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EARTH SCIENCES (467 journals)                  1 2 3 | Last

Showing 1 - 200 of 371 Journals sorted alphabetically
Acta Geochimica     Hybrid Journal   (Followers: 7)
Acta Geodaetica et Geophysica     Hybrid Journal   (Followers: 2)
Acta Geodaetica et Geophysica Hungarica     Full-text available via subscription   (Followers: 2)
Acta Geophysica     Open Access   (Followers: 10)
Acta Geotechnica     Hybrid Journal   (Followers: 7)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 3)
Advances in High Energy Physics     Open Access   (Followers: 19)
Advances In Physics     Hybrid Journal   (Followers: 20)
Aeolian Research     Hybrid Journal   (Followers: 5)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 13)
Algological Studies     Full-text available via subscription   (Followers: 2)
Alpine Botany     Hybrid Journal   (Followers: 5)
AMBIO     Hybrid Journal   (Followers: 15)
Anales del Instituto de la Patagonia     Open Access   (Followers: 1)
Andean geology     Open Access   (Followers: 13)
Annales Henri Poincaré     Hybrid Journal   (Followers: 3)
Annales UMCS, Geographia, Geologia, Mineralogia et Petrographia     Open Access  
Annals of Geophysics     Open Access   (Followers: 13)
Annals of GIS     Hybrid Journal   (Followers: 24)
Annual Review of Marine Science     Full-text available via subscription   (Followers: 11)
Anthropocene     Hybrid Journal   (Followers: 4)
Anthropocene Review     Hybrid Journal   (Followers: 6)
Applied Clay Science     Hybrid Journal   (Followers: 5)
Applied Geochemistry     Hybrid Journal   (Followers: 14)
Applied Geomatics     Hybrid Journal   (Followers: 4)
Applied Geophysics     Hybrid Journal   (Followers: 8)
Applied Ocean Research     Hybrid Journal   (Followers: 7)
Applied Petrochemical Research     Open Access   (Followers: 3)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 36)
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: 21)
Asia-Pacific Journal of Atmospheric Sciences     Hybrid Journal   (Followers: 20)
Asian Journal of Earth Sciences     Open Access   (Followers: 20)
Asian Review of Environmental and Earth Sciences     Open Access   (Followers: 2)
Atlantic Geology : Journal of the Atlantic Geoscience Society / Atlantic Geology : revue de la Société Géoscientifique de l'Atlantique     Full-text available via subscription   (Followers: 11)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 12)
Atmospheric and Climate Sciences     Open Access   (Followers: 28)
Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia     Hybrid Journal   (Followers: 11)
Boletim de Ciências Geodésicas     Open Access  
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 12)
Bragantia     Open Access   (Followers: 2)
Bulletin of Earthquake Engineering     Hybrid Journal   (Followers: 11)
Bulletin of Geosciences     Open Access   (Followers: 11)
Bulletin of the Lebedev Physics Institute     Hybrid Journal   (Followers: 1)
Bulletin of the Seismological Society of America     Full-text available via subscription   (Followers: 21)
Bulletin of Volcanology     Hybrid Journal   (Followers: 21)
Cadernos de Geociências     Open Access  
Canadian Mineralogist     Full-text available via subscription   (Followers: 6)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 22)
Carbonates and Evaporites     Hybrid Journal   (Followers: 3)
CATENA     Hybrid Journal   (Followers: 8)
Chemical Geology     Hybrid Journal   (Followers: 23)
Chemie der Erde - Geochemistry     Hybrid Journal   (Followers: 5)
Chinese Geographical Science     Hybrid Journal   (Followers: 5)
Chinese Journal of Oceanology and Limnology     Hybrid Journal   (Followers: 4)
Ciencia del suelo     Open Access   (Followers: 2)
Ciencias Espaciales     Open Access  
Climate and Development     Hybrid Journal   (Followers: 13)
Coastal Management     Hybrid Journal   (Followers: 25)
Cogent Geoscience     Open Access  
Comptes Rendus Geoscience     Full-text available via subscription   (Followers: 9)
Computational Geosciences     Hybrid Journal   (Followers: 15)
Computational Mathematics and Mathematical Physics     Hybrid Journal   (Followers: 3)
Computers and Geotechnics     Hybrid Journal   (Followers: 11)
Contemporary Trends in Geoscience     Open Access   (Followers: 3)
Continental Shelf Research     Hybrid Journal   (Followers: 9)
Contributions to Mineralogy and Petrology     Hybrid Journal   (Followers: 12)
Contributions to Plasma Physics     Hybrid Journal   (Followers: 4)
Coral Reefs     Hybrid Journal   (Followers: 18)
Cretaceous Research     Hybrid Journal   (Followers: 9)
Cybergeo : European Journal of Geography     Open Access   (Followers: 6)
Depositional Record     Open Access   (Followers: 1)
Developments in Geotectonics     Full-text available via subscription   (Followers: 3)
Developments in Quaternary Science     Full-text available via subscription   (Followers: 4)
Développement durable et territoires     Open Access   (Followers: 3)
Diatom Research     Hybrid Journal   (Followers: 2)
Doklady Physics     Hybrid Journal   (Followers: 1)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 13)
E&S Engineering and Science     Open Access  
E3S Web of Conferences     Open Access   (Followers: 1)
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 154)
Earth and Space Science     Open Access   (Followers: 14)
Earth Interactions     Full-text available via subscription   (Followers: 13)
Earth Science Frontiers     Full-text available via subscription   (Followers: 7)
Earth Science Research     Open Access   (Followers: 8)
Earth Surface Dynamics (ESurf)     Open Access   (Followers: 6)
Earth Surface Processes and Landforms     Hybrid Journal   (Followers: 20)
Earth System Dynamics     Open Access   (Followers: 9)
Earth System Dynamics Discussions     Open Access   (Followers: 6)
Earth's Future     Open Access   (Followers: 1)
Earth, Planets and Space     Open Access   (Followers: 71)
Earthquake Engineering and Engineering Vibration     Hybrid Journal   (Followers: 9)
Earthquake Science     Hybrid Journal   (Followers: 12)
Earthquake Spectra     Full-text available via subscription   (Followers: 21)
Ecohydrology     Hybrid Journal   (Followers: 12)
Ecological Questions     Open Access   (Followers: 6)
Electromagnetics     Hybrid Journal   (Followers: 8)
Energy Efficiency     Hybrid Journal   (Followers: 11)
Energy Exploration & Exploitation     Hybrid Journal   (Followers: 4)
Environmental Earth Sciences     Hybrid Journal   (Followers: 27)
Environmental Geology     Hybrid Journal   (Followers: 20)
Environmental Geosciences     Full-text available via subscription   (Followers: 5)
Environmental Geotechnics     Hybrid Journal   (Followers: 5)
Erwerbs-Obstbau     Hybrid Journal  
Estuaries and Coasts     Hybrid Journal   (Followers: 17)
Estuarine, Coastal and Shelf Science     Hybrid Journal   (Followers: 34)
Estudios Geográficos     Open Access  
European Journal of Mineralogy     Full-text available via subscription   (Followers: 16)
European Journal of Remote Sensing     Open Access   (Followers: 5)
Exploration Geophysics     Hybrid Journal   (Followers: 4)
Facies     Hybrid Journal   (Followers: 10)
Fieldiana Life and Earth Sciences     Full-text available via subscription   (Followers: 1)
Física de la Tierra     Open Access  
Folia Musei rerum naturalium Bohemiae occidentalis. Geologica et Paleobiologica     Open Access  
Folia Quaternaria     Open Access  
Forestry Chronicle     Full-text available via subscription   (Followers: 10)
Frontiers in Earth Science     Open Access   (Followers: 5)
Frontiers in Geotechnical Engineering     Open Access   (Followers: 3)
Frontiers of Earth Science     Hybrid Journal   (Followers: 9)
Fundamental and Applied Limnology / Archiv für Hydrobiologie     Full-text available via subscription   (Followers: 4)
GEM - International Journal on Geomathematics     Hybrid Journal   (Followers: 1)
Geo-Marine Letters     Hybrid Journal   (Followers: 7)
Geoacta     Open Access   (Followers: 4)
Geobiology     Hybrid Journal   (Followers: 9)
Geocarto International     Hybrid Journal   (Followers: 22)
Geochemistry : Exploration, Environment, Analysis     Hybrid Journal   (Followers: 8)
Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 32)
Geochimica et Cosmochimica Acta     Hybrid Journal   (Followers: 52)
Geochronometria     Hybrid Journal   (Followers: 3)
Geoderma Regional : The International Journal for Regional Soil Research     Full-text available via subscription   (Followers: 4)
Geodinamica Acta     Open Access   (Followers: 3)
Geodynamics & Tectonophysics     Open Access   (Followers: 2)
Geoenvironmental Disasters     Open Access   (Followers: 3)
Geofluids     Open Access   (Followers: 5)
Geoforum     Hybrid Journal   (Followers: 24)
Géographie physique et Quaternaire     Full-text available via subscription   (Followers: 1)
Geography and Natural Resources     Hybrid Journal   (Followers: 8)
Geoheritage     Hybrid Journal   (Followers: 1)
Geoinformatica Polonica : The Journal of Polish Academy of Arts and Sciences     Open Access  
Geoinformatics & Geostatistics     Hybrid Journal   (Followers: 11)
Geological Journal     Hybrid Journal   (Followers: 16)
Geological Magazine     Hybrid Journal   (Followers: 16)
Geology Today     Hybrid Journal   (Followers: 29)
Geology, Geophysics and Environment     Open Access   (Followers: 2)
Geomagnetism and Aeronomy     Hybrid Journal   (Followers: 3)
Geomatics, Natural Hazards and Risk     Hybrid Journal   (Followers: 11)
Geomechanics for Energy and the Environment     Full-text available via subscription   (Followers: 1)
GEOmedia     Open Access   (Followers: 1)
Geomorphology     Hybrid Journal   (Followers: 31)
Geophysical & Astrophysical Fluid Dynamics     Hybrid Journal   (Followers: 2)
Geophysical Journal International     Hybrid Journal   (Followers: 34)
Geophysical Prospecting     Hybrid Journal   (Followers: 7)
GeoResJ     Hybrid Journal  
Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards     Hybrid Journal   (Followers: 9)
Geoscience Canada : Journal of the Geological Association of Canada / Geoscience Canada : journal de l'Association Géologique du Canada     Full-text available via subscription   (Followers: 5)
Geoscience Data Journal     Open Access   (Followers: 2)
Geoscience Frontiers     Open Access   (Followers: 10)
Geoscience Letters     Open Access   (Followers: 1)
Geoscience Records     Open Access  
Geosciences     Open Access   (Followers: 2)
Geosciences Journal     Hybrid Journal   (Followers: 11)
Geoscientific Instrumentation, Methods and Data Systems     Open Access   (Followers: 4)
Geoscientific Model Development     Open Access   (Followers: 2)
Geostandards and Geoanalytical Research     Hybrid Journal   (Followers: 2)
Geosystem Engineering     Hybrid Journal   (Followers: 1)
Geotectonic Research     Full-text available via subscription   (Followers: 5)
Geotectonics     Hybrid Journal   (Followers: 7)
GISAP : Earth and Space Sciences     Open Access   (Followers: 2)
Glass Physics and Chemistry     Hybrid Journal   (Followers: 4)
Global and Planetary Change     Hybrid Journal   (Followers: 19)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 16)
Gondwana Research     Hybrid Journal   (Followers: 10)
GPS Solutions     Hybrid Journal   (Followers: 23)
Grassland Science     Hybrid Journal  
Ground Water     Hybrid Journal   (Followers: 36)
Ground Water Monitoring & Remediation     Hybrid Journal   (Followers: 19)
Groundwater for Sustainable Development     Full-text available via subscription   (Followers: 3)
Helgoland Marine Research     Open Access   (Followers: 3)
History of Geo- and Space Sciences     Open Access   (Followers: 4)
Hydrobiologia     Hybrid Journal   (Followers: 19)
Hydrogeology Journal     Hybrid Journal   (Followers: 22)
Hydrological Processes     Hybrid Journal   (Followers: 31)
Hydrology and Earth System Sciences     Open Access   (Followers: 31)
ICES Journal of Marine Science: Journal du Conseil     Hybrid Journal   (Followers: 53)
IEEE Journal of Oceanic Engineering     Hybrid Journal   (Followers: 13)
Indian Geotechnical Journal     Hybrid Journal   (Followers: 4)
Indonesian Journal on Geoscience     Open Access   (Followers: 2)
Interdisciplinary Environmental Review     Hybrid Journal   (Followers: 3)
International Geology Review     Hybrid Journal   (Followers: 16)
International Journal of Advanced Geosciences     Open Access   (Followers: 2)
International Journal of Advanced Remote Sensing and GIS     Open Access   (Followers: 39)
International Journal of Advancement in Earth and Enviromental Sciences     Open Access   (Followers: 4)
International Journal of Advancement in Remote Sensing, GIS, and Geography     Open Access   (Followers: 32)
International Journal of Applied Earth Observation and Geoinformation     Hybrid Journal   (Followers: 36)
International Journal of Coal Geology     Hybrid Journal   (Followers: 3)
International Journal of Disaster Risk Reduction     Hybrid Journal   (Followers: 19)
International Journal of Earth Sciences     Hybrid Journal   (Followers: 39)
International Journal of Earthquake and Impact Engineering     Hybrid Journal   (Followers: 4)
International Journal of Geo-Engineering     Open Access   (Followers: 3)

