国家科技基础条件平台
  • 你好,请
  • 登录
    • logotext
    Permo-Triassic arc magmatism in central Tibet， Evidence from zircon U-Pb geochronology,Hf isotopes,rare earth elements,and bulk geochemistry [查看] T.N.Yang、H.R.Zhang、Y.X.Liu、Z.L.Wang、Y.C.Song、Z.S.Yang、S.H.Tian、H.Q.Xie、K.J.Hou
    There is hot debate on whether there is a Paleo-Tethyan suture within Qiangtang and on how the suture extends in central Tibet. In situ Hf and U–Pb isotopes, and rare earth element (REE) analyses of zircons, together with bulk chemistry, have helped us identify a significant, and previously unknown stage of subduction-related magmatism along the southern part of the eastern Qiangtang block, north of the Shuanghu suture, central Tibet. SHRIMP and LA-ICP-MS zircon U–Pb data demonstrate that the magmatism started as early as 275 Ma, lasted until 248 Ma, and took place at the same time as blueschist and eclogite were forming in the central Qiangtang high- to ultrahigh-pressure metamorphic belt (QMB). The positive εHf(t) values of the magmatic zircons range from 9.71 to 16.73, and indicate derivation of magma from a relatively uncontaminated, depleted mantle. Variations in εHf(t) values and the REE patterns of magmatic zircons,combined with substantial heterogeneities in the whole-rock chemistry, suggest that the arc-related magmatism occurred in pulses, and was long-lived. The present data can be interpreted in terms of a history of progressive subduction during the Early Permian and Early Triassic, during which time continental fragments of EQ affinity were tectonically eroded and subducted into the mantle, along with the subducted oceanic slab.The temporal and spatial correlations between the arc-like volcanic belt and the high-pressure metamorphic belt suggest a Late Paleozoic ocean (Paleo-Tethys) existed between the western and eastern Qiangtang blocks, and that the ocean was closed by northwards subduction.
    Palaeoproterozoic tectonothermal evolution and deep crustal processes in the Jiao-Liao-Ji Belt,North China Cratona review [查看] S.Z.LI、G.C.ZHAO、SANTOSH、X.LIU、L.M.DAI
    The Palaeoproterozoic Jiao-Liao-Ji Belt is located in the eastern margin of the Eastern Block of the North China Craton. In this paper, we synthesize the tectonothermal evolution and deep crustal processes in the Jiao-Liao-Ji Belt based on recent information. A mantle plumerelated underplating from 2.53 to 2.36 Ga is envisaged which led to the emplacement of the 2.47–2.33 Ga alkali granite plutons and mafic dyke swarms, followed by the development of the Jiao-Liao-Ji Rift and bi-modal volcanism. The underplating resulted not only in different sedimentary environments in the upper crust, but also in a differentiation of the initial thermal structure in the rift. This controlled the metamorphism and style of P-T-t paths in the different parts of the rift. Subsequent underplating resulted in the emplacement of the A-type Liaoji granites of ca. 2.17 Ga in the lower crust, and the formation of associated pegmatites of 2.2 and 2.0 Ga, together with the development of a bedding-parallel extension. However, the main orogeny occurred between 1.93 and 1.88 Ga with closing of the rift, compressional deformation and high-pressure granulite metamorphism in the southern part of the orogen. Subsequently, lithospheric blocks were possibly delaminated at 1.85 Ga; anorogenic magmatic rocks such as rapakivi granite, alkaline granites and syenite were intruded, and pegmatite veins and mafic dyke swarms were emplaced cross-cutting all the earlier structural traces. We identify that the underplating styles, collision processes and delamination types in the deep lithosphere controlled the tectonothermal evolution of the crust in the Jiao-Liao-Ji region.
    Mtamorphic patterns and SHRIMP zircon ages of medium-to-high grade rocks from the Tongbai orogen,central China,implications for ultiple accretion,col,lision processes pe=rior to terminal continental collision [查看] X.C.LIU、B.-M.JAHN、J.HU、S.Z.LI、X.LIU、B.SONG
    The Qinling-Tongbai-Dabie-Sulu orogenic belt comprises a Palaeozoic accretion-dominated system in the north and a Mesozoic collision-dominated system in the south. A combined petrological and geochronological study of the medium-to-high grade metamorphic rocks from the diverse Palaeozoic tectonic units in the Tongbai orogen was undertaken to help elucidate the origins of Triassic ultrahighpressure metamorphism and collision dynamics between the Sino-Korean and Yangtze cratons. Peak metamorphic conditions are 570–610 C and 9.3–11.2 kbar for the lower unit of the Kuanping Group,630–650 C and 6.6–8.9 kbar for the upper unit of the Kuanping Group, 550–600 C and 6.3–7.7 kbar for the Erlangping Group, 770–830 C and 6.9–8.5 kbar for the Qinling Group and 660–720 C and 9.1–11.5 kbar for the Guishan complex. Reaction textures and garnet compositions indicate clockwise P–T paths for the amphibolite facies rocks of the Kuanping Group and Guishan complex, and an anticlockwise P–T path for the granulite facies rocks of the Qinling Group. Sensitive high-resolution ion microprobe U–Pb zircon dating on metamorphic rocks and deformed granite ⁄ pegmatites revealed two major Palaeozoic tectonometamorphic events. (i) During the Silurian-Devonian (c. 440–400 Ma), the Qinling continental arc and Erlangping intra-oceanic arc collided with the Sino-Korean craton.The emplacement of the Huanggang diorite complex resulted in an inverted thermal gradient in the underlying Kuanping Group and subsequent thermal relaxation during the exhumation. Meanwhile, the oceanic subduction beneath the Qinling continental arc produced magmatic underplating and intrusion,leading to granulite facies metamorphism followed by a near-isobaric cooling path. (ii) During the Carboniferous (c. 340–310 Ma), the northward subduction of the Palaeo-Tethyan ocean generated a medium P ⁄ T Guishan complex in the hangingwall and a high P ⁄ T Xiongdian eclogite belt in the footwall. The Guishan complex and Xiongdian eclogite belt are therefore considered to be paired metamorphic belts. Subsequent separation of the paired belts is inferred to be related to the juxtaposition of the Carboniferous eclogites with the Triassic HP metamorphic complex during continental subduction and exhumation.
    © BJSHRIMP 2013 - bjshrimp.cn