甘肃龙首山芨岭地区古生代正长岩成因及构造意义  

Petrogenesis and Tectonic Significances of the Paleozoic Jiling Syenite in the Mountain Longshou Area,Gansu Province

作　　者：张志强 王凯兴 王刚[3] 刘晓东 刘文恒[5] 邬斌 ZHANG Zhiqiang;WANG Kaixing;WANG Gang;LIU Xiaodong;LIU Wenheng;WU Bin(School of Earth Sciences,East China University of Technology,Nanchang,330013;State Key Laboratory Breeding Base of Nuclear Resources and Environment,Nanchang,330013;The No.203 Institute of Nuclear Industry,Xianyang,Shaaxi,712000;Jiujiang University,Jiujiang,Jiangxi,332005;Key Laboratory of Jiangxi Digital Land,School of Earth Sciences,Nanchang,330013)

机构地区：[1]东华理工大学地球科学学院,南昌330013 [2]核资源与环境国家重点实验室培育基地,东华理工大学,南昌330013 [3]核工业203研究所,陕西咸阳712000 [4]九江学院,江西九江332005 [5]江西省数字国土重点实验室,东华理工大学,南昌330013

出　　处：《地质论评》2018年第4期1017-1029,共13页Geological Review

基　　金：国家自然科学基金资助项目(编号：41602071);中国核工业地质局铀矿勘查项目(编号：201619);中国核工业地质局“十三五”高校科研攻关项目的成果.

摘　　要：甘肃龙首山芨岭正长岩产于芨岭复式岩体中,产有我国少见的交代岩型铀矿床。为揭示正长岩成因,并探讨其构造意义,本文对正长岩进行了岩相学、年代学、地球化学特征等研究。部分斜长石和石英呈椭圆或圆形以包裹体的形式出现在钾长石中、针状磷灰石和角闪石熔蚀现象都暗示芨岭正长岩可能由两种不同性质的岩浆混合形成。锆石LA-ICP-MS U-Pb定年结果显示,芨岭正长岩形成于427.2±3.6 Ma,与北祁连地区同碰撞花岗岩成岩年龄吻合。芨岭正长岩Si O_2含量中等,全碱含量为8.49%~11.74%,K_2O/Na_2O值为1.07~1.20,属于钾玄岩系列;芨岭正长岩相对富集Rb、Ba、Th、U和Pb,亏损Nb、Ta、P和Ti等元素;稀土元素总量高且相对富集轻稀土,中等Eu亏损;[n(^(87)Sr)/n(^(86)Sr)]_i值为0.70798~0.70799,ε_(Nd)(t)值变化于-3.57^-3.35,与区域I型花岗岩类似。综合岩相学、年代学和地球化学特征表明,芨岭正长岩是由壳—幔岩浆混合而成。芨岭正长岩的形成可能与古祁连洋闭合之后,祁连—柴达木板块和阿拉善板块的碰撞有关。由于古祁连洋在奥陶纪晚期(445 Ma)封闭,祁连—柴达木板块与阿拉善板块碰撞,并俯冲到阿拉善板块之下,碰撞引发龙首山断裂右旋走滑形成的局部伸展环境导致软流圈地幔上涌,并加热大陆地壳物质形成长英质岩浆,该长英质岩浆与地幔岩浆混合形成芨岭正长岩。Objectives： Jiling syenites occur in the Jiling batholith, developing metasomatite related uranium deposit which is rarely presented in China. To explore, the genesis and tectonic significant, petrographic, geochronologic, and geochemical analyses were conducted on the Jiling syenites.Methods：Field investigation, syenite sampling and observation under a microscope were performed to obtain lithology, LA ICP MS zircon U Pb dating, analysis of geochemical characteristics of major, trace and rear earth elements, isotopic geochemical analysis were used.Result： Both plagioclase and quartz grains as ellipse or round-shape in the K-feldspar, acicular apatite and porous amphibole indicate that the Jiling syenites may be formed by magma mixing. LA ICP MS zircon U Pb dating reveals the Jiling syenites emplaced at 427±3.6Ma, which is consistent with those of collision related granitoids in northern Qilian Mountains area. The Jiling syenites show intermediate SiO2 contents, total alkaline contents ranging from 8.49% to 11.74% with K2O/Na2O from 1.07 to 1.20, can be classified as shoshonitic type. In the Jiling syenites, Rb, Ba, Th, U and Pb are enriched, while Nb, Ta, P and Ti are depleted; REE contents are high with moderate negative Eu anomalies; the initial Sr isotopic compositions display ranging from 0.70798 to 070799, and εNd（t） from -3.57 to -3.35, which fall in the I type granitoids area of northern Qilian Mountains area. Combined with petrographic, geochronologic, and geochemical characteristics, writers consider that the Jiling syenites were formed by mixing of crustal derived and mantle derived magmas.Conclusions：The formation of the Jiling syenites may have relationship with collision between the Alax and Qilian-Qaidam Blocks. Due to the closure of the Paleo Qilian Ocean at 445 Ma, the Qilian-Qaidam Block collided with the Alax Block, and subducted underneath the Alax Block. It would lead right lateral strike slip of the Mountain Longshou fault, and generate in an extensional

关 键 词：正长岩 伸展环境 岩浆混合 交代型铀矿床 甘肃龙首山 

分 类 号：P534.4[天文地球—古生物学与地层学] P588.122[天文地球—地质学]