasites indicates that these rocks were derived from a subcontinental lithospheric mantle source. The BHG and associated metabasites are coeval with other similar aged metagranites and gneisses from Iranian basements exposed in central Iran, Sanandaj-Sirjan and Alborz zones. These rocks were formed due to continental arc magmatism of Neoproterozoic–early Cambrian, bordering the northern active margin of Gondwana.


      PubDate: 2015-07-06T19:15:26Z
       
  • Principal component analysis and hierarchical cluster analyses of arsenic
           groundwater geochemistry in the Hetao basin, Inner Mongolia
    • Abstract: Publication date: June 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 2
      Author(s): Yuxiao Jiang , Huaming Guo , Yongfeng Jia , Yongsheng Cao , Chao Hu
      Although high As groundwater has been observed in shallow groundwater of the Hetao basin, little is known about As distribution in deep groundwater. Quantitative investigations into relationships among chemical properties and among samples in different areas were carried out. Ninety groundwater samples were collected from deep aquifers of the northwest of the basin. Twenty-two physicochemical parameters were obtained for each sample. Statistical methods, including principal component analysis (PCA) and hierarchical cluster analysis (HCA), were used to analyze those data. Results show that As species were highly correlated with Fe species, NH4-N and pH. Furthermore, result of PCA indicates that high As groundwater was controlled by geological, reducing and oxic factors. The samples are classified into three clusters in HCA, which corresponded to the alluvial fans, the distal zone and the flat plain. Moreover, the combination of PCA with HCA shows the different dominant factors in different areas. In the alluvial fans, groundwater is influenced by oxic factors, and low As concentrations are observed. In the distal zone, groundwater is under suboxic conditions, which is dominated by reducing and geological factors. In the flat plain, groundwater is characterized by reducing conditions and high As concentrations, which is dominated by the reducing factor. This investigations indicate that deep groundwater in the alluvial fans mostly contains low As concentrations but high NO3 and U concentrations, and needs to be carefully checked prior to being used for drinking water sources.


      PubDate: 2015-07-06T19:15:26Z
       
  • A GIS-based approach for detecting pollution sources and bioavailability
           of metals in coastal and marine sediments of Chabahar Bay, SE Iran
    • Abstract: Publication date: June 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 2
      Author(s): Behnam Keshavarzi , Pooria Ebrahimi , Farid Moore
      Chabahar Bay in SE of Iran is a shallow semi-enclosed environment affected by anthropogenic activities. In this paper, 19 sediment samples were collected and concentration of selected metals (Cu, Pb, Zn, Cd, Ni, Cr, Co, V and Fe) was determined using ICP-MS analytical method. Sediment samples from five stations were also selected for sequential extraction analysis and concentration of metals in each fraction was determined using ICP-OES. In order to investigate the environmental quality of Chabahar Bay, geographic information system (GIS) along with geochemical data, environmental indices and statistical analyses were used. Calculated contamination degree (C d ) revealed that most contaminated stations (Ch3, S1 and S3) are located SE of Chabahar Bay and contamination decreases in a NW direction. The S9 station, west of the bay, is also contaminated. High organic matter (OM) content in the sediments is most likely the result of fuel and sewage discharge from fishing vessels along with discharge of fishing leftovers. Significant correlation coefficient among OM, Fe, Cu, Pb, Zn and Cd seemingly reflects the importance of the role that OM and Fe oxy-hydroxides play in the metals mobility. The results of hierarchical cluster analysis (HCA), computed correlation coefficient and sequential extraction analysis suggest that Cu, Pb, Zn and Cd probably come from antifouling and sea vessel paints, while Ni, Cr, Co, V and Fe are most likely contributed by ophiolitic formations located north of the bay and/or deep sea sediments. Average individual contamination factors (ICFs) indicated that the highest health hazard from the bay is posed by Cu, Pb and Zn.


      PubDate: 2015-07-06T19:15:26Z
       
  • Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of
           meteorites
    • Abstract: Publication date: June 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 2
      Author(s): David W. Mittlefehldt
      The howardite, eucrite and diogenite (HED) clan of meteorites are ultramafic and mafic igneous rocks and impact-engendered fragmental debris derived from a thoroughly differentiated asteroid. Earth-based telescopic observation and data returned from vestan orbit by the Dawn spacecraft make a compelling case that the asteroid (4) Vesta is the parent asteroid of HEDs, although this is not universally accepted. Diogenites are petrologically diverse and include dunitic, harzburgitic and noritic lithologic types in addition to the traditional orthopyroxenites. Diogenites form the lower crust of Vesta. Cumulate eucrites are gabbroic rocks formed by accumulation of pigeonite and plagioclase from a mafic magma at depth within the crust, while basaltic eucrites are melt compositions that likely represent shallow-level dikes and sills, and flows. Some basaltic eucrites are richer in incompatible trace elements compared to most eucrites, and these may represent mixed melts contaminated by partial melts of the mafic crust. Differentiation occurred within a few Myr of formation of the earliest solids in the Solar System. Evidence from oxygen isotope compositions and siderophile element contents favor a model of extensive melting of Vesta forming a global magma ocean that rapidly (period of a few Myr) segregated and crystallized to yield a metallic core, olivine-rich mantle, orthopyroxene-rich lower crust and basaltic upper crust. The igneous lithologies were subjected to post-crystallization thermal processing, and most eucrites show textural and mineral-compositional evidence for metamorphism. The cause of this common metamorphism is unclear, but may have resulted from rapid burial of early basalts by later flows caused by high effusion rates on Vesta. The observed surface of Vesta is covered by fragmental debris resulting from impacts, and most HEDs are brecciated. Many eucrites and diogenites are monomict breccias indicating a lack of mixing. However, many HEDs are polymict breccias. Howardites are the most thoroughly mixed polymict breccias, yet only some of them contain evidence for residence in the true regolith. Based on the numbers of meteorites, compositions of howardites, and models of magma ocean solidification, cumulate eucrites and their residual ferroan mafic melts are minor components of the vestan crust.


