Internal Drainage Has Sustained Low-Relief Tibetan Landscapes Since the Early Miocene
Internal Drainage Has Sustained Low-Relief Tibetan Landscapes Since the Early Miocene
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自中新世早期以来，内部排水一直维持着低地势的西藏景观
DOI：
10.1029/2019gl083019
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发表时间：
2019-08-16
影响因子：
5.2
通讯作者：
Cao, Shuo
中科院分区：
文献类型：
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作者：
Han, Zhongpeng;Sinclair, Hugh D.;Cao, Shuo
青藏高原低坡度、内部排水地貌的形成时间，是了解整个高原演化的基础。利用河流入湖内部排泄的沉积记录揭示了这一演化的时间。在这里，我们重新测定了西藏中部伦波拉盆地最年轻的大陆沉积序列，并提出了大约35-9 Ma的新年龄范围，比之前认为的要年轻得多。我们证明了西藏中部自晚始新世以来长期存在的内部排泄，以及至少自早中新世以来稳定的沉积环境、物源区和低地形起伏。我们认为，内部排水的泥沙堆积和侵蚀导致的坡度降低是低起伏景观形成的主导因素，西藏中部晚新生代流域盆地的形成是对下地壳和(或)地幔岩石圈流动的响应。内部排水为藏族河流创造了当地栖息的基准面，使地貌与喜马拉雅山及其周边地区迅速切割的河流隔离开来。然而，低起伏高原地貌的形成时间问题在很大程度上被忽视了，其形成机制也存在争议。本文报道了西藏中部伦波拉盆地的详细调查，并提出了约35-9 Ma的新的沉积年龄范围。我们证明，至少自始新世晚期以来，内部排水一直在侵蚀山脉并填满周围的低地。不晚于中新世早期，西藏中部形成了一片平缓的地貌。西藏中部晚新生代盆地发育于深部地壳或地幔流动及其伴生的上地壳变形。
The timing of formation of the low-gradient, internally drained landscape of the Tibetan Plateau is fundamental to understanding the evolution of the plateau as a whole. Well-dated sedimentary records of internal drainage of rivers into lakes are used to reveal the timing of this evolution. Here we redate the youngest continental sedimentary successions of central Tibet in the Lunpola Basin and propose a new age range of ca. 35 to 9 Ma, significantly younger than previously thought. We demonstrate long-standing internal drainage in central Tibet since the late Eocene and stable sedimentary environments, source regions, and low topographic relief since at least the early Miocene. We suggest that sediment aggradation of internal drainage and reduction of hillslope gradients by erosion dominate the formation of low-relief landscapes and that the late Cenozoic drainage basins in central Tibet developed in response to flow in the lower crust and/or mantle lithosphere.Plain Language Summary: Internal drainage of rivers into lakes is a characteristic of the high plateaus of the world and, most notably, the Tibetan Plateau. Internal drainage generates local perched base levels for Tibetan rivers, enabling geomorphic isolation from the rapidly incising rivers of the Himalaya and surrounding regions. However, the question of when the low-relief plateau topography was initiated has been largely ignored, and its formation mechanism is controversial. Here we report a detailed investigation in the Lunpola Basin of central Tibet and propose a new depositional age range of ca. 35-9 Ma. We demonstrate that the internal drainage kept eroding the mountain ranges and filling the surrounding lowlands since at least the late Eocene. By no later than the early Miocene, a gentle landscape formed in central Tibet. The late Cenozoic basins in central Tibet developed in response to deep crustal or mantle flow and associated upper crustal deformation.