沙捞越盆地的盆地类型分析

BASIN TYPE ANALYSIS FOR SARAWAK BASIN

针对沙捞越盆地盆地类型的不同观点,通过盆地区域构造背景、构造演化阶段、构造沉降曲线的分析以及构造地质事件的恢复,得到以下认识:①盆地的构造演化可划分为晚白垩世—晚始新世,拉让洋壳向婆罗洲基底俯冲,并在婆罗洲中部形成火山岛弧的俯冲增生期;渐新世—早中新世,拉让洋壳俯冲消减完毕,路科尼亚地块与婆罗洲碰撞,并俯冲于婆罗洲基底之下,形成周缘前陆盆地的前陆盆地期;中中新世至今,南中国海开启、婆罗洲碰撞抬升引起盆地稳定沉降的被动边缘期3个阶段。②盆地所选井的构造沉降曲线具有早期缓慢沉降、晚期快速沉降这一前陆盆地的典型特征。③盆地构造地质事件复原图表明,盆地晚期处于被动大陆边缘构造背景。由此,认为沙捞越盆地为复合型盆地,即早期为前陆盆地,晚期则转化为大陆边缘型盆地。

Controversies occur with the type of Saraw background, evolutionary stages, subsidence curves ak Basin. Through analyzing the regional tectonic and reconstructing geological events, we acquire the following results. 1） The evolution of the basin can be divided into three phases, a） Subduction- accretion phase （Late Cretaceous-Late Eocene）--The Rajang oceanic crust subducted into Borneo base and formed volcanic island arc along the subducted edge ; b）Foreland basin phase （Oligocene-Early Miocene）--the collision between the Luconia plate and Borneo following the termination of oceanic crust subduction resulted to the development of peripheral foreland basin~ c）Passive margin phase （Middle Miocene to present）--the opening of South China Sea, collision and uplift of Borneo leading to the stable subsidence of this basin. 2） Tectonic subsidence curves for the selected wells in Sarawak Basin resemble with the theoretical subsidence curves of a foreland basin--slow subsidence in early stage and rapid subsidence in later stage. 3）Reconstruction of geotectonic events for this basin reveals that in the late evolutionary stage, it is located at the passive margin setting. Based on the evidence mentioned above, it is concluded that the basin has experienced the process from peripheral foreland basin to passive continent margin basin.