华北克拉通太古宙登封杂岩变基性-超基性岩成因及大地构造意义

Archean tectonic evolution and crustal growth as well as the onset of plate tectonics are frontier problems for geosciences research. The Archean Dengfeng Complex which is one of the terranes in the North China Craton and has not been largely overlapped by the Paleoproterozoic (ca. 1.9-1.8 Ga) tectonic and metamorphic event, is an ideal area to study early crustal growth and tectonic evolution of the North China Craton. Based on recently identified important field evidence of a Neoarchean accretionary complex forming in a convergent plate boundary in the Dengfeng Complex, this study focuses on studying meta-mafic and ultramafic rocks (basalt, gabbro and pyroxenite) in the Dengfeng Complex. Combined large-scale high-precision structural-petrological mapping of key geological profiles and representative outcrops, with structural analysis, tectonic facies analysis, petromineralogy, geochemistry and isotopic chronology etc, we will determine their structural deformation sequence, formation age, tectonic genesis and dynamic mechanism of tectonic juxtaposition, in order to illuminate tectonodynamics significance of formation process of the Dengfeng Complex. Conclusively, this study will provide critical geological constraints of unraveling formational tectonic evolution and mechanism of crustal growth for Archean basements of the Southern North China Craton, and provide insights into understanding several great geological problems, such as tectonic evolution and tectonodynamics mechanism of the North China Craton during late Archean.

太古宙构造演化机制、地壳生长样式和板块构造启动时间是地球科学研究的前沿和难点课题。太古宙登封杂岩是华北克拉通中部造山带少数未大面积被古元古代（约1.9-1.8Ga）构造和变质事件叠加的地体之一，为研究华北克拉通早期地壳生长和构造演化提供有力条件。本研究以申请人在登封杂岩识别出的形成于板块汇聚边缘新太古代增生杂岩野外重要证据为基础，以登封杂岩变基性-超基性岩序列（玄武岩、辉长岩和辉石岩）为重点研究对象，开展关键地质剖面和露头大比例尺高精度构造-岩石填图，结合构造解析、大地构造相分析、岩石矿物学、地球化学及同位素年代学等研究方法，厘定变基性-超基性岩构造变形序列、形成时代、大地构造成因和构造拼贴动力学机制，阐明登封杂岩形成过程的构造动力学意义，探讨华北克拉通南缘太古宙基底形成构造演化和地壳生长样式，为华北克拉通太古宙晚期大地构造演化和构造动力学机制等重大地质科学问题提供重要地质依据。

太古宙构造演化机制、地壳生长样式和板块构造启动时间是地球科学研究的前沿和难点课题。太古宙登封杂岩和林山杂岩是华北克拉通中部造山带少数未大面积被古元古代（约1.9-1.8Ga）构造和变质事件叠加的地体之一，为研究华北克拉通早期地壳生长和构造演化提供有力条件。依托本项目，申请人以登封杂岩和林山杂岩为重点研究对象，对两地区太古宙绿岩带关键露头开展了大比例尺高精度构造-岩石填图，结合构造解析、大地构造相分析、岩石矿物学、地球化学及同位素年代学等研究方法，厘定岩石类型、构造变形序列、地球化学特征、形成时代和岩石成因，提出构造拼贴动力学机制，阐明登封杂岩和林山杂岩形成过程的构造动力学意义，并进一步探讨华北克拉通南缘太古宙基底形成构造演化和地壳生长样式。. 研究结果表明，登封杂岩内存在2.55Ga MORB型辉长岩-玄武岩以及2.50Ga岛弧型“高镁玄武安山岩-富Nb玄武岩-埃达克质TTG花岗岩”两套构造岩浆组合。据此，提出登封杂岩新太古代期间记录了从初始俯冲到成熟岛弧的连续演化动力学机制，并且“热俯冲作用”可能在太古宙岛弧相关岩浆活动的产生中发挥了重要作用。此外，在位于登封杂岩西部的林山杂岩内识别出一套2.50Ga具岛弧型和MORB型双重特征的变玄武岩，提出林山杂岩可能形成于新太古代期间的弧后盆地环境。由此，我们提出华北克拉通南缘新太古代中部造山带包含至少两个洋内岛弧地体，两者被一弧后盆地岩浆带所隔开，最终由于弧-陆碰撞而最终闭合的构造旋回。项目研究成果能为华北克拉通太古宙晚期大地构造演化和构造动力学机制等重大地质科学问题提供了重要地质依据，相关成果分别发表于国际SCI重要期刊GSA Bulletin和Precambrian Research。