华北克拉通破坏过程中岩浆作用的动力学机制

Cratons are known to be stable for billions of years, however, the North China craton (NCC) has experienced destruction since Mesozoic, making it a type example for studying the evolution of continents. Igneous rocks are direct samples that record information from deep mantle. Previous studies have shown that there is little magmatism since the cratonization of NCC. However, magmatism occurs since Mesozoic, with the Early Cretaceous magmatism widely developed. Analysis of igneous rocks reveals that the initial thick, refractory mantle lithosphere beneath the eastern NCC has been replaced by thin, fertile mantle lithosphere. Although such observations provide direct evidences for the destruction of NCC, the implications on the mechanism of craton destruction remain controversial. The key reason is that a link between geodynamic processes and corresponding magmatism is lacking. Geodynamic numerical modeling is a promising method to establish such a link. Comparing mantle temperature from numerical models and mantle solidus from laboratory data may predict whether partial melting occurs, thus building a thermo-mechanical-melting coupled model. Recent studies on igneous rocks have created a detailed database for analyzing the patterns of magmatism activity. Considering constrains from igneous rocks, thermo-mechanical-melting models are able to refine characteristic geodynamic process related to observed magmatism activities, which may help to establish a comprehensive framework of craton destruction.

克拉通是稳定的大陆，但华北克拉通却在中新生代发生了破坏，使之成为研究大陆演化的天然实验场所。岩浆岩是反映深部动力学过程的窗口。资料显示华北克拉通中生代以来开始出现明显的岩浆活动，在白垩纪岩浆活动达到高峰。对岩浆岩的分析显示华北克拉通东部已经由厚的古老难熔型岩石圈转变为薄的新生饱满型岩石圈。上述岩浆活动为克拉通破坏提供了直接证据，但对其动力学内涵还存在较大争议，根源在于岩浆活动与动力学过程之间的联系尚不明确。地球动力学数值模拟是厘定上述关联的有效手段。利用动力学模拟获取温度、压力的分布，结合地幔固相线数据，就能够计算部分熔融程度，建立动力学-部分熔融耦合模型。近年来的观测已经积累了详尽的华北地区岩浆活动资料，为深入分析岩浆活动规律创造了极佳条件。以岩浆活动资料为约束，利用动力学数值模拟系研究不同动力学过程的岩浆活动响应，将能够为深入认识华北克拉通岩浆活动的动力学意义提供基础依据。

克拉通是稳定的大陆，但华北克拉通却在中新生代发生了破坏，使之成为研究大陆演化的天然实验场所。岩浆岩是反映深部动力学过程的窗口，变质核杂岩是地表变形历史的天然记录，本项目围绕华北克拉通破坏这一科学问题，利用地球动力学数值模拟从深部岩浆和浅部变质核杂岩两个方向开展研究。首先针对幔源岩浆部分熔融问题，建立“干”、“湿”地幔条件下的部分熔融分数计算方法，计算上地幔条件下常见岩石含水量相图，完成理论方法的构建。模拟洋壳随着大洋板块俯冲脱水形成岛弧岩浆过程，发现蛇纹石化地幔可使洋壳与岩石圈地幔发生解耦，洋壳物质在海沟堆叠而出现一个缺少岩浆活动的弧后带，解释造山带的贫岩浆俯冲阶段以及蛇绿岩的就位。针对变质核杂岩问题，结合岩石弱化机制，模拟变质核杂岩低角度拆离断层的形成机制，约束变质核杂岩的形成条件，揭示克拉通破坏与岩石圈减薄的程度。最后，针对板块构造驱动力问题，提出了最初的俯冲起始需要其他俯冲板块来启动的悖论，系统梳理板块俯冲起始的机制，揭示地幔流动对板块运动不可忽视的驱动作用，解决了俯冲起始悖论，为板块构造理论添加了新的内容。