Overview of the crustal and upper-mantle structures of the Mongolian Plateau

doi:10.13745/j.esf.sf.2023.4.30

Abstract

Abstract:

Geophysical survey and comprehensive geological analysis show that the crustal structure of the Mongolian Plateau is mainly formed under the effects of terrane amalgamation and closures of the Paleo-Asian and Mongolia-Okhotsk Oceans. Among them, the closure of the Paleo-Asian Ocean affected mainly the west and south of the Mongolian Plateau, causing the crustal uplift in the Altai collisional orogenic belt and the subsidence of the Ubuds-Bayanhonggol crust, and affecting the secondary uplift of the Hangai Mountain massif. In the east of the Mongolian Plateau, there was no strong collision at the closing of the ancient Mongolia-Okhotski Ocean in the Mesozoic Era, and the upper and lower Amur massifs and the Xilinhot land block completely merged together into one land block. This type of terrane amalgamation indicated slow land-to-land subduction played a major role. Of course, slow land-land subduction might also cause numerous crustal deformation and magma intrusions leading to continental accretion. The closure of the Mongolian-Okhotsk Ocean did not result in obvious shortening and thickening of the Earth’s crust, but large-scale mantle source magma intrusions occurred, which caused the crust to melt and the crystalline bedrock to cratonize rapidly. In the upper mantle beneath Mongolia, there are residual traces of a plume reflecting the thermal fluid upwelling to the uppermost mantle.

Key words: continental dynamics, Mongolia Plateau, terrane amalgamation, crust structure, continental accretion

CLC Number:

P542

YANG Wencai, CHEN Zhaoxi, SHI Zhanjie. Overview of the crustal and upper-mantle structures of the Mongolian Plateau[J]. Earth Science Frontiers, 2023, 30(4): 218-228.

Figures/Tables 7

Fig.1 (a) Simplified geological map and (b) tectonic units (modified after [1]) of the Mongolia Plateau

Fig.2 Reconstructed paleomaps showing terrane distributions along the Central Asian Orogenic Belt in the Devonian (a), Early Carboniterous (b), Jurassic (c) and Cretaceous (d). a modified from [3]; c-d modified from [18]. AMR—Amur; MON—Mongolia; KAZ—Kazakhstan; SIB—Siberia; TM—Tarim; NCB—North China; SCB—South China; INC—Indochina; SH—South China Sea; EUP—Europe.

Fig.3 (a) Deep seismic reflection profile across Western Siberia-Northern Mongolia (modified from [16]), (b) surface Bouguer gravity anomaly map of Mongolia, and (c) model of crustal evolution of the Xilinhot block (modified from [20]).

Fig.4 (a) Geomagnetic anomaly map of Central Asia and (b) surface Bouguer gravity anomaly map of Mongolia

Fig.5 Regional Bouguer gravity anomaly maps using gravity filtering by wavelet transformation. (a) Shallow crust; (b) Deep upper crust; (c) middle crust; (d) lower crust.

Fig.6 (a) Tectonic setting of Mongolia and (b, c) geological sections along transect lines TW and TE (after [9]). Location of transect lines see Fig.6a.

Fig.7 Seismic S-wave velocity maps of Central Asia at 50°N (a) and 110°E (b). Modified from [26].

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