Three-dimensional strain accumulation and partitioning in an arcuate orogenic wedge: An example from the Himalaya
Three-dimensional strain accumulation and partitioning in an arcuate orogenic wedge: An example from the Himalaya
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DOI：
10.1130/b35528.1
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发表时间：
2021-01-01
影响因子：
4.9
通讯作者：
Murphy, Michael A.
中科院分区：
文献类型：
--
作者：
Fan, Suoya;Murphy, Michael A.
在这项研究中，我们利用已发表的地质图和剖面，构建了构成喜马拉雅造山带的主要剪切带的三维地质模型。该模型结合了微震活动性、大逆冲耦合和各种地形衍生物，以解决有关观测到的地壳应变模式及其在景观中如何表达的几个问题。这些问题包括：(1)垂直增厚沿造山带走向如何变化？(2)斜辐合作用对沿走向厚度变化和变形类型有何影响？(3)逆冲构造耦合变化对上覆构造样式有何影响？(4)巨型逆冲构造是否存在侧向斜坡？(5)什么样的构造样式是形成高海拔低地势景观的基础和可能的原因？模型显示，西喜马拉雅和中喜马拉雅造山心厚度沿走向变化明显，从西喜马拉雅近似于25-26 km到中喜马拉雅近似于34-42 km。在古拉曼达塔变质核杂岩的西部边界剪切带，造山核的厚度发生了突变，表明该地区的应变样式发生了变化。压力-温度-时间结果表明，37 Ma造山心厚度为17 km。假设从东经81度到东经85度的走向是恒定的，则尼泊尔喜马拉雅山脉的西部和中部分别增厚了0.5倍和1-1.5倍。在Gurla Mandhata以西，造山心明显较薄，位于11000 km(2)的大型新近纪盆地（Zhada）之下。在尼泊尔西部的木古-多尔巴地区，与逆冲叠合作用相关的宽厚造山心与8500公里(2)的高海拔低起伏地表相匹配。我们认为这些结果可以用巨型逆冲斜向辐合来解释，这种斜向辐合具有受巨型逆冲前缘和斜斜斜坡影响的顺走向和下倾非均质耦合模式。
In this study, we use published geologic maps and cross-sections to construct a three-dimensional geologic model of major shear zones that make up the Himalayan orogenic wedge. The model incorporates microseismicity, megathrust coupling, and various derivatives of the topography to address several questions regarding observed crustal strain patterns and how they are expressed in the landscape. These questions include: (1) How does vertical thickening vary along strike of the orogen? (2) What is the role of oblique convergence in contributing to along-strike thickness variations and the style of deformation? (3) How do variations in the coupling along the megathrust affect the overlying structural style? (4) Do lateral ramps exist along the megathrust? (5) What structural styles underlie and are possibly responsible for the generation of high-elevation, low-relief landscapes? Our model shows that the orogenic core of the western and central Himalaya displays significant along-strike variation in its thickness, from similar to 25-26 km in the western Himalaya to similar to 34-42 km in the central Himalaya. The thickness of the orogenic core changes abruptly across the western bounding shear zone of the Gurla Mandhata metamorphic core complex, demonstrating a change in the style of strain there. Pressuretemperature-time results indicate that the thickness of the orogenic core at 37 Ma is 17 km. Assuming this is constant along strike from 81 degrees E to 85 degrees E indicates that, the western and central Nepal Himalaya have been thickened by 0.5 and 1-1.5 times, respectively. West of Gurla Mandhata the orogenic core is significantly thinner and underlies a large 11,000 km(2) Neogene basin (Zhada). A broad, thick orogenic core associated with thrust duplexing is collocated with an 8500 km(2) high-elevation, low-relief surface in the Mugu-Dolpa region of west Nepal. We propose that these results can be explained by oblique convergence along a megathrust with an along-strike and down-dip heterogeneous coupling pattern influenced by frontal and oblique ramps along the megathrust.