摘要
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在220 Ma左右。在越南北部,Song Chay地体的岩石和构造特征与云开地体极其相似:平缓的面理,北东—南西向的矿物拉伸线理和上部指向北东的剪切变形是其主要的构造特征,这些构造特征均表现为向北东的逆冲推覆,变形时间从晚三叠世至早侏罗世。这期构造事件的动力学机制被认为同印支板块与华南板块晚古生代—早中生代的构造拼合密切相关。我们认为新发现的Song Chay蛇绿混杂带是华南板块同印支板块的碰撞拼合界线。因此,华南板块南缘云开地体和Song Chay地体被一同卷入同印支板块的碰撞造山体系之中。
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. 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. Det
出处
《地质科学》
CAS
CSCD
北大核心
2011年第1期134-145,共12页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家重点基础研究发展计划项目01课题"中国海相碳酸盐岩层系形成与后期演化"(编号:2005CB422101)
中国科学院知识创新工程重大项目(编号:KZCX1-YW-15-1)资助
