华南板块南缘早中生代的逆冲推覆构造及其相关的动力学背景

作为理解华南构造演化的关键地区,在华南板块南缘的云开地体和越北的Song Chay地体发育了早中生代的向北东逆冲推覆的韧性变形.在云开地体,经历角闪岩相和绿片岩相变质的矿物指示了产状平缓的面理上发育明显的北东-南西向矿物拉伸线理.沿着这些矿物拉伸线理,具有上部指向北东的剪切变形.同位素年代学的定年结果指示了变形事件发生...

The Early Mesozoic thrust and folds sheet structure along the southern margin of South China Block and its geodynamic

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 flat lying to moderately dipping foliation with a clear NE SW stretching and mineral lineation is indicated by amphibolite and greenschist facies metamorphic minerals.Along this lineation，top to the NE ductile shearing is indicated by sigma type K feldspar 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 NE SW mineral and stretching lineation，and top to the NE 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 Permian Early 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.