      PubDate: 2015-07-06T19:15:26Z
       
  • Editorial board members
    • Abstract: Publication date: June 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 2




      PubDate: 2015-07-06T19:15:26Z
       
  • Total concentration, speciation and mobility of potentially toxic elements
           in soils around a mining area in central Iran
    • Abstract: Publication date: Available online 7 June 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Giti Forghani , Ahamd Reza Mokhtari , Gholam Abbas Kazemi , Mozhde Davoodi Fard
      The current study was designed to investigate the extent and severity of contamination as well as the fractionation of potentially toxic elements (As, Cd, Cr, Cu, Pb, Zn, Ni) in minesoils and agricultural soils around a Pb–Zn mine in central Iran. For this purpose, 20 agricultural soils and eight minesoils were geochemically characterized. Results showed that minesoils contained elevated concentrations of As (12.9–254mgkg−1), Cd (1.2–55.1mgkg−1), Pb (137–6239mgkg−1) and Zn (516–48,889mgkg−1). The agricultural soils were also polluted by As (5.5–57.1mgkg−1), Cd (0.2–8.5mgkg−1), Pb (22–3451mgkg−1) and Zn (94–9907mgkg−1). The highest recorded concentrations for these elements were in soils influenced directly by tailing ponds. Chromium, Cu and Ni content in agricultural soils (with average value of 74.1, 34.6 and 50.7mgkg−1, respectively) were slightly higher than the minesoils (with average value of 54.5, 33.1 and 43.4mgkg−1, respectively). Sequential extraction data indicated that there were some differences between the speciation of PTEs in soil samples. In the agricultural soils, Zn and Cd were mainly associated with carbonate bound fraction, As and Pb with reducible fraction, Cu with oxidisable fraction and Cr and Ni with residual phase. With respect to mobility factor values, Zn and Cd in the agricultural soils have been found to be the most mobile while As mobility is negligible. Also, the mobility factor of As, Cd and Pb in agricultural soils adjoining tailing ponds was high. In minesoil sample Cd was most abundant in the carbonate form, whereas other studied elements were mainly present in the reducible and residual fractions; therefore, despite the high total concentrations of As, Pb and Zn in the minesoils, the environmental risk of these elements was low. Based on the obtained data, a portion of Cu, Cr and Ni input was from agricultural activities.


      PubDate: 2015-07-06T19:15:26Z
       
  • Chemical and isotopic characteristics and origin of spring waters in the
           Lanping–Simao Basin, Yunnan, Southwestern China
    • Abstract: Publication date: Available online 10 June 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Ying Bo , Chenglin Liu , Yanjun Zhao , Licheng Wang
      The chemical and isotopic characteristics (oxygen, hydrogen, and strontium) of spring waters and isotopic compositions of helium (He) and neon (Ne) in gases escaping from spring waters in the Lanping–Simao Basin are studied. A total of twenty-one spring water samples (twelve hot springs, four cold springs, and five saline springs) and eleven gas samples were collected from the study area, including one spring and one gas sample from northern Laos. It is found that saline spring waters in the study area are of chloride type, cold spring waters are of carbonate type or sulfate type, and hot spring waters are of various types. High total dissolved solids levels in saline springs are significantly related to Upper Cretaceous–Paleocene salt-bearing strata. On the basis of hydrochemical geothermometry, the reservoir temperatures (T r) for hot springs, cold springs, and saline springs are 65.5–144.1, 37.8–64.4, and 65.1–109.0°C, respectively, and the circulation depths of saline springs are much larger than those of hot and cold springs. The oxygen and hydrogen isotopic compositions of springs in the Lanping–Simao Basin and northern Laos are primarily controlled by meteoric waters with obvious latitude and altitude effects, and are also influenced by δ18O exchange to some extent. Most Sr2+ in spring waters of the study area is derived from varied sources (carbonate, evaporite, and silicate mineral dissolution), and the Sr isotopic compositions are greatly influenced by volcanic rocks. Wide distribution of crust-derived He in the Lanping–Simao Basin and northern Laos reveal that faults in these areas may not descend to the upper mantle. It is concluded that water circulation in the study area may be limited above the upper mantle, while saline springs may originate from the Upper Cretaceous–Paleocene evaporites. Hydrochemical characteristics demonstrate affinities among the Lanping–Simao Basin, northern Laos, and Yanjing, eastern Tibet, while disaffinities are observed between these areas and Tengchong on the basis of the hydrochemical characteristics and noble gas isotopic compositions.