        1 2 3 | Last

Journal Cover Chemie der Erde - Geochemistry
  [SJR: 0.881]   [H-I: 34]   [5 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0009-2819
   Published by Elsevier Homepage  [3177 journals]
  • Petrogenesis and geochronology of Mishao peraluminous I-type granites,
           Shalair valley area, NE Iraq
    • Abstract: Publication date: Available online 15 February 2018
      Source:Chemie der Erde
      Author(s): Imad Kadhim Abdulzahra, Ayten Hadi, Yoshihiro Asahara, Hossein Azizi, Koshi Yamamoto
      The Shalair area, which is located in northeastern Iraq, is considered to be part of the northern Sanandaj-Sirjan Zone (SaSZ) and contains several granitoid bodies. One of these bodies, the Mishao porphyritic-granite (MG), was crystallized at 111.6 ± 2.4 Ma, based on its zircon U-Pb age. Its geochemical characteristics suggest that the MG rocks are calc-alkaline, peraluminous, I-type granites with microgranular mafic enclaves. They are enriched in SiO2, Na2O, Al2O3 and Zr and depleted in MgO, Fe2O3, Nb and Ti; in contrast, the enclave sample records lower SiO2 content and higher contents of MgO and Fe2O3. These rocks show an enrichment of LREE relative to HREE, and pronounced negative Eu anomalies implying feldspar fractionation. The isotopic and geochemical characteristics of the MG samples suggest that these rocks are evolved through fractional crystallization. In the La/Nb-Nb diagram and Sm/Nd ratios, the MG rocks and the enclave samples exhibit strong evidence for crustal contamination. The MG rocks record high initial 87Sr/86Sr (0.70625–0.70740) and low 143Nd/144Nd(i) (0.51235–0.51274) ratios. These Sr-Nd isotopic data, combined with the presence of high Th/U and Rb/Sr ratios and significant depletions of Nb, Ta and Ti, show a relation of these bodies to an active continental margin regime. Based on the age and geochemical data of the MG, this study presents new information about the occurrence of Middle Cretaceous magmatic activities, which are related to the active continental margins in the SaSZ that run parallel to the Zagros Fold-Thrust Belt.

      PubDate: 2018-02-26T13:35:32Z
  • Mineral chemistry and Ti in zircon thermometry: Insights into magmatic
           evolution of the Sangan igneous rocks, NE Iran
    • Abstract: Publication date: Available online 15 February 2018
      Source:Chemie der Erde
      Author(s): Fatemeh Sepidbar, Hassan Mirnejad, Changqian Ma
      The Sangan Magmatic complex (SMC) is, a large I-type magmatic complex, located in the northeastern Iran. Zircons extracted from the intrusive and volcanic rocks within the SMC record a similar Hf compositions and REE patterns, indicating that these chemical signatures have likely been inherited from the same source and simple history of magmatic crystallization during the evolution of the orogeny. The zircon from volcanic rocks yield Ti-in-zircon crystallization temperatures of 667–1145 °C with average temperatures of 934 °C while those from granitoids indicate crystallization temperatures of 614–898 °C with an average of 812 °C. Ti-in-zircon, Ti in biotite thermometries also indicates that the crystallization temperatures of volcanic rocks are relatively higher than those of granitoids. The biotite chemistry studies reveal that this mineral crystallized at approximately 725°–800 °C and 758° to 816 °C for granitoid and volcanic rocks, respectively, which is similar to obtained temperatures by Zir-saturation of Eq. (1). Tzicsat and Tmagma trend lines on the T-SiO2 diagram cross at high silica contents of ∼68 wt.%, at which temperature the magma becomes zircon-saturated and new zircons are crystallized. The zircon REE data including Ce/Ce*, Eu/Eu*, and Th/U ratios suggest that SMC igneous rocks are formed from oxidized magma. However, the zircon Th/U and Hf data suggest that the SMC became progressively more oxidized and also indicate lower temperatures from volcanic and plutonic rock with decreasing time.

      PubDate: 2018-02-26T13:35:32Z
  • Thermal behavior of ferric selenite hydrates (Fe2(SeO3)3·3H2O,
           Fe2(SeO3)3·5H2O) and the water content in the natural ferric selenite
    • Abstract: Publication date: Available online 3 February 2018
      Source:Chemie der Erde
      Author(s): Astrid Holzheid, Marina V. Charykova, Vladimir G. Krivovichev, Brendan Ledwig, Elena L. Fokina, Ksenia L. Poroshina, Natalia V. Platonova, Vladislav V. Gurzhiy
      Any progress in our understanding of low-temperature mineral assemblages and of quantitative physico-chemical modeling of stability conditions of mineral phases, especially those containing toxic elements like selenium, strongly depends on the knowledge of structural and thermodynamic properties of coexisting mineral phases. Interrelation of crystal chemistry/structure and thermodynamic properties of selenium-containing minerals is not systematically studied so far and thus any essential generalization might be difficult, inaccurate or even impossible and erroneous. Disagreement even exists regarding the crystal chemistry of some natural and synthetic selenium-containing phases. Hence, a systematic study was performed by synthesizing ferric selenite hydrates and subsequent thermal analysis to examine the thermal stability of synthetic analogues of the natural hydrous ferric selenite mandarinoite and its dehydration and dissociation to unravel controversial issues regarding the crystal chemistry. Dehydration of synthesized analogues of mandarinoite starts at 56–87 °C and ends at 226–237 °C. The dehydration happens in two stages and two possible schemes of dehydration exist: (a) mandarinoite loses three molecules of water in the first stage of the dehydration (up to 180 °C) and the remaining two molecules of water will be lost in the second stage (>180 °C) or (b) four molecules of water will be lost in the first stage up to 180 °C and the last molecule of water will be lost at a temperature above 180 °C. Based on XRD measurements and thermal analyses we were able to deduce Fe2(SeO3)3·(6-x)H2O (x = 0.0–1.0) as formula of the hydrous ferric selenite mandarinoite. The total amount of water apparently affects the crystallinity, and possibly the stability of crystals: the less the x value, the higher crystallinity could be expected.

      PubDate: 2018-02-26T13:35:32Z
  • Petrology, phase equilibria modelling, noble gas chronology and thermal
           constraints of the El Pozo L5 meteorite
    • Abstract: Publication date: Available online 10 January 2018
      Source:Chemie der Erde
      Author(s): Pedro Corona-Chávez, María del Sol Hernández-Bernal, Pietro Vignola, Rufino Lozano-Santacruz, Juan Julio Morales-Contreras, Margarita Reyes-Salas, Jesús Solé-Viñas, José F. Molina
      We present the results of physical properties, petrography, bulk chemistry, mineral compositions, phase relations modelling and Noble gases study of the meteorite El Pozo. The petrography and mineral compositions indicate that the meteorite is an L5 chondrite with a low shock stage of S2-S3. Heterogenous weathering was preferentially along shock structures. Thermobarometric calculations indicate thermal equilibrium conditions between 768 °C and 925 °C at ∼4 to 6 kb, which are substantially consistent with the petrological metamorphism type 5. A pseudosection phase diagram is relatively consistent with the mineral assemblage observed and PT conditions calculated. Temperature vs. fO2 diagram shows that plagioclase compositional stability is very sensitive to Tschermack substitution in orthopyroxene, clinopyroxene and XAn plagioclase during the high temperature metamorphic process. Based on noble gases He, Ne, Ar and K contents a cosmogenic exposure age CRE of 1.9 Myr was calculated. The 21Ne would be totally cosmogenic, with no primordial Ne. The 21Ne/22Ne value (0.97) is higher than solar value. According to the cosmogenic Ne content, we argue that El Pozo chondrite originally had a pre-atmospheric mass of 9–10 kg, which would have been produced by a later collision after the recognized collision of the L-chondrite parent body ∼470 Ma ago.

      PubDate: 2018-02-26T13:35:32Z
  • Olympus Mons volcano, Mars: A photogeologic view and new insights
    • Abstract: Publication date: Available online 27 December 2017
      Source:Chemie der Erde
      Author(s): Peter Mouginis-Mark
      The volcano Olympus Mons is probably the best known extraterrestrial volcano. In the past decade, an unprecedented selection of high-resolution images with a spatial resolution of up to 25 cm/pixel has been collected, and these images now allow detailed morphologic analysis of the entire volcano. The summit comprises a nested caldera with six overlapping collapse pits. There are numerous wrinkle ridges and graben on the caldera floor, and topographic data indicate that the location of these features is controlled by subsidence of the central portion of the floor. Examination of the caldera walls reveals numerous layers interpreted to be lava flows. No clear evidence for eruption sites on the flanks of the volcano exist; rather, many previously identified sources of lava appear to be break-outs from flows up-slope which are controlled by local breaks in slope. The vents for these eruptions were most likely within the summit caldera but have been removed by the set of six large collapse events that have produced the 60 × 80 km diameter caldera, which are collectively called the “Olympus Paterae”. The origin of the basal escarpment surrounding the volcano remains enigmatic, but it is probably related to the origin of the surrounding lobate materials collectively called the Olympus Mons aureole. In places, this escarpment is >5 km high, but the elevation of the back-wall varies from ∼1 km to ∼8 km relative to the Mars datum. Inspection of kilometer-scale blocks within the aureole indicates that this material is not composed of lava flows, suggesting that the base of Olympus Mons consists of fragmented material comparable to the hyaloclastite material forming the base of Hawaiian volcanoes. Numerous additional features on Olympus Mons are discussed, including two large impact craters near the summit of the volcano, glacial deposits on the lower western flanks, channels and small shields around the base of the volcano, and ridges north of the escarpment which may have formed via the emplacement of dikes into ice-rich materials. Comparison with other Martian volcanoes may also help the analysis of Olympus Mons; the morphology of the basal escarpment of Apollinaris Patera suggests that erosion by wind or water may be restricted to the lowest elevations on Mars. If the basal materials of Olympus Mons are unconsolidated, then Olympus Mons may have been similar to Alba Mons or Tyrrhena Mons during the early phases of volcano growth. Certain basaltic volcanoes on Earth may serve as good analogs for features seen on Olympus Mons; the summit of Masaya volcano, Nicaragua, displays similar features to Olympus Patera at the summit caldera of Olympus Mons.

      PubDate: 2018-01-10T08:40:33Z
  • Age and origin of subvolcanic rocks from NE Iran: Link between magmatic
           “flare-up” and mineralization
    • Abstract: Publication date: Available online 26 December 2017
      Source:Chemie der Erde
      Author(s): A. Ghiasvand, M.H. Karimpour, A. Malekzadeh Shafaroudi, M.R. Hidarian Shahri
      Paleogene igneous rocks from ∼600 km Quchan-Sabzevar-Torud magmatic belt include a thick pile of volcanic and pyroclastic rocks which intruded by younger felsic-mafic plutons. Various types of mineralization including Iron Oxide-Copper-Gold (e.g., Firouzeh mine) and porphyry Cu-Au deposits (e.g., Jalambadan mine) are associated with the Quchan-Sabzevar magmatism. In this study, we describe new zircon U-Pb ages and geochemical-isotopic data of the subvolcanic rocks from near the Firouzeh mine. The Firouzeh subvolcanic rocks consist of (quartz-bearing) monzosyenites, monzodiorites and monzonites. These rocks have typical calc-alkaline signature and are mainly metaluminous in nature. Subvolcanic rocks display enrichment in Light Rare Earth Elements (LREEs) with negative Eu anomaly. Enrichment in Large Ion Lithophile Elements (LILEs) and depletion in High-Field Strength Elements (HFSEs) are geochemical characteristics of these rocks. The Firouzeh volcanic rocks also display calc-alkaline signature and are metaluminous to peraluminous. Volcanic rocks show both enrichment in LREEs and LILEs, associated with negative Eu anomaly. Zircon U-Pb indicates ages of 43.2 ± 0.4, 42.1 ± 0.4 and 41.8 ± 0.4 Ma for monzosyenites, monzodiorites and monzonites respectively. Zircon epsilon Hf(t) shows average values of −1.49 for monzonites, +9.07 for monzodiorites and −1.06 for monzosyenites. The Hf model ages for these rocks are in the range of 850–730, 270–180 and 3150–450 Ma, respectively. Inherited zircons are abundant in monzonites and have variable Hf isotope values. The wide range of zircon εHf(t) values and abundance of inherited/xenocrystic zircons suggest a multiple source(s) for the generation of the Firouzeh subvolcanic rocks, including a mantle melt and an old crustal component. Xenocrystic zircons indicate complex crustal components. We suggest the NE Iran subvolcanic rocks including the Firouzeh igneous rocks, generated above the Sabzevar subduction zone. This subduction zone was active since Late Cretaceous time.

