The Urad Zhongqi mafic intrusions crop out in western Inner Mongolia and are dominated by hornblende gabbro.Zircon LA-ICP-MS U-Pb dating indicates that the mafic pluton was emplaced in the Early Permian(272 ± 3Ma...The Urad Zhongqi mafic intrusions crop out in western Inner Mongolia and are dominated by hornblende gabbro.Zircon LA-ICP-MS U-Pb dating indicates that the mafic pluton was emplaced in the Early Permian(272 ± 3Ma).The hornblende gabbro rocks have low concentrations of Si O2,high total Fe2O3,Mg O,Ni,Co,Sc and Cr.The rocks are characterized by selective enrichment of large ion lithophile elements(LILE) and light rare earth elements(LREE),and depletion in high field strength elements(HFSE)(e.g.Nb,Ta,Zr,Hf,P and Ti).It suggests that they formed from a primary magma generated by the partial melting of lithospheric mantle material had been previously modified by subduction-related fluids.According to the geochemical data and the geology of the region,the authors found that the Early Permian hornblende gabbroic in western Inner Mongolia formed in a post-collisional extensional setting.展开更多
Garnet amphibolite in the Baoyintu Group, Inner Mongolia, is mainly composed of garnet, hornblende, plagioclase, quartz and minor rutile/ilmenite. Garnet occurs as porphyroblasts surrounded by plagioclase, forming typ...Garnet amphibolite in the Baoyintu Group, Inner Mongolia, is mainly composed of garnet, hornblende, plagioclase, quartz and minor rutile/ilmenite. Garnet occurs as porphyroblasts surrounded by plagioclase, forming typical ＂white-eye socket＂ texture. Garnet shows grossular content of 0.26-0.28 and pyrope of 0.11-0.13, without significant zoning. Plagioclase is generally zoned with anorthite （An） increasing from core to rim. The P-T pseu- dosection calculated using THERMOCALC in the system MnNCKFMASHTO shows that the garnet amphibolite experienced a clockwise P-T path with a peak at 1.3 GPa/725 ℃ defined from the minimum An content in plagioclase and maximum pyrope content in garnet, followed by an isothermal decompression. LA-ICP-MS zircon dating for the garnet amphibolite indicates metamorphic ages of 399 ± 6 Ma. The peak P-T condition corresponds to a thermal gradient of ～ 18 ℃/km, indi- cating typical medium-pressure type that commonly occurs in orogenic process with crustal thickening. We prefer to interpret this orogenic event to be a result of collision, following the closure of the Paleo-Asian Ocean before the early Devonian although there is a popular view that the Paleo-Asian Ocean may have lasted to the early Mesozoic.展开更多
基金supported by Research Program "Au-Co-Ni Mineralization potential estimation of Tugurige gold mine and periphery in Urad Zhongqi,Inner Mongolia" from Geological Brigade No.208 of China National Nuclear Corporation
文摘The Urad Zhongqi mafic intrusions crop out in western Inner Mongolia and are dominated by hornblende gabbro.Zircon LA-ICP-MS U-Pb dating indicates that the mafic pluton was emplaced in the Early Permian(272 ± 3Ma).The hornblende gabbro rocks have low concentrations of Si O2,high total Fe2O3,Mg O,Ni,Co,Sc and Cr.The rocks are characterized by selective enrichment of large ion lithophile elements(LILE) and light rare earth elements(LREE),and depletion in high field strength elements(HFSE)(e.g.Nb,Ta,Zr,Hf,P and Ti).It suggests that they formed from a primary magma generated by the partial melting of lithospheric mantle material had been previously modified by subduction-related fluids.According to the geochemical data and the geology of the region,the authors found that the Early Permian hornblende gabbroic in western Inner Mongolia formed in a post-collisional extensional setting.
基金supported by the National Basic Research Program of China(‘‘973’’Program)(2013CB429801)the China Survey of Geology(1212011121077)
文摘Garnet amphibolite in the Baoyintu Group, Inner Mongolia, is mainly composed of garnet, hornblende, plagioclase, quartz and minor rutile/ilmenite. Garnet occurs as porphyroblasts surrounded by plagioclase, forming typical ＂white-eye socket＂ texture. Garnet shows grossular content of 0.26-0.28 and pyrope of 0.11-0.13, without significant zoning. Plagioclase is generally zoned with anorthite （An） increasing from core to rim. The P-T pseu- dosection calculated using THERMOCALC in the system MnNCKFMASHTO shows that the garnet amphibolite experienced a clockwise P-T path with a peak at 1.3 GPa/725 ℃ defined from the minimum An content in plagioclase and maximum pyrope content in garnet, followed by an isothermal decompression. LA-ICP-MS zircon dating for the garnet amphibolite indicates metamorphic ages of 399 ± 6 Ma. The peak P-T condition corresponds to a thermal gradient of ～ 18 ℃/km, indi- cating typical medium-pressure type that commonly occurs in orogenic process with crustal thickening. We prefer to interpret this orogenic event to be a result of collision, following the closure of the Paleo-Asian Ocean before the early Devonian although there is a popular view that the Paleo-Asian Ocean may have lasted to the early Mesozoic.
