There are significant differences of Nd and Pbisotopic compositions between Mesozoic mafic igneous rocks from the North China Block (NCB) and the South ChinaBlock (SCB). Mesozoic mantle-derived igneous rocks fromthe N...There are significant differences of Nd and Pbisotopic compositions between Mesozoic mafic igneous rocks from the North China Block (NCB) and the South ChinaBlock (SCB). Mesozoic mantle-derived igneous rocks fromthe North China Block have very low e Nd values (-15 to -21), and 206Pb/204Pb ratios (< 17.9), while those in the SCB are characterized by e Nd > -10 and 206Pb/204Pb > 18.3. The verylow e Nd values (-16 to -20) and 206Pb/204Pb ratios (< 17.3) of the early Cretaceous mafic-ultramafic intrusions developedin the north part of the Dabie orogen (NDZ) suggest that the deep lithosphere underneath the NDZ belongs to the NCBbut not the SCB. Therefore, although the surface suture be-tween the NCB and SCB is located on the north side of theNDZ, the subsurface suture between the NCB and SCBshould be located to the south side of the NDZ. This is con-sistent with the previous suggestion that the subsurface su-ture in the Sulu terrane east of the Tanlu fault was the south displacement, but contradictory to northward continentalsubduction of the SCB. A continent-collisional lithospheric-wedging model can interpret the decoupling of the surface and subsurface sutures in the Dabie-Sulu orogen. After slabbreak-off, the continuing convergence of two continental blocks must increase the compression force acting on the suture zone, which might induce the lithosphere splitting of SCB. Thus, the lower crust and lithospheric mantle on thesouth margin of the NCB can wedge into the north margin of the lithosphere of the SCB along the Dabie-Sulu collisionzone. This process caused the overthrust of the mid-upper continental crust with exhumed ultrahigh pressure meta-morphic (UHPM) rocks and underthrust of the deep litho-sphere of the SCB. It could be an important mechanism re-sponsible for the second rapid cooling and uplifting of theUHPM rocks and lithospheric delamination as well as thecorresponding magmatism in Jurassic in the Dabie orogen.The southward movement of subsurface suture in theDabie-Sulu orogen may also provide a tecto展开更多
Based on 40Ar-39Ar results of hornblendes and biotites and fission track dating results of apatites separated from the same rock samples, cooling history of rocks from Dabie orogen is discussed. Rocks from both Southe...Based on 40Ar-39Ar results of hornblendes and biotites and fission track dating results of apatites separated from the same rock samples, cooling history of rocks from Dabie orogen is discussed. Rocks from both Southern Dabie Terrain (SDT) and Northern Dabie Terrain (NDT) have an early fast cooling followed by a more recent slow cooling. Rocks from SDT cooled to about 540℃ at about 190 Ma B.C., while rocks from NDT cooled to about 540℃ at 125 Ma B C. Until about 110-120 Ma B.C., rocks from both SDT and NDT cooled to about 100℃. This suggests that a relative movement among rocks from SDT, NDT and ul-Ira-high pressure metamorphic rocks exis-ts before 110-120 Ma B.C.展开更多
The Yangxin composite intrusive consists of three generations of plutons, among which 90% are the second generation intrusions. The second generation intrusion has U-Pb SHRIMP zircon age of 134±2 Ma, substantiall...The Yangxin composite intrusive consists of three generations of plutons, among which 90% are the second generation intrusions. The second generation intrusion has U-Pb SHRIMP zircon age of 134±2 Ma, substantially younger than the early stage of the Yanshanian. Amphibole and biotite, major mafic minerals in the Yangxin plutons, are rich in magnesium, suggesting a deep source of their parental magma, possibly derived from the upper mantle. Whole rock geochemical data on these rocks show that they have high Al2O3 (15.92%―16.38%), relatively high alkali (Na2O+K2O = 6.95%―7.37%) and higher Na2O contents than K2O (Na2O/K2O = 1.47―1.94). They also have high Sr con-tents (816―897 μg/g) are enriched in strong incompatible elements such as Rb, U, Th, K and LREE, but depleted in HREE and Y. Strong fractionation of LREE from HREE as indicated by high (La/Yb)N ratios ranging from 17.83 to 20.86. Although with little difference, the whole characteristics of the Yangxin intrusive body are greatly similar to the adakite, referring that the formation of the parental magma may relate with the partial melting of the basalt underplating from the mantle after delamina-tion of the mountain root of the Dabie orogen. The body has been uplifted about 5 km since cooling concretion, the average rate was only about 0.04 mm/a,much slower than that of the Dabie orogen in late Mesozoic, but the rates of denudation in two area are similar in Cenozoic.展开更多
