论文部分内容阅读
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+K20 =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) erupted in the new Proterozoic,association with the breakup and assembly of Rondina supercontinent;and 478±48 Ma for dibase veins emplaced in Malieziken Group,emplaced in the Late Ordovician.In addition,there are the other two ages for basalt dykes emplaced in Qigebulak Formation (Z2g);one of concordia ages 2 090 Ma indicating of forming of columbia supercontinent;the other is 455.4± 10.8 Ma,recording the age of hydrothermal alteration of magmatic activities in the Middle and Late Caledonian.