南海北缘中生代古俯冲带位置探讨

Discussion location of Mesozoic paleo-subduction zone in north margin of South China Sea

系统论述九所—陵水断裂带南北两侧地球物理特征差异、地质、地球化学记录差异和断裂带地质构造特征;在分析南海北缘重力、磁力和地震资料特征的基础上,提出南海北缘中生代古俯冲带西起九所—陵水断裂带,向东呈近EW走向延伸至E112°30′附近被NW走向的右行走滑断层(F1)错断,之后向NEE方向延伸至E116°附近被NW走向的右行走滑断层(F2)错断,再向东沿着NEE方向延伸至E119°30′附近再次被NW走向的右行走滑断层(F3)错断,此后一直延伸至台湾岛。该古俯冲带在布格重力异常上显示为强的水平梯度峰值带,其东段北侧出现与之平行的高磁异常带,指示发育与古俯冲带形成过程有关的火山弧。现有的钻井资料和九所—陵水断裂带的年代学数据研究揭示古俯冲带形成于晚中生代。上述认识与南海北部现有的重力、磁力、地震剖面和钻井等地质地球物理资料是相吻合的。该古俯冲带向西与红河断裂带莺歌海段东侧的分支断层(Ⅰ号断层)相接,向NE方向与台湾寿丰断裂相连。

The differences in geophysics characteristics, differences in geology and geochemistry between the north and south of Jiusuo-Lingshui Fault Belt, and the geological structure features of above fault belt were systematically discussed. The results show that the Mesozoic paleo-subduction zone in north margin of South China Sea starts from Jiusuo-Lingshui Fault Belt in the western, first extending in EW direction to the east, cut by the dextro strike-slip fault which strikes in NW direction nearby El12°30′, then extending in NEE direction until to nearby E116°cut by dextro strike-slip fault which strikes in NW direction again, and extending in NEE direction until to nearby E119°30′ cut by dextro strike-slip fault which strikes in NW direction again, and then extending in NEE direction until to Taiwan Island further in east. This paleo-subduction zone displays as strong horizontal gradient peak zones in bouguer gravity anomaly. The north of paleo-subduction zone appears high magnetic anomaly zone which is parallel to this paleo-subduction zone. This high magnetic anomaly zone is explained as the volcanic-arc related to the information of this paleo-subduction zone. The borehole data of the researched area and chronology research on the Jiusuo-Lingshui Fault Belt show that this paleo-subduction zone was formed in late Mesozoic. And the geology and geophysics data such as gravity, magnetic, seismic profiles and drilling wells in north of South China Sea hold up above conclusion about the location of Mesozoic paleo-subduction zone. This Mesozoic paleo-subduction zone in north margin of South China Sea joins the eastern branch fault （No. I fault） of Red River Fault Zone in the Yinggehai Basin in the west, and links Shoufeng Fault in Taiwan Island in the northeast.