青藏高原东南缘晚渐新世-早中新世中下地壳流动:滇西瑶山与玉龙变质杂岩构造解析

Late Oligocene-Early Miocene crustal flow in the southeastern Tibet Plateau:Structural analysis of the Yao Shan and Yulong metamorphic complexes in western Yunnan

通常认为位于青藏高原东南缘的巽他地块侧向刚性块体挤出调节了印度-欧亚板块碰撞及后碰撞。然而,最近的研究表明,低粘度的中下地壳流动可以解释青藏高原向外扩张的现象。关于哪种机制在巽他地块挤出过程中起着主导作用仍未解决。在本研究中,我们重点围绕哀牢山-红河构造带南部的瑶山杂岩以及构造带北部邻区的玉龙杂岩开展构造研究。详细的宏观构造解析、显微构造以及组构分析说明切向剪切作用在瑶山与玉龙穹隆的形成与剥露中起着重要作用,组成穹窿的岩石均具有分层流变学特点。瑶山穹隆是发育在较深岩石层位的穹隆构造,而玉龙穹隆是发育在较浅岩石层位的穹隆构造。向南或东南切向剪切可能是上地壳向南的重力滑动和粘滞下地壳相对中上地壳向北流动共同作用的结果。前者可能与高原重力塌陷有关,但后者的驱动力有待进一步研究。

It is generally believed that the lateral rigid block extrusion of the Sundaland block located at the southeastern Tibetan Plateau adjusts the India-Eurasia plates collision and post-collision.However,recent studies have shown that the low-viscosity middle and lower crustal flow can explain the outward expansion of the Tibet Plateau.The question of which mechanism plays a leading role in the extrusion of Sundaland block remains unresolved.In this study,we focus on the Yao Shan complex in the southern part of the Ailao Shan-Red River tectonic belt and the Yulong complex in the adjacent area of northern part.Detailed macrostructure,microstructure and fabric analyses show that the tangential shearing in the Yao Shan and Yulong complexes plays an important role in formation and exhumation of dome structures,and both complexes are characterized by layered rock rheology.Yao Shan dome is developed in a deep level,whereas the Yulong dome is developed in a shallow layer.The southward or southeastward tangential shearing may be the result of the southward gravity sliding of the upper crust and the north flow of the viscous lower crust relative to the middle-upper crust.The former may be related to the gravity collapse of the plateau,but the driving force of the latter needs further study.