中国大陆显生宙俯冲型、碰撞型和复合型片麻岩穹窿(群)

片麻岩穹窿(gneiss dome)是中下地壳热动力学过程产生的、与岩浆作用(或混合岩化作用)密切相关的穹窿状构造。片麻岩穹窿大部分是地壳深层次变动的产物,在世界范围内几乎出露在所有的折返造山带中,反映了所在地区地壳的大幅度抬升。片麻岩穹窿核部主要是无或弱岩浆组构的花岗岩体和高级变质岩(例如混合岩),边部是具有岩浆组构的花岗片麻岩,幔部由来自地壳深部的高级片岩和片麻岩组成。片麻岩穹窿的形成经历从垂直上升的地壳流导致的岩浆上涌的挤压收缩机制到岩浆体侵位的顶部伸展机制的转化过程。根据片麻岩穹窿的岩石组合、组构特征、成因机制和大地构造背景以及片麻岩穹窿与地壳流关系的分析,结合中国大陆典型片麻岩穹窿的研究,提出中国大陆显生宙的片麻岩穹窿和片麻岩穹窿群可以划分为与大洋岩石圈板片俯冲增生与随后的折返造山相关的"俯冲型"片麻岩穹窿(群),如秦岭片麻岩穹窿;与陆陆碰撞折返造山有关的"碰撞型"片麻岩穹窿(群),如北喜马拉雅拉轨岗日片麻岩穹窿(群)和松潘甘孜雅江片麻岩穹窿(群);与俯冲和碰撞的叠合作用有关的"复合式"片麻岩穹窿(群),如帕米尔空喀山片麻岩穹窿和东冈底斯林芝片麻岩穹窿(群)。

The Chinese Phanerozoic gneiss domes: Subduction-related type, collision-related type and combination type of subduction-collision

Gneiss domes are ubiquitous domal structures in all exhumed orogens, and their formation is closely associated with the thermal-tectonic processes (magmatism and/or migmatization) in middle-lower crust. Their occurrence indicates that the middle-lower crust has been exhumed to shallow depth. In general, gneiss domes are primarily cored by granitoid plutons (with weak or no magmatic fabrics) and high-grade metamorphic rocks (e.g. migmatite) that are immediately margined by granitic gneisses showing magmatic fabrics, and mantled by high-grade schists and gneisses. Most commonly in the whole evolutionary process, the formation of gneiss domes will be subject to the contraction regime triggering by the vertical ascent of crustal flow and subsequent extension regime at the top of the intrusions. Based on the rock assemblages, fabrics, formation mechanism and geological settings of gneiss domes and their relationship with the crustal flow, we analyzed typical gneiss domes in China and classified these Chinese Phanerozoic gneiss domes and gneiss dome systems into three types, namely the subduction-related type, the collision-related type and the combination type of subduction and collision. The subduction-related type is represented by the gneiss domes in the Qinling terrane, the collision-related type is the North Himalayan gneiss domes and the Yajiang ones in the Songpan-Ganze terrane, and the combination type of subduction-collision is the Kongur gneiss domes in the northeastern Pamir and the Linzhi gneiss domes in the eastern Gangdese magmatic belt.