Shan Q.,CAS Guangzhou Institute of Geochemistry |
Liao S.,Jiangxi Provincial Institute of Geological Survey |
Lu H.,CAS Guangzhou Institute of Geochemistry |
Lu H.,University of Quebec at Chicoutimi |
And 5 more authors.
Acta Petrologica Sinica | Year: 2011
Qitianling granite is a complex massif with multi-stage intrusions during the Early Yanshanian Period. Petrochemical data show that it belongs to alkali-rich and highly evolved A-type granite formed in tension setting within a plate. The centimetre- and metre-sized pegmatoid cystidium and miarolitic quartz widely occurred in the second stage medium-fine grain biotite granite, implying that it is resulted from differentiation of the oversaturated-volatile magma. In addition, the coexist of melt-fluid inclusions and fluid inclusions in quartz indicated that the pegmatoid cystidium and miarolitic quartz were produced in the transition stage from granite magmatic melt to hydrothermal solution. The data of micro-thermometry showed that the trapped temperatures of melt-fluid inclusions are over 530°C, the homogenization temperatures of fluid inclusions are between 172°C and 454°C, indicating the temperature of fluids in hydrothermal stage, and the homogenization temperatures of fluid inclusions in sphalerite are between 285°C and 417°C, indicating the temperature and salinity of ore-forming fluid. Their evolution process from middle-fine grain biotite granite to pegmatoid cystidium to miarolitic quartz implied that magmatic and hydrothermal system underwent an evolution process: from volatile-rich fluid to melt and high salinity fluid to high salinity fluid to low salinity fluid and finally formed magmatic hydrothermal fluid in the CaCl2-NaCl-H2O-CO2 system. Based on the data of petrography and Raman spectrum of fluid inclusions, the existence of feldspar, calcite, rutile and metallic oxides in the fluid and crystal-rich melt-fluid inclusions implies that the captured fluids have a competent ore-forming potentiality.
Tian S.,Chinese Academy of Geological Sciences |
Tian S.,China University of Geosciences |
Hou Z.,Chinese Academy of Geological Sciences |
Su A.,Chinese Academy of Geological Sciences |
And 6 more authors.
Geochimica et Cosmochimica Acta | Year: 2015
Lithium concentrations and isotopic compositions of 38 carbonatites and associated syenites from the Maoniuping, Lizhuang, and Dalucao in western Sichuan, along with previously published and new Pb-Sr-Nd-C-O isotope data and whole-rock analyses, are used to constrain their mantle source and genesis. Carbonatites and syenites are characterized by extremely varying Li concentrations (0.8-120ppm) and highly variable Li isotopic compositions (-4.5‰ to +10.8‰). Among them, the majority of the carbonatites and syenites have δ7Li values between +0.2‰ and +5.8‰, which overlap with the reported values for MORB and OIB; 3 carbonatites have higher δ7Li values between +8.7‰ and +10.8‰; 5 carbonatites and 4 syenites have lighter δ7Li values between -4.5‰ and -0.3‰. These highly variable δ7Li compositions could not have been produced by diffusive-driven isotopic fractionation of Li and thus may record the isotopic signature of the late Proterozoic subcontinental lithospheric mantle (SCLM). This paper demonstrates the existence of anomalous δ7Li within the late Proterozoic subcontinental lithospheric mantle, suggesting that the ancient SCLM beneath western Sichuan was modified by interaction with fluids derived from the subducted oceanic crust and marine sediments.The modeling curves of fluids derived from a dehydrated slab (ratios: AOC80-SED20 to AOC40-SED60) with a representative mantle composition can account for the majority of lithium compositional variations. Some samples with unusual Pb-Sr-Nd-O isotopic compositions and highly variable δ7Li compositions are affected by significant involvement of marine sediments in their source region, not contaminated by crustal materials. The carbonatites and syenites in western Sichuan were generated by the partial melting of subcontinental lithospheric mantle, which was metasomatized by the Li-rich fluids derived from the subducted oceanic crust and marine sediments. This melting was most likely triggered by a Cenozoic asthenospheric mantle diapir related to Indian-Asian continental collision and post- or late-collisional stress relaxation in the Oligocene. © 2015 Elsevier Ltd.
Guo C.,Chinese Academy of Geological Sciences |
Chen Z.,Chinese Academy of Geological Sciences |
Lou F.,Jiangxi Provincial Institute of Geological Survey |
Xu Y.,Southern Hunan Institute of Geology and Survey
Geotectonica et Metallogenia | Year: 2014
Late Jurassic, especially 150-160 Ma, is the most important period of W-Sn polymetallic mineralization in the Nanling region. The ore bearing granitoids are alkaline and high-potassium, and their major and trace element concentrations and Sr-Nd isotopic compositions are reviewed in this contribution. The ore bearing granites can be divided into two subgroups which are characterized by "sea-gull type-" and "inclining type-" REE patterns. Moreover, the two subgroups show distinct major and trace element and Sr-Nd isotopic characteristics. Ca/(Mg+Fe) vs. Al/(Mg+Fe) diagram shows that the two subgroups of granites were derived from different sources. SiO2 vs. P2O5, Rb vs. Y and Rb vs. Th diagrams also demonstrate that the W and Sn bearing granites are of different genetic types.