      PubDate: 2015-07-06T19:15:26Z
       
  • Hirnantian (Late Ordovician) δ13C HICE excursion in a North Gondwanan
           (NE Spain) periglacial setting and its relationship to glacioeustatic
           fluctuations
    • Abstract: Publication date: Available online 21 June 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Ignacio Subías , Enrique Villas , J. Javier Álvaro
      In the Iberian Chains of northeastern Spain, the Hirnantian Orea Shale comprises three erosive glaciogenic unconformities punctuating two transgressive glaciomarine sequences. These sequences represent ice retreat episodes of grounded ice on a North Gondwanan region of 50–60°S of estimated palaeolatitude. In contrast, the same formation recorded in the Hesperian Chains repeated episodes of extensional tectonic activity: diamictites were associated with slope-related debris flows and slumps commonly interrupted by truncating discontinuities. An analysis of δ13Corg in the Orea Shale has revealed that the lower Orea sequence displays isotopically light baseline values (∼ −27‰) punctuated by minor (2–3‰) shifts. In distal parts, the upper sequence is characterised by a rapid rise in δ13Corg values, which mark a positive excursion, in the range of 2.5‰ to 7‰ over 40cm of thickness. The stratigraphic gap involved in the intra-Orea erosive unconformity appears to be greater both in proximal exposures and slope-related (Hesperian) areas, where the chemostratigraphic shift was not recorded. Upsection in the three studied sections, the δ13C values display upsection a sharp return to baseline values of −26‰ to −28‰. The Hirnantian strata of the Iberian and Hesperian Chains have recorded three major correlatable events: (i) a the karstic surface that caps upper Katian limestones and reflects the maximum glacial extension; (ii) a single δ13Corg positive peak of ∼6‰ that is recognisable in distal ramp settings, marking the beginning of the second ice retreat episode and probably representing the late Hirnantian HICE shift; and (iii) the erosive unconformity marked by the progradation of the Los Puertos shoreline complexes.


      PubDate: 2015-07-06T19:15:26Z
       
  • Spatial and temporal variability of surface water and groundwater before
           and after the remediation of a Portuguese uranium mine area
    • Abstract: Publication date: Available online 30 June 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Ana Margarida Ribeiro Neiva , Paula Cristina Simões de Carvalho , Isabel Margarida Horta Ribeiro Antunes , António Carlos Tavares dos Santos , Marina Marques da Silva Cabral-Pinto
      The old Senhora das Fontes uranium mine, in central Portugal, consists of quartz veins which penetrated along fracture shear zones at the contact between graphite schist and orthogneiss. The mine was exploited underground until a depth of 90m and was closed down in 1971. The ores from this mine and two others were treated in the mine area by the heap-leach process which ended in 1982. Seven dumps containing a total of about 33,800m3 of material and partially covered by natural vegetation were left in the mine area. A remediation process took place from May 2010 to January 2011. The material deposited in dumps was relocated and covered with erosion resisting covers. Surface water and groundwater were collected in the wet season just before the remediation, in the following season at the beginning of the remediation and also after the remediation in the following dry season. Before, at the beginning and after the remediation, surface water and groundwater have an acid-to-alkaline pH, which decreased with the remediation, whereas Eh increased. In general, before the remediation, uranium concentration was up to 83μg/L in surface water and up to 116μg/L in groundwater, whereas at the beginning of the remediation it increases up to 183μg/L and 272μg/L in the former and the latter, respectively, due to the remobilization of mine dumps and pyrite and chalcopyrite exposures, responsible for the pH decrease. In general, after the remediation, the U concentration decreased significantly in surface water and groundwater at the north part of the mine area, but increased in both, particularly in the latter up to 774μg/L in the south and southwest parts of this area, attributed to the remobilization of sulphides that caused mobilization of metals and arsenic which migrated to the groundwater flow. Uranium is adsorbed in clay minerals, but also in goethite as indicated by the geochemical modelling. After the remediation, the saturation indices of oxyhydroxides decrease as pH decreases. The remediation also caused decrease in Cd, Co, Cr, Ni, Pb, Zn, Cu, As, Sr and Mn concentrations of surface water and groundwater, particularly in the north part of the mine area, which is supported by the speciation modelling that shows the decrease of most dissolved bivalent species. However, in general, after the remediation, Th, Cd, Al, Li, Pb, Sr and As concentrations increased in groundwater and surface water at south and southwest of the mine area. Before and after the remediation, surface water and groundwater are contaminated in U, Cd, Cr, Al, Mn, Ni, Pb, Cu and As. Remediation caused only some improvement at north of the mine area, because at south and southwest part, after the remediation, the groundwater is more contaminated than before the remediation.


      PubDate: 2015-07-06T19:15:26Z
       
  • Petrology and geochemistry of the Karaj Dam basement sill: Implications
           for geodynamic evolution of the Alborz magmatic belt
    • Abstract: Publication date: June 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 2
      Author(s): Reza Maghdour-Mashhour , Dariush Esmaeily , Amir Ali Tabbakh Shabani , Massimo Chiaradia , Rais Latypov
      The northeastward subduction of the Neo-Tethyan oceanic lithosphere beneath the Iranian block produced vast volcanic and plutonic rocks that now outcrop in central (Urumieh–Dokhtar magmatic assemblage) and north–northeastern Iran (Alborz Magmatic Belt), with peak magmatism occurring during the Eocene. The Karaj Dam basement sill (KDBS), situated in the Alborz Magmatic Belt, comprises gabbro, monzogabbro, monzodiorite, and monzonite with a shoshonitic affinity. These plutonic rocks are intruded into the Karaj Formation, which comprise pyroclastic rocks dating to the lower–upper Eocene. The geochemical and isotopic signatures of the KDBS rocks indicate that they are cogenetic and evolved through fractional crystallization. They are characterized by an enrichment in LREEs relative to HREEs, with negative Nb–Ta anomalies. Geochemical modeling using Sm/Yb versus La/Yb and La/Sm ratios suggests a low-degree of partial melting of a phlogopite–spinel peridotite source to generate the KDBS rocks. Their low I Sr =0.70453–0.70535, ɛNd (37.2Ma)=1.54–1.9, and T DM ages ranging from 0.65 to 0.86Ga are consistent with the melting of a Cadomian enriched lithospheric mantle source, metasomatized by fluids derived from the subducted slab or sediments during magma generation. These interpretations are consistent with high ratios of 206Pb/204Pb=18.43–18.67, 207Pb/204Pb=15.59, and 208Pb/204Pb=38.42–38.71, indicating the involvement of subducted sediments or continental crust. The sill is considered to have been emplaced in an environment of lithospheric extension due to the slab rollback in the lower Eocene. This extension led to localized upwelling of the asthenosphere, providing the heat required for partial melting of the subduction-contaminated subcontinental lithospheric mantle beneath the Alborz magmatic belt. Then, the shoshonitic melt generates the entire spectrum of KDBS rocks through assimilation and fractional crystallization during the ascent of the magma.