      PubDate: 2017-12-27T07:18:33Z
  • Geochemistry, petrogenesis and radioactive mineralization of two coeval
           Neoproterozoic post-collisional calc-alkaline and alkaline granitoid
           suites from Sinai, Arabian Nubian Shield
    • Abstract: Publication date: Available online 21 December 2017
      Source:Chemie der Erde
      Author(s): Mohammed Z. El-Bialy, Ahmed E. Shata
      The Younger Granites of Yahmid-Um Adawi area, located in the southeastern part of Sinai Peninsula, comprise two coeval Late Neoproterozoic post-collisional alkaline (hypersolvous alkali-feldspar granites; 608–580 Ma) and calc-alkaline (transsolvous monzo- and syenogranites; 635–590 Ma) suites. The calc-alkaline suite granitoids are magnesian and peraluminous to metaluminous, whereas the alkaline ones are magnesian to ferroan alkaline to slightly metaluminous. Both granitoid suites exhibit many of the typical geochemical features of A-type granites such as enrichment in Nb (>20 ppm), Zr (>250 ppm), Zn (>100 ppm) and Ce (>100 ppm) and high 10000*Ga/Al2O3 ratios (>2.6) and Zr + Nb + Y + Ce (>350 ppm). Accessory mineral saturation thermometers demonstrated former crystallization of apatite at high temperatures prior to zircon and monazite separation from the magma for both granitoid suites. The mild zircon saturation temperatures of the studied Younger Granites (around 800 °C) imply low-temperature crustal fusion and incomplete melting of the largely refractory zircon. The two Younger Granite suites were semi-synchronously evolved during the post-collisional stage of the Arabian-Nubian Shield subsequent to the collision between the juvenile shield crust and the older pre-Neoproterozoic continental blocks of west Gondwana. Their parental magmas has been generated by melting of crustal source rocks with minor involvement from mantle, which might participated chiefly as a source of heat necessary for fusion of the crustal precursor. Extensive in-situ gamma-ray spectrometry revealed anomalously high radioactivity of some Younger Granite exposures along Wadi Um Adawi (eU; 388–746 ppm and eTh; 1857–2527 ppm) and pegmatitic pockets pertaining to the calc-alkaline suite (equivalent U and Th; 212–252 ppm and 750–1757 ppm, respectively). The radioactivity of the syngenetic pegmatites arises from the primary radioactive minerals uranothorite and thorite together with the U- and/or Th-bearing minerals zircon, columbite, samarskite and monazite. The anomalously high radioactivity of some Younger Granite exposures in Wadi Um Adawi stem from their appreciable enclosure of the epigenetic uranium minerals metatorbenite and uranophane.

      PubDate: 2017-12-27T07:18:33Z
  • Editorial board members
    • Abstract: Publication date: December 2017
      Source:Chemie der Erde - Geochemistry, Volume 77, Issue 4

      PubDate: 2017-12-27T07:18:33Z
  • Field evidence, mineral chemical and geochemical constraints on
           mafic-felsic magma interactions in a vertically zoned magma chamber from
           the Chotanagpur Granite Gneiss Complex of Eastern India
    • Abstract: Publication date: Available online 1 December 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Bibhuti Gogoi, Ashima Saikia, Mansoor Ahmad
      The Nimchak granite pluton (NGP) of Chotanagpur Granite Gneiss Complex (CGGC), Eastern India, provides ample evidence of magma interaction in a plutonic regime for the first time in this part of the Indian shield. A number of outcrop level magmatic structures reported from many mafic-felsic mixing and mingling zones worldwide, such as synplutonic dykes, mafic magmatic enclaves and hybrid rocks extensively occur in our study domain. From field observations it appears that the Nimchak pluton was a vertically zoned magma chamber that was intruded by a number of mafic dykes during the whole crystallization history of the magma chamber leading to magma mixing and mingling scenario. The lower part of the pluton is occupied by coarse-grained granodiorite (64.84–66.61wt.% SiO2), while the upper part is occupied by fine-grained granite (69.80–70.57wt.% SiO2). Field relationships along with textural and geochemical signatures of the pluton suggest that it is a well-exposed felsic magma chamber that was zoned due to fractional crystallization. The intruding mafic magma interacted differently with the upper and lower granitoids. The lower granodiorite is characterized by mafic feeder dykes and larger mafic magmatic enclaves, whereas the enclaves occurring in the upper granite are comparatively smaller and the feeder dykes could not be traced here, except two late-stage mafic dykes. The mafic enclaves occurring in the upper granite show higher degrees of hybridization with respect to those occurring in the lower granite. Furthermore, enclaves are widely distributed in the upper granite, whereas enclaves in the lower granite occur adjacent to the main feeder dykes. Geochemical signatures confirm that the intermediate rocks occurring in the Nimchak pluton are mixing products formed due to the mixing of mafic and felsic magmas. A number of important physical properties of magmas like temperature, viscosity, glass transition temperature and fragility have been used in magma mixing models to evaluate the process of magma mixing. A geodynamic model of pluton construction and evolution is presented that shows episodic replenishments of mafic magma into the crystallizing felsic magma chamber from below. Data are consistent with a model whereby mafic magma ponded at the crust-mantle boundary and melted the overlying crust to form felsic (granitic) magma. The mafic magma episodically rose, injected and interacted with an overlying felsic magma chamber that was undergoing fractional crystallization forming hybrid intermediate rocks. The intrusion of mafic magma continued after complete solidification of the magma chamber as indicated by the presence of two late-stage mafic dykes.

      PubDate: 2017-12-27T07:18:33Z
  • Petrogenesis of Rabor-Lalehzar magmatic rocks (SE Iran): Constraints from
           whole rock chemistry and Sr-Nd isotopes
    • Abstract: Publication date: Available online 29 November 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Mohsen Chekani Moghadam, Zahra Tahmasbi, Ahmad Ahmadi-Khalaji, José Francisco Santos
      The Urumieh-Dokhtar magmatic arc (UDMA) of Central Iran has been formed during Neotethyan Ocean subduction underneath Eurasia. The Rabor-Lalehzar magmatic complex (RLMC), covers an area ∼1000km2 in the Kerman magmatic belt (KMB), SE of UDMA. RLMC magmatic rocks include both granitoids and volcanic rocks with calc-alkaline and adakitic signatures but with different ages. Miocene adakitic rocks are characterd by relatively enrichmented in incompatible elements, high (Sr/Y)(N) (>40), and (La/Yb)(N) (>10) ratios with slightly negative Eu anomalies (EuN/Eu*≈ 0.9), depletion in HFSEs, and relatively non-radiogenic Sr isotope signatures (87Sr/86Sr=0.7048–0.7049). In contrast, the Oligocene granitoids exhibit low Sr/Y (<20) and La/Yb (<9) ratios, negative Eu anomalies (EuN/Eu*≈0.5), and enrichment in HFSEs and radiogenic Sr isotope signatures (87Sr/86Sr=0.7050–0.7052), showing affinity to the island arc rocks. Eocene volcanic rocks which crusscut the younger granitoid rocks comprise andesites and dacites. Geochemically, lavas show calc-alkaline character without any Eu anomaly (EuN/Eu*≈1.0). Based on the geochemical and isotopic data we propose that melt source for both calc-alkaline and adakitic rocks from the RLMC can be related to the melting of a sub-continental lithospheric mantle (SCLM). Basaltic melts derived from a metasomatized mantle wedge might be emplaced at the mantle-crust boundary and formed the juvenile mafic lower crust. However, some melts fractionated in the shallow magma chambers and continued to rise forming the volcanic intermediate-mafic rocks at the surface. On the other hand, the assimilation and fractional crystallization in the shallow magma chambers of may have been responsible for the development of Oligocene granitoids with calc-alkaline affinity. In the mid-Late Miocene, following the collision between Afro-Arabia and Iranian block the juvenile mafic crust of UDMA underwent thickening and metamorphosed into garnet-amphibolites. Subsequent upwelling of a hot asthenosphere during Miocene was responsible for partial melting of thickened juvenile crust of the SE UDMA (RLM complex). The adakitic melts ascended to the shallow crust to form the adakitic rocks in the KMB.

      PubDate: 2017-12-27T07:18:33Z
  • Mineralogy, microchemistry and fluid inclusion studies of the Besshi-type
           Nudeh Cu-Zn VMS deposit, Iran
    • Abstract: Publication date: Available online 27 November 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Sajjad Maghfouri, Ebrahim Rastad, David R. Lentz, Fardin Mousivand, Flavien Choulet
      The southwestern Sabzevar basin is the north of Central Iranian Microcontinent hosts abundant mineral deposits, including exhalative Mn mineralization and Cu-Zn volcanogenic massive sulfide (VMS) deposits. Amongst them, the Nudeh Besshi-type Cu–Zn volcanogenic massive sulfide (VMS) deposit is hosted within the lower part of a Late Cretaceous volcano-sedimentary sequence composed of alkali olivine basalt flows and tuffaceous silty sandstone. Based on investigations into the ore geometry, mineralogy, and texture, we recognized three different ore facies: (1) a stockwork of sulfide-bearing quartz veins cutting across the footwall volcano-sedimentary rocks and representing the stringer zone; (2) a massive ore type, displaying replacement texture with pyrite, chalcopyrite, sphalerite, friedrichite, and minor magnetite; and (3) a bedded ore type, with laminated to disseminated pyrite and chalcopyrite. EPMA studies indicate a distinctive minor element distribution between the different ore types of the Nudeh deposit. The Fe content in the sphalerite ranges from 0.65–1.80wt.%, indicating the Fe-poor nature of the sphalerite. However, the Cd content in sphalerite ranged between 0.164–0.278wt.%. According to the mineral compositions, Zn, Se, and Ag are found in bornite as minor elements. In the bedded ore facies, the pyrite contains higher levels of Se (up to 0.35wt.%). The Zn content in the friedrichite in all of the ore samples is low. The Co/Ni ratios in pyrite from the Nudeh ore are lower than those of most magmatic deposits, but are similar to those from volcanogenic deposits, and hence support the proposed hydrothermal origin of the deposit. Two generations of quartz, Q1 and Q2 in the stockwork veins, contain primary fluid inclusions and these contain two phases (liquid and vapor). The lack of vapor-rich inclusions or variable liquid/vapor ratios indicate that the fluids did not boil at the site of trapping. Salinity for both Q1 and Q2 fluid inclusions ranges between 2.2–6.8wt.% eq. NaCl. Homogenization temperatures for inclusions in the Q1 and Q2 veins average at about 296°C and are similar to the temperatures of hydrothermal fluids discharged through vents in many modern seafloor VMS deposit. The Nudeh Besshi-type VMS deposit appears to have formed on the seafloor and based on the salinity and temperature constraints from the underlying stockwork, a buoyancy plume model is proposed as a mechanism for precipitation.

      PubDate: 2017-12-27T07:18:33Z
  • Sugarloaf Mountain, central Arizona, USA: A small-scale example of Miocene
           basalt-rhyolite magma mixing to yield andesitic magmas
    • Abstract: Publication date: Available online 20 November 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Ellen J. Craig, R.V. Fodor
      Sugarloaf Mountain is a 200-m high volcanic landform in central Arizona, USA, within the transition from the southern Basin and Range to the Colorado Plateau. It is composed of Miocene alkalic basalt (47.2–49.1wt.% SiO2; 6.7–7.7wt.% MgO) and overlying andesite and dacite lavas (61.4–63.9wt.% SiO2; 3.5–4.7wt.% MgO). Sugarloaf Mountain therefore offers an opportunity to evaluate the origin of andesite magmas with respect to coexisting basalt. Important for evaluating Sugarloaf basalt and andesite (plus dacite) is that the andesites contain basaltic minerals olivine (cores Fo76-86) and clinopyroxene (∼Fs9-18Wo35-44) coexisting with Na-plagioclase (An48-28Or1.4–7), quartz, amphibole, and minor orthopyroxene, biotite, and sanidine. Noteworthy is that andesite mineral textures include reaction and spongy zones and embayments in and on Na-plagioclase and quartz phenocrysts, where some reacted Na-plagioclases have higher-An mantles, plus some similarly reacted and embayed olivine, clinopyroxene, and amphibole phenocrysts. Fractional crystallization of Sugarloaf basaltic magmas cannot alone yield the andesites because their ∼61 to 64wt.% SiO2 is attended by incompatible REE and HFSE abundances lower than in the basalts (e.g., Ce 77–105 in andesites vs 114–166ppm in basalts; Zr 149–173 vs 183–237; Nb 21–25 vs 34–42). On the other hand, andesite mineral assemblages, textures, and compositions are consistent with basaltic magmas having mixed with rhyolitic magmas, provided the rhyolite(s) had relatively low REE and HFSE abundances. Linear binary mixing calculations yield good first approximation results for producing andesitic compositions from Sugarloaf basalt compositions and a central Arizona low-REE, low-HFSE rhyolite. For example, mixing proportions 52:48 of Sugarloaf basalt and low incompatible-element rhyolite yields a hybrid composition that matches Sugarloaf andesite well − although we do not claim to have exact endmembers, but rather, viable proxies. Additionally, the observed mineral textures are all consistent with hot basalt magma mixing into rhyolite magma. Compositional differences among the phenocrysts of Na-plagioclase, clinopyroxene, and amphibole in the andesites suggest several mixing events, and amphibole thermobarometry calculates depths corresponding to 8–16km and 850° to 980°C. The amphibole P-T observed for a rather tight compositional range of andesite compositions is consistent with the gathering of several different basalt-rhyolite hybrids into a homogenizing ‘collection' zone prior to eruptions. We interpret Sugarloaf Mountain to represent basalt-rhyolite mixings on a relatively small scale as part of the large scale Miocene (∼20 to 15 Ma) magmatism of central Arizona. A particular qualification for this example of hybridization, however, is that the rhyolite endmember have relatively low REE and HFSE abundances.

