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 ...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 amphibolites 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 XCa(or XMg). Clinopyroxene contain varying amounts of Na_2O and Al_2O_3 as well as amphibole of TiO_2, while plagioclases are different in calcium contents. Peak metamorphic P-T conditions are calculated by the smallest garnet x(g)(Fe^(2+)/(Fe^(2+)+Mg)) contours and the smallest plagioclase ca(pl)(Ca/(Ca+Na)) contours in NCFMASHTO(Na_2O-CaO-FeO-MgO-Al_2O_3-SiO_2-H_2O-TiO_2-Fe_2O_3) 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 decompressional 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 Paleoproterozoic collisional orogen in the eastern block of the NCC.展开更多
The discovery of ultrahigh-pressure(UHP)index minerals such as coesite and micro-diamond in supracrustal rocks indicate that a large amount of crustal rocks were subducted to mantle depths and subsequently returned to...The discovery of ultrahigh-pressure(UHP)index minerals such as coesite and micro-diamond in supracrustal rocks indicate that a large amount of crustal rocks were subducted to mantle depths and subsequently returned to the Earth’s surface.However,exhumation mechanism of the deeply subducted crustal rocks has been a hot topic in geodynamic community and remains controversial.Previous studies have been performed by petrologic observations,analogue experiments and numerical simulations for exhumation processes and mechanisms of deeply subducted crustal rocks,and a series of important results have been achieved.In this paper,we summerize in detail recent progresses and existing problems on types of subduction zones,exhumation processes and mechanisms of deeply subducted crustal rocks,and related factors.Based on these,three forthcoming prospects are presented:(1)The geological processes within the exhuming crust;(2)the interaction between the exhuming crust and the surface process;(3)the interaction between the exhuming crust and the mantle.展开更多
The kyanite quartzite from the ultrahigh-pressure metamorphic belt in the eastern Dabie Mountains is composed mainly of quartz, kyanite, talc and epidote, which contains a typical mineral assemblage of white schist. I...The kyanite quartzite from the ultrahigh-pressure metamorphic belt in the eastern Dabie Mountains is composed mainly of quartz, kyanite, talc and epidote, which contains a typical mineral assemblage of white schist. It suffered an eclogite facies metamorphism of P =(2 4±0 3) GPa and T =630℃ together with coexisting eclogite. The protolith may be an aplite replaced by high-pressure fluid of eclogite facies.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.90814008,40634023 and 40973043)the National Basic Research Program of China (Grant No.2009CB825002)
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 amphibolites 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 XCa(or XMg). Clinopyroxene contain varying amounts of Na_2O and Al_2O_3 as well as amphibole of TiO_2, while plagioclases are different in calcium contents. Peak metamorphic P-T conditions are calculated by the smallest garnet x(g)(Fe^(2+)/(Fe^(2+)+Mg)) contours and the smallest plagioclase ca(pl)(Ca/(Ca+Na)) contours in NCFMASHTO(Na_2O-CaO-FeO-MgO-Al_2O_3-SiO_2-H_2O-TiO_2-Fe_2O_3) 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 decompressional 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 Paleoproterozoic collisional orogen in the eastern block of the NCC.
基金the National Basic Research Program of China(Grant No.2015CB856104)the National Natural Science Foundation of China(Grant No.41773020).Author information。
文摘The discovery of ultrahigh-pressure(UHP)index minerals such as coesite and micro-diamond in supracrustal rocks indicate that a large amount of crustal rocks were subducted to mantle depths and subsequently returned to the Earth’s surface.However,exhumation mechanism of the deeply subducted crustal rocks has been a hot topic in geodynamic community and remains controversial.Previous studies have been performed by petrologic observations,analogue experiments and numerical simulations for exhumation processes and mechanisms of deeply subducted crustal rocks,and a series of important results have been achieved.In this paper,we summerize in detail recent progresses and existing problems on types of subduction zones,exhumation processes and mechanisms of deeply subducted crustal rocks,and related factors.Based on these,three forthcoming prospects are presented:(1)The geological processes within the exhuming crust;(2)the interaction between the exhuming crust and the surface process;(3)the interaction between the exhuming crust and the mantle.
文摘The kyanite quartzite from the ultrahigh-pressure metamorphic belt in the eastern Dabie Mountains is composed mainly of quartz, kyanite, talc and epidote, which contains a typical mineral assemblage of white schist. It suffered an eclogite facies metamorphism of P =(2 4±0 3) GPa and T =630℃ together with coexisting eclogite. The protolith may be an aplite replaced by high-pressure fluid of eclogite facies.
