北部湾盆地福山凹陷古近纪辉长岩地球化学特征及构造意义

发布时间：2018-01-04 20:42

本文关键词：北部湾盆地福山凹陷古近纪辉长岩地球化学特征及构造意义　出处：《大地构造与成矿学》2016年05期 　论文类型：期刊论文

【摘要】：北部湾盆地福山凹陷古近系流沙港组二段泥岩中发育大面积巨厚辉长岩?地球化学分析表明,辉长岩具有中等TiO_2含量(2.15%~2.24%),较低MgO(5.77%~5.86%)、K_2O(1.18%~1.25%),P_2O_5(0.36%~0.39%)含量,且Na_2OK_2O,指示其类似于板内拉斑玄武岩。辉长岩ΣREE为105.61×10~( 6)~111.26×10~( 6),富集LREE,(La/Yb)_N=8.74~9.64,具有右倾型稀土配分模式;与原始地幔相比,富集Rb、Ba、Th、U等大离子亲石元素以及高场强元素Nb、Ta、Zr、Hf,呈现板内碱性玄武岩特征,是地幔物质上涌与上覆薄而年轻的岩石圈地幔相互作用的产物?结合LA-ICP-MS锆石U-Pb测年结果显示,辉长岩形成时间介于37~32 Ma,代表福山凹陷古近系辉长岩的侵位年龄,是古近纪岩石圈持续伸展环境下的产物?这对探讨福山凹陷以及中国东南部古近纪构造活动及岩浆演化具有重要的意义。
[Abstract]:A large area of giant gabbro developed in the mudstone of the second member of the Liushagang formation of the Paleogene Liushagang formation in Fushan Sag, Beibu Bay Basin. Geochemical analysis shows that the gabbro has a moderate TiO_2 content of 2.15 and 2.24, and a lower MgO 5.77 and 5.86. K2O1.18 / 1.25 / P2OS / P _ 2O _ T _ s _ 50.36 and 0.39) and Na_2OK_2O. This indicates that it is similar to intraplate tholeiite. The 危 REE of gabbro is 105.61 脳 10 ~ (-1) (111.26 脳 10 ~ (-1)) LREE. The La- / Ybfen is 8.740.64, and it has a right-dip rare-earth distribution model. Compared with the original mantle, it is rich in large ion lithophile elements, such as RB, Ba-Th, U, and the high field strength element, NB _ (+) Tahlr _ (Zr) _ (Hf), which shows the characteristics of intraplate alkaline basalts. Is the material upwelling of the mantle interacting with the thin and young lithospheric mantle? Combined with LA-ICP-MS zircon U-Pb dating results show that the pyroxenite formation time is between 37 and 32 Ma.It represents the emplacement age of Paleogene gabbro in Fushan depression. Is it a product of the Paleogene lithosphere in a continuous extensional environment? This is of great significance to the study of Paleogene tectonic activity and magmatic evolution in Fushan depression and southeastern China.
【作者单位】：中国石化石油物探技术研究院;中国石油冀东油田公司勘探开发研究院;中国地质大学(武汉)资源学院;中国石油南方石油勘探开发有限责任公司;
【基金】：国家重点基础研究发展计划(973)项目(2014CB239201) 国家自然科学基金项目(41272722)联合资助
【分类号】：P736.1;P588.124
【正文快照】： 0 引言北部湾盆地属板内裂谷盆地,由于接近板块边缘,同时受到板块碰撞、分离的影响,其构造活动比内陆盆地要强一些(田在艺和王善书,1985)。而福山凹陷所处的构造位置更为特殊,其古近系发育,详细记录着大量新生界早期中国南海陆架区的构造事件。本文首次对北部湾盆地南缘的福

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