塔里木盆地西北缘震旦系玄武质岩墙和西南缘奥陶系中辉绿岩脉地质年代及构造环境的对比研究  

The age and tectonic settings constraint on the basalt dykes and dibase veins in the western Tarim

作　　者：钱一雄[1] 张洪安[2] 杨圣彬 李慧莉[4] 雷明[4] 陈跃[1] 贾存善[1] 邵志兵[1] 

机构地区：[1]中国石化石油勘探开发研究院无锡石油地质研究所,江苏无锡214151 [2]中国石化中原油田分公司,河南濮阳457001 [3]中国华电集团公司,北京100031 [4]中国石化石油勘探开发研究院,北京100083

出　　处：《地质科学》2017年第4期1079-1096,共18页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家重点基础研究发展计划“973”项目（编号：2012CB214802）和国家科技重大专项（编号：2011ZX05005-0023,2011ZX05008-003-11）资助.致谢 参加野外地质考察的还有金之钧,张仲培,刘士林,贾存善,田蜜,张永东等同志,金之钧院士对此项研究作了有益的指导,在此一并致谢!

摘　　要：本文对塔西北震旦系中的苏盖特布拉克组玄武质岩墙以及塔西南奥陶系玛列兹肯群中辉绿岩脉的区域地质、岩石学、地球化学等进行了对比研究，同时对锆石的微区 U-Pb 同位素年代学及其构造环境等进行了研究。 前者为顺层侵入、包裹了中酸性的捕虏体， 发育了枕状构造、球形风化和柱状节理等玄武岩喷发等特征；后者穿插于韧性剪切带中碳酸盐质糜棱岩化中。 它们的常量组分变化较大：不包括 SiO2 外其它 9 种常量组分的含量为 36.3%～45.3%， 全碱 （Na2O＋K2O）为 3.83%～7.16%；TiO2 含量较低， 为 0.63%～1.89%；MgO 为 3.72%～6.74%；前者中的常量组分、微量元素 Sr 、Ta、Nb、Ti、Yb、Ni、Cu、Zn、Y 含量明显高于后者对应值， 但大离子亲石、造岩元素中 Cs、Rb 等元素、La/Nb、K/T 元素比相对较低。 相比于原始地幔， 两者均相对富集造岩元素 Li、Rb、Ba、Ga、Sr 和稀有元素 Nb、Ta， 轻稀土中等富集；相对亏损铁族元素 Cr、Co 及 Mo、Pb、Bi、U 等；前者 ΣREE 为 227.72×10^-6～426.32×10^-6 、L/H = 2.51～2.61、δEu = 0.48～0.52、δCe = 0.56；后者的 ΣREE 为 142.37×10^-6 ～187.92×10^-6 、L/H = 2.34～3.99、δEu = 0.63～0.84、δCe = 0.52～0.54；综合判识表明， 前者主要来自于未混染或较弱混染的幔源、发育于新元古（878～808.6 Ma）板内伸展的构造环境， 变质和残留核锆石谐和年龄为 2 090 Ma， 记录了早元古的联合大陆的形成时代， 蚀变锆石 455.4±10.8 Ma 代表了加里东中晚期的岩浆热事件；后者岩浆锆石的 U-Pb 年龄为晚奥陶世 478±48 Ma， 发育于弧后盆地、与韧性剪切带有关的加里东中晚期岩浆活动。The comparative studies on basalt dykes and dibase veins emplaced either in Qigebulak Formation （Z2q） of the Upper Sinian at Xianerbulak of Aksu, northwestern or Malieziken Group of the Early Ordovician at Qiate, southwestern Tarim, with a regard to field characteristics, geochemical analysis, and zircon SHRIMP U-Pb dating ages, yields constraints on magmatic activities. The former one is of characteristic of intrusion along the stratum with acidic xenoliths inclusion, similar to the features of basalts, such as the pillow structure, spherical weathering and columnar joints; while the latter has intruded into the ductile shear zone in the carbonate mylonitization. Both basalt dykes and dibase veins varies in the great contents with 36.3%～45.3% for 9 major geochemical composition exception for the contents of SiO2 , Na2O＋K2O = 3.83% ～7.16% , TiO2 = 0.63% ～1.89% ; MgO = 3.72% ～6.74% ; compare with that of the latter dibase dykes. The former one are rich in the major composition, trace elements such as Sr, Ta, Nb, Ti, Yb, Ni, Cu, Zn, Y; depleted in the large ions and lithophile and petrogenetic element of Cs, Rb and the element ratios of La/Nb, K/Tl. However, both of them enriched in lithophile and petrogenetic elements of Li, Rb, Ba, Ga, Sr and rare elements of Nb,Ta; moderate richness light rare elements, depleted in Cr, Co iron family elements and Mo, Pb, Bi, U elements. The former basalt dykes is of REE = 227.72×10^-6～426.32×10^-6 , L/H = 2.51～2.61, δEu = 0.48～0.52, δCe = 0.56. The latter dibase veins REE = 142.37×10^-6 ～187.92×10^-6 , L/H = 2.34～3.99, δEu = 0.63～0.84, δCe = 0.52～0.54; comprehensive judgement indicated that the former basalt dykes origin mantle source without or weak lithosphere contamination, associated with the activities of deep faults in extensional intraplate setting; and the later connected with ductile shear in back-arc basin. The ages recorded by magmatic zircon SHRIMP U-Pb dating is 878～808.6 Ma for basalt dykes in Qigebulak Formation（Z2g）erupte

关 键 词：辉绿岩与玄武岩 岩石地球化学 锆石U—Pb年龄 苏盖特布拉克组 玛列兹肯群 

分 类 号：P588.124[天文地球—岩石学] P597[天文地球—地质学]