湖南白马山复式花岗岩基年代学及对区域构造变形时间的约束

雪峰山东麓新元古界-中生界发育有南北向、近东西向、北东-北北东向三组褶皱,它们是华南古生代以来多期构造变形的产物,其形成时代是讨论江南古陆属性的重要依据。白马山复式花岗岩基侵入到这几组褶皱之中,成为限定这三期褶皱时代的重要地质体。岩基中最老的水车超单元花岗岩至少在411 Ma就已侵位并至少延续到381 Ma。该期岩浆侵入到南北向褶皱核部,结合卷入褶皱的最新地层,确定南北向褶皱形成于中志留-晚志留世。北东-北北东向褶皱为晚三叠世岩浆直接侵入,其形成至少在200 Ma之前,结合前人资料,北东-北北东向褶皱形成于晚三叠世。近东西向褶皱被北东-北北东向褶皱和断裂叠加或切割,卷入褶皱的最新地层为下三叠统,该方向褶皱形成时代为中三叠世。近南北向褶皱代表了早古生代末的广西运动,近东西向和北东-北北东向褶皱均形成于印支运动,是扬子地块与华夏地块在三叠纪顺时针旋转过程中不同阶段相互作用的结果。华南内陆的变形受控于板块边缘构造作用影响。

Geochronology of Baimashan Granitic Composite Batholith of Hunan Province and Its Constraints on the Timing of Regional Deformation

Three groups of folds: NS-trending fold, EW-trending fold, NE-NNE-trending fold to the east of Xuefeng Shan, are the direct products of multi-phase tectonic deformation since the Paleozoic in South China. Their ages are important constraints on the attribute of Jiangnan Old Land. Baimashan composite granitic batholith intrusing the above three groups of folds is an important geological unit to determine the timing of the three tectonic events. Granite of the Shuiche super-unit intruded before 411Ma at latest and lasted till 381Ma. This magma intruded into the core of the NS-trending folds. Given the youngest strata deformed in the NS-trending folds, we think that the NS-trending fold occurred during the Middle to Late Silurian. Late Triassic magma intruded into the NE-NNE-trending folds before 200Ma. Based on previous research results, we suggest that the NE-NNE-trending folds formed in the Late Triassic. The EW-trending folds were transformed or cut by the NE-NNE-trending folds and related faults. The timing of NE-NNE-trending fold is the Middle Triassic because the youngest strata (the Late Triassic) were deformed into the folds. The NS-trending folds developed in the Guangxi Orogeny during the end of the Early Palaeozoic. The EW-trending folds and the NNE-trending folds both resulted from the Indosinan Orogeny, which represents the interaction between the Yangtze and Cathaysian blocks in different stages during the clockwise rotation of these jointed blocks in the Triassic. The deformation in the interior of South China was controlled by the tectonics along the plate margins in different stages.