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  

Geochemistry and Tectonic Implications of the Paleogene Gabbros in Fushan Sag,Beibu Gulf Basin

作　　者：林正良[1] 李红敬[1] 张永超[2] 廖远涛[3] 马庆林 刘恩涛[3] LIN Zhengliang LI Hongjing ZHANG Yongchao LIAO Yuantao MA Qinglin LIU Entao(Sinopec Geophysical Research Institute, Nanjing 210014, Jiangsu, China PetroChina Jidong Oilfield Company, Tangshan 063004, Hebei, China Faculty of Earth Resources, China University of Geoscience, Wuhan 430074, Hubei, China China Southern Petroleum Exploration and Development Corporation, Guangzhou 510240, Guangdong, China)

机构地区：[1]中国石化石油物探技术研究院,江苏南京210014 [2]中国石油冀东油田公司勘探开发研究院,河北唐山063004 [3]中国地质大学(武汉)资源学院,湖北武汉430074 [4]中国石油南方石油勘探开发有限责任公司,广东广州510240

出　　处：《大地构造与成矿学》2016年第5期1064-1074,共11页Geotectonica et Metallogenia

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

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_2O>K_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。Thick-layered gabbros were found widespread in the mudstone of the second member of the Paleogene Liushagang Formation in the Fushan Sag. The rocks are of sub-alkaline series with SiO_2 contents of 52.12%- 52.61%, MgO 5.77%- 5.86%, Fe_2O_3 11.06%- 11.49%, K_2O 1.18%- 1.25%, P_2O_5 0.36%- 0.39% and relatively high TiO_2 contents of 2.15%6- 2.24%. The gabbros have high ΣREE contents（105.61×10^（-6）- 111.26×10^（–6）） showing LREE-enriched type with（La/Yb）_N ratios of（8.74- 9.64）, and enrichment of large iron lithophile elements（including Rb, Ba, Th, U, Sr）, showing typical features of within plate basalt. The gabbros in the Fushan Sag were likely resulted from the interaction between the upwelling asthenosphere and the young and thin lithospheric mantle that formed by the predated underplating. LA-ICP-MS zircon U-Pb dating showed that the gabbros were crystallized at 37- 32 Ma as the products of the Paleogene lithosphere extension environment.

关 键 词：地球化学 LA-ICP-MS锆石U-PB定年 辉长岩 福山凹陷 北部湾盆地 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学]