      PubDate: 2015-07-06T19:15:26Z
       
  • Arsenic accumulation in the roots of Helianthus annuus and Zea mays by
           irrigation with arsenic-rich groundwater: Insights from synchrotron X-ray
           fluorescence imaging
    • Abstract: Publication date: June 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 2
      Author(s): H. Neidhardt , U. Kramar , X. Tang , H. Guo , S. Norra
      The aim of this study was to investigate the accumulation of arsenic (As) in and on roots of Zea mays (maize) and Helianthus annuus (sunflower) by means of synchrotron-based micro-focused X-ray fluorescence imaging (μ-XRF). Plant and soil samples were collected from two field sites in the Hetao Plain (Inner Mongolia, China) which have been regularly irrigated with As-rich groundwater. Detailed μ-XRF element distribution maps were generated at the Fluo-beamline of the Anka synchrotron facility (Karlsruhe Institute of Technology) to assess the spatial distribution of As in thin sections of plant roots and soil particles. The results showed that average As concentrations in the roots (14.5–27.4mgkg−1) covered a similar range as in the surrounding soil, but local maximum root As concentrations reached up to 424mgkg−1 (H. annuus) and 1280mgkg−1 (Z. mays), respectively. Importantly, the results revealed that As had mainly accumulated at the outer rhizodermis along with iron (Fe). We therefore conclude that thin crusts of Fe-(hydr)oxides cover the roots and act as an effective barrier to As, similar to the formation of Fe plaque in rice roots. In contrast to permanently flooded rice paddy fields, regular flood irrigation results in variable redox conditions within the silty and loamy soils at our study site and fosters the formation of Fe-(hydr)oxide plaque on the root surfaces.


      PubDate: 2015-07-06T19:15:26Z
       
  • Synthesis and optical characterization of Gd-neso-borate single crystals
    • Abstract: Publication date: Available online 1 June 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Christoph Reuther , Robert Möckel , Jens Götze , Margitta Hengst , Gerhard Heide
      Single crystals of Ca4GdO[BO3]3 and Sr3Gd2[BO3]4 were synthesized using the Czochralski method, both in different crystallographic directions. Best result were obtained for 0 1 0 orientated seeds and growth rates of 1 mmh−1. The morphology of the as-grown crystals reflects the symmetry and for Ca4GdO[BO3]3-crystals a typical rhombohedral and for Sr3Gd2[BO3]4-crystals almost circular cross section are formed. UV–VIS and IR measurements show a wide range of transmission of light. Between 350–1100 and 1600–2500nm no absorption was observed. Below 350nm the crystals show distinct absorption peaks caused by electron transitions of Gd. In the IR region most vibration modes can be assigned to [BO3]3−-groups and Gd/Ca-O or Gd/Sr-O-polyhedra.


      PubDate: 2015-07-06T19:15:26Z
       
  • Sr and Nd isotopes as tracers in pedogenic studies: Evidence for Saharan
           dust contribution to the soils of Muravera (Sardinia, Italy)
    • Abstract: Publication date: Available online 20 May 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Francesca Castorina , Umberto Masi
      Sr and Nd isotopes were applied to 5 soil profiles from the Muravera area, in south-eastern Sardinia. All the soils, which have developed during the Quaternary on the Lower Paleozoic metamorphic basement except for one on Eocene carbonates, are located far from major sources of pollution. Therefore, they are suitable for testing pedogenic processes and geochemical evolution to benefit for environmental studies. The Sr isotopic ratios range largely (δ87Sr=1.7–65.9‰), even in each soil profile. In particular, the observed increase of δ87Sr with depth in the most of the metamorphic rock-based soils can be accounted for by the downward decrease of Sr contributions from organic matter and Saharan dust, both displaying lower isotopic ratios than the soil bedrocks. The carbonate rock-based soil exhibits δ87Sr higher (1.7–18.1‰) than the bedrock, indicating a significant contribution of radiogenic Sr from the siliciclastic fraction of the soil, and probably from dust input. The Nd isotopic ratios are slightly variable through the profiles (ɛ Nd from −7.8 to −14.5), confirming little mobility of Nd and Sm during the pedogenesis. Among the minerals present in the soils, phosphates, albite, and calcite are those important in providing low radiogenic Sr and Nd to organic matter of the soils. Lastly, this isotopic study has in particular allowed for evaluating the potential proportion of contribution of Saharan dust to south-eastern Sardinia, thus corroborating the findings of other studies related to soils from the central-western Mediterranean.


