Lin Wei1 Michel Faure2 Claude Lepvrier3 陈泽超1|4 褚杨1|4 王清晨1 N'guyen Van Vuong5 Vu Van Tich5
1.中国科学院地质与地球物理研究所岩石圈演化国家重点实验室 北京 100029； 2.Institue des Sciences de la Terre dOrléans|Université dOrléans|France； 3.UMR7072CNRS|Université PierreetMarieCurie|France； 4.中国科学院研究生院 北京 100049； 5.Faculty of Geology|Hanoi University of Science|Hanoi University|Vietnam
The Early Mesozoic thrust and folds sheet structure along the southern margin of South China Block and its geodynamic
Lin Wei1 Michel Faure2 Claude Lepvrier3 Chen Zechao1,4 Chu Yang1,4 Wang Qingchen1 N'guyen Van Vuong5 Vu Van Tich5
(1.State Key Laboratory of Lithopheric Evolution| Institute of Geology and Geophysics|Chinese Academy of Sciences|Beijing 100029； 2.Institue des Sciences de la Terre dOrléans|Université dOrléans|France； 3.UMR7072CNRS| Université PierreetMarieCurie|France； 4.Graduate University of Chinese Academy of Sciences|Beijing 100049； 5.Faculty of Geology|Hanoi University of Science|Hanoi University|Vietnam
The Early Mesozoic tectonic and geodynamic evolutions of the South China Block(SCB)are still debated questions.Along the southern margin of the SCB，the Yunkai and Song Chay massifs are key regions to address these questions.In both of these massifs，an Early Mesozoic ductile deformation with thrust and folds structures have been observed.In the Yunkai massif，a flatlying to moderately dipping foliation with a clear NESW stretching and mineral lineation is indicated by amphibolite and greenschist facies metamorphic minerals.Along this lineation，toptotheNE ductile shearing is indicated by sigma type Kfeldspar porphyroclast systems，sigmoidal quartz veins，and it has been considered as the main ductile deformation in this area.In the north of the Yunkai massif，foliated granite and gneiss overthrust strongly sheared and folded Late Paleozoic strata by Carboniferous.Geochronological works indicate the time of deformation around 220 Ma.In north Vietnam，the Song Chay massif presents quite similar lithological and structural features with the Yunkai massif.It is formed by augen orthogneiss，the protolith of which is an Early Paleozoic porphyritic granite that intruded a Cambrian pelite and limestone series.Alike for the Yunkai massif，in the Song Chay massif，the flat lying foliation，a NESW mineral and stretching lineation，and toptotheNE ductile deformation are the main structures.These features are interpreted in terms of nappe stacking.To the north of the Song Chay massif，the weakly metamorphosed but strongly deformed Paleozoic sedimentary series overthrusts Lower to Middle Triassic turbidite.The age of the deformation ranges from Late Triassic to Early Jurassic.
〖JP2〗The geodynamic significance of this Early Mesozoic deformation in the Yunkai and Song Chay massifs are not settled yet.A link with the tectonics of Indochina appears likely.The closure age of the oceanic domain，which separated Indochina from South China and the subsequent collision of the two blocks，remains controversial.Detailed structural investigations and geochronological dating，along the Song Ma zone，show that the major collisional event occurred during the Late PermianEarly Triassic.However，as the Song Ma suture is located south of the Red River fault，it cannot be considered as the Triassic boundary between the South China Block and Indochina Block due to several hundred of kilometers of Cenozoic displacement along the Red River fault.Furthermore，the newly discovered Song Chay ophiolitic suture might account for the Triassic plate boundary in the southern margin of SCB in North of Vietnam.The Yunkai and Song Chay massifs，that both belong to the southern margin of SCB，are involved in this Indosinian orogenic belt that probably extends in NW China along the Jinshajiang.