地幔不均一性与地幔循环的多维表征和原因思考

Multidimensional characterization and causes of mantle heterogeneity and mantle cycle

地幔早先经核-幔-壳分异形成,后受不同尺度对流和循环的影响,因而具有不均一性特征。近三十年来,地幔化学通过研究大洋玄武岩发现了多样地幔端元和非放射性同位素证据并证明了地幔不均一性,逐渐建全了地幔地球化学体系。然而,地幔不均一性如何对应于时空尺度的地幔循环,以及地球演化如何影响地幔不均一性等,仍不清楚。此外,地球物理研究显示,岩石圈厚度差异、中下地幔的波速异常体以及俯冲板片形态的观测为纵横向对流系统提供了空间不均一性证据支持。联合地球化学和地球物理手段对研究地幔不均一性至关重要,用好透视地幔成分与结构的“双目镜”已成为共识。本文从地幔不均一性结合地球化学场、地球物理的不同表现形式,以及现今及历史时期的洋陆格局的对比,多维度联系地幔循环和演化,思考了超大陆旋回与地幔不均一化的内在逻辑。强调了从全球演化角度看地幔不均一性的重要性和提出多手段联合建立地幔循环驱动模型的展望。

The mantle experienced core-mantle-crust differentiation in its early stages,followed by convection circulation at various scales,resulting in mantle heterogeneity.Overthe past three decades,the study of oceanic basalt has gradually established a comprehensive geochemical system of the mantle,revealing the presence of various mantle end members and non-radioactive isotopic evidence,confirmingthe existence of mantle heterogeneity.However,the relationship between mantle heterogeneity and mantle cycling in terms of time and space scales remains unclear,as well as the evolutionary history and laws governing mantle heterogeneity.Geophysical studies have provided evidence for the spatial heterogeneity of the traversal convective system through observations of differences in thickness of the upper mantle lithosphere between the ocean and the continent,velocity anomalies in the middle and lower mantle,and the morphology of subduction plates.The combination of geochemical and geophysical methods is crucial for studying mantle heterogeneity,and it has been widely accepted to use this “binocular” approach to better understand the composition and structure of the mantle.This paper considers the internal logic of the superficial supercontinent cycle and mantle heterogeneity by integrating different manifestations of the geochemical field and geophysics,and contrasting oceanic and continental patterns in both present and historical periods.The significance of mantle heterogeneity in the context of global evolution is emphasized,and the potential for establishing amantle cycle driving model through multiple approaches is proposed.