Formation of the Tibetan Metamarphic Domes

在喜马拉雅山和西藏之间的边界区域发生的一系列变质圆顶暴露了最初形成于中地壳的岩石，然后才被带到地球表面，它们提供了一个窗口，可以了解在其他无法进入的地区发生的过程。这些圆顶可能包含有关喜马拉雅山和西藏地壳深部结构如何联系的重要信息。然而，它们很少被研究。我们的目标是通过对圆顶区域进行实地和实验室研究来填补我们知识中的这一空白。我们还进行了一些相关研究，这些研究对于了解其他相关区域地壳深处发生的过程具有重要意义。与藏南变质穹隆直接相关的最重要的研究成果如下：穹隆的定义变质穹隆是指产于藏南地区的变质岩和火成岩的宽椭圆形区域。穹顶的核心是花岗岩， ...更多信息 同心巴罗型变质作用主要变形可分为D1和D2两个阶段。D1与地壳增厚和自上而下的剪切方向有关。D2与地壳减薄和自上而下的剪切方向有关。D2可与喜马拉雅山北方缘沿着的藏南拆离带（STD）正断层对比。花岗岩与变形变质作用之间的空间组合表明这些特征都是相关的。穹丘的时代变质穹丘一般被认为是20-10 Ma。相反，中央花岗岩被认为是500 Ma左右，与喜马拉雅造山运动无关。这种成见阻碍了将花岗岩侵入与穹丘变形和变质作用联系起来的模型的考虑。然而，在马拉山穹隆，我们显示花岗岩核心形成约18马。因此，这种花岗岩是在喜马拉雅造山带期间侵入的。这些穹丘之间的大量相似之处表明，它们的核心都含有类似的年轻花岗岩。我们的建议意味着，现在有可能检查模型，花岗岩侵入与圆顶的形成。圆顶的形成和喜马拉雅构造我们认为圆顶直接形成的花岗岩岩浆侵入的结果。伴随的接触变质作用在中央岩体周围形成同心变质带。此外，热弱化的岩石造成的变化，从地壳增厚在D1到地壳减薄有关D2。挤压构造背景下伸展变形的驱动力是重力对喜马拉雅前缘地表斜坡的作用。少

A series of metamorphic domes that occur in the boundary domain between the Himalayas and Tibet expose rocks originally formed in the mid crust before being brought to the Earth's surface and they offer a window into processes occurring in otherwise inaccessible regions. These domes potentially contain important information about how the structures of the Himalayas and the deep crust of Tibet are linked. However, they have been very little studied. We aimed to help fill this gap in our knowledge by carrying out field based and laboratory studies of the dome regions. We also carried out a number of related studies important for understanding the processes occurring deep in the crust in other related regions. The most important results directly related to the southern Tibet metamorphic domes are as follows.Definition of Domes The metamorphic domes are broadly elliptical domains of metamorphic and igneous rocks that occur in southern Tibet. The domes have a granite core surrounded by roug … More hly concentric Barrovian type metamorphism. The main deformation can be divided into two stages, D1 and D2. D1 is associated with crustal thickening and top-to-the-south sense of shear. D2 is associated with crustal thinning and top-to-the-north sense of shear. D2 can be correlated with the major normal fault the Southern Tibetan Detachment(STD) that lies along the northern margin of the Himalayas. The spatial association between the granites and the deformation and metamorphism suggests these features are all related.Age of the Domes The metamorphic domes are generally thought to be 20-10 Ma. In contrast, the central granites are considered to be around 500 Ma and unrelated to the Himalayan orogeny. This preconception has prevented consideration of models that link granite intrusion with the deformation and metamorphism of the domes. However, in the Malashan dome we show the granitic core formed around 18 Ma. This granite, therefore, intruded during the Himalayan orogen. The large number of similarities between the domes suggests that all of them contain similar young granites at their cores. Our proposal means that it is now possible to examine models that link granite intrusion with the formation of the domes.Dome Formation and Himalayan Tectonics We suggest the domes formed directly as a result of intrusion of granitic magma. Associated contact metamorphism produced the concentric metamorphic zones around the central grantie bodies. In addition, the thermal weakening of the rocks caused a change from crustal thickening during D1 to crustal thinning related to D2. The driving force for the extensional deformation in a compressive tectonic setting is the generated by the action of gravity on the surface slope of the Himalayan front. Less