华南中生代构造演化过程的多地质要素约束——湘东南及湘粤赣边区中生代地质研究的启示

MULTIPLE GEOLOGICAL ELEMENTS CONSTRAINT ON THE MESOZOIC TECTONIC EVOLUTION OF SOUTH CHINA: APOCALYPSE OF THE MESOZOIC GEOLOGICAL EVOLUTION IN SOUTHEASTERN HUNAN AND THE HUNAN-GUANGDONG-JIANGXI BORDER AREA

目前对华南内陆中生代构造环境与演化过程的认识存在分歧,一定程度上与对多种地质要素的综合研究不够有关。笔者研究认识到湘东南及湘粤赣边区中生代不同构造阶段发育不同的代表性地质要素,并分别指示不同的构造环境。早三叠世-中三叠世早期为前造山阶段,主要发育海相沉积。中三叠世后期-中侏罗世初为陆内造山阶段,其中中三叠世后期发生强烈陆内汇聚挤压,形成的主要地质要素是NNE向的逆冲断裂与褶皱,以及NW向的基底走滑断裂等;中三叠世末-晚三叠世后期为同造山阶段的后碰撞构造环境,形成的主要地质要素是印支期强过铝花岗岩;晚三叠世末-早侏罗世为同造山上隆伸展环境,形成的主要地质要素是裂陷盆地与拉斑玄武岩;中侏罗世初期为挤压环境,形成的主要地质要素是山前冲断收缩盆地及盆地边缘的逆冲断裂。中侏罗世早期-晚侏罗世为后造山阶段,形成的主要地质要素是大量后造山花岗岩以及与花岗岩相关的大量有色金属矿床。白垩纪为陆内裂谷阶段,形成的代表性地质要素有AA型花岗岩、大量陆相红色断陷盆地、基性火山岩、双峰式次火山岩等。结合上述成果和区域资料,提出应通过多种地质要素综合研究华南地区中生代构造演化过程,注意构造环境判别的地质要素代表性、地质要素时限性以及构造发展过程的关联性。

There are recognizant divergences on the Mesozoic tectonic evolution of south China, which is to a certain extent related to inadequacy of integrated study on multiple geological elements. The authors have recognized that there were different representative geological elements at different Mesozoic tectonic stages in Southeastern Hunan and the border area among Hunan, Guangdong and Jiangxi provinces. The different geological elements suggest different tectonic environment settings. The Early Triassic to the early episode of Middle Triassic is the pre-orogenic stage for occurrence of marine deposits mainly. The late episode of Middle Triassic to the early stage of Middle Jurassic is the intracontinental orogenic stage, which can be further divided into four sub-stages listed as follows： the late episode of Middle Triassic is a peak stage for intracontinental subduction - convergence characterized mainly by a great number of NNE-trending thrusts and folds and NW-trending basement strike-slip faults. A post-collisional tectonic setting exists corresponding to the syn-orogenic stage in the late episode of Middle Triassic-latest Triassic, which is characterized mainly by occurrence of Indosinian highly peraluminous granitoids; A syn-orogenic uplift-extensional tectonic setting occurs in the late episode of Late Triassic-Early Jurassic, which is characterized mainly by down-faulted basins and tholeiite; A compressional tectonic setting occurs in the early episode of Middle Jurassic, which is characterized mainly by occurrence of piedmont thrust-compressional basins and thrusts at basinal margin. The early episode of Middle Jurassic-Late Jurassic is a post-orogenic stage, which is characterized mainly by occurrence of voluminous post-oregenic granite and nonferrous metallic mineral deposits related to granite. The Cretaceous is an intraplate-rifting stage, characterized by representative geological elements such as AA-type granite, red down-faulted basins, bimodal subvolcanic rocks and basic volcanic rocks. Based on these achievements and regional geological study results, the authors hold that the Mesozoic tectonic evolution of South China should be studied in terms of multiple geological elements, and particular attention shall be paid to whether the geological elements for discrimination of structural environment are representative in terms of time limits for geological elements and conjunction of tectonic evolution events.