华南早中生代板内沉积-构造特征及其对邻区碰撞事件的响应

EARLY MESOZOIC INTRA-PLATE TECTONIC FEATURES OF SOUTH CHINA AND ITS RESPONSE TO COLLISION WITH EVENT OF NEIGHBORING AREAS

对华南晚古生代—早中生代地层层序及其岩石组合、早中生代花岗岩特征、构造变形样式等进行了研究,以解决对华南晚古生代—早中生代的地质环境和早中生代构造变形属性一直存在的不同认识。研究表明,发育在赣东北地区的蛇绿岩套,其时代不是晚古生代—早中生代,而是新元古代;新元古代洋壳沉积岩中不存在放射虫,而发育较多的新元古代疑源类。沉积学分析表明,晚古生代—早中生代期间华南为一个向南东倾斜的滨海—浅海沉积环境,广泛发育碳酸盐岩石组合、含放射虫等生物碎屑灰岩、含煤层砂岩和浅海相生物群落,未见同期大规模火山岩分布。早—中三叠世,华南块体发生强烈构造变形和花岗岩浆活动,以朝北西方向运移的褶皱和逆冲推覆为特征,花岗质岩体形成时代集中在245～210Ma,属过铝质花岗岩,不是岛弧型花岗岩。研究表明,早中生代是一个全球规模的构造—岩浆活动期,在此构造背景下,研究区北侧的扬子块体沿大别山断裂带与华北块体发生强烈碰撞,南侧的华夏块体则沿越南马江一带与印支块体碰撞拼贴。受南北两侧此时期碰撞事件的影响,研究区发生了强烈的板内构造—岩浆活动,奠定了华南的基本构造格架。

The tectonic setting of South China and the nature of structural deformation during early Meso- zoic have been debated. The late Paleozoic-early Mesozoic stratigraphic sequences and rock assemblages, syntectonic S-type granitoids and patterns of structural deformation were analyzed in this study. Results suggest that the ophiolite in northeastern Jiangxi Province was formed in the Neoproterozoic, not in the In- dosinian period as previously suggested. No radiolarian fossils have been found in the Neoproterozoi ophi- olitic rocks; in contrast, some samples yielded abundant acritarchs dating to the Neoproterozoic. Sedimen- tological analysis suggests that a SE-dipping littoral-neritic framework was developed during the late Paleo- zoic-early Mesozoic, which is characterized by radiolarian-bearing carbonate rocks, coal-bearing sandstones and neritic facies biomes, suggesting that these areas were not in a deep-sea environment. Coeval volcanic rock was rarely developed. In the early-middle Triassic, a strong tectono-magmatic event took place in South China and neighboring areas. Large-scale fold-and-thrust belt shows a top-to-the-northwest displace- ment, and the granitoids （245~210 Ma） belong to the peraluminous granites. The geodynamic settings of the different parts of the South China Block during the early Mesozoic are discussed. An accretion-colli- sion-type orogeny can be excluded from studied area; instead, intra-plate tectono-magmatism with little in- put of mantle components, as a response to collision with neighboring plates, can explain the early Meso- zoic tectonic history of South China.