地质科技通报 (Mar 2023)
Characteristics of flexural isostatic gravity anomalies in the Tibetan Plateau and its geological significances
Abstract
The Tibetan Plateau underwent rapid uplift and complex lithospheric modification during the Cenozoic under the continuing collision and subduction of the Indian Plate, but the present-day vertical dynamic motion and crustal deformation of the plateau remain controversial. This paper calculates the flexural isostatic gravity anomalies on the Tibetan Plateau and its neighboring blocks based on the flexural model with variable effective elastic thickness and using topographic data and Earth's gravity field model. The results show that the isostatic gravity anomalies on the Tibetan Plateau range from -120 to 90 mGal, with the central part characterized by distinct positive anomalies and the margins by significant negative anomalies. Minimal values occur in the northwest Tibetan Plateau and its adjacent Pamir Plateau, while maximal values occur in the northwest part of the Himalaya block. In addition, to the north and east of the Tibetan Plateau, the Tarim Basin and Sichuan Basin show large areas of positive isostatic anomalies. These features suggest that the crust of the Tibetan Plateau and its surroundings is now in a nonisostatic state, with the overall uplift of the older block under the effect of plate collision and compression, leading to positive isostatic anomalies. In younger orogenic regions, crustal deformation is primarily characterized by surface uplift and strong thickening of the lower crust, resulting in negative isostatic anomalies. In the central and northern parts of the plateau, the direction of isostatic adjustment is consistent with the trend of crustal vertical motion. However, south and east of the plateau (e.g., the Himalaya block and Sichuan Basin), the direction of isostatic adjustment is opposite to that observed for surface deformation. This suggests that the Indian Plate collision and subduction still control the crustal deformation processes in the southern and eastern parts of the Tibetan Plateau and its neighboring blocks. However, further north, the crust regains an isostatic state through isostatic adjustment.
Keywords
