南海边缘海减薄陆壳成因剖析

南海中央海盆南、北两侧陆缘分布着面积较广的减薄陆壳，正确认识海盆减薄陆壳的成因是研究南海构造演化的重要一环.通过分析基于地壳伸展因子公式计算的南海地壳拉张伸展特征和解释中生代以来的陆壳隆升特征等，证实晚中生代以来至渐新世末，该区不仅发生了地壳拉张伸展作用，还发生了较长期的地壳隆升挤压作用，致使酸性侵入岩出露地表，减薄陆壳区的上地壳厚薄分布不均.始新世南海南部发育海陆过渡相和海相沉积、北部仅为陆相沉积，暗示始新世南海古地理格局是南、北陆缘具有不同沉积环境的盆地群，二者之间应该被隆起所隔.这些地质现象说明该区地壳隆升剥蚀与地壳拉张伸展活动时间有较长的重叠.南海中央海盆两侧减薄陆壳的成因不仅仅是地壳拉张伸展所致，而是拉张伸展与隆升剥蚀共同作用的结果，因此可以认为在曾经发生了地壳隆升挤压而遭受长期剥蚀的区域，如果用全地壳伸展因子的公式来估算地壳拉张伸展程度，将得出错误的结论. 

Analysis on the Formation of the Thin Continental Crust in the South China Sea

The thin continental crust in the South China Sea belonging to the margin sea is distributed at the sides of the Center basin. The correct understanding of the formation causes of the thin crust is a key link to the tectonic evolution of the South China Sea. Based on the calculation of the crust stretching factors and the interpretation of the crust uplift and erosion since Mesozoic, the formation of the thin continental crust in the South China Sea is considered to be not only by stretch and extension but also by uplift and erosion from Late-Mesozoic to End-Oligocene resulting in the exposure of acid-intrusive rocks on ground and the heterogeneous thickness of the upper crust at thin continental crust. In the South China Sea, the strata in Eocene with both land-marine transitive facies and marine facies deposited at the south margin, but only continental facies deposited at the north margin, which suggests that the basins developed at the north and south continental margins of the South China Sea were of different depositional environments with uplift zones between them. All of the geological characteristics mentioned above indicate that there was ever an occasion of overlap occurring time between the uplift event and extension event. The formation of the thin continental crust in the South China Sea was not only by stretching and extension but also by both extension and erosion. It will reach a wrong conclusion that the extension extent of thin continental crust is still calculated by the formula of the total crustal extensive factor at an area where long-time uplift and erosion once occurred.