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甘肃龙首山芨岭地区古生代正长岩成因及构造意义
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引用本文:张志强,王凯兴,王刚,刘晓东,刘文恒,邬斌.2018.甘肃龙首山芨岭地区古生代正长岩成因及构造意义[J].地质论评,64(4):1017-1029
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作者单位E-mail
张志强 1) 东华理工大学地球科学学院,南昌,330013 1270822341@qq.com 
王凯兴 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 
xy2gmo02@ecit.cn 
王刚 3) 核工业 203 研究所,陕西咸阳,712000  
刘晓东 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
4) 九江学院江西九江,332005 
 
刘文恒 5) 江西省数字国土重点实验室东华理工大学南昌,330013  
邬斌 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  
基金项目:本文为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。
中文摘要: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±3.6Ma,与北祁连地区同碰撞花岗岩成岩年龄吻合。芨岭正长岩SiO2含量中等,全碱含量为8.49%~11.74%,K2O/Na2O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; \[n(87Sr)/n(86Sr)\]i比值为0.70798~0.70799,εNd(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(445Ma)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。
中文关键词:正长岩  伸展环境  岩浆混合  交代型铀矿床  甘肃龙首山
 
Petrogenesis and Tectonic Significances of the Paleozoic Jiling Syenite in the Mountain Longshou Area, Gansu Province
NameInstitution
ZHANG Zhiqiang1) School of Earth Sciences, East China University of Technology, Nanchang, 330013
WANG Kaixing1) School of Earth Sciences, East China University of Technology, Nanchang, 330013;2) State Key Laboratory Breeding Base of Nuclear Resources and Environment, Nanchang, 330013
WANG Gang3) The No. 203 Institute of Nuclear Industry, Xianyang, Shaaxi, 712000
LIU Xiaodong2) State Key Laboratory Breeding Base of Nuclear Resources and Environment, Nanchang, 330013;4) Jiujiang University, Jiujiang, Jiangxi, 332005
LIU Wenheng5) Key Laboratory of Jiangxi Digital Land, School of Earth Sciences, Nanchang, 330013
WU Bin2) State Key Laboratory Breeding Base of Nuclear Resources and Environment, Nanchang, 330013
Abstract: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 SiO2 contents, total alkaline contents ranging from 8.49% to 11.74% with K2O/Na2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 environment. The continental crust heated by the upwelling of asthenosphere, and generate the felsic magmas. Mixing of the felsic magma and the mantle derived magma formed the Jiling syenites.
keywords:syenite  extensional environment  magma mixing  metasomatism-type uranium deposit  Mountain Longshou, Gansu
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