Eocene Metamorphism and Anatexis in the Kathmandu Klippe, Central Nepal: Implications for Early Crustal Thickening and Initial Rise of the Himalaya
Eocene Metamorphism and Anatexis in the Kathmandu Klippe, Central Nepal: Implications for Early Crustal Thickening and Initial Rise of the Himalaya
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DOI：
10.1029/2020tc006532
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发表时间：
2021-03
期刊：
影响因子：
4.2
通讯作者：
G. Khanal;Jia-Min Wang;K. Larson;Fu-Yuan Wu;S. M. Rai;Jian‐Gang Wang;Lei Yang
中科院分区：
文献类型：
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作者：
G. Khanal;Jia-Min Wang;K. Larson;Fu-Yuan Wu;S. M. Rai;Jian‐Gang Wang;Lei Yang
早始新世以来，印度和亚洲之间的大陆碰撞一直在进行，但造山记录主要是中新世和更年轻的变形和变质作用，这些变形和变质作用很大程度上重叠了早始新世-渐新世的事件。这阻碍了我们理解地壳增厚是如何对最初的碰撞做出反应的，以及喜马拉雅山脉最初是什么时候上升的。然而，空间精确岩石年代学技术的进步，提供了穿透中新世叠印的手段，并使喜马拉雅不同地区始新世变质作用的表征成为可能。目前的研究提出了尼泊尔喜马拉雅中部加德满都klippe的新的独居石岩石年代学和配对热气压计。这些数据表明始新世的进阶变质作用（44 ~ 38 Ma）和部分熔融作用（38 ~ 35 Ma）发生在峰值P - T条件下，温度为730℃~ 760℃，最高温度为10.5 kbar。加德满都断裂带内的混合岩相当于上或上喜马拉雅结晶岩，应该是在始新世-渐新世期间发掘的。本文提出的始新世变质作用和深熔作用的新证据，增加了详细描述早期大陆碰撞期间初始地壳增厚的数据体。中始新世地壳增厚事件表明，在初始碰撞的10-20 Myr内，喜马拉雅长英地壳增厚至~ 35 km的深度，这可能是喜马拉雅原始山脉初始地形上升的原因。描述这种早期造山带的影响，对于理解保存较好的中新世变质作用和深溶作用记录之前的喜马拉雅构造，以及造山带如何为更年轻阶段做好准备，至关重要。
The continental collision between India and Asia has been ongoing since early Eocene time, but the orogenic record is typically dominated by Miocene and younger deformation and metamorphism that largely overprinted earlier Eocene‐Oligocene events. This hinders our understanding of how crustal thickening responds to initial collision and when the Himalayan mountains initially rise. The advancement of spatially precise petrochronology techniques, however, has provided the means to see through the Miocene overprint and enabled the characterization of Eocene metamorphism in different parts of the Himalaya. The current study presents new monazite petrochronology and paired thermobarometry from the Kathmandu klippe in the central Nepalese Himalaya. These data reveal Eocene prograde metamorphism (44‐38 Ma) and partial melting (38‐35 Ma) under peak P‐T conditions of 730 °C–760 °C and up to 10.5 kbar. The migmatites within the Kathmandu klippe is equivalent to the Upper or Uppermost Greater Himalayan Crystallines and should have been exhumed during Eocene‐Oligocene. The new evidence of Eocene metamorphism and anatexis presented herein adds to a growing body of data detailing initial crustal thickening during the early continent collision. The mid‐Eocene crustal thickening event indicates that the Himalayan felsic crust was thickened to a depth of ∼35 km shortly within 10–20 Myr of the initial collision, which was probably responsible for the initial topographic rise of the Himalayan proto‐mountains. Characterizing the effects of this early orogenesis is critical in understanding the Himalayan architecture prior to the better‐preserved Miocene metamorphism and anatexis record and how the orogen may have been preconditioned for the younger stage.