闽西北罗古延岩体侵位机制的构造约束及意义

In recent years, a large number of Triassic A-type granites have been discovered in the eastern Cathaysia Block, indicating that the eastern Cathaysia Block may have experienced a special dynamic process in the Indosinian intracontinental orogenic background. Previous studies have focused on the study of granite formation age, rock type and source composition from the chronology and geochemistry, and neglected the study of granite structure and emplacement mechanism. The granites structure and emplacement mechanism are both a record of the magma emplacement process and a response to the regional tectonic processes. The study of granite emplacement mechanism can provide regional tectonic dynamics information. To this end, based on the analysis of the deformation, magmatic fabric and magnetic fabric of the Luoguyan granite body and surrounding rock in northwest Fujian, the project studies the process of magma migration and place, reveals the influence of the regional tectonic in the process of granite emplacement, and determine the regional structural properties of granite to understand the deep dynamic process of the eastern Cathaysia Block in the Triassic period.

近年来，华夏地块东部印支期陆内造山背景下发现了大量的A型花岗岩，预示该地区深部可能经历了特殊的动力学过程。前人的研究多侧重从年代学和地球化学角度对花岗岩的形成时代、岩石类型、源区组成等开展研究，相对忽视了花岗岩构造和岩体侵位机制的研究。花岗岩的变形和侵位，能够揭示造山演化的动力学信息，对花岗岩的显微构造和岩石组构特征进行研究，可以揭示花岗岩侵位的动力学机制。本项目以闽西北武夷山罗古延花岗岩体为对象，通过对围岩及岩体中的变形、岩石组构和磁组构的研究，恢复岩浆运移、就位的过程，揭示花岗岩侵位过程中受到的区域构造动力的影响，明确花岗岩的区域构造属性，深入理解三叠纪时期华夏地块东部深部动力学过程。

华南东部早中生代由何时从挤压向伸展转变存在分歧。本项目拟通过对闽西北罗古延岩体的年代学、地球化学及岩体及围岩的构造及侵位机制的综合分析，试图从岩体侵位的角度提供关键证据。研究表明，罗古延岩体的锆石U-Pb年龄为221±5Ma，地球化学特征显示其具有过铝质A型花岗岩的特征，岩体侵位到前寒武基底变质岩中，但岩体本身不发育变形组构，磁组构分析显示岩体受到一组NW-SE方向的最大主应力影响，通过对围岩韧性剪切的分析，指示围岩发育两期变形，D2期面理上发育缓倾的拉伸线理指示为NE向SW的走滑型剪切；变形岩石的石英C轴组构均表现为简单的点极密、 环带极密以及点极密和环带极密叠加，指示变形温度在350℃-550℃之间，D2变形黑云母40Ar/39Ar坪年龄为228.3Ma±1.5Ma，指示区域上在中三叠纪又发生了一次显著的构造热活动。综合研究表明，华南东部晚三叠世的铝质A型花岗岩可能形成在区域挤压应力背景下，这表明，形成在后造山背景下的铝质A型花岗岩可能也会受到区域挤压应力的持续影响。