岩石圈地幔分层性对克拉通稳定性的影响  

Effects of lithospheric mantle layering on craton stability

作　　者：邱启佳 陈林[2] 张智[1] 向宵 徐涛[4] 陈赟[2] 白志明[2] 梁晓峰[2] 武澄泷 QIU QiJia;CHEN Lin;ZHANG Zhi;XIANG Xiao;XU Tao;CHEN Yun;BAI ZhiMing;LIANG XiaoFeng;WU ChengLong(College of Earth Sciences,Guilin University of Technology,Guilin 541006,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]桂林理工大学地球科学学院,桂林541006 [2]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029 [3]中国科学院大学地球与行星科学学院,北京100049 [4]中国科学院地质与地球物理研究所矿产资源研究院重点实验室,北京100029

出　　处：《地球物理学报》2024年第3期916-934,I0001,共20页Chinese Journal of Geophysics

基　　金：国家自然科学基金(41974048,42374059,42104042);广西科技计划项目(2023GXNSFDA026055,桂科AD23026130)联合资助。

摘　　要：克拉通是大陆岩石圈中长期稳定存在的古老构造单元,通常被相对年轻的活动带所包围,二者之间岩石圈厚度的横向差异会诱发边界驱动地幔对流.近年来,越来越多的证据显示克拉通岩石圈地幔内部存在成分和结构的垂向分层性.在边界驱动地幔对流的环境中,岩石圈地幔分层性如何影响克拉通的稳定性仍然不清楚.本文利用二维热-力学数值模拟方法,系统探讨了在边界驱动对流作用下,克拉通岩石圈地幔密度和黏度的垂向分层性以及中岩石圈不连续面(MLD)的分布样式对克拉通稳定性的影响.模拟结果显示:(1)当克拉通岩石圈内部不存在MLD时,即使克拉通具有密度分层的岩石圈地幔,克拉通岩石圈减薄的水平范围也是有限的(<100 km),且主要发生在克拉通边缘处;(2)当克拉通岩石圈内部存在一层连续的MLD时,克拉通岩石圈减薄的水平范围随着克拉通下层岩石圈地幔密度的增加而增大,岩石圈地幔的减薄方式随着其强度的增加从缓慢丝状剥离转变为快速块状拆沉;(3)当克拉通岩石圈内部存在一层不连续分布的MLD时,分段MLD之间的间隙可以有效延缓岩石圈地幔的减薄,间隙越稀岩石圈减薄越快,反之亦然,减薄方式表现为:早期缓慢丝状剥离,中后期快速块状拆沉.华北克拉通破坏持续时间长(>100 Ma),破坏的峰期集中在早白垩世(130~120 Ma),且现今东部陆块岩石圈破坏的前缘位置与华北中部造山带下方MLD的东端对应.根据模拟结果,我们推测华北克拉通破坏的时空范围主要是由岩石圈地幔分层性和MLD不连续分布引发的岩石圈地幔逐段拆沉所导致.Cratons are long-term stable, ancient tectonic units in the continental lithosphere. They are usually surrounded by relatively young mobile zones. The lateral variation in lithospheric thickness between the two can induce edge-driven mantle convection. In recent years, increasing evidence indicates that the vertical composition and structure layering are widely found in the cratonic lithospheric mantle. How the vertical layering structure of the lithospheric mantle affects craton's stability in the context of edge-driven mantle convection remains unclear. Here, we use two-dimensional thermo-mechanical numerical simulations to systematically explore the vertical density and viscosity variations and distribution pattern of the mid-lithosphere discontinuity (MLD) in the cratonic lithospheric mantle affect craton's stability under the condition of edge-driven convection. Modeling results show that: (1) When no MLD is included in the cratonic lithospheric mantle, the horizontal extent of lithospheric thinning is limited (< 100 km), mainly occurring at the craton's edge, even if the craton has a density-layered lithospheric mantle. (2) When the cratonic lithospheric mantle has a continuous MLD layer, the horizontal extent of lithospheric thinning enlarges as the lower portion of the lithospheric mantle becomes dense. As the strength of the lower portion of the lithospheric mantle increases, the lithospheric thinning style transforms from filiform dripping to block detachment. (3) When the cratonic lithospheric mantle has a discontinuous MLD layer, we find that the gaps between two adjacent MLD segments effectively delay the speed of lithospheric thinning. The sparse the MLD gaps, the rapid the lithospheric thinning, and vice versa. In this case, the lithospheric thinning style changes from slow filiform dripping at the early stage to rapid block detachment at the later stage. The North China Craton (NCC) experienced a long-lasting process (>100 Ma) of destruction, and the peak period of destruction mainly occurred at t

关 键 词：克拉通 岩石圈地幔 边界驱动对流 数值模拟 

分 类 号：P313[天文地球—固体地球物理学] P315[天文地球—地球物理学]