大青山太古宙高级变质岩近水平顺层伸展变形--地球上早期的伸展构造

The Horizontal Bedding Extensional Deformation in the Archean High-Grade Metamorphic Rocks from Daqingshan Region——The Oldest Extensional Structure on Earth

内蒙古大青山—乌拉山位于华北克拉通北缘,是我国高级区发育较好的区域之一。区内高级变质杂岩总体上呈近东西向延伸,经历多期变质变形作用改造。近水平顺层伸展变形是高级变质杂岩中最早的塑性流动变形作用,发生在下地壳麻粒岩相环境下。变形作用伴随麻粒岩相变质作用、深熔作用,形成了顺层滑动韧性变形带、穹隆构造、层内底辟褶皱和L构造岩等构造形迹组合。这期变形作用不仅导致区内的孔兹岩系和麻粒岩系以近水平构造面接触,也造成孔兹岩系中各个地层单位具有以透镜状岩片堆叠的地层结构,并且还伴随有不同类型的深熔片麻岩形成。近水平顺层伸展变形作用的确立,对研究早前寒武纪高级区地壳形成演化和高级变质地层构造格架的建立具有重要的理论意义。

Located in the northern margin of North China craton, Daqingshan - Wulashan district is one of well-developed high-grade metamorphic regions in China. The high-grade metamorphic complexes, extending from east to west, experienced multiple phases of deformation and metamorphism. The horizontal bedding extensional deformation occuring in granulite facies rocks can be taken as the oldest plastic flow deformation in high grade metamorphic complex. Due to the deformation, accompanied by metamorphism in granulite facies and anatexis, such structural features were formed as bedding slid ductile belts, dome, intra-bedding diapiric folds and L-tectonite. The deformation is also responsible for horizontal structural contact between khondalite suite and granulites, the stack stratigraphic frameworks of lens slices among different stratigraphic units in khondalite suite, as well as different types of anatectic gneisses. The confirmation of horizontal bedding extensional deformation has an important theoretical significance on studying the crustal evolution of Early Precambrian high-grade metamorphic region and the high-grade metamorphic stratigraphic frameworks.