南海南、北大陆边缘盆地烃源岩热演化差异及成因分析

对横跨南海南、北共轭大陆边缘的两条骨干剖面所经过的沉积盆地烃源岩热演化进行模拟，分析了南、北陆缘盆地烃源岩热演化差异。结果表明，南海南部陆缘盆地生烃门限整体比北部陆缘盆地的生烃门限浅，南部陆缘盆地生烃门限整体在2 200~2 300 m之间，中新统烃源岩基本已进入生烃门限；北部陆缘盆地生烃门限整体位于2 500~2 600 m之间，渐新统及其以下烃源岩进入生烃门限。南海南、北陆缘盆地生烃门限的规律性与南海现今热流分布南高北低、西高东低的整体趋势相对应，高热流有利于烃源岩的成熟与生烃，因此热流值高的区域对应生烃门限较浅。造成南、北陆缘主力烃源岩的热演化程度差异的主要原因可能是由南海扩张及古南海俯冲引起的地温场变化所引起。

Thermal Evolution of Source Rocks and Contributing Factors of the Northern and Southern Continental Marginal Basins in the South China Sea

This paper simulated the thermal evolution of source rocks in the northern and southern continental marginal sedimentary basins in the South China Sea on the basis of two profiles crossing from the north to the south of the South China Sea, and compared the thermal evolution differences of these basins. The result reveals that the hydrocarbon generation threshold of the southern continental marginal basins is lower than that of the northern continental marginal basins. The hydrocarbon generation threshold of the southern continental marginal basins is between 2,200 m and 2,300 m, and the source rock in Miocene has attained the threshold. The hydrocarbon generation threshold of the northern continental marginal basins is between 2,500 m and 2,600 m, and the source rock in and below Oligocene has attained the threshold. This regular pattern of the source rocks in the southern and northern continental marginal basins is accordance with the nowadays changing law of heat flow which is high in the south and low in the north,and high in the west and low in the east; the high heat-flow value is beneficial to source rock to become mature and to generate hydrocarbon, thereby, where the heat-flow value is high, the hydrocarbon generation threshold is low. It is revealed that the expanding of the South China Sea and the underthrusting of the Old South China Sea causes the changing of the geothermal field of this area，resulting the difference of source rocks- thermal evolution between the southern and northern continental marginal basins in the South China Sea.