      PubDate: 2015-07-06T19:15:26Z
       
  • Asteroid (4) Vesta II: Exploring a geologically and geochemically complex
           world with the Dawn Mission
    • Abstract: Publication date: Available online 24 March 2015
      Source:Chemie der Erde - Geochemistry
      Author(s): Timothy J. McCoy , Andrew W. Beck , Thomas H. Prettyman , David W. Mittlefehldt
      More than 200 years after its discovery, asteroid (4) Vesta is thought to be the parent body for the howardite, eucrite and diogenite (HED) meteorites. The Dawn spacecraft spent ∼14 months in orbit around this largest, intact differentiated asteroid to study its internal structure, geology, mineralogy and chemistry. Carrying a suite of instruments that included two framing cameras, a visible-near infrared spectrometer, and a gamma-ray and neutron detector, coupled with radio tracking for gravity, Dawn revealed a geologically and geochemically complex world. A constrained core size of ∼110–130km radius is consistent with predictions based on differentiation models for the HED meteorite parent body. Hubble Space Telescope observations had already shown that Vesta is scarred by a south polar basin comparable in diameter to that of the asteroid itself. Dawn showed that the south polar Rheasilvia basin dominates the asteroid, with a central uplift that rivals the large shield volcanoes of the Solar System in height. An older basin, Veneneia, partially underlies Rheasilvia. A series of graben-like equatorial and northern troughs were created during these massive impact events 1–2Ga ago. These events also resurfaced much of the southern hemisphere and exposed deeper-seated diogenitic lithologies. Although the mineralogy and geochemistry vary across the surface for rock-forming elements and minerals, the range is small, suggesting that impact processes have efficiently homogenized the surface of Vesta at scales observed by the instruments on the Dawn spacecraft. The distribution of hydrogen is correlated with surface age, which likely results from the admixture of exogenic carbonaceous chondrites with Vesta's basaltic surface. Clasts of such material are observed within the surficial howardite meteorites in our collections. Dawn significantly strengthened the link between (4) Vesta and the HED meteorites, but the pervasive mixing, lack of a convincing and widespread detection of olivine, and poorly-constrained lateral and vertical extents of units leaves unanswered the central question of whether Vesta once had a magma ocean. Dawn is continuing its mission to the presumed ice-rich asteroid (1) Ceres.


      PubDate: 2015-07-06T19:15:26Z
       
  • Editorial board members
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1




      PubDate: 2015-07-06T19:15:26Z
       
  • Impact features of enstatite-rich meteorites
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Alan E. Rubin
      Enstatite-rich meteorites include EH and EL chondrites, rare ungrouped enstatite chondrites, aubrites, a few metal-rich meteorites (possibly derived from the mantle of the aubrite parent body), various impact-melt breccias and impact-melt rocks, and a few samples that may be partial-melt residues ultimately derived from enstatite chondrites. Members of these sets of rocks exhibit a wide range of impact features including mineral-lattice deformation, whole-rock brecciation, petrofabrics, opaque veins, rare high-pressure phases, silicate darkening, silicate-rich melt veins and melt pockets, shock-produced diamonds, euhedral enstatite grains, nucleation of enstatite on relict grains and chondrules, low MnO in enstatite, high Mn in troilite and oldhamite, grains of keilite, abundant silica, euhedral graphite, euhedral sinoite, F-rich amphibole and mica, and impact-melt globules and spherules. No single meteorite possesses all of these features, although many possess several. Impacts can also cause bulk REE fractionations due to melting and loss of oldhamite (CaS) – the main REE carrier in enstatite meteorites. The Shallowater aubrite can be modeled as an impact-melt rock derived from a large cratering event on a porous enstatite chondritic asteroid; it may have been shock melted at depth, slowly cooled and then excavated and quenched. Mount Egerton may share a broadly similar shock and thermal history; it could be from the same parent body as Shallowater. Many aubrites contain large pyroxene grains that exhibit weak mosaic extinction, consistent with shock-stage S4; in contrast, small olivine grains in some of these same aubrites have sharp or undulose extinction, consistent with shock stage S1 to S2. Because elemental diffusion is much faster in olivine than pyroxene, it seems likely that these aubrites experienced mild post-shock annealing, perhaps due to relatively shallow burial after an energetic impact event. There are correlations among EH and EL chondrites between petrologic type and the degree of shock, consistent with the hypothesis that collisional heating is mainly responsible for enstatite-chondrite thermal metamorphism. Nevertheless, the apparent shock stages of EL6 and EH6 chondrites tend to be lower than EL3-5 and EH3-5 chondrites, suggesting that the type-6 enstatite chondrites (many of which possess impact-produced features) were shocked and annealed. The relatively young Ar–Ar ages of enstatite chondrites record heating events that occurred long after any 26Al that may have been present initially had decayed away. Impacts remain the only plausible heat source at these late dates. Some enstatite meteorites accreted to other celestial bodies: Hadley Rille (EH) was partly melted when it struck the Moon; Galim (b), also an EH chondrite, was shocked and partly oxidized when it accreted to the LL parent asteroid. EH, EL and aubrite-like clasts also occur in the polymict breccias Kaidun (a carbonaceous chondrite) and Almahata Sitta (an anomalous ureilite). The EH and EL clasts in Kaidun appear unshocked; some clasts in Almahata Sitta may have been extensively shocked on their parent bodies prior to being incorporated into the Almahata Sitta host.


      PubDate: 2015-07-06T19:15:26Z
       
  • Metal sorption onto soils loaded with urban particulate matter
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Jiřina Száková , Denisa Zimmermannová , Michael Komárek , Jiřina Sysalová , Pavel Tlustoš
      The potential effect of urban particulate matter (PM) accumulation on metal sorption onto two contrasting soils (Chernozem and Fluvisol) was investigated in a batch sorption experiment. While the Freundlich isotherms did not indicate any effect of PM addition to the soils, the Langmuir isotherm allowed us to estimate the potential behaviour of the PM in the soil. The PM added to the Chernozem did not lead to substantial changes in sorption of Cd, Cu, Mn, Ni, Pb, and Zn. On the contrary, the presence of PM in the Fluvisol increased the number of potential sorption sites in the soil. However, the results of the approximation showed a lower affinity of Cd, Mn and Ni for the Fluvisol and a better stability and a lower bioavailability of these elements in the Chernozem. In the case of Pb and Cu, no significant changes were observed in PM-enriched soils regardless of the soil properties.