      PubDate: 2017-12-27T07:18:33Z
  • Mineralogical and petrological features of the Cemilköy ignimbrite,
           Cappadocia, Turkey
    • Abstract: Publication date: Available online 13 November 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Gullu Deniz Dogan-Kulahci, Abidin Temel, Alain Gourgaud
      The Cemilköy ignimbrite is one of the voluminous ignimbrite deposits in Cappadocia. The Cemilköy ignimbrite contains pumice and lithic clasts of volcanic and ophiolitic origin in an ash matrix. The unwelded Cemilköy ignimbrite is distinguished from other deposits in Cappadocia by flattened pumices, elongate vesicles and a slaty fabric. The mineral assemblage of the Cemilköy ignimbrite is plagioclase, biotite, quartz and oxides (magnetite and Ti-magnetite) and the matrix is glassy. Eutaxitic texture is dominant and all pumice clasts have a vitrophyric-porphyritic texture. The same textural properties were observed throughout the spatial distribution of Cemilköy ignimbrite. Microprobe studies reveal that plagioclase compositions range from albite through oligoclase-andesine. Estimated plagioclase-liquid temperatures (T) and pressures (P) are varying between 806 and 847°C and 4.2–7.1 (kbar), and the H2O content of the melt is estimated to have been 5wt.% from the pumice clasts. Based on geochemical data, the Cemilköy ignimbrite is rhyolitic and calc-alkaline in character, and all pumice clasts are enriched in LIL and LRE elements relative to HFS elements. Negative Nb, Ta and Ti anomalies, ratios of Ba/Nb >28 (56–77), Ba/Ta ˃450 (590–700) and Th/Yb vs. Ta/Yb are consistent with a subduction-related origin. According to the geochemical and mineralogical-petrographical data, the Cemilköy ignimbrite originated from partial melting of a mantle source which was enriched during previous subduction processes with variable degrees of assimilation fractional crystallization (AFC) through time and Cemilköy ignimbrite erupted from a crustal magma chamber at shallow to intermediate depth.

      PubDate: 2017-11-16T15:09:34Z
  • Hydrogeochemical characteristics of mine water in the Harz Mountains,
    • Abstract: Publication date: Available online 28 October 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Elke Bozau, Tobias Licha, Wilfried Ließmann
      Water samples (springs, creeks, mine adits) from different former mining districts of the Harz Mountains and the nearby Kupferschiefer (copper shale) basin of Sangerhausen were analysed for major ions and trace metals. Due to more intensive water rock interactions including the ore minerals, the mine water concentrations of main components and trace metals are generally higher compared to non mining affected surface waters of the mountain range. Furthermore, the content of major ions in mine water is enriched by mixing processes with saline waters from Permian layers in the Kupferschiefer district and at the deeper levels of the mines in the Upper Harz Mountains. The waters of the different mining districts can be distinguished by trace metal occurrences and concentrations derived from the different ore bodies. Water from the Kupferschiefer mines shows the highest Na, Cl, Cu, Mo and U concentrations, whereas a combination of elevated As and Se concentrations is typical for most of the samples from the mines around St. Andreasberg. However, there are exceptions, and some water samples of all the investigated mining districts do not follow these general trends. Despite the influence of mining activities and ore mineralisation, hydrochemical effects due to rain water dilution can be seen in most of the waters. According to the elevation of the mountain range, higher precipitation rates decrease the ion concentrations in the waters of springs, creeks and mine adits.

      PubDate: 2017-11-02T18:03:05Z
  • Geochemistry of black shales from the Mesoproterozoic Srisailam Formation,
           Cuddapah basin, India: Implications for provenance, palaeoweathering,
           tectonics, and timing of Columbia breakup
    • Abstract: Publication date: Available online 27 October 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Himadri Basu, P.S. Dandele, K. Ramesh Kumar, K.K. Achar, K. Umamaheswar
      The Mesoproterozoic Srisailam Formation, exposed along the northern part of the Cuddapah basin, India, comprises mainly medium- to fine-grained siliciclastics, and is devoid of any carbonate sediment. Preliminary sedimentological studies helped in recognizing fifteen distinct facies (five facies associations) in Chitrial outlier of the Srisailam Formation deposited in continental half-graben basin(s). Black shales (sensu lato) are minor components of the Srisailam Formation, and inferred to have deposited in deep lacustrine and prodelta facies of the half-graben(s). The black shales show restricted thickness (up to 29.0m), and are characterized by overall high ‘black shale' to ‘total shale' ratio (>0.51). Their geochemical characteristics were studied to constrain provenance, palaeoclimate, and tectonic setting of deposition of the Srisailam Formation. Further, an attempt has been made to use the Srisailam black shales as proxy for constraining the timing of breakup of the supercontinent Columbia. The Srisailam black shales are geochemically quite distinct. At similar SiO2 contents they are considerably different from PAAS. They are characterized by considerably lower ΣREE (Av. 136.0±50.4ppm) but a more conspicuous negative Eu-anomaly (Av. 0.34±0.09) than PAAS. Al2O3/TiO2 and TiO2/Zr ratios coupled with Eu/Eu*, GdCN/YbCN, La/Sc, Th/Sc, and Th/Cr ratios suggest their derivation from granite and granodiorite. The CIA values (65–90, Av. 72±9) as a whole indicate moderate chemical weathering under semiarid climate. Discriminating geochemical parameters indicate passive margin depositional setting. The combined sedimentological and geochemical characteristics reveal deposition of the Srisailam sediments in continental rift basin(s). Thick succession of black shales (with high CIA values) that deposited with shelf carbonates proxy for mantle superplume and supercontinent breakup events. The sedimentological characteristics and geochemical data of the Srisailam black shales plausibly exclude any large-scale breakup of Columbia during the interval (1400–1327Ma) of deposition of the Srisailam Formation.

      PubDate: 2017-11-02T18:03:05Z
  • Editorial board members
    • Abstract: Publication date: September 2017
      Source:Chemie der Erde - Geochemistry, Volume 77, Issue 3

      PubDate: 2017-11-02T18:03:05Z
  • A crustal source for ca. 165 Ma post-collisional granites related to
           mineralization in the Jianglang dome of the Songpan-Ganzi Orogen, eastern
           Tiebtan Plateau
    • Abstract: Publication date: Available online 24 October 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Yanpei Dai, Yudi Zhu, Tongzhu Li, Huihua Zhang, Gaolin Tang, Zhanwu Shen
      The Wenjiaping and Wulaxi granite plutons are located in the Jianglang dome, which is a key domain for providing deep insight into the tectonic evolution of the Songpan-Ganzi Orogen. Two granites are composed chiefly of K-feldspar, quartz, biotite with minor plagioclase and hornblende. This study presents zircon U-Pb chronology, geochemistry and Hf isotope data to explore their petrogenesis and metallogenic implications. Zircon U-Pb dating provides crystallization ages of 164.5±0.9 Ma and 163.4±0.9 Ma for the Wenjiaping granite, and 164.3±1.7 Ma for the Wulaxi granite. This indicates that they were formed synchronously. They also contain inherited zircons related to the Rodinia and Gondwana supercontinents and the Emeishan large igneous province. Their mineral assemblages lack peraluminous (e.g., garnet and cordierite) and high-temperature (e.g., pyroxene and fayalite) minerals. They are characterized by low A/CNK (1.10–0.99), FeOT/MgO (8.55–2.83) and K2O/N2O ratios (1.34–0.51) with low Zr+Nb+Ce+Y concentrations (average 258ppm) and zircon saturation temperatures (781–651°C). Their Al2O3, P2O5 and SiO2 contents show negative correlations, and they thus fit the I-type granite definition. Some major and trace elements exhibit strong correlations, implying extensive fractional crystallization (e.g., hornblende and ilmenite) during the magma evolution. Two granites show enrichment in light rare earth elements and large ion lithophile elements, and depletion in high field strength elements. They have low Mg# values (38.7–17.3) and Y/Nb ratios (0.45–0.16), and yield dominantly negative εHf(t) values (1.4–−13.9), indicating a heterogeneous source and their derivation from remelting of ancient continental crust (e.g., Mesoproterozoic Liwu Group in this region) with minor juvenile crust. Combined with prior studies, we conclude that the Wenjiaping and Wulaxi granites were formed in a post-collisional extensional regime, and were responsible for the 163.7–151.1 Ma magmatic hydrothermal Cu-W mineralization in the Jianglang dome. In addition, two granite plutons intrude this dome and they are undeformed, implying that the doming was during the Early to Middle Jurassic.

      PubDate: 2017-10-25T16:45:25Z
  • Compositional variability of spinel-group minerals from the shergol
           serpentinized peridotites along indus suture zone, ladakh himalaya
           (India): constraints on tectonomagmatic history
    • Abstract: Publication date: Available online 16 October 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Irfan Maqbool Bhat, Talat Ahmad, D.V. Subba Rao
      The Shergol ophiolitic peridotites along ISZ, Ladakh Himalaya are serpentinized to various degrees and are harzburgite in composition. Electron microprobe analyses of spinels from Shergol Serpentinized Peridotites (SSPs) were carried out in order to evaluate their compositional variation with alteration. Chemical discontinuity was observed from core to rim in analyzed spinel grains with Cr-rich cores rimmed by Cr-poor compositions. From unaltered cores to rims it was observed that Cr3+# and Fe3+# increases while Mg2+# decreases due to Mg2+ − Fe2+ and Al3+ (Cr3+) − Fe3+ exchange with surrounding silicates during alteration. These peridotites contain Al-rich spinels forming subhedral to anhedral grains with lobate and corroded grain boundaries; altered to ferritchromite or magnetite along cracks and boundaries by later metamorphism episode. The unaltered Cr-spinel cores are identified as Al-rich and are characterized by lower values of Cr3+# (0.34–0.40), high Al3+# (0.58–0.68) and Mg2+# (0.52–0.70). Mineral chemistry of these Al-rich Cr-spinels suggest that host peridotites have an affinity to abyssal and alpine-type peridotites. High TiO2 concentration of magmatic Cr-spinel cores are in agreement with MORB melt-residual peridotite interaction. Presence of unaltered magmatic Cr-spinel cores suggest that they do not have re-equilibrated completely with metamorphic spinel rims and surrounding silicates. Cr-spinel core compositions of SSPs suggest an ophiolitic origin derivation by low degrees of melting of a less-moderate depleted peridotite in a mid-ocean ridge tectonic setting. Based on textural and chemical observations the alteration conditions of studied spinel-group minerals match those of transitional greenschist-amphibolite facies metamorphism consistent with estimated metamorphic equilibration temperature of∼500–600 °C.

      PubDate: 2017-10-18T15:50:05Z
  • Rare earth elements in Permian salts and brines, Thuringia, Germany
    • Abstract: Publication date: Available online 30 September 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Anja Grawunder, Daniel Raabe, Martin Lonschinski, Dirk Merten, Georg Büchel
      Salts and brines have very low rare earth element (REE, La-Lu) concentrations. Thus, there is less knowledge of possible transfer of REE patterns during salt dissolution in water-rock interaction. REE levels in both media are close to or rather below limit of detection of commonly used methods. By dissolving salt samples in water followed by REE pre-concentration, REE contents of about 6.2 to 322ngg−1 were measured for four samples from the Merkers salt mine, Germany. These salts previously were identified to consist mainly of carnallite, halite and/or sylvite. Assuming congruent dissolution, REE patterns of brines and salts differ. Thus, a more complex interaction with (secondary) phases and complexation of REE should be taken into account to explain REE patterns in brines.

