蒙古高原的地壳和上地幔构造概况

doi:10.13745/j.esf.sf.2023.4.30

摘要/Abstract

摘要：

地球物理调查和地质资料的综合分析表明,现今蒙古高原的地壳构造主要是由于古亚洲洋和蒙古-鄂霍茨克洋两次大洋闭合和拼合造山作用形成的。其中古亚洲洋闭合作用主要发生在蒙古高原的西部和南部,造成阿尔泰碰撞造山带地壳隆升、乌布斯-巴彦洪戈尔地壳沉降,也牵连到杭爱山地块发生次级的地壳隆升。蒙古高原的东部,中生代古蒙-鄂洋封闭时没有发生强烈的碰撞,上、下阿穆尔地体和锡林浩特地体就完全拼合成陆地。这种类型的拼合造山,速度缓慢的陆-陆俯冲起主要作用。当然,速度缓慢的陆-陆俯冲作用同样会造成众多的地壳变形和岩浆侵入,使大陆增生。蒙-鄂洋的闭合没有发生明显的地壳缩短加厚,而是发生大规模幔源岩浆侵入,使地壳熔解和结晶基底快速克拉通化。在蒙古下方的上地幔,有反映上地幔羽毛状热流体上涌的痕迹残留。

关键词: 大陆动力学, 蒙古高原, 拼合造山, 地壳构造, 大陆增生

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

中图分类号:

P542

杨文采, 陈召曦, 石战结. 蒙古高原的地壳和上地幔构造概况[J]. 地学前缘, 2023, 30(4): 218-228.

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.

图/表 7

图1 蒙古高原地质略图(a)及蒙古高原大地构造略图(b) (图1(b)据文献[1]修改)

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

图2 根据古地磁资料恢复的中亚造山带演化图(图2(a)据文献[3]修改,图2(c,d)据文献[18]修改) (a)—泥盆纪北亚大陆块分布;(b)—石炭纪北亚大洋分布;(c)—中侏罗世北亚大陆块分布;(d)—早白垩世北亚大陆块分布。古亚洲洋构造域地体符号:AMR—阿穆尔;MON—蒙古,包括AMR 和后加拼合带;SIB—西伯利亚;TM—塔里木;NCB—中国华北;SCB—中国华南;INC—印支;SH—南海—苏拉威西;EUR—欧洲;KAZ—哈萨克斯坦。

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.

图3 蒙古高原地区地球物理资料及岩石圈演化剖面(图3(a)据文献[16]修改,图3(c)据文献[20]修改) (a)—从西伯利亚西部到蒙古国北部的深反射地震剖面;(b)—地面布格重力异常图;(c)—从华北北部到蒙古国南部的晚古生代岩石圈演化剖面。

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]).

图4 中亚地区卫星地磁异常图(a)及地面布格重力异常图(b)

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

图5 蒙古高原布格重力场小波细节系列图 (a)—小波细节D3,对应上地壳浅部,等效层中心深度5 km;(b)—小波细节D4对应上地壳深部,等效层中心深度11 km;(c)—小波细节D5,对应中地壳,等效层中心深度19 km;(d)—小波细节D6,对应下地壳,等效层中心深度38 km。

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.

图6 蒙古大地构造背景及地学断面切片图 (图6(b,c)引自文献[9]) (a)—蒙古大地构造背景图,TW、TE分别标识两条地学断面位置;(b)—西线地学断面TW;(c)—东线地学断面TE。

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.

图7 过50°N的地震S波速扰动剖面图(a)及过110°E的地震S波速扰动剖面图(b) (图7据文献[26]修改)

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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