华北克拉通太古宙混杂岩带构造和运动学分析：太古宙古俯冲带地球动力学

Archean accretionary complexes containing mélange record the opening and closing of ocean basins in the early Earth, and represent a natural laboratory to study Archean paleo-subduction system dynamics. The North China Craton contains several belts of Neoarchean mélange in accretionary complexes that separate an Archean arc sequence in the Central Orogenic Belt from the Eastern Block, offering a unique opportunity to document 1) the location and nature of an Archean suture, 2) the dynamic, structural, and thermal processes in an Archean paleo-subduction zone. We propose to complete comprehensive research on a recently identified Neoarchean mélange belt in the Zanhuang massif, and its possible correlatives in the Zunhua Structural Belt. Detailed structural analysis based on field mapping and lab measurements will be done to analyize the complex relationships between the different units in the mélange and bounding tectonic blocks, including assessment of the kinematics and ages of shear zones, sequence of structural and metamorphic fabric development, and PT-time conditions of different deformation events. The relative timing of fabric development in the mélanges and late cross-cutting plutons and dikes will be determined by dating cross-cutting igneous rocks, datable metamorphic minerals, and metamorphic overgrowths on zircons, and used to place constraints on the age of the mélanges.We will investigate the origin and age of different units and exotic mafic-ultramafic blocks using geochronology and existing geochemical data. This will result in a better understanding of the tectonic evolution of this ancient melange-bearing accretionary complex and an assessment of different tectonic models for the evolution of the North China Craton. Further, our quantitative results will be used to place constraints on Archean paleo-subduction dynamics using numerical modeling, giving our results global geodynamic significance with important implications for the dynamics of Archean paleo-subduction systems in general.

太古宙增生杂岩记录着古洋盆闭合，是研究太古宙古俯冲带地球动力学的天然实验室。华北克拉通中部造山带内增生杂岩带中保留数条新太古代混杂岩带，将中部造山带内的太古宙岛弧序列与东部陆块分隔开，为研究太古宙古缝合带位置、性质及古俯冲带的动力学和热构造演化过程提供有利条件。拟综合研究申请人在中部造山带赞皇地块中新近识别出的新太古代混杂岩带及其北部遵化构造杂岩带中与该混杂岩带可能相关地质构造单元，以检验两者是否与同期古俯冲带相关。结合野外详细构造解析和室内多学科分析，确定混杂岩带内不同岩石构造单元和外来构造岩块之间的复杂构造成因关系，如剪切带运动学和时代、构造变形序列和变质组构期次及不同变质变形事件P-T-t条件，最终限定混杂岩带形成背景和时代。同时，基于所获定量数据设定华北克拉通古俯冲带地球动力学数值模拟的边界条件，该研究将对华北克拉通早前寒武纪构造演化和全球太古宙古俯冲系统动力学研究提供重要参考。

华北克拉通作为中国最古老的克拉通之一，其碰撞模式、板块汇聚时间和俯冲极性等问题一直存在争议。混杂岩、增生杂岩和蛇绿岩等可经常用来作为显生宙板块构造边界（缝合带）的标志，但在太古代造山带中很少被识别。项目以华北中部造山带赞皇地块中新近识别出的新太古代混杂岩带及其北部遵化构造杂岩带为切入点，结合野外详细构造解析和室内多学科分析，确定混杂岩带内不同岩石构造单元和外来构造岩块之间的复杂构造成因关系，如剪切带运动学和时代、构造变形序列和变质组构期次及不同变质变形事件P-T-t条件，最终限定混杂岩带形成背景和时代。在赞皇混杂岩的工作基础上，进一步向南北拓展到新太古代登封杂岩和建平杂岩，通过构造填图、构造解析、地球化学、年代学等多学科多尺度综合研究，厘定这些变质杂岩形成时代、变形变质、岩石成因和构造背景。..本项目经过四年实施，对研究课题进行了深入的研究工作，发现和厘定华北克拉通内最古老的汇聚板块边界指示标志（约25亿年的构造混杂岩和增生杂岩等），为华北晚太古代期间南北向近1600公里长的板块拼合边界提供关键地质证据，为华北克拉通基底拼合过程及板块构造样式提供了新的证据和研究思路。新太古代地体中识别出的与显生宙造山带内相似的构造样式表明板块构造启动时间不晚于新太古代。相关论文成果发表于Earth-Science Reviews（2篇）、GSA Bulletin（4篇）、Precambrian Research（5篇）、Lithos（2篇）和Geophysical Research Letters等国内外知名地学期刊。