西藏改则扎嘎尔勒尖早始新世A型花岗岩年代学、地球化学及地质意义  

The Chronology, Geochemistry and Geological Significance of Early Eocene A-type Granite in Zhagaerlejian,Gaize,Tibet

作　　者：魏永峰 肖渊甫[1] 罗巍[1,2] 邓泽锦 赵志强[2] 林美英[2] Wei Yongfeng;Xiao Yuanfu;Luo Wei;Deng Zejin;Zhao Zhiqiang;Lin Meiying(College of Earth Sciences,Chengdu University of Technology,Chengdu,Sichuan,610059,China;Geology Exploring and District Surveying Team,Shuangliu,Sichuan,610213,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]四川省地质矿产勘查开发局区域地质调查队,四川双流610213

出　　处：《新疆地质》2018年第1期51-59,共9页Xinjiang Geology

基　　金：西藏改则别若则错1:5万(I44E022020;I44E022021;I44E023020;I44E023021)4幅地质矿产调查(12120113036600)项目资助;所属计划项目为:西藏班公湖-怒江成矿带地质矿产调查

摘　　要：西藏改则扎嘎尔勒尖A型花岗岩体侵位于晚石炭世拉嘎组碎屑岩夹碳酸盐岩地层中,呈独立岩株产出,内部可见较多闪长质包体,岩性以正长花岗岩为主,少量二长花岗岩。岩体LA-ICP-MS锆石U-Pb年龄为(53.60±0.38)Ma,时代为早始新世。岩石具富SiO_2(72.40%~77.49%)、K2O(4.91%~5.62%),贫Al2O3(11.88%~15.58%)、Mg O(0.076%~0.384%)、TiO_2(0.088%~0.237%)、P_2O_5(0.019%~0.071%),高Al_2O_3、Na_2O和低TiO_2、Mg O、Mn O特征,属准铝质-弱过铝质碱性系列。稀土元素总量为106.39×10^(-6)~161.45×10^(-6),(La/Yb)_N为6.91~18.12,δEu=0.15~0.89,在球粒陨石标准化稀土元素分布模式上表现为右倾海鸥型。在原始地幔标准化蛛网图上,富集Rb,Th,Zr,Hf和Y等高场强元素,亏损Nb,Ta,Sr,Ba,Ti和P。岩石地球化学特征表明,扎嘎尔勒尖岩体为A1型花岗岩。初步认为,扎嘎尔勒尖A型花岗岩产出于碰撞高峰之后的短暂应力松驰阶段,形成于该阶段的造山带岩石圈地幔刚刚发生拆离之时,是新特提斯洋板片发生断离、拆沉,软流圈物质透过板片断离窗上涌,诱发地幔楔、上覆加厚的镁铁质下地壳熔融、侵位而形成的。The A-type granite in Zhagaerle tip,Gaize,Tibet was emplaced in the late carboniferous debris construction carbonatite-bearing formation as an independent stock.Lots of dioritic enclaves could be founded inside,mainly syenogranite and a few adamellite.The LA-ICP-MS zircon U-Pb age of the rock mass was(53.60±0.38)Ma,Early Eocene.The character of the rock is rich in SiO2(72.40%~77.49%)and K2O(4.91%~5.62%),poor Al2O3(11.88%~15.58%),MgO(0.076%~0.384%),TiO2(0.088%~0.237%)and P2O5(0.019%~0.071%),high Al2O3 and Na2O,low TiO2,MgO and MnO.The rock belonged to the metaluminous-weakly peraluminous,alkaline series.The value of the rare earth elements was 106.39×10-6~161.45×10-6,(La/Yb)N with 6.91~18.12,δEu=0.15~0.89.The chondrite-normalized REE patterns was right deviation seagull type.The primitive mantle normalized spider diagram showed enrichment in high field strength elements such as Rb,Th,Zr,Hf,Y etc,and depletion in Nb,Ta,Sr,Ba,Ti,P.The Geochemistry indicated the rock was A-type granite.Preliminary,the study showed the A-type granite in Zhagaerle tip,Gaize was formed in the stage of transient stress relaxation after the collision peak,when the orogenic belt lithosphere mantle were just separated.The separation and delamination of the sheet space of the Neo-Tethys ocean,and the upwelling of the asthenospheric material,induced the mantle wedge and mafic lower crustal melting and emplacement.

关 键 词：西藏改则 冈底斯带 早始新世 A型花岗岩 LA-ICP-MS锆石U-PB测年 地球化学 地质意义 

分 类 号：P588.12[天文地球—岩石学] P597[天文地球—地质学]