Megathrust Heterogeneity, Crustal Accretion, and a Topographic Embayment in the Western Nepal Himalaya: Insights From the Inversion of Thermochronological Data
Megathrust Heterogeneity, Crustal Accretion, and a Topographic Embayment in the Western Nepal Himalaya: Insights From the Inversion of Thermochronological Data
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DOI：
10.1029/2021tc007071
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发表时间：
2021-09
期刊：
影响因子：
4.2
通讯作者：
Suoya Fan;M. Murphy;D. Whipp;J. Saylor;P. Copeland;A. K. Hoxey;M. Taylor;D. Stockli
中科院分区：
文献类型：
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作者：
Suoya Fan;M. Murphy;D. Whipp;J. Saylor;P. Copeland;A. K. Hoxey;M. Taylor;D. Stockli
在东经81°30至83°之间，喜马拉雅山脉的“完美”弧形被一个海湾打断。我们假设，逆冲断层的几何形状和沿沿着巨型逆冲断层在中下地壳深度发挥主导作用的海湾以及青藏高原南缘的增长。为了验证这一假设，我们对尼泊尔喜马拉雅西部地形和构造海湾的已发表热年代学数据进行了热运动学建模，以研究中下地壳深度巨型逆冲断层的三维几何形状和运动学。能够最好地再现观测到的冷却年龄的模型表明，尼泊尔喜马拉雅山西部的大型逆冲断层最好被描述为由一条长平地连接的两个坡道，该平地向北延伸，而不是向东和向西延伸。这些模型表明，高斜坡带沿着海湾位于逆冲断层上的反形式地壳增生带的前陆边缘上方，在中下地壳深度有横向和斜向斜坡。侧向和倾斜斜坡可能是由大约。十马。这一过程可能控制了喜马拉雅高原生长的沿着走向变化，从而控制了地形海湾的发展。最后，我们分析了地质和形态特征，并提出了一个演化模型，在该模型中，喜马拉雅中西部的景观和排水系统响应于深部地壳增生和大型逆冲断层的三维几何形状而演化。我们的工作突出了地壳增生在造山楔生长中的重要性，中低地壳增生决定了高原边缘的位置。
Between 81°30ʹE and 83°E, the Himalayan range's “perfect” arcuate shape is interrupted by an embayment. We hypothesize that thrust geometry and duplexing along the megathrust at midlower‐crustal depths play a leading role in growth of the embayment as well the southern margin of the Tibetan plateau. To test this hypothesis, we conducted thermokinematic modeling of published thermochronologic data from the topographic and structural embayment in the western Nepal Himalaya to investigate the three‐dimensional geometry and kinematics of the megathrust at midlower‐crustal depths. Models that can best reproduce observed cooling ages suggest that the megathrust in the western Nepal Himalaya is best described as two ramps connected by a long flat that extends further north than in segments to the east and west. These models suggest that the high‐slope zone along the embayment lies above the foreland limb of an antiformal crustal accretion zone on the megathrust with lateral and oblique ramps at midlower‐crustal depths. The lateral and oblique ramps may have initiated by ca. 10 Ma. This process may have controlled along‐strike variation in Himalayan‐plateau growth and therefore development of the topographic embayment. Finally, we analyze geological and morphologic features and propose an evolution model in which landscape and drainage systems across the central‐western Himalaya evolve in response to crustal accretion at depth and the three‐dimensional geometry of the megathrust. Our work highlights the importance of crustal accretion at different depths in orogenic‐wedge growth and that the midlower crustal accretion determines the location of plateau edge.