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Acta Geologica Sinica 2018 No.1
clicks:243 |
Title:
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Author:
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LI Yong1 , YAN Zhaokun1, *, ZHOU Rongjun2 , YAN Liang1 , DONG Shunli1 , SHAO Chongjian1 and LAURENCE Svirchev1 |
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Abstract:
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This study examines the relationship between high positive isostatic gravity anomalies (IGA),
steep topography and lower crustal extrusion at the eastern margin of the Tibetan Plateau. IGA data has
revealed uplift and extrusion of lower crustal flow in the Longmen Shan Mountains (the LMS). Firstly,
The high positive IGA zone corresponds to the LMS orogenic belt. It is shown that abrupt changes in
IGA correspond to zones of abrupt change of topography, crustal thickness and rock density along the
LMS. Secondly, on the basis of the Airy isostasy theory, simulations and inversions of the positive IGA
were conducted using three-dimensional bodies. The results indicated that the LMS lacks a mountain
root, and that the top surface of the lower crust has been elevated by 11 km, leading to positive IGA,
tectonic load and density load. Thirdly, according to Watts’s flexural isostasy model, elastic deflection
occurs, suggesting that the limited (i.e. narrow) tectonic and density load driven by lower crustal flow in
the LMS have led to asymmetric flexural subsidence in the foreland basin and lifting of the forebulge.
Finally, based on the correspondence between zones of extremely high positive IGA and the presence of
the Precambrian Pengguan-Baoxing complexes in the LMS, the first appearance of erosion gravels from
the complexes in the Dayi Conglomerate layer of the Chengdu Basin suggest that positive IGA and lower
crustal flow in the LMS took place at 3.6 Ma or slightly earlier. |
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