莺歌海盆地构造转折界面的确定及其地质意义

中国西南部红河断裂带的活动演化历史长期以来备受国内外学者的关注,该断裂从陆地向海域延伸进入莺歌海盆地,并对莺歌海盆地的形成和演化起重要的控制作用。目前,红河断裂带经历早期的左旋走滑运动和后期的右旋走滑运动已经得到公认,但对于其精细的构造演化历史及其左旋走滑向右旋走滑运动转换的时间还未能达成共识。本文利用构造控制沉积、沉积反映构造的思想,通过对莺歌海盆地三维地震资料的构造解析,从T27界面上下地层厚度存在"跷跷板"式的变化、沉积中心的迁移、沉积速率的变化、陆架-陆坡坡折带的出现、微小断裂的特征以及底辟构造等方面的研究,确定莺歌海盆地红河断裂带的左旋走滑运动停止于T40(10.5Ma);T40~T30(10.5~5.5Ma)是构造变形的平静期;T30~T27(5.5~2.4 Ma)为左旋走滑运动向右旋走滑运动转换时期;T27(2.4 Ma)以后右旋走滑活动开始,并控制坡折带(包括莺歌海盆地和琼东南盆地)和底辟构造等的形成;T20(1.9 Ma)以来,右旋走滑活动逐渐减弱。

Determination of the Tectonic Transformation Surface in Yinggehai Basin and its Geological Significance

The evolution of the Red River Fault Zone in Southwestern China has been subject of many studies. The fault extends into and controls the formation and evolution of the Yinggehai Basin. The early sinistral and late dextral strike-slip movement of the Red River Fault Zone has been widely recognized. However, details of the tectonic evolution of the Red River Fault Zone and the time of sinistral to dextral transformation are still controversy. Given that the tectonics controls sedimentation and sedimentation reflects the tectonics, on the bases of structural analysis of the three-dimensional seismic data of the Yinggehai Basin, we defined the seesaw-type variation of the stratum thickness near the T27 interface, migration of accumulation centers, changes of deposition rates, appearance of the continental shelf slope break, characteristics of minor faults, and diapir structures. We argue that the sinistral strike-slip movement of the Red River Fault Zone in the Yinggehai Basin ended at T40(10.5 Ma), followed by a quiescence during T40–T30(10.5–5.5 Ma), a sinistral to dextral transition during T30–T27(5.5–2.4 Ma), and a dextral strike-slipping after T27(2.4 Ma) that controlled the formation of the shelf slope break(including the Yinggehai and Qiongdongnan basins) and diapir structures. The dextral strike-slip activity weakened since T20(1.9 Ma).