      PubDate: 2015-07-06T19:15:26Z
       
  • Platinum-group elemental chemistry of the Baima and Taihe Fe–Ti
           oxide bearing gabbroic intrusions of the Emeishan large igneous province,
           SW China
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): J. Gregory Shellnutt , George S.-K. Ma , Liang Qi
      Nickel-, copper-, and platinum group element (PGE)-enriched sulphide mineralization in large igneous provinces has attracted numerous PGE studies. However, the distribution and behavior of PGEs as well as the history of sulphide saturation are less clear in oxide-dominated mineralization. Platinum group elements of oxide-bearing layered mafic intrusions from the Emeishan large igneous province are examined in this study. Samples collected from the Baima and Taihe oxide-bearing layered gabbroic intrusions reveal contrasting results. The samples from Baima gabbroic rocks have low total PGE abundances (ΣPGE<4ppb) whereas the Taihe gabbroic rocks, on average, have more than double the concentration but are variable ranging from ΣPGE<2ppb to ΣPGE∼300ppb. The Baima gabbro is platinum-subgroup PGE (PPGE=Rh, Pt and Pd) enriched and iridium-subgroup PGE (IPGE=Os, Ir and Ru) depleted, with a distinct positive Ru anomaly on a primitive mantle normalized multi-element plot. The Taihe gabbros are also PPGE enriched but with negative Ru and Pd anomalies on a primitive mantle normalized multi-element plot. The PGE concentrations of Baima rocks are indicative of fractionation of a relatively evolved, mafic, S-undersaturated parental magma that was affected by earlier sulphide segregation. In contrast, the Taihe rocks record evidence of both S-saturated and S-undersaturated conditions and that the parental magma was likely emplaced very close to S-saturation. Comparisons of the platinum group element contents in the Emeishan flood basalts and the Emeishan oxide-bearing intrusions suggest that the PGE budget in a magma is not controlled by magma series (high-Ti vs. low-Ti), but very much by crustal contamination. The unlikelihood of substantial crustal contamination in the Taihe magma allowed the magma to remain S-undersaturated for a longer duration. PGE and sulphide mineralization was not identified in the Taihe intrusion but the presence of one PGE-enriched sample (Pt+Pd=∼300ppb) suggests that the parental magma likely did not experience sulphide segregation and is a potential target for further prospecting.


      PubDate: 2015-07-06T19:15:26Z
       
  • The iron/manganese occurrences of the Desná Unit NE of the
           Sobotín Amphibolite Massif, Silesicum, Czech Republic: A reply to the
           paper of Kropáč et al. (2012)
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Arno Mücke , Zdeněk Losos
      Our reply deals with the investigations of Kropáč et al. (2012) concerning the evolution of Mn-rich garnetites (=coticules) in the Silesian Desná Unit which are closely associated with Fe-rich rocks. Pouba (1970) who described these mineralizations in greater detail, postulated an origin identical with banded iron-formations of the Algoma type. However, Mücke and Losos (2007) excluded a banded iron-formation origin for the magnetite mineralizations and came to the conclusion that these are connected with the Devonian amphibolite of the Sobotín Massif. The older garnetites were inferred to be identical with coticules and, therefore, are comparable with Mn-rich iron-formations of the Algoma type. Concerning the coticules, Kropáč et al. (2012) confirmed the same origin as proposed by us. For the magnetite-rich rocks, on the other hand, Kropáč et al. (2012) strictly followed Pouba (1970), but did neither present new results or data, nor considered the arguments of Mücke and Losos (2007). In this reply, the most important results of Mücke and Losos (2007) are discussed in comparison with banded iron-formations.


      PubDate: 2015-07-06T19:15:26Z
       
  • The geochemistry of platinum group elements in marine oil shale—A
           case study from the Bilong Co oil shale, northern Tibet, China
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Xiugen Fu , Jian Wang , Yuhong Zeng , Fuwen Tan , Chen Wenbing , Xinglei Feng
      The Bilong Co oil shale zone is located in the South Qiangtang depression. This zone, together with the Shengli River-Changshe Mountain oil shale zone in the North Qiangtang depression, northern Tibet plateau, represents the potentially largest marine oil shale resource in China. Seventeen samples including oil shale and micritic limestone were collected from the Bilong Co oil shale area to determine the concentrations, distribution patterns, occurrences and origins of platinum group elements (PGEs) in marine oil shale. The oil shale samples from the Bilong Co area exhibit very low total PGE contents ranging from 1.04 to 2.96ng/g with a weighted mean value of 1.686ng/g, while the micritic limestone samples from the Bilong Co area exhibit a little lower PGE value ranging from 0.413 to 1.11ng/g. PGEs in oil shale samples are characterized by high contents in Pd (average 0.79ng/g), Os (average 0.123ng/g) and Pt (average 0.644ng/g) compared with Ru (average 0.068ng/g), Rh (average 0.033ng/g) and Ir (average 0.026ng/g). The highest values for individual PGEs are not uniformly distributed in the section. Clearly, the PGEs are generally enriched in the oil shale samples near the boundary between micritic limestone and oil shale. The individual PGEs in oil shale samples from the Bilong Co area exhibit various modes of occurrence. Ruthenium and Pt occur mainly in pyrite, while Pd is associated mainly with organic matter and Mg-minerals. Rhodium and Os are controlled mainly by pyrite and organic matter. Iridium is present mainly in other Fe-bearing minerals, rather than pyrite. The PGEs in the Bilong Co oil shale are mainly of seawater origin and possibly influenced by terrigenous supply.


