甘肃合黎山古元古代花岗岩锆石U-Pb年龄、岩石地球化学特征及其对阿拉善地块南缘构造环境的约束  

Zircon U−Pb age,petrogeochemical characteristics of Paleoproterozoic granite inthe Helishan area,Gansu Province,and its constraints for tectonic environment of the southern Alxa block

作　　者：董国强[1] 余君鹏[1] 吴义布[1] 刘涛 张炜[1] DONG Guoqiang;YU Junpeng;WU Yibu;LIU Tao;ZHANG Wei(Geological Survey of Gansu Province,Lanzhou 730020,Gansu,China)

机构地区：[1]甘肃省地质调查院,甘肃兰州730020

出　　处：《地质通报》2024年第10期1830-1840,共11页Geological Bulletin of China

基　　金：甘肃省省级基础地质调查项目《甘肃省高台县臭泥墩-西小口子地区三幅1∶5万矿产远景调查》(编号:甘国土资勘发[2017]64号)。

摘　　要：分布于阿拉善地块南缘的龙首山岩群是金川镍矿的直接围岩,其形成时代和构造背景存在较大争议。在阿拉善地块南缘新发现的侵入于龙首山岩群的合黎山古元古代花岗岩体岩性为二长花岗岩、正长花岗岩及正长岩。岩石地球化学分析结果显示,合黎山花岗岩Al_(2)O_(3)/(CaO+Na_(2)O+K_(2)O)值为0.91~1.06,K_(2)O/Na_(2)O为1.10~1.44,属钾质碱钙性花岗岩,岩石相对富集Rb、Ba、Th、K等大离子亲石元素,亏损Ta、Nb、P、Zr、Hf、Ti等高场强元素,具有弧岩浆的地球化学特征,形成于俯冲带岩浆弧构造环境。LA−ICP−MS锆石U−Pb测年结果表明,合黎山二长花岗岩的形成年龄为1859±12 Ma,侵位于古元古代晚期,揭示龙首山岩群变质地层的形成时代大于1.85 Ga,反映阿拉善地块南缘在古元古代晚期可能处于俯冲消减过程。As the direct surrounding rock of Jinchuan nickel mine,the Longshoushan rock group distributed in the southern margin ofAlxa block has great controversy on its formation age and tectonic background.This paper reports that the Paleoproterozoic granitebody of Helishan,which intrudes into Longshoushan rock group,is newly discovered in the southern margin of Alxa block,whichlithology is monzogranite,syenogranite and syenite.According to the petrogeochemical analysis,the Al_(2)O_(3)/(CaO+Na_(2)O+K_(2)O)ofHelishan granite is 0.91~1.06 and K_(2)O/Na_(2)O is 1.10~1.44,it belongs to potassium alkali calcium granite.The rock is relatively rich inlarge ion lithophile elements such as Rb,Ba,Th,K,etc.,and lack in high field strength elements such as Ta,Nb,P,Zr,Hf,Ti,etc.,which has the geochemical characteristics of arc magma and is formed in the magmatic arc tectonic environment of subduction zone.The zircon U−Pb dating result of LA−ICP−MS shows that the formation age of Helishan monzogranite is 1859±12 Ma and theintrusion occurred in the Late Paleoproterozoic,it reveals that the formation age of metamorphic strata of Longshoushan group isgreater than 1.85 Ga,reflecting that the southern margin of Alxa block may be in the process of subduction in the LatePaleoproterozoic.

关 键 词：花岗岩 锆石U-PB定年 古元古代 岩石地球化学 岩浆弧构造环境 阿拉善地块南缘 

分 类 号：P588.121[天文地球—岩石学] P595[天文地球—地质学] P597.3