      PubDate: 2017-10-03T14:21:04Z
  • Geochemistry of organic matter and elements of black shale during
           weathering in Northern Guizhou, Southwestern China: Their mobilization and
    • Abstract: Publication date: Available online 19 September 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Xuan Tang, Jinchuan Zhang, Yang Liu, Chao Yang, Qian Chen, Wei Dang, Panwang Zhao
      Different from previous studies on effect of weathering upon geochemical variation along a single weathered profile, this paper provides a new methodology validated by comparing a weathered outcrop samples and their stratigraphic counterpart un-weathered core samples in a nearby shallow borehole. This outcrop and borehole penetrated the Ordovician-Silurian Wufeng–Longmaxi shales, located in the same anticline structure in the northern part of Guizhou Province, Southern China. The mineral composition, major, trace and rare earth elements (REEs) composition and Rock-Eval parameters of outcrop and core samples were analyzed and compared. Organic matter (OM) was observed in the microscope and extracted for elements analysis. The results show that short-term weathering still has significant influence on OM, mineral and elemental composition of black shales. The elements composition shows the outcrop profile was moderately weathered. The REEs compositions do not alter much during weathering process and the REEs composition and their relative ratios still are valid for rock origin determination. The OM, mainly composed by graptolite and bitumen, even entering the highly-over thermal maturity, is still sensitive to the weathering with a systematic loss 30–50% of TOC along the outcrop profile, which suggests that the OM consumption is predominantly controlled by weathering duration and the distance from the weathering surface. In turn, OM has significant influence on the trace elements transportation behavior during weathering. Some trace elements associated with the OM such as V, Cr, Th, U, Ni and Co, change significantly in their absolute concentration during weathering, but their relative ratios do not necessarily change too much and might be still reliable proxies for paleo-environmental determination. The mobility of shale minerals during weathering is in the following order: plagioclase>potassium feldspar and dolomite >pyrite and OM. Short-term weathering can also result in considerable transportation of elements and significant variation of minerals content in black shale, which may pose potentially high environmental and engineering risk in the regions rich in black shale.

      PubDate: 2017-09-26T13:12:07Z
  • Physical properties of the stone meteorites: Implications for the
           properties of their parent bodies
    • Abstract: Publication date: Available online 13 September 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): George J. Flynn, Guy J. Consolmagno, Peter Brown, Robert J. Macke
      The physical properties of the stone meteorites provide important clues to understanding the formation and physical evolution of material in the Solar protoplanetary disk as well providing indications of the properties of their asteroidal parent bodies. Knowledge of these properties is essential for modeling a number of Solar System processes, such as bolides in planetary atmospheres, the thermal inertia of atmosphereless solid body surfaces, and the internal physical and thermal evolution of asteroids and rock-rich icy bodies. In addition, insight into the physical properties of the asteroids is important for the design of robotic and crewed reconnaissance, lander, and sample return spacecraft missions to the asteroids. One key property is meteorite porosity, which ranges from 0% to more than 40%, similar to the range of porosities seen in asteroids. Porosity affects many of the other physical properties including thermal conductivity, speed of sound, deformation under stress, strength, and response to impact. As a result of the porosity, the properties of most stone meteorites differ significantly from those of compact terrestrial rocks, whose physical properties have been used in many models of asteroid behavior. A few physical properties, such as grain density, magnetic susceptibility, and heat capacity are not functions of porosity. Taken together, the grain density and the magnetic susceptibility can be used to classify unweathered or minimally weathered ordinary chondrites. This provides a rapid screening technique to identify heterogeneous samples, classify new samples, and identify misclassified meteorites or interlopers in strewn fields.

      PubDate: 2017-09-19T12:32:46Z
  • Gold mineralizing efficiency during hydrothermal alteration of the
           Mesozoic granitoids in the northwest Jiaodong Peninsula: Contrasting
           conditions between the Guojialing and Linglong plutons
    • Abstract: Publication date: Available online 12 August 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Wen-Gang Xu, Hong-Rui Fan, Kui-Feng Yang, Fang-Fang Hu, Ya-Chun Cai
      Mesozoic granitoids were extensively altered by hydrothermal fluids in the northwest Jiaodong Peninsula, and gold precipitated from the fluids developing prevalent mineralization in this district. The 160–158Ma Linglong granite and 130–120Ma Guojialing granodiorite are the major Mesozoic granitoids in this district, both of which are hydrothermally altered and intimately associated with gold mineralization. Although numerous studies were carried out by previous researchers, mainly focusing on tectonics, lithology, mineralogy, geochronology, and fluid geochemistry, knowledge about hydrothermal alteration processes of these granitoids and their gold mineralization efficiency (i.e. which one is more effective to precipitate the gold from its parent solution) is far beyond clear illumination. Geochemical simulation software GEM-Selektor (based on the Gibbs energy minimization algorithm) was applied in this study, which aims to test the gold mineralization efficiency of these two granitoids during the hydrothermal alteration processes. Simulation results indicate that solutions in equilibrium with the Linglong granite are capable of hosting more sulfur than that with the Guojialing granodiorite, since the latter contains more Fe. However, the solutions with these two granitoids display similar gold solubility. “Bulk cooling” simulation results show that the gold mineralization pattern is similar between the Linglong and Guojialing case; “Rock titration” simulation results reveal that the Guojialing granodiorite is prone to precipitate gold more strongly than the Linglong granite, as gold-bearing solutions (or ore-forming fluids) flowing-through at high temperature, equivalent to a deeper level, implying that if the gold mineralization is developed at depth, the Guojialing rock will precipitate more gold. If the gold-bearing solution flow-through the wall rocks relatively fast, and gold mineralization fails to take place, then the Guojialing granodiorite is probably unfavorable for subsequent gold enrichment of the ore-forming fluid. The Linglong granite will precipitate the gold more efficiently from its parent solution at low temperature or at a shallower level, and this is consistent with previous mining prospecting results. Therefore, we suggest that the Guojialing granodiorite should be treated as the main target during future deep prospecting project.

      PubDate: 2017-09-02T16:37:19Z
  • Geochemical characteristics of modern river sediments in Myanmar and
           Thailand: Implications for provenance and weathering
    • Abstract: Publication date: Available online 12 August 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): H.M. Zakir Hossain, Hodaka Kawahata, Barry P. Roser, Yoshikazu Sampei, Takuya Manaka, Souya Otani
      The elemental composition of organic matter and the major and trace element compositions of stream sediments from Myanmar (Ayeyarwady and Sittaung rivers) and Thailand (Mekong and Chao Phraya rivers, and their tributaries) were determined to examine their distributions, provenance, and chemical weathering processes. Higher total organic carbon (TOC) and total nitrogen (TN) contents in the finer grained sediments indicate hydrodynamic energy may control their distributions. TOC/TN ratios indicate inputs of both aquatic macrophyte and higher vascular plant material to the river sediments. The major element abundances of the sediments are characterized by predominance of SiO2 in coarser fractions and a marked negative correlation with Al2O3, representing primary grain size primarily control on SiO2 content. Marked depletion of most labile elements (Na2O, CaO, K2O, Ba and Sr) relative to UCC (upper continental crust), indicate destruction of feldspar during chemical weathering in the source area or during transport. However, enrichment of some high field strength elements (Zr, Th, Ce and Y) relative to UCC and higher Zr/Sc ratios indicate moderate concentration of resistant heavy minerals in finer-grained samples. Discriminant diagrams and immobile trace element characteristics indicate that the Mekong, and Chao Phraya river sediments were largely derived from felsic sources with compositions close to typical rhyolite, dacite/granodiorite, UCC, I- and S-type granites. Relative enrichment of ferromagnesian elements (e.g. MgO, Cr, Ni) and high Cr/V and low Y/Ni ratios in Ayeyarwady and Sittaung sediments indicate the presence of a mafic or ultramafic component in their sources. The ICV (Index of Compositional Variability), CIA (Chemical Index of Alteration), PIA (Plagioclase Index of Alteration), αAl, Rb/Sr and K2O/Rb ratios indicate that the Ayeyarwady and Sittaung sediments record low to moderate degrees of chemical weathering in their source, compared to moderate to intense chemical weathering in the Mekong and Chao Phraya river basins. These results are compatible with existing major ion data for river waters collected at the same locations.

      PubDate: 2017-09-02T16:37:19Z
  • Mineral geochemistry of the Sangan skarn deposit, NE Iran: Implication for
           the evolution of hydrothermal fluid
    • Abstract: Publication date: Available online 4 August 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Fatemeh Sepidbar, Hassan Mirnejad, Jian-Wei Li, Chunjing Wei, Luke L. George, Kingsley Burlinson
      The Sangan iron skarn deposit is located in the Sabzevar-Dorouneh Magmatic Belt of northeastern Iran. The skarn contains zoned garnet, clinopyroxene and magnetite. Cores and rims of zoned garnets are generally homogeneous, having a relatively high ΣREE, low ΣLREE/ΣHREE ratios, and positive Eu anomalies. The cores of the zoned clinopyroxenes are exceptionally HREE-rich, with relatively high ΣREE and HREE/LREE ratios, as well as positive Eu anomalies. Clinopyroxene rims are LREE-rich, with relatively low ΣREE contents and HREE/LREE ratios, and do not have Eu anomalies. Magnetite grains are enriched in LREEs in comparison with the HREEs and lack Eu anomalies. Variations of fluid composition and physicochemical conditions rather than YAG-type substitution mechanism are considered to have major control on incorporating trace elements, including REE, into the skarn mineral assemblage. Based on baro-acoustic decrepitation analysis, the calc-silicate and magnetite dominant stages were formed at similar temperatures, around 350–400°C. In the Sangan skarns, hydrothermal fluids shifted from near-neutral pH, reduced conditions with relatively high ΣREE, low LREE/HREE ratios, and U-rich characteristics towards acidic, oxidized conditions with relatively low ΣREE, high LREE/HREE ratios, and U-poor characteristics.

      PubDate: 2017-09-02T16:37:19Z
  • P-T evolution of metapelites from the Bajgan complex in the Makran
           accretionary prism, south eastern Iran
    • Abstract: Publication date: Available online 2 August 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Maryam Dorani, Mohsen Arvin, Roland Oberhänsli, Sara Dargahi
      The Bajgan Complex, one of the basement constituents of the arc massif in Iranian Makran forms a rugged, deeply incised terrain. The complex consists of pelitic schists with minor psammitic and basic schists, calc silicate rocks, amphibolites, marbles, metavolcanosediments, mafic and felsic intrusives as well as ultramafic rocks. Metapelitic rocks show an amphibolite facies regional metamorphism and contain garnet, biotite, white mica, quartz, albite±rutile±apatite. Thermobarometry of garnet schist yields pressure of more than 9kbar and temperatures between 560 and 675°C. The geothermal gradient obtained for the peak of regional metamorphism is 19°C/km, corresponding to a depth of ca. 31km. Replacement of garnet by chlorite and epidote suggest greenschist facies metamorphism due to a decrease in temperature and pressure through exhumation and retrograde metamorphism (370–450°C and 3–6kbar). The metapelitic rocks followed a ‘clockwise’ P–T path during metamorphism, consistent with thermal decline following tectonic thickening. The formation of medium-pressure metamorphic rocks is related to presence of active subduction of the Neotethys Oceanic lithosphere beneath Eurasia in the Makran.

      PubDate: 2017-08-03T12:27:46Z
  • Magnetic evidence of anthropogenic dust deposition in urban soils of
           Shanghai, China
    • Abstract: Publication date: Available online 26 July 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Guan Wang, Feifan Ren, Jiao Chen, Yuan Liu, Fangzhou Ye, Frank Oldfield, Weiguo Zhang, Xiaodong Zhang
      The magnetic particulates from anthropogenic activities can be detected by magnetic methods rapidly and cost-effectively. This study focused on the investigation of vertical variations in magnetic properties in soil profiles and magnetic enhancement originating in Baoshan, Shanghai. Also the feasibility of using arable and urban park soils as a new context for magnetic monitoring was explored. A combination of magnetic and scanning electron microscopic (SEM) techniques was applied to three soil profiles. Non-pedogenic magnetic enhancement in topsoil was recorded at all three sites accompanied by coarsening of magnetic grain size. The dominant magnetic properties reflect multi-domain (MD) and pseudo-stable single domain (PSD) ferrimagnetic minerals. Both of magnetic concentrations and grain size decrease with the depth, depending on the pollutant input, soil type and degree of vertical mixing. SEM images confirmed the presence of anthropogenic particulates fly-ash. It was concluded from this study that topsoil magnetic enhancement arising from atmospheric contaminants was readily identifiable in both arable fields and urban parks, thus broadening the scope of magnetic research on urban and industrial pollution.

      PubDate: 2017-08-03T12:27:46Z
  • Distribution of base metals and the related elements in the
           stream-sediments around the Ahar area (NW Iran) and their implications
    • Abstract: Publication date: Available online 22 July 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Vartan Simmonds, Fatemeh Jahangiryar, Mohssen Moazzen, Ahmad Ravaghi
      The study area is located in the Ahar region, NW Iran. Volcanic rocks of Eocene cover major parts of the area, within which granitic-granodioritic intrusive bodies of Oligocene intruded and produced hydrothermal alterations and Cu-Au mineralization. This paper aims to explore anomalies of base metals and related elements across the region based on systematic sampling of stream sediments and using the secondary geochemical halos. In this regard, by taking into account factors such as stratigraphy, lithology, tectonics and the topologic center of the drainage system, 620 samples were taken from stream sediments and analyzed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-OES) method. All the distinguished anomalies correlate well with Oligocene granitic-granodioritic rocks and the related hydrothermal alterations occurred within the Eocene andesitic-basaltic volcanics, especially at the NE part of the quadrangle, as well as with alterations within trachy-andesitic and andesitic volcanics of Pliocene at the SE part of the quadrangle, where epithermal gold and Pb-Zn mineralization is found. Most of he studied elements also show moderate to strong anomalies over the Sonajil porphyry-type Cu mineralization. Copper, and to some extent Mo, as well as Pb, Zn, Sn, W, As and Sb are the best examples of this association. Bismuth has more limited anomalies across the region, showing correlation with the granitoid intrusion at the east of Ahar and the hydrothermal alterations within the Pliocene andesitic and basaltic rocks at SE of Ahar quadrangle which, considering the presence of epithermal gold and Pb-Zn veins in both areas, can be attributed to epithermal processes. However, anthropogenic pollutions are also found for As, Fe, V, Ti, Ni and Co downstream the urban and rural areas. In this regard, besides the Sonajil area, where porphyry-type Cu mineralization is discovered, the NE and SE parts of the quadrangle present promising areas for further investigations.