      PubDate: 2015-07-06T19:15:26Z
       
  • Stable isotopic signatures of the modern land snail Eremina desertorum
           from a low-latitude (hot) dry desert—A study from the Petrified
           Forest, New Cairo, Egypt
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Kamaleldin M. Hassan
      This study was conducted on recent desert samples—including (1) soils, (2) plants, (3) the shell, and (4) organic matter from modern specimens of the land snail Eremina desertorum—which were collected at several altitudes (316–360m above sea level) from a site in the New Cairo Petrified Forest. The soils and shell E. desertorum were analyzed for carbonate composition and isotopic composition (δ18O, δ13C). The plants and organic matter E. desertorum were analyzed for organic carbon content and δ13C. The soil carbonate, consisting of calcite plus minor dolomite, has δ18O values from −3.19 to −1.78‰ and δ13C values −1.79 to −0.27‰; covariance between the two values accords with arid climatic conditions. The local plants include C3 and C4 types, with the latter being dominant. Each type has distinctive bulk organic carbon δ13C values: −26.51 to −25.36‰ for C3-type, and −13.74 to −12.43‰ for C4-type plants. The carbonate of the shell E. desertorum is composed of aragonite plus minor calcite, with relatively homogenous isotopic compositions (δ18Omean =−0.28±0.22‰; δ13Cmean =−4.46±0.58‰). Most of the δ18O values (based on a model for oxygen isotope fractionation in an aragonite-water system) are consistent with evaporated water signatures. The organic matter E. desertorum varies only slightly in bulk organic carbon δ13C values (−21.78±1.20‰) and these values suggest that the snail consumed more of C3-type than C4-type plants. The overall offset in δ13C values (−17.32‰) observed between shell E. desertorum carbonate and organic matter E. desertorum exceeds the value expected for vegetation input, and implies that 30% of carbon in the shell E. desertorum carbonate comes from the consumption of limestone material.


      PubDate: 2015-07-06T19:15:26Z
       
  • Petrology, geochemistry and tectonic significance of serpentinized
           ultramafic rocks from the South Arm of Sulawesi, Indonesia
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Adi Maulana , Andrew G. Christy , David J. Ellis
      Serpentinized ultramafic rocks occur in two separate basement complexes in the South Arm of Sulawesi, the Bantimala and Barru Blocks. We present petrographic, mineral chemical and geochemical data for these rocks, and interpret them in terms of petrogenesis and tectonic setting. The rocks of both blocks show strong serpentinization of original anhydrous silicates. The Bantimala ultramafics consist mainly of peridotite (harzburgite and dunite) and clinopyroxenite, with lenses of podiform chromitite. Metamorphism is evidenced by the occurrence of amphibolite-facies tremolite schist. In contrast, the Barru ultramafics consist of harzburgite peridotite and podiform chromitite, which also show an amphibolite-facies overprint that in this case may be related to intrusion by a large dacite/granodiorite body. Whole-rock trace element analyses and spinel compositions show that the Barru harzburgite is depleted relative to primitive mantle, and has had some melt extracted. In contrast, the Bantimala dunite, harzburgite and clinopyroxenite are cumulates. Both are derived from a supra-subduction zone environment, and were obducted during the closure of small back-arc basins. If there has been no rotation of the blocks, then the Bantimala ultramafics were emplaced from an ENE direction, while the Barru ultramafics were emplaced from the WNW. The ultramafic suites from these two blocks are juxtaposed with metamorphic assemblages, which were later intruded by younger volcanics, particularly in the Barru Block.


      PubDate: 2015-07-06T19:15:26Z
       
  • Gondwanan magmatism with adakite-like signature linked to Cu (Mo)-porphyry
           deposits from the San Rafael Massif, Mendoza Province, Argentina
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Anabel L.R. Gómez , Nora A. Rubinstein , Víctor A. Valencia
      The gondwanan magmatism in the San Rafael Massif, known as Choiyoi Magmatic Cycle, was emplaced during the inception of a magmatic arc setting during the early Permian. Two different sections can be differentiated in this volcanic sequence. The lower section (∼281 up to ∼265 Ma) consisting of andesites and dacitic to low-silica rhyolitic ignimbrites has geochemical characteristics that indicate a subduction zone setting. The upper section (∼265 up to ∼252 Ma) composed of rhyolitic ignimbrites and lava flows, dacitic to rhyolitic subvolcanics and alkalic basaltic andesites has geochemical characteristics transitional between subduction and continental intraplate settings. Several Cu–(Mo) porphyry deposits are genetically linked to the lower section (Infiernillo, San Pedro and La Chilca-Zanjón del Buitre). In this paper, we discussed the petrogenesis of the magmatism linked to the porphyry deposits from the San Rafael Massif. The petrogenetic analysis suggests that the lower section was produced in a thickened crust resulting in an adakite-like signature magmatism. The U/Pb LA-ICP-MS age of magmatic zircons from an intrusive associated to the San Pedro porphyry (263.1±4.2 Ma) allowed confirming that the emplacement of Cu–Mo porphyry deposits in the San Rafael Massif occurred during the change in the geodynamical conditions from a transpressive to a transtensive tectonic regime.


      PubDate: 2015-07-06T19:15:26Z
       
  • Geochemistry of the Eocene Jijuntun Formation oil shale in the Fushun
           Basin, northeast China: Implications for source-area weathering,
           provenance and tectonic setting
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Rong Liu , Zhaojun Liu , Pingchang Sun , Yinbo Xu , Dongqing Liu , Xiaohong Yang , Chao Zhang
      Within the fault-bound Fushun Basin of northeastern China, the Eocene Jijuntun Formation hosts extensive deposits of thick lacustrine oil shale. Systematic sampling and geochemical analysis of these deposits has revealed that the parent rocks of the oil shale underwent moderate chemical weathering; and that its mineralogy and trace and rare earth element geochemistry were mainly controlled by parent rock composition, with no synsedimentary changes in the source terrain. Based on source rock and tectonic setting discrimination diagrams, we concluded that the parent rocks of the oil shale were mostly basalts of the Paleogene Laohutai Formation. These basalts originated in a continental back arc environment and contain abundant nutrient elements such as Fe, P, Ni, Cu and Zn, all of which are essential for the growth of aquatic photoautotrophs in lakes. Continuous, high primary productivity in the Jinjuntun lacustrine depocentre, combined with a stable tectonic setting and underfilled sedimentary environment, were key factors in the genesis of its oil shale.


