大陆岩石圈地幔榴辉岩对克拉通演化影响的数值模拟

Eclogites have high density, and their related negative buoyancy is a key trigger for lithospheric instabilities. The felsic melt produced by partial melting of eclogites is an important material source for crustal growth and accretion. Recent studies have shown that eclogites exist both in the thickened lower crust and in the sub-continental lithosphere mantle (SCLM) under some cratonic areas. The existence of the SCLM eclogites involves two significant hot and controversial issues: (1) The genesis of the SCLM eclogites is controversial and may involve imbrication of subducted oceanic plates, and/or basic magma underplating, closely related to the origin and later modification of cratons. (2) Influences of the SCLM eclogites on the stability of cratonic lithosphere and accretion of continental crust need quantitative constraints. Thus, in this proposal, we plan to solve these two problems from the point of view of quantitative analysis via numerical modeling: (1) Models of imbrication of subducted oceanic plates and basic magma underplating will be designed respectively. These model results will be compared with the geological and geophysical characteristics of different cratons, to quantitatively explore the genesis of the SCLM eclogites in different cratons. (2) The effects of different genesis and composition of the SCLM eclogites on the stability of the cratonic lithosphere and crustal accretion will be analyzed. This study will provide new understandings of the genesis of the SCLM eclogites, the stability of the cratonic lithosphere and the evolution of the continental crust.

榴辉岩密度高，其所产生负浮力是岩石圈失稳的关键驱动因素。榴辉岩部分熔融产生的长英质熔体是地壳生长、增生的重要物质来源。近来研究表明，榴辉岩不仅在于加厚下地壳，也存在于某些克拉通大陆岩石圈地幔（SCLM）中。SCLM榴辉岩的存在涉及两个重要热点争议问题：（1）SCLM榴辉岩成因存在争议，包括俯冲大洋板片叠置和/或基性岩浆底侵，与克拉通起源和后期改造密切相关；（2）SCLM榴辉岩对克拉通岩石圈稳定性以及陆壳增生的影响亟需定量约束。因此，本研究拟从数值模拟定量分析角度来探讨这两个问题：（1）设计俯冲大洋板片叠置和基性岩浆底侵模型，将其演化结果与不同克拉通地质、地球物理实测特征作对比，定量探讨不同克拉通的SCLM榴辉岩成因。（2）分析不同成因，不同组成的SCLM榴辉岩对克拉通岩石圈稳定性和陆壳增生的不同影响。该研究将为克拉通SCLM榴辉岩成因、克拉通岩石圈稳定性、陆壳演化提供新认识。

深源捕虏体数据表明克拉通岩石圈地幔中存在一定量的榴辉岩。其成因、含量、分布以及地球动力学效应尚不明确。本项目对克拉通岩石圈地幔中的榴辉岩开展地球动力学数值模拟研究，主要对其成因、含量、分布以及地球动力学效应进行了约束，取得了一系列阶段性成果。一、确定了俯冲叠置成因的洋壳变质榴辉岩可以部分保存在克拉通岩石圈地幔内。二、约束了该方式保存的榴辉岩含量约占岩石圈地幔总体积的10%左右，与地质和地球物理观测结果一致。三、约束了该方式保存的榴辉岩主要呈现出两种分布形式，一种保持俯冲叠置状存在于岩石圈浅部，一种以离散状分布于岩石圈深部。本研究解决了克拉通岩石圈的俯冲叠置成因模型中的榴辉岩演化之谜，合理解释了榴辉岩的去向、现存状态以及克拉通岩石圈的层状构造和长期稳定性，对于早期板块构造的启动和克拉通岩石圈的形成具有重要意义。受资助期间，课题组成员在Geology、EPSL、ESR，PR发表第一作者及通讯作者论文4篇，其中包括2篇自然指数文章。并多次在国际和国内相关领域大会上做特邀报告宣传研究成果。