      PubDate: 2017-07-23T15:12:55Z
  • Geochemistry of coastal sands of Eastern Mediterranean: The case of
           Nisyros volcanic materials
    • Abstract: Publication date: Available online 20 July 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): I.T. Tzifas, P. Misaelides, A. Godelitsas, P.N. Gamaletsos, P. Nomikou, A.G. Karydas, V. Kantarelou, A. Papadopoulos
      Coastal sand samples collected from the northern part of Nisyros volcanic island (Dodecanese, Greece) were investigated for first time for their potential in strategic metals and compared with parental rocks of the island which are Quaternary volcanics with alternating lava flows, pyroclastic layers and lava domes and relevant materials located near granitoids of Northern Greece. The PXRD and SEM-EDS study of the sands revealed enhanced content of feldspars, Fe-Mn oxides, magnetite, tourmaline, pyroxenes, ilmenites, along with zircons, apatite and sulfide inclusions. The fresh hydrothermally deposited clayely material collected from the Nisyros caldera crater had a rather different mineralogical composition from the coastal one (alunite, anhydrite, opal-CT, quartz, kaolinite). UCC-normalized spidergrams indicated that the weathering processes contributed to accumulation of heavy minerals (mainly ilmenite), and strategic metals including V (1920mg/kg) and Nb (245mg/kg), in the coastal sand. The low REE concentration (ΣREE+Y=240mg/kg) could be attributed to the absence of REE-rich minerals. Moreover, the sands exhibit different geochemical patterns compared to the volcanic source rocks of the island, which are especially enriched in Large-Ion Lithophile Elements (LILE) and depleted in High Field Strength Elements (HFSE), such as Nb and Ta. On the other hand, the caldera material is enriched in volatile components, sulfur, chalcophile elements (Se, Bi, Hg, As, Pb) and Ba. Micro-XRF analyses of representative crystals showed that the high Nb content of the sands was associated with the Ti/Fe-rich phases (e.g. ilmenites). The geochemical composition of N Greece sands showed, because of their origin, enrichment not only in HFSE but also in REE. The study of the coastal heavy mineral sands originating from different geological environments of Greece provides information about the association of their mineral components with REE, other elements of economic interest (e.g. Co, Nb, Ta) and natural actinides. In addition, the study of the black sands of Nisyros island could be considered as a characteristic example of those from other parts of Hellenic Volcanic Arc (HVA) and other relevant Mediterranean regions.

      PubDate: 2017-07-23T15:12:55Z
  • Rutile geochemistry and thermometry of eclogites and associated
           garnet-mica schists in the Biga Peninsula, NW Turkey
    • Abstract: Publication date: Available online 17 July 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Firat Şengün, Thomas Zack, Gültekin Topuz
      In northwest Turkey, high-pressure metamorphic rocks occur as exotic blocks within the Çetmi mélange located on the south of the Biga Peninsula. Rutile chemistry and rutile thermometry obtained from the eclogite and associated garnet-mica schist in the Çetmi mélange indicate significant trace element behaviour of subducted oceanic crust and source-rock lithology of detrital rutiles. Cr and Nb contents in detrital rutile from garnet-mica schist vary from 355 to 1026μg/g and 323 and 3319μg/g, respectively. According to the Cr-Nb discrimination diagram, the results show that 85% of the detrital rutiles derived from metapelitic and 15% from metamafic rocks. Temperatures calculated for detrital rutiles and rutiles in eclogite range from 540°C to 624°C with an average of 586°C and 611°C to 659°C with an average of 630°C at P=2.3GPa, respectively. The calculated formation temperatures suggest that detrital rutiles are derived from amphibolite- and eclogite-facies metamorphic rocks. Amphibolite-facies rocks of the Kazdağ Massif could be the primary source rocks for the rutiles in the garnet-mica schist from the Çetmi mélange. Nb/Ta ratios of metapelitic and metamafic rutiles fall between 7–24 and 11–25, respectively. Nb/Ta characteristics in detrital rutiles may reflect a change in source-rock lithology. However, Nb/Ta ratios of rutiles in eclogite vary from 9 to 22. The rutile grains from eclogites are dominated by subchondritic Nb/Ta ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration.

      PubDate: 2017-07-23T15:12:55Z
  • Acapulcoite-lodranite meteorites: Ultramafic asteroidal partial melt
    • Abstract: Publication date: Available online 14 July 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Klaus Keil, Timothy J. McCoy
      Acapulcoites (most ancient Hf-W ages are 4,563.1±0.8 Ma), lodranites (most ancient Hf-W ages are 4,562.6±0.9 Ma) and rocks transitional between them are ancient residues of different degrees of partial melting of a chondritic source lithology (e.g., as indicated by the occurrence of relict chondrules in 9 acapulcoites), although the precise chondrite type is unknown. Acapulcoites are relatively fine- grained (∼150–230μm) rocks with equigranular, achondritic textures and consist of olivine, orthopyroxene, Ca-rich clinopyroxene, plagioclase, metallic Fe,Ni, troilite, chromite and phosphates. Lodranites are coarser grained (540–700μm), with similar equigranular, recrystallized textures, mineral compositions and contents, although some are significantly depleted in eutectic Fe,Ni-FeS and plagioclase- clinopyroxene partial melts. The acapulcoite-lodranite clan is most readily distinguished from other groups of primitive achondrites (e.g., winoanites/IAB irons) by oxygen isotopic compositions, although more than 50% of meteorites classified as acapulcoites currently lack supporting oxygen isotopic data. The heat source for melting of acapulcoites-lodranites was internal to the parent body, most likely 26Al, although some authors suggest it was shock melting. Acapulcoites experienced lower temperatures of ∼980–1170°C and lower degrees of partial melting (∼1–4vol.%) and lodranites higher temperatures of ∼1150–1200°C and higher degrees (∼5≥10vol.%) of partial melting. Hand-specimen and thin section observations indicate movement of Fe,Ni-FeS, basaltic, and phosphate melts in veins over micrometer to centimeter distances. Mineralogical, chemical and isotopic properties, Cosmic Ray Exposure (CRE) ages which cluster around 4–6 Ma and the occurrence of some meteorites consisting of both acapulcoite and lodranite material, indicate that these meteorites come from one parent body and were most likely ejected in one impact event. Whereas the precise parent asteroid of these meteorites is unknown, there is general agreement that it was an S-type object. There is nearly total agreement that the acapulcoite-lodranite parent body was <∼100km in radius and, based on the precise Pb–Pb age for Acapulco of 4555.9±0.6 Ma, combined with the Hf/W and U/Pb records and cooling rates deduced from mineralogical and other investigations, that the parent body was fragmented during its cooling which the U/Pb system dates at precisely 4556±1 Ma. Hf-W chronometry suggests that the parent body of the acapulcoites-lodranites and, in fact, the parent bodies of all “primitive achondrites” accreted slightly later than those of the differentiated achondrites and, thus, had lower contents of 26Al, the heat producing radionuclide largely responsible for heating of both primitive and differentiated achondrites. Thus, the acapulcoite-lodranite parent body never experienced the high degrees of melting responsible for the formation of the differentiated meteorites, but arrested its melting history at relatively low degrees of ∼15vol.%.

      PubDate: 2017-07-23T15:12:55Z
  • Isotope geochemistry of Mississippi Valley Type stratabound F-Ba-(Pb-Zn)
           ores of Hammam Zriba (Province of Zaghouan, NE Tunisia)
    • Abstract: Publication date: Available online 12 July 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Nejib Jemmali, Emmanuel John M. Carranza, Balkiss Zemmel
      The Hammam Zriba F-Ba-(Zn-Pb) ore deposit in the Province of Zaghouan in north-eastern Tunisia is hosted in the shallow dipping unconformity between green marls with chalky biomicritic limestones of Campanian age and Uppermost Jurassic carbonates. The mineralization consists mainly of fluorite and barite with minor sphalerite and galena. Calcite is the main gangue mineral. Two types of Zn-Pb sulfides can be distinguished according to the geometry of the orebodies, i.e., lenticular or stratiform ores, intra-karstic fillings. Sulfur isotope compositions (δ34S) of barite range from 14.7 to 17.2‰, indicating that sulfur was derived from Triassic evaporites and the higher ones (19–25.7‰) are due to reservoir effect associated with thermo-chemical sulfate reduction (TSR) or bacterial sulfate reduction (BSR) under conditions of restricted sulfate supply. δ34S of galena and sphalerite in lenticluar and intra-karstic orebodies range from −13.8 to 2.1‰, and could be explained by multiple sources of reduced sulfur: Triassic evaporites, diagenetic primary sulfides as well as sulfur from organic matter. Both TSR and BSR as potential contributors of sulfur are needed for sulfide precipitation. Lead isotope compositions of galena exhibit very similar: 206Pb/204Pb (18.858–18.876), 207Pb/204Pb (15.667–15.684), and 208Pb/204Pb (38.680–38.747) ratios, and plot between the upper crust and orogene average growth curves, reflecting involvement of a mixing and subsequent homogenization of Pb isotopic compositions of different source Pb reservoirs. The underlying Paleozoic basement rocks were the plausible source of metals. The economic ore (fluorite F1) mineralization was formed during the Eocene-Miocene compressional phase. During this deformation phase, deep-seated basinal brines have been circulated as hydrothermal fluids that have interacted with the Paleozoic rocks, thereby leaching metals, and have been channelized through subsidiary faults associated with the major regional NE–SW-trending deep-seated Zaghouan-Ressas fault. Hydrothermal fluids then migrated to the site of deposition where they got mixed with shallow, cooler, metal-depleted, TSR- and BSR-derived sulfur-rich fluids, which triggered the precipitation of the ores.

      PubDate: 2017-07-23T15:12:55Z
  • What we know about elemental bulk chondrule and matrix compositions:
           Presenting the ChondriteDB Database
    • Abstract: Publication date: Available online 11 July 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Dominik C. Hezel, Markus Harak, Guy Libourel
      Chondrules and matrix are the major components of chondritic meteorites and represent a significant evolutionary step in planet formation. The formation and evolution of chondrules and matrix and, in particular, the mechanics of chondrule formation remain the biggest unsolved challenge in meteoritics. A large number of studies of these major components not only helped to understand these in ever greater detail, but also produced a remarkably large body of data. Studying all available data has become known as ‹big data› analyses and promises deep insights – in this case – to chondrule and matrix formation and relationships. Looking at all data may also allow one to better understand the mechanism of chondrule formation or, equally important, what information we might be missing to identify this process. A database of all available chondrule and matrix data further provides an overview and quick visualisation, which will not only help to solve actual problems, but also enable students and future researchers to quickly access and understand all we know about these components. We collected all available data on elemental bulk chondrule and matrix compositions in a database that we call ChondriteDB. The database also contains petrographic and petrologic information on chondrules. Currently, ChondriteDB contains about 2388 chondrule and 1064 matrix data from 70 different publications and 161 different chondrites. Future iterations of ChondriteDB will include isotope data and information on other chondrite components. Data quality is of critical importance. However, as we discuss, quality is not an objective category, but a subjective judgement. Quantifiable data acquisition categories are required that allow selecting the appropriate data from a database in the context of a given research problem. We provide a comprehensive overview on the contents of ChondriteDB. The database is available as an Excel file upon request from the senior author of this paper, or can be accessed through MetBase.

