The Precambrian lower crust rocks at the southeastern margin of the North China Craton （NCC） are mainly exposed as granulite xenoliths hosted by Mesozoic dioritic porphyry and metamorphic terrains in the Xuzhou-Suzh...The Precambrian lower crust rocks at the southeastern margin of the North China Craton （NCC） are mainly exposed as granulite xenoliths hosted by Mesozoic dioritic porphyry and metamorphic terrains in the Xuzhou-Suzhou area. Garnet amphiholites and garnet granulites are two kinds of typical lower-crustal xenoliths and were selected to reconstruct different stages of the metamorphic process. In this study, in view of multistage metamorphic evolution and reworking, phase equilibria modeling was used for the first time to better constrain peak P-T conditions of the xenoliths. Some porphyroblastic garnets have a weak zonal structure in composition with homogeneous cores and were surrounded by thin rims with an increase in XMg and a decrease in X Ca （or X Mg）- Clinopyroxene contain varying amounts of Na2O and Al2O3 as well as amphibole of TiO2, while plagioclases are different in calcium contents. Peak metamorphic P-T conditions are calculated by the smallest garnet x（g） （Fe2＋/（Fe2＋＋Mg）） contours and the smallest plagioclase ca（pl） （Ca/（Ca＋Na）） contours in NCFMASHTO （Na2O-CaO-FeO-MgO-Al2O3-SiO2- H20-TiO2-Fe2O3） system, which are consistent with those estimated by conventional geothermobarometry. The new results show that the peak and decompressional P-T conditions for the rocks are 850-900 ℃/ 1.4-1.6 GPa and 820-850 ℃/0.9-1.3 GPa, respectively, suggestive of high and middle-low pressure granulite-facies metamorphism. Combined with previous zircon U-Pb dating and conventional geothermobarometry data, it is indicated that the xenoliths experienced a clockwise P-T-t evolution with nearisothermal deeompressional process, suggestive of the Paleoproterozoic subduction-collision setting. In this regard, the studied region together with Jiao-Liao-Ji belt is further documented to make up a Paleopro- terozoic collisional orogen in the eastern block of the NCC.展开更多
On the basis of distribution of active fault and regional rheological structure, a three-dimensional finite element model of Sichuan-Yunnan region, China, is constructed to simulate contemporary crustal motion and str...On the basis of distribution of active fault and regional rheological structure, a three-dimensional finite element model of Sichuan-Yunnan region, China, is constructed to simulate contemporary crustal motion and stress distribution and discuss the dynamic mechanism of crustal motion and deformation in the Sichuan-Yunnan region. Linear Maxwell visco-elastic model is applied, which includes the active fault zones, the elastic upper crust and viscous lower crust and upper mantle. Four different models with different boundary conditions and deep structure are calculated. Some conclusions are drawn through comparison. Firstly, the crustal rotation about the eastern syntaxis of the Himalaya in the Sicuan-Yunnan region may be controlled by the special dynamic boundary condition. The drag force of the lower-crust on the upper crust is not negligible. At the same time, the main active fault zones play an important role in the contemporary crustal motion and deformation in Sichuan-Yunnan region.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 41773020)the National Basic Research Program of China (No. 2015CB856104)the PhD Foundation of the Ministry of Education of China (No. 20133402130008)
文摘The Precambrian lower crust rocks at the southeastern margin of the North China Craton （NCC） are mainly exposed as granulite xenoliths hosted by Mesozoic dioritic porphyry and metamorphic terrains in the Xuzhou-Suzhou area. Garnet amphiholites and garnet granulites are two kinds of typical lower-crustal xenoliths and were selected to reconstruct different stages of the metamorphic process. In this study, in view of multistage metamorphic evolution and reworking, phase equilibria modeling was used for the first time to better constrain peak P-T conditions of the xenoliths. Some porphyroblastic garnets have a weak zonal structure in composition with homogeneous cores and were surrounded by thin rims with an increase in XMg and a decrease in X Ca （or X Mg）- Clinopyroxene contain varying amounts of Na2O and Al2O3 as well as amphibole of TiO2, while plagioclases are different in calcium contents. Peak metamorphic P-T conditions are calculated by the smallest garnet x（g） （Fe2＋/（Fe2＋＋Mg）） contours and the smallest plagioclase ca（pl） （Ca/（Ca＋Na）） contours in NCFMASHTO （Na2O-CaO-FeO-MgO-Al2O3-SiO2- H20-TiO2-Fe2O3） system, which are consistent with those estimated by conventional geothermobarometry. The new results show that the peak and decompressional P-T conditions for the rocks are 850-900 ℃/ 1.4-1.6 GPa and 820-850 ℃/0.9-1.3 GPa, respectively, suggestive of high and middle-low pressure granulite-facies metamorphism. Combined with previous zircon U-Pb dating and conventional geothermobarometry data, it is indicated that the xenoliths experienced a clockwise P-T-t evolution with nearisothermal deeompressional process, suggestive of the Paleoproterozoic subduction-collision setting. In this regard, the studied region together with Jiao-Liao-Ji belt is further documented to make up a Paleopro- terozoic collisional orogen in the eastern block of the NCC.
基金Ministry of Science and Technology (2004CB418406, 2005DKA64000)the Basic Science Research Plan of the Institute of Earthquake Science, China Earthquake Administration (02076902-03).
文摘On the basis of distribution of active fault and regional rheological structure, a three-dimensional finite element model of Sichuan-Yunnan region, China, is constructed to simulate contemporary crustal motion and stress distribution and discuss the dynamic mechanism of crustal motion and deformation in the Sichuan-Yunnan region. Linear Maxwell visco-elastic model is applied, which includes the active fault zones, the elastic upper crust and viscous lower crust and upper mantle. Four different models with different boundary conditions and deep structure are calculated. Some conclusions are drawn through comparison. Firstly, the crustal rotation about the eastern syntaxis of the Himalaya in the Sicuan-Yunnan region may be controlled by the special dynamic boundary condition. The drag force of the lower-crust on the upper crust is not negligible. At the same time, the main active fault zones play an important role in the contemporary crustal motion and deformation in Sichuan-Yunnan region.
