广西横县马山晚侏罗世钾玄质侵入岩的年代学和地球化学研究:兼论钦杭成矿带西南段燕山期构造背景  

Geochronology and geochemistry of the Mashan Late Jurassic shoshonitic intrusives in Hengxian,Guangxi:With a discussion on Yanshanian tectonic settings of the southwestern segment of Qinzhou-Hangzhou metallogenic belt

作　　者：劳妙姬[1,2] 邹和平[1,2] 杜晓东[1,2] 丁汝鑫[1,2] 

机构地区：[1]中山大学地球科学与地质工程学院,广东广州510275 [2]广东省地质过程与矿产资源探查重点实验室,广东广州510275

出　　处：《地学前缘》2015年第2期95-107,共13页Earth Science Frontiers

基　　金：中国地质调查局项目(1212011121064);国家自然科学基金项目(41102131)

摘　　要：广西横县马山杂岩体位于钦杭成矿带西南段,出露于防城—灵山断裂带的西侧,为一套包括辉长岩、玄武（玢）岩、闪长（玢）岩、二长（斑）岩、普通角闪正长岩、石英正长岩、花岗岩在内的从基性到中、酸性的岩浆岩岩系。文中对其中的中性浅成侵入岩进行研究,获得二长闪长玢岩样品的40Ar/39Ar坪年龄为（153.8±0.6）Ma,表明岩石形成于晚侏罗世。所研究的岩石样品富K、富碱、w（K2O＋Na2O）=5.73%~8.54%、K2O/Na2O=0.87~1.76,富集大离子亲石元素Rb、Ba、Th、U和轻稀土元素,无明显的Nb-Ta-Ti负异常,为典型板内钾玄质岩石。其（87Sr/86Sr）i变化范围在0.705 11~0.705 47,εNd（t）变化范围在0.6~1.4,206Pb/204Pb为19.019~19.228,207Pb/204Pb为15.720~15.737,208Pb/204Pb为39.372~39.518,元素和同位素地球化学特征指示岩浆来源于亏损的软流圈地幔（DMM）和富集岩石圈地幔（EMⅡ）两个端员的混合。结合前人对南岭西部侏罗纪岩浆岩的研究成果,认为马山杂岩体的岩浆成分和源区特征反映桂东南在晚侏罗世发生了区域软流圈地幔上涌和岩石圈伸展-减薄作用,这是钦杭带西南段燕山期花岗岩和相关矿床形成的重要的地质构造背景。The Mashan igneous complex, occurring in the southwestern segment of the Qinzhou-Hangzhou metallogenic belt with outcropping in the west side of the Fangcheng-Lingshan fault zone, is composed of alkali shoshonitic rocks in which basic, mediosilicic and acid rocks are included. Geochronology and geochemistry of the mediosilicic intrusive rocks have been studied in detail in this paper. A sample of the rocks have a 40Ar/39Ar plateau age of 153. 8±0. 6 Ma, indicating that the rocks were formed in the Late Jurassic. Samples of the rocks are all abundant in alkaline elements of K and Na, with K2O＋Na2O being of 5. 73%- 8. 54%, K2O/ Na2O=0.87 - 1.76. They are enriched in the large-ion lithosphile elements of Rb, Ba, Th, U and LREE, and their isotopic compositions are characterized by that the ratios of （87Sr/86Sr）~ range from 0. 70511 to 0. 70547, eNd（t） from 0. 6 to 1.4,206Pb/204Pb=19. 019- 19. 228, 207Pb/204Pb= 15. 720- 15. 737, and 208Pb/204pb=39. 372- 39. 518. These geochemical data show that the magma was derived from the sources mixed by two end-members of the DMM asthenosphere and the EM U lithosphere It suggests that upwelling of the asthenosphere and extension of the lithosphere probably took place in southeast Guangxi during the Late Jurassic, which possibly were the tectonic settings of formation for the Yanshanian granites and the related mineral deposits in the southwestern segment of the Qinzhou-Hangzhou metallogenic belt.

关 键 词：马山杂岩体 钾玄质岩石 40Ar/39Ar同位素年龄 地球化学 钦杭成矿带 

分 类 号：P595[天文地球—地球化学] P597.3[天文地球—地质学]