      PubDate: 2017-07-23T15:12:55Z
  • Cyanobacterial mineralisation of posnjakite (Cu4(SO4)(OH)6·H2O) in
           Cu-rich acid mine drainage at Yanqul, northern Oman
    • Abstract: Publication date: Available online 26 June 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Bernhard Pracejus, Aliya Al-Ansari, Huda Al-Battashi
      This is the first detailed account of the copper sulfate posnjakite (Cu4(SO4)(OH)6·H2O) coating cm-long filaments of a microbial consortium of four cyanobacteria and Herminiimonas arsenicoxydans. It was first observed on immersed plant leaves and stalks in a quarry sump of the abandoned Yanqul gold mine in the northern region of Oman; rock surfaces in the immediate vicinity show no immediate evidence of posnjakite. However, a thin unstructured layer without filaments but also containing the brightly coloured turquoise posnjakite covers ferruginous muds in the sump. Although copper is a potent bactericide, the microbes seem to survive even at the extreme heavy metal concentrations that commonly develop in the sump during the dry season (Cu2+≈2300ppm; Zn2+=750ppm; Fe2+≈120ppm; Ni2+=37ppm; Crtotal=2.5ppm; Cl−=8250ppm; and SO42−=12,250ppm; pH ∼2.6), thus leading to the precipitation of posnjakite over a large range of physicochemical conditions. Upon exposure to the prevailing arid climate, dehydration and carbonation quickly replace posnjakite with brochantite (Cu4(SO4)(OH)6) and malachite (Cu2(CO3)(OH)2). To characterise and understand the geochemical conditions in which posnjakite precipitates from undersaturated fluids (according to our thermodynamic modelling of the dominant elements), waters from rainy and dry periods were analysed together with various precipitates and compared with the observed field occurrences. The findings imply that posnjakite should not form in the examined environment through purely inorganic mechanisms and its origin must, therefore, be linked to the encountered microbial activities.
      Graphical abstract image

      PubDate: 2017-07-02T21:30:47Z
  • Geochemistry and petrogensis of the Eocene back arc mafic rocks in the
           Zagros suture zone, northern Noorabad, western Iran
    • Abstract: Publication date: Available online 21 June 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Fatemeh Nouri, Yoshihiro Asahara, Hossein Azizi, Koshi Yamamoto, Motohiro Tsuboi
      The northern Noorabad area in western Iran contains several gabbro and basalt bodies which were emplaced along the Zagros suture zone. The basalts show pillow and flow structures with amygdaloidal textures, and the gabbroic rocks show massive and foliated structures with coarse to fine-grained textures. The SiO2 contents of the gabbros and basalts are similar and range from 46.1–51.0wt.%, and the Al2O3 contents vary from 12.3–18.8wt.%, with TiO2 contents of 0.4–3.0wt.%. The Nb concentrations of some gabbros and basalts are high and can be classified as Nb-enriched arc basalts. The positive εNd(t) values (+3.7 to +9.8) and low 87Sr/86Sr(initial) ratios (0.7031–0.7071) of both bodies strongly indicate a depleted mantle source and indicate that the rocks were formed by partial melting of a depleted lithospheric mantle and interaction with slab fluids/melts. The chemical composition of trace elements, REE pattern and initial 87Sr/86Sr-143Nd/144Nd ratios show that the rocks have affinities to tholeiitic magmatic series and suggest an extensional tectonic regime over the subduction zone for the evolution of these rocks. We propose an extensional tectonic regime due to the upwelling of metasomatized mantle after the late Cretaceous collision in the Harsin-Noorabad area. These rocks can be also considered as Eocene back arc magmatic activity along the Zagros suture zone in this area.

      PubDate: 2017-07-02T21:30:47Z
  • Trace elements indicating humid climatic events in the
           Ordovician–early Silurian
    • Abstract: Publication date: Available online 8 June 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Enli Kiipli, Tarmo Kiipli, Toivo Kallaste, Siim Pajusaar
      The chemical composition of the clay fraction separated from the carbonate rock of the north-eastern Baltoscandian Basin was analysed and interpreted. Increased contents of Rb, Zr, Nb, Ti and their Al2O3-normalised ratios were detected at several stratigraphical levels in the geological sections of the Middle Ordovician–Upper Llandovery. In the weathering areas, Rb, Zr, Nb, Ti and Al are sensitive to moist conditions in the clay-forming process. In the sedimentary basin, the contents of these elements in clay are preserved and allow to infer past climates. Humid events occurred in the Dapingian, Sandbian, early Katian and Hirnantian (Ordovician) and in the Middle and Late Llandovery (Silurian). Juxtaposition with the sea-level curve shows correlation of five humid climate intervals with eustatic transgressions, suggesting global causes for these climatic changes. The warm and humid events, lasting one to two million years, occurred as climaxes between ice ages. An exceptional humid event within the Hirnantian glacial time occurs during mid-Hirnantian transgression, i.e. at a time of relative warming, as well.

      PubDate: 2017-06-11T19:14:41Z
  • Editorial board members
    • Abstract: Publication date: May 2017
      Source:Chemie der Erde - Geochemistry, Volume 77, Issue 2

      PubDate: 2017-06-11T19:14:41Z
  • Tectonic regime switchover of Triassic Western Qinling Orogen: Constraints
           from LA-ICP-MS zircon U–Pb geochronology and Lu–Hf isotope of
           Dangchuan intrusive complex in Gansu, China
    • Abstract: Publication date: Available online 4 June 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Jian-Zhen Geng, Kun-Feng Qiu, Zong-Yang Gou, Hao-Cheng Yu
      The Qinling Orogenic Belt, linking the Kunlun and Qilian Mountains to the west and continuing farther east to the Dabie Mountain, was assembled by the convergence and collision between the Greater South China and the North China blocks. The precise timing of the subduction and collision processes between these continental blocks and tectonic regime switchover is very equivocal. Zircon in-situ LA-ICP-MS U–Pb dating in this contribution indicates that the biotite monzogranite and monzogranite phases of the Dangchuan complex were crystallized at ca. 239.8±2.3Ma and 227.8±1.2Ma, respectively. The ca. 240Ma biotite monzogranite displays εHf(t) values ranging from −2.4 to +2.9, and corresponding TDM2 of 1.72–1.94Ga and TDM1 of 0.77–0.88Ga. The ca. 228Ma monzogranite exhibits εHf(t) values ranging from −4.3 to +1.9, and corresponding TDM2 of 1.73–2.08Ga and TDM1 of 0.81–0.88Ga. Lutetium–Hf isotopic composition indicates that the biotite monzogranite and monzogranite probably have the same parental magmas which were originated from hybrid sources of both reworking of Paleoproterozoic ancient crust and partial melting of the Neoproterozoic juvenile crust. The more negative εHf(t) values of the monzogranite suggest more contribution of the ancient crust during the source contamination, or more possible crustal assimilation during their crystallization at ca. 228Ma than precursor biotite monzogranite. Integrated with previous research and our detailed petrography, we propose that the Dangchuan complex underwent an episodic growth documenting the tectonic regime switchover from early Paleozoic to Triassic. The ca. 439Ma inherited zircon recorded the persistent subduction of the oceanic crust, the ca. 240Ma biotite monzogranite emplaced during the northward subduction of the Mianlue oceanic crust beneath the South Qinling block, and the ca. 228Ma monzogranite emplaced during the syn-collisional process in a compressional setting.

      PubDate: 2017-06-06T18:48:54Z
  • Geochemical characteristics of stream sediments from an urban-volcanic
           zone, Central Mexico: Natural and man-made inputs
    • Abstract: Publication date: Available online 9 May 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): V.C. Shruti, M.P. Jonathan, P.F. Rodríguez-Espinosa, R. Nagarajan, D.C. Escobedo-Urias, S.S. Morales-García, E. Martínez-Tavera
      Geochemical characteristics of stream sediments [n=31; Upstream section: Zahuapan River (1–12) and Atoyac River (13–20); Downstream section (21–31)] from Atoyac River basin of Central Mexico have been evaluated. The study focuses on the textural, petrography and chemical composition of the fluvial sediments with the aim of analyzing their provenance, the chemical weathering signature and their potential environmental effects. The fluvial sediments are mostly composed of sand and silt sized particles dominated by plagioclase, pyroxenes, amphiboles, K-feldspar, biotite, opaque and quartz. The sediments were analyzed for determination of major (Al, Fe, Ca, Mg, Na, K, P, Si, Ti), trace elements (As, Ba, Be, Co, Cr, Cu, Mo, Mn, Ni, Pb, Sc, V, Y, Zn, Zr, Ga) and compared with Upper continental crust (UCC), source area composition and local background values. The elemental concentrations were comparable with the average andesite and dacitic composition of the source area and the local background values except for enrichment of Cu (56.27ppm), Pb (34ppm) and Zn (235.64ppm) in the downstream sediments suggesting a significant external influence (anthropogenic). The fluvial sediments of Atoyac River basin display low CIA and PIA values implying predominantly weak to moderate weathering conditions in the source region. Based on the provenance discrimination diagrams and elemental ratios, it is understood that the collected sediments are derived from intermediate to felsic volcanic rocks dominated in the study region. Metal contamination indices highlight the enrichment of Cu, Pb, Zn, Mo, Cr and S clearly indicating the influences from natural (weathering and volcanic activity) and external (anthropogenic) sources. Ecological risk assessment results indicate that Cr, Ni and Zn will cause adverse biological effects to the riverine environment.
      Graphical abstract image

      PubDate: 2017-05-13T04:56:45Z
  • Geochemistry and petrogenesis of Kolah-Ghazi granitoids of Iran: Insights
           into the Jurassic Sanandaj-Sirjan magmatic arc
    • Abstract: Publication date: Available online 29 April 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Marzieh Bayati, Dariush Esmaeily, Reza Maghdour-Mashhour, Xian-Hua Li, Robert J. Stern
      Kolah-Ghazi granitoid (KGG), situated in the southern part of the Sanandaj–Sirjan Zone (SNSZ), Iran, is a peraluminous, high K calc-alkaline, cordierite-bearing S-type body that is mainly composed of monzogranite, granodorite and syenogranite. Zircon U–Pb ages indicate that the crystallization of the main body occurred from 175 Ma to 167 Ma. Two kinds of xenoliths are found in KKG rocks: (i) xenoliths of partially melted pelites including cordierite xenocrysts and aluminoslicates, and (ii) mafic microgranular enclaves that reflect the input of mantle-derived mafic magmas. Field observations and geochemical data of KGG rocks are consistent with their derivation from a multiple sources including melts of metasediments and mantle-derived melts. We infer that these magmas originated by the anatexis of a metasedimentary source (mixture of metapelite and metagreywacke) in the mid- to lower-crust under low water-vapor pressures (0.5-1 Kbar) and temperature of ∼800°C. KGG is the product of biotite incongruent melting of this metasedimentary source. S-type granites are commonly thought to be produced in continent-continent collision tectonic environment. However, trace element discrimination diagrams show that S-type KGG rocks formed in an arc-related environment. The roll-back of Neo- Tethyan subducting slab accompanying oblique subduction in Late Triassic to Early Jurassic time induced trench rollback, back arc basin opening and filling with turbidite flysch and molasse- type siliciclastic sediments of the Shemshak Group on the overriding plate. Further changes in the subducting slab to flat subduction in Middle Jurassic time, the time of peak magmatism in the SNSZ, led to thickening and high temperature-low pressure metamorphism of the backarc turbidite deposits and consequent anatexis of the metasedimentary source to produce the KGG S- type rocks along with several other I-type granitoids in the SNSZ.

      PubDate: 2017-05-02T04:03:04Z
  • Utilization of sodium waterglass from sugar cane bagasse ash as a new
           alternative hardener for producing metakaolin-based geopolymer cement
    • Abstract: Publication date: Available online 24 April 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Hervé Kouamo Tchakouté, Claus Henning Rüscher, Malte Hinsch, Jean Noël Yankwa Djobo, Elie Kamseu, Cristina Leonelli
      Sugar cane bagasse ash from SOSUCAM company in Cameroon was used to synthesize sodium waterglass as a new alternative hardener. The new hardener was used to prepare metakaolin-based geopolymer cements. The compressive strength of the resulting geopolymer cement cured at room temperature for 28days was 32.9MPa. Samples soaked for 28 days in water in parallel experiments revealed a strength of 31.4MPa. This shows that exposure of water does not lead to any weakening. The value of water absorption was 7.1% in the water-soaked cements, indicating the presence of fewer pores and voids than in the dry cements. However, in SEM micrographs, the microstructure of geopolymer cement appears rather homogeneous and compact without any change by water soaking. It can thus be concluded that sodium waterglass from sugar cane bagasse ash can be used as an alternative hardener or reactive ingredient for producing geopolymer cement with a high degree of cross-linking geopolymer framework. The use of this low-value silica-rich waste for producing sodium waterglass results in environmental benefits including a significant reduction of CO2 emission and energy consumption compared to the production of commercial sodium waterglass.

      PubDate: 2017-04-25T03:34:32Z
  • Mopping up leaking carbon: A natural analog at Wadi Namaleh, Jordan
    • Abstract: Publication date: Available online 18 April 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Nizar Abu-Jaber
      Carbon capture and sequestration (CCS) is one of the important options available for partially stemming greenhouse gas emissions from large point sources. The possibility of leaking from deep storage needs to be addressed. The Wadi Namaleh area in southern Jordan provides an interesting case study of how excess CO2 can be trapped in the form of carbonates in the near surface, even when the local geology is not obviously conducive for such a process. Carbonate veins are formed in surface alteration zones of rhyolite host rock in this arid region. The alteration zones are limited to areas where surface soil or colluvium are present. Oxygen, deuterium and carbon isotopes of the carbonates and near-surface ground water in the area suggest that the source of carbon is deep seated CO2, and that the carbonate precipitated in local meteoric water under ambient temperature conditions. Analysis of strontium in the carbonate, fresh rhyolite and altered host shows that the source for calcium is aeolian. Trace elements show that metal and REE mobility are constrained to the alteration zone. Thus, interaction of H2O, CO2 and atmospheric wet and dry deposition lead to the formation of the clayey (montmorillonite) alteration zone. This zone acts to trap seeping CO2 and water, and thus produces conditions of progressively more efficient trapping of carbon dioxide by means of a positive feedback mechanism. Replication of these conditions in other areas will minimize CO2 leakage from man-made CCS sites.

