南海西沙隆起基底成因新认识

发布时间：2018-06-05 07:05

  本文选题：南海 + 西沙　； 参考：《中国科学:地球科学》2017年12期

【摘要】：基底年龄对重建海洋区域的构造演化历史具有重要意义.南海西沙隆起盆地基底方面的研究主要局限在重磁和地震资料以及20世纪70年代西永一井的分析资料上,长期没有新的突破.本文针对新获取的西科一井两个基底样品开展了岩石学分析和锆石U-Pb同位素测年,来研究西沙群岛基底的形成时间及构造属性.结果表明,基底成分为晚侏罗世角闪斜长片麻岩,锆石~(206)Pb/~(238)U平均年龄为(152.9±1.7)Ma,但是最年轻年龄为(137±1)Ma,说明变质作用结束时间大致在早白垩世.变质岩底部与二长花岗岩突变接触,为早白垩世晚期((107.8±3.6)Ma)岩浆侵入的结果,与西永一井早期测得的前寒武纪基底年龄(全岩Rb-Sr法,627Ma)明显不同,西科一井的基底锆石都属于晚中生代岩浆活动的产物.晚侏罗世-早白垩世的区域变质作用和花岗质岩浆侵入不仅出现于西沙,在南海的珠江口盆地和南沙群岛等区域都有报道,与东亚陆缘受到古太平洋板块大规模、长时间的俯冲密切相关,其可能导致了中特提斯洋在南海的关闭.对于南海是否发育有统一的前寒武纪变质结晶基底仍存在争议,但是可以肯定的是,中生代板块俯冲挤压与新生代裂陷拉张已经显著改造了南海地区的原始基底
[Abstract]:The basement age is of great significance for the reconstruction of the tectonic evolution history of the marine area. The research on the basement of Xisha uplift basin in the South China Sea is mainly confined to the gravity and magnetic data and seismic data and the analysis data of Xiyong Yiyi well in the 1970s. There has been no new breakthrough for a long time. In this paper, petrological analysis and zircon U-Pb isotopic dating have been carried out for two basement samples obtained from Xichiyi well to study the formation time and tectonic properties of the basement of Xisha Islands. The results show that the basement composition is a late Jurassic hornblende gneiss with an average age of 152.9 卤1.7 Ma for zircon Zircon 206Pb / L / 238U, but the youngest age is 137 卤1 Ma, indicating that the end time of metamorphism was probably in the early Cretaceous. The metamorphic rock bottom is in contact with the monzomorphic granite, which is the result of magmatic intrusion in late early Cretaceous (107.8 卤3.6 Ma), which is obviously different from the Precambrian basement age (whole-rock Rb-Sr method 627Ma), which was obtained in the early stage of Xiyong first well. The basement zircon of Xiceyi well is the product of late Mesozoic magmatic activity. The late Jurassic-early Cretaceous regional metamorphism and granitic magmatic intrusion occurred not only in Xisha, but also in the Pearl River mouth basin and Nansha Islands in the South China Sea. Long-term subduction may have led to the closure of the Middle Tethys in the South China Sea. It is still controversial whether there is a unified Precambrian metamorphic crystalline basement in the South China Sea, but it is certain that the Mesozoic plate subduction and Cenozoic rift extension have significantly altered the primitive basement in the South China Sea.
【作者单位】： 同济大学海洋地质国家重点实验室;中国地质大学构造与油气资源教育部重点实验室;中海石油中国有限公司湛江分公司;西北大学地质学系;
【基金】：国家科技重大专项项目(编号:2017ZX05-26-005) 国家自然科学基金项目(批准号:91128207、41576059)资助
【分类号】：P736.1
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本文编号：1981092