The Dabie orogen underwent deep continental subduction, rapid exhumation, and the huge amount of erosion during the Mesozoic. Its tectonic evolution, especially how its evolution was recorded by sedimentary basins at ...The Dabie orogen underwent deep continental subduction, rapid exhumation, and the huge amount of erosion during the Mesozoic. Its tectonic evolution, especially how its evolution was recorded by sedimentary basins at the flanks of the Dabie orogen is one of the most important issues of the world's attention. These years, newly studies of basin sedimentology, combined with structural geology, have shown a fundamental progress. The overall distribution of different basin types in the orogen indicates that shortening and thrusting at the margins of the orogen from the Late Triassic to the Early Cretaceous controlled the foreland basins, and extension, doming and rifting were initiated in the core of the orogen from the Jurassic to the Early Cretaceous and were expanded to the whole orogen after the Late Cretaceous. Therefore, The Dabie orogen records gradual transition from overall shortening and thrusting to dominantly extension and rift basin formation expanded from its core to its margins, although these shortening and extension overlapped in time from the Jurassic through Early Cretaceous at crustal levels. The unroofing ages of the ultra-high pressure (UHP) metamorphic rocks in the Dabie orogen change from Early Jurassic to Late Jurassic westward. The depth of exhumation increases eastwards. The sediment sources for the Hefei basin are mostly composed of the deeply exhumed, axial Dabie metamorphic complex, and the sediment sources for the Middle Yangtze basin are mostly from cover strata in the southern orogen and related strata with subjacent (i.e. subsequently overthrusted) Mianlue suture belt. Geodynamic analysis represents that continental collision between the North China Block and the South China Block along the Shangdan and Mianlue sutures, subsequently northwestward progradation of the Jiangnan fold and thrust belt, and the underthrusting of the North China Block along the Northern Boundary Fault of Qinling Range led to crustal thickening, gravitational spreading and balanced rebound of the resultant th展开更多
基金This work was supported by the Major Srate Basic Research Program(Grant No.G1999075503)the National Natural Science Foundation of China(Grant No.49873006)the Chinese Aeademy of Sciences(Grant No.KZCXZ-107).
文摘There are significant differences of Nd and Pbisotopic compositions between Mesozoic mafic igneous rocks from the North China Block (NCB) and the South ChinaBlock (SCB). Mesozoic mantle-derived igneous rocks fromthe North China Block have very low e Nd values (-15 to -21), and 206Pb/204Pb ratios (< 17.9), while those in the SCB are characterized by e Nd > -10 and 206Pb/204Pb > 18.3. The verylow e Nd values (-16 to -20) and 206Pb/204Pb ratios (< 17.3) of the early Cretaceous mafic-ultramafic intrusions developedin the north part of the Dabie orogen (NDZ) suggest that the deep lithosphere underneath the NDZ belongs to the NCBbut not the SCB. Therefore, although the surface suture be-tween the NCB and SCB is located on the north side of theNDZ, the subsurface suture between the NCB and SCBshould be located to the south side of the NDZ. This is con-sistent with the previous suggestion that the subsurface su-ture in the Sulu terrane east of the Tanlu fault was the south displacement, but contradictory to northward continentalsubduction of the SCB. A continent-collisional lithospheric-wedging model can interpret the decoupling of the surface and subsurface sutures in the Dabie-Sulu orogen. After slabbreak-off, the continuing convergence of two continental blocks must increase the compression force acting on the suture zone, which might induce the lithosphere splitting of SCB. Thus, the lower crust and lithospheric mantle on thesouth margin of the NCB can wedge into the north margin of the lithosphere of the SCB along the Dabie-Sulu collisionzone. This process caused the overthrust of the mid-upper continental crust with exhumed ultrahigh pressure meta-morphic (UHPM) rocks and underthrust of the deep litho-sphere of the SCB. It could be an important mechanism re-sponsible for the second rapid cooling and uplifting of theUHPM rocks and lithospheric delamination as well as thecorresponding magmatism in Jurassic in the Dabie orogen.The southward movement of subsurface suture in theDabie-Sulu orogen may also provide a tecto
基金Project supported by the National Natural Science Foundation of China and Lithosphere Open Laboratory, Chinese Academy of Sciences.