      PubDate: 2017-04-25T03:34:32Z
  • Editorial board members
    • Abstract: Publication date: April 2017
      Source:Chemie der Erde - Geochemistry, Volume 77, Issue 1

      PubDate: 2017-04-25T03:34:32Z
  • Meteoritic minerals and their origins
    • Abstract: Publication date: Available online 30 March 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Alan E. Rubin, Chi Ma
      About 435 mineral species have been identified in meteorites including native elements, metals and metallic alloys, carbides, nitrides and oxynitrides, phosphides, silicides, sulfides and hydroxysulfides, tellurides, arsenides and sulfarsenides, halides, oxides, hydroxides, carbonates, sulfates, molybdates, tungstates, phosphates and silico phosphates, oxalates, and silicates from all six structural groups. The minerals in meteorites can be categorized as having formed by a myriad of processes that are not all mutually distinct: (1) condensation in gaseous envelopes around evolved stars (presolar grains), (2) condensation in the solar nebula, (3) crystallization in CAI and AOI melts, (4) crystallization in chondrule melts, (5) exsolution during the cooling of CAIs, (6) exsolution during the cooling of chondrules and opaque assemblages, (7) annealing of amorphous material, (8) thermal metamorphism and exsolution, (9) aqueous alteration, hydrothermal alteration and metasomatism, (10) shock metamorphism, (11) condensation within impact plumes, (12) crystallization from melts in differentiated or partially differentiated bodies, (13) condensation from late-stage vapors in differentiated bodies, (14) exsolution, inversion and subsolidus redox effects within cooling igneous materials, (15) solar heating near perihelion, (16) atmospheric passage, and (17) terrestrial weathering.

      PubDate: 2017-04-04T02:33:31Z
  • C-N elemental and isotopic investigation in agricultural soils: Insights
           on the effects of zeolitite amendments
    • Abstract: Publication date: Available online 6 March 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Giacomo Ferretti, Dario Di Giuseppe, Claudio Natali, Barbara Faccini, Gianluca Bianchini, Massimo Coltorti
      In this paper we present an elemental and isotopic investigation of carbon and nitrogen in the soil-plant system. Plants grown in an unamended soil were compared to plants grown in a soil amended with natural and NH4 +-enriched zeolitites. The aim was to verify that zeolitites at natural state increase the chemical fertilization efficiency and the nitrogen transfer from NH4 +-enriched zeolitites to plants. Results showed that plants grown on plots amended with zeolitites have generally a δ15N approaching that of chemical fertilizers, suggesting an enhanced nitrogen uptake from this specific N source with respect to the unamended plot. The δ15N of plants grown on NH4 +-enriched zeolitites was strongly influenced by pig-slurry δ15N (employed for the enrichment process), confirming the nitrogen transfer from zeolitites to plants. The different agricultural practices are also reflected in the plant physiology as recorded by the carbon discrimination factor, which generally increases in plots amended with natural zeolitites, indicating better water/nutrient conditions.

      PubDate: 2017-03-09T00:45:37Z
  • Geology, geochemistry and petrogenesis of post-collisional adakitic
           intrusions and related dikes in the Khoynarood area, NW Iran
    • Abstract: Publication date: Available online 21 February 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Hossein Mahmoudi Nia, Saeid Baghban, Vartan Simmonds
      The Khoynarood area is located in the northwest of Iran, lying at the northwestern end of the Urumieh–Dokhtar volcano-plutonic belt and being part of the Qaradagh–South Armenia domain. The main intrusive rocks outcropped in the area have compositions ranging from monzonite–quartz monzonite, through granodiorite, to diorite–hornblende diorite, accompanied by several dikes of diorite–quartz diorite and hornblende diorite compositions, which were geochemically studied in order to provide further data and evidence for the geodynamic setting of the region. The SiO2, Al2O3 and MgO contents of these rocks are about 58.32–68.12%, 14.13–18.65% and 0.68–4.27%, respectively. They are characterized by the K2O/Na2O ratio of 0.26–0.58, Fe2O3 +MnO+MgO+TiO2 content about 4.27–13.13%, low Y (8–17ppm) and HREE (e.g., 1–2ppm Yb) and high Sr contents (750–1330ppm), as well as high ratios of Ba/La (13.51–50.96), (La/Yb)N (7–22), Sr/Y (57.56–166.25), Rb/La (1.13–2.96) and La/Yb (10–33.63), which may testify to the adakitic nature of these intrusions. Their chemical composition corresponds to high-silica adakites, displaying enrichments of LREEs and LILEs and preferential depletion of HFSEs, (e.g., Ti, Ta and Nb). The REE differentiation pattern and the low HREE and Y contents might be resulted from the presence of garnet and amphibole in the solid residue of the source rock, while the high Sr content and the negative anomalies of Ti, Ta and Nb may indicate the absence of plagioclase and presence of Fe and Ti oxides in it. As a general scenario, it may be concluded that the adakitic rocks in the Khoynarood were most likely resulted from detachment of the subducting Neo-Tethyan eclogitic slab after subduction cessation between Arabian and Central Iranian plates during the upper Cretaceous–early Cenozoic and partial melting of the detached slab, followed by interactions with metasomatized mantle wedge peridotite and contamination with continental crust.

      PubDate: 2017-02-23T17:39:49Z
  • Geochemistry of S, Cu, Ni, Cr and Au-PGE in the garnet amphibolites from
           the Akom II area in the Archaean Congo Craton, Southern Cameroon
    • Abstract: Publication date: Available online 4 February 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Beyanu Anehumbu Aye, Elisé Sababa, Paul-Désiré Ndjigui
      The fresh and weathered garnet amphibolites, from the Akom II area in the Archaean Congo Craton, were investigated to determine the S, Cu, Ni, Cr, and Au-PGE values. The garnet amphibolites are composed of amphibole, plagioclase, garnet, quartz, and accessory apatite, spinel, sericite, pyrite, chalcopyrite and non-identified opaque minerals. The presence of apatite, sericite, and two generations of opaque minerals suggests that they might be affected by hydrothermal alteration. They are characterized by moderate Al2O3, Fe2O3, CaO, V, Zn, and Co contents with negative Eu- and Ce-anomalies. The sulfur concentrations are variable (380–1710ppm). According to the sulfur contents, amphibolites can be grouped into two: amphibolites with low contents, ranging between 380 and 520ppm (av.=457ppm); and amphibolites with elevated contents, varying from 1140 to 1710ppm (av.=1370ppm). Amphibolites contain contrast amounts of Cu (∼1800 to 5350ppm) while nickel contents attain 121ppm. Chromium contents vary from 43 to 194ppm. Sulfur correlates positively with Cu and Cr, but negatively with Ni and Ni/Cr ratio. The total Au-PGE contents attain 59ppb. The presence of amphibole and feldspars confirms the low degree of amphibolite weathering. The secondary minerals are constituted of kaolinite, gibbsite, goethite and hematite. Despite the accumulation of some elements, the major and trace element distribution is quite similar to that of fresh amphibolites. Nevertheless, the weathering processes lead to the depletion of several elements such as S (239–902ppm), Cu (520–2082ppm), and Ni (20–114ppm). Chromium and Au-PGE show an opposite trend marked by a slight enrichment in the weathered amphibolites. Amidst the Au-PGE, Pd (60ppb) and Pt (23ppb) have elevated contents in the fresh rocks as well as in the weathered materials. The PPGE contents are much higher than IPGE contents in both types of materials. The Pd/Pt, Pd/Rh, Pd/Ru, Pd/Ir, Pd/Os, and Pd/Au values indicate that Pt, Rh, Ru, Ir, Os and Au are more mobile than Pd. Chondrite-normalized base metal patterns confirm the abundance of Pd and the slight enrichment of Au-PGE in weathered rocks. Palladium, Rh and Ir are positively correlated with S. Conversely Pt and Ru are negatively correlated with S and Au is not correlated with S. Despite the high and variable S and Cu contents, the garnet amphibolites possess low Au-PGE and other base metals contents.

      PubDate: 2017-02-10T16:30:51Z
  • An improved EPMA analytical protocol for U-Th-Pbtotal dating in xenotime:
           Age constraints from polygenetic Mangalwar Complex, Northwestern India
    • Abstract: Publication date: Available online 27 January 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Pranjit Hazarika, Biswajit Mishra, Manoj Kumar Ozha, Kamal Lochan Pruseth
      EPMA U-Th-Pbtotal dating in U- and Th bearing minerals (e.g., monazite, zircon, and xenotime) is a low-cost and reliable technique used for retrieving age information from detrital, diagenetic and low to high-T metamorphic, as well as magmatic rocks. Although, the accuracy on measured ages obtained using EPMA is considered to be poor compared to isotopic ages, the superior spatial resolution, ability to integrate textural and age information by in-situ measurement, lack of sample damage and easier and cheaper data generation in EPMA make chemical dating a very valuable tool to decipher diverse petrological processes. This contribution presents an improved analytical protocol to obtain precise estimates of U, Th and Pb concentrations in xenotime. Results were tested on monazite standard (Moacyr pegmatite, Brazil; TIMS age: 487±1Ma) as the reference material. The proposed analytical protocol has been successfully applied to achieve an analytical uncertainty of less than 10% in U, Th and Pb measurements in xenotime. The protocol was further used to resolve polygenetic xenotime ages (ca. 1.82, 1.28 and 0.93Ga) in metapelite samples from the Mangalwar Complex, Northwestern India. Monazites in the same samples were also analyzed and found to preserve the two younger ages (i.e., ca. 1.28 and 1.0Ga). The obtained ages from the xenotime and monazite very well corroborate with the earlier published ages from the area validating the proposed analytical protocol.

      PubDate: 2017-02-03T15:17:16Z
  • The nature, origin and modification of insoluble organic matter in
           chondrites, the major source of Earth’s C and N
    • Abstract: Publication date: Available online 26 January 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): C.M.O’D. Alexander, G.D. Cody, B.T. De Gregorio, L.R. Nittler, R.M. Stroud
      All chondrites accreted ∼3.5wt.%C in their matrices, the bulk of which was in a macromolecular solvent and acid insoluble organic material (IOM). Similar material to IOM is found in interplanetary dust particles (IDPs) and comets. The IOM accounts for almost all of the C and N in chondrites, and a significant fraction of the H. Chondrites and, to a lesser extent, comets were probably the major sources of volatiles for the Earth and the other terrestrial planets. Hence, IOM was both the major source of Earth’s volatiles and a potential source of complex prebiotic molecules. Large enrichments in D and 15N, relative to the bulk solar isotopic compositions, suggest that IOM or its precursors formed in very cold, radiation-rich environments. Whether these environments were in the interstellar medium (ISM) or the outer Solar System is unresolved. Nevertheless, the elemental and isotopic compositions and functional group chemistry of IOM provide important clues to the origin(s) of organic matter in protoplanetary disks. IOM is modified relatively easily by thermal and aqueous processes, so that it can also be used to constrain the conditions in the solar nebula prior to chondrite accretion and the conditions in the chondrite parent bodies after accretion. Here we review what is known about the abundances, compositions and physical nature of IOM in the most primitive chondrites. We also discuss how the IOM has been modified by thermal metamorphism and aqueous alteration in the chondrite parent bodies, and how these changes may be used both as petrologic indicators of the intensity of parent body processing and as tools for classification. Finally, we critically assess the various proposed mechanisms for the formation of IOM in the ISM or Solar System.

      PubDate: 2017-01-27T18:42:47Z
  • X-ray computed tomography of planetary materials: A primer and review of
           recent studies
    • Abstract: Publication date: Available online 21 January 2017
      Source:Chemie der Erde - Geochemistry
      Author(s): Romy D. Hanna, Richard A. Ketcham
      X-ray computed tomography (XCT) is a powerful 3D imaging technique that has been used to investigate meteorites, mission-returned samples, and other planetary materials of all scales from dust particles to large rocks. With this technique, a 3D volume representing the X-ray attenuation (which is sensitive to composition and density) of the materials within an object is produced, allowing various components and textures to be observed and quantified. As with any analytical technique, a thorough understanding of the underlying physical principles, system components, and data acquisition parameters provides a strong foundation for the optimal acquisition and interpretation of the data. Here we present a technical overview of the physics of XCT, describe the major components of a typical laboratory-based XCT instrument, and provide a guide for how to optimize data collection for planetary materials using such systems. We also discuss data processing, visualization and analysis, including a discussion of common data artifacts and how to minimize them. We review a variety of recent studies in which XCT has been used to study extraterrestrial materials and/or to address fundamental problems in planetary science. We conclude with a short discussion of anticipated future directions of XCT technology and application.

      PubDate: 2017-01-27T18:42:47Z
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