Zhang J.,Jiangxi Provincial Institute of Geological Survey |
Zhang J.,China University of Geosciences |
Wang D.,Chinese Academy of Geological Sciences |
Liu S.,Chinese Academy of Geological Sciences |
And 3 more authors.
Acta Petrologica Sinica | Year: 2012
The northern Wuyi region, located in the conjoining area of the Yangtze plate and Cathaysian plate, is an important part of the Qinzhou-Hangzhou juncture zone and is characterized by series of Mesozoic volcanic basins. Systematic geochronological researches on its adjacent areas such as Lengshuikeng, Lizikeng and Xianxialing have been conducted, while in this area less research has been done. In this investigation, sphalerite was selected for isotopic chronological analyses. The Rb-Sr dating and Sm-Nd dating yields isochron ages of 135. 4 ±4. 4Ma (SMWD =0. 52) and 139 ± 15Ma (SMWD =0. 118), respectively. In addition, the C, O, S isotope compositions on lead-zinc ores and the associated calcite veins have been analyzed and 34SV-CDT of the lead and zinc minerals are 2. 5‰ ∼5. 1‰, 13CV-PDB of the calcite veins are - 2. 6%‰ ∼ -4. 7‰, 18OV-PDB are - 23. 9‰ ∼ -27. 7‰ and 18OV-PDB are 2. 3‰ ∼ 6. 2‰. These data suggest that S in the ores was derived from magmatic source, C and O in the calcite veins were originated not only from basic rocks or mantle source, but also from meteoric water. It is suggested that these deposits are magmatic deposits formed in the Early Cretaceous and that sphalerite can be used as an ideal mineral for dating. Our results provide new geochronological data for the volcanic belt in northern Wuyi, and reveal that metallogenetic age in Mesozoic became younger from west to east in general. The magmatic source of calcite veins leads to assumption that basement faults in northern Wuyi might extend deep to mantle, providing new evidences for constraining the south boundary of the Qinzhou-Hangzhou juncture.
Tian S.-H.,Chinese Academy of Geological Sciences |
Yang Z.-S.,Chinese Academy of Geological Sciences |
Hou Z.-Q.,Chinese Academy of Geological Sciences |
Mo X.-X.,China University of Geosciences |
And 3 more authors.
Gondwana Research | Year: 2015
New major and trace elemental, Sr-Nd-Pb isotope, and zircon U-Pb geochronological and Hf-O isotope data of post-collisional potassic and ultrapotassic volcanic rocks (PVRs and UPVs, respectively) along with geochemical data of PVRs, UPVs, and Mg-rich potassic rocks (MPRs) in the literature are used to constrain their mantle source and genesis. The PVRs, UPVs, and MPRs share similar geochemical features but with some discrepancies, suggesting that they were derived from subcontinental lithospheric mantle (SCLM) with isotopic heterogeneity resulting from the varying contributions of subducted Indian lower crust into the mantle source (ca. 6-20%, ca. 8-30%, and ca. 9-30%, respectively). The zircon Hf-O isotopic compositions of these rocks can be classified into two groups, including Group I rocks with high δ18O (6.7-11.3‰), low εHf(t) (-17.0 to -12.0), and old Hf crustal model ages (1.87-2.19Ga) that indicate an ancient SCLM source, and Group II rocks with δ18O values of 6.8-10.7‰, εHf(t) values of -11.8 to -6.3, and younger Hf crustal model ages (1.50-1.86Ga). The negative correlation defined by δ18O and εHf(t) of Group II samples suggests a two-component mixing between mantle- and crust-derived melts, in which the latter would be the subducted Indian lower crust as indicated by the similar negative εHf(t) values between Group II samples (-11.8 to -6.3) and the High Himalayan gneiss (-14.2 to +0.3). Thus we propose two enrichment events to account for the Hf-O isotopic compositions of the PVRs and UPVs/MPRs: the first involves the enrichment of the overlying SCLM that was metasomatized by fluids derived from dehydration of the subducted Indian lower crust, and the second invokes the enrichment of the overlying SCLM metasomatized by melts of the already dehydrated different proportions of the Indian lower crust. We argue that break-off of the northwards subducted Indian Plate in the early Miocene caused the asthenospheric upwelling under the Indian plate through slab window, resulting in varying degrees of partial melting of the overlying metasomatized heterogeneous SCLM to produce the primitive magmas of the PVRs, UPVs, and MPRs in an extensional setting. These observations and interpretations imply that the Indian lower crust was subducted beneath the Lhasa terrane in the Early-Middle Miocene. © 2015 International Association for Gondwana Research.