      PubDate: 2015-07-06T19:15:26Z
       
  • Application of classical statistics, logratio transformation and
           multifractal approaches to delineate geochemical anomalies in the
           Zarshuran gold district, NW Iran
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Ahad Nazarpour , Nematolah Rashidnejad Omran , Ghodratolal Rostami Paydar , Behnam Sadeghi , Fatemeh Matroud , Ali Mehrabi Nejad
      The aim of this study is to discriminate the geochemical anomalies in the Zarshuran district, NW Iran, using different geochemical methods and present a more useful method where anomalous areas better coincide with the geological features. For this methods of delineation, geochemical anomalies were compared using geological features, occupied area of anomalies respect to the total study area, and field observations. Frequency based analysis such as mean+2SDEV and median+2MAD and concentration–area (C–A) multifractal methods were adopted for estimating thresholds and separating geochemical anomalies in uni-element data, as well as multi-element ones. Threshold values obtained from mean+2SDEV and median+2MAD, from original point geochemical data, are smaller than those of the pixel values; this may be due to the stronger variance of pixel values. In addition, the C–A multifractal method, as a useful tool to identify weak geochemical anomalies, was applied for defining the threshold values. Robust principal component analysis (RPCA) methods coupled with isometric log-ratio (ilr) transformations were utilized to open the geochemical data in order to reduce the effects of the data closure problem. The 20-quantile intervals decomposed anomaly maps from PC1 were obtained from the classical PCA, robust PCA showed that the upper quintile (>80 quintile) of classical PCA covers a larger area (32.54%) than the robust PCA (18.16%), and as a result, the robust PCA displayed smaller areas and has good spatial associations with outcrops of hydrothermal Au–As mineralization in this area; coincident with the known Zarshuran former mining area (ore field), Zarshuran unit, Ghaldagh silicified limestone occurrence and newly explored works confirmed by field observation. Although the C–A model shows a smaller area (8.06%), this anomaly location is limited to the Zarshuran old mining area with no new exploration targets. Comparison of the models indicates that the RPCA model is not only beneficial to further Au exploration in the study area, but also provides a meaningful geological study to the community of the compositional data analysis.


      PubDate: 2015-07-06T19:15:26Z
       
  • Stable isotope characterization of pedogenic and lacustrine carbonates
           from the Chinese Tian Shan: Constraints on the Mesozoic–Lower
           Cenozoic palaeoenvironmental evolution
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): G. Heilbronn , P. Boulvais , E. Marchand , C. Robin , S. Bourquin , L. Barrier , Y. Jia , B. Fu , M. Jolivet
      In the Mesozoic–Cenozoic continental deposits of the Tian Shan area, two main levels containing pedogenic carbonates have been identified on both the southern and northern foothills of the range: one in the Upper Jurassic series and one in the Upper Cretaceous–Lower Palaeocene series. In order to reconstruct the palaeoenvironmental and palaeotopographic characteristics of the Tian Shan area during these two periods, we measured the oxygen and carbon isotope composition of these pedogenic carbonates (calcrete and nodules). The stable isotope compositions are homogeneous: most δ18O values are between 21 and 25‰ and most δ13C values are between −4 and −6‰. No distinction can be made between the calcrete and nodule isotopic compositions. The constancy of isotopic values across the Tian Shan is evidence of a development of these calcification features in similar palaeoenvironmental conditions. The main inference is that no significant relief existed in that area at the Cretaceous−Palaeogene boundary, implying that most of the present relief developed later, during the Cenozoic. In addition to the pedogenic carbonates, few beds of limestones interstratified in the Jurassic series of the southern foothills display oxygen and carbon isotope compositions typical of lacustrine carbonates, ruling out brackish water incursion at that period in the region.


      PubDate: 2015-07-06T19:15:26Z
       
  • Available contents of potentially toxic elements in soils from the Eastern
           Amazon
    • Abstract: Publication date: March 2015
      Source:Chemie der Erde - Geochemistry, Volume 75, Issue 1
      Author(s): Sannah Mohamad Birani , Antonio Rodrigues Fernandes , Anderson Martins de Souza Braz , Augusto José Silva Pedroso , Luís Reynaldo Ferracciú Alleoni
      Background Values of potentially toxic elements (PTEs) in soils are typically obtained from total or pseudo-total contents, but not represent the fraction of these elements available for plant uptake due to the predominance of the stable forms. Available contents to plants, in turn, tend to be positively correlated with the potential risk of contamination of PTEs. In this study, we determined the available contents, extracted with Mehlich-III solution, of Ba, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in Oxisols and Ultisols in the state of Pará, Eastern Amazon, Brazil. Available contents ranged from low to very low when compared to soils from other Brazilian regions and from other countries. Contents of PTE were higher in Oxisols than in Ultisols, except for Cu and Ni. In the Oxisols, PTEs were positively correlated with clay content. However, PTEs were not correlated with soil pH, organic matter and cation exchange capacity. In the Ultisols, Ba, Cu, Pb, and Mn contents were significantly correlated with pH, while Ni contents were correlated with the contents of silt.


      PubDate: 2015-07-06T19:15:26Z
       
 
 
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