文摘Based on 40Ar-39Ar results of hornblendes and biotites and fission track dating results of apatites separated from the same rock samples, cooling history of rocks from Dabie orogen is discussed. Rocks from both Southern Dabie Terrain (SDT) and Northern Dabie Terrain (NDT) have an early fast cooling followed by a more recent slow cooling. Rocks from SDT cooled to about 540℃ at about 190 Ma B.C., while rocks from NDT cooled to about 540℃ at 125 Ma B C. Until about 110-120 Ma B.C., rocks from both SDT and NDT cooled to about 100℃. This suggests that a relative movement among rocks from SDT, NDT and ul-Ira-high pressure metamorphic rocks exis-ts before 110-120 Ma B.C.
基金supported by the Chinese Ministry of Science and Technology(Grant Nos.2003CB716502 and TG1999075505)the National Natural Science Foundation of China(Grant No.40472035).
文摘The Yangxin composite intrusive consists of three generations of plutons, among which 90% are the second generation intrusions. The second generation intrusion has U-Pb SHRIMP zircon age of 134±2 Ma, substantially younger than the early stage of the Yanshanian. Amphibole and biotite, major mafic minerals in the Yangxin plutons, are rich in magnesium, suggesting a deep source of their parental magma, possibly derived from the upper mantle. Whole rock geochemical data on these rocks show that they have high Al2O3 (15.92%―16.38%), relatively high alkali (Na2O+K2O = 6.95%―7.37%) and higher Na2O contents than K2O (Na2O/K2O = 1.47―1.94). They also have high Sr con-tents (816―897 μg/g) are enriched in strong incompatible elements such as Rb, U, Th, K and LREE, but depleted in HREE and Y. Strong fractionation of LREE from HREE as indicated by high (La/Yb)N ratios ranging from 17.83 to 20.86. Although with little difference, the whole characteristics of the Yangxin intrusive body are greatly similar to the adakite, referring that the formation of the parental magma may relate with the partial melting of the basalt underplating from the mantle after delamina-tion of the mountain root of the Dabie orogen. The body has been uplifted about 5 km since cooling concretion, the average rate was only about 0.04 mm/a,much slower than that of the Dabie orogen in late Mesozoic, but the rates of denudation in two area are similar in Cenozoic.
基金supported by the National Natural Science Foundation of China(41030318 and 91114203)
文摘The Dabie orogen underwent deep continental subduction, rapid exhumation, and the huge amount of erosion during the Mesozoic. Its tectonic evolution, especially how its evolution was recorded by sedimentary basins at the flanks of the Dabie orogen is one of the most important issues of the world's attention. These years, newly studies of basin sedimentology, combined with structural geology, have shown a fundamental progress. The overall distribution of different basin types in the orogen indicates that shortening and thrusting at the margins of the orogen from the Late Triassic to the Early Cretaceous controlled the foreland basins, and extension, doming and rifting were initiated in the core of the orogen from the Jurassic to the Early Cretaceous and were expanded to the whole orogen after the Late Cretaceous. Therefore, The Dabie orogen records gradual transition from overall shortening and thrusting to dominantly extension and rift basin formation expanded from its core to its margins, although these shortening and extension overlapped in time from the Jurassic through Early Cretaceous at crustal levels. The unroofing ages of the ultra-high pressure (UHP) metamorphic rocks in the Dabie orogen change from Early Jurassic to Late Jurassic westward. The depth of exhumation increases eastwards. The sediment sources for the Hefei basin are mostly composed of the deeply exhumed, axial Dabie metamorphic complex, and the sediment sources for the Middle Yangtze basin are mostly from cover strata in the southern orogen and related strata with subjacent (i.e. subsequently overthrusted) Mianlue suture belt. Geodynamic analysis represents that continental collision between the North China Block and the South China Block along the Shangdan and Mianlue sutures, subsequently northwestward progradation of the Jiangnan fold and thrust belt, and the underthrusting of the North China Block along the Northern Boundary Fault of Qinling Range led to crustal thickening, gravitational spreading and balanced rebound of the resultant th
