西秦岭早三叠世陆缘弧环境岩浆作用:来自那扎岩体锆石U-Pb年龄、地球化学特征的证据  

Magmatism in the Early Triassic continental margin arc environment in the West Qing mountains:Evidence from zircon U-Pb ages

作　　者：曾俊杰 蒲万峰 刘斌 袁臻 杨壮 ZENG Junjie;PU Wanfeng;LIU Bin;YUAN Zhen;YANG Zhuang(Third Geological and Mineral Exploration Institute of Gansu Provincial Bureau of Geology and Mineral Eesources,Lanzhou 730050,Gansu,China;Gansu Xinyuan Dituo Mining Co.,Ltd.,Lanzhou 730050,Gansu,China)

机构地区：[1]甘肃省地质矿产勘查开发局第三地质矿产勘查院,甘肃兰州730050 [2]甘肃鑫源地拓矿业有限责任公司,甘肃兰州730050

出　　处：《地质通报》2023年第6期1001-1012,共12页Geological Bulletin of China

基　　金：中国地质调查局项目《甘肃省合作矿集区深部找矿预测》(编号:DD2019057010)和《甘肃省合作矿集区深部找矿预测(早子沟一带)》(编号:中地调研合同[2020]第211号)。

摘　　要：甘肃合作那扎岩体岩性为花岗斑岩。对岩体地质学、LA-ICP-MS锆石U-Pb年龄及岩石地球化学特征进行研究,探讨岩体的成因机制及构造意义,为该地区印支期的构造演化提供新证据。岩石地球化学分析表明,SiO_(2)含量为69.50%~73.48%,TiO_(2)含量为0.008%~0.084%,CaO含量为0.22%~2.07%,Na_(2)O含量为2.96%~3.40%,K_(2)O含量为4.38%~4.84%,Al2O3含量为14.74%~16.19%,铝饱和指数A/CNK值为1.49~1.91,>1.1,里特曼指数σ为1.88~2.27,属高钾钙碱性过铝质S型花岗岩。稀土元素总量为42.82×10^(-6)~62.85×10^(-6),LREE/HREE值为16.55~24.19,轻稀土元素含量相对富集,δEu值为0.79~1.41;高场强元素P、Ti相对亏损,Nb、Ta略有亏损,大离子亲石元素和轻稀土元素Th、Rb、K相对富集。岩石地球化学特征显示,那扎岩体起源于地壳变质砂岩和变质泥岩等物质部分熔融,Mg#值高(67~77),稀土元素总量低,成岩过程中有幔源组分的加入。花岗斑岩中获得LA-ICP-MS锆石U-Pb年龄为249.7±1.8 Ma,形成于早印支期。结合区域地质背景,认为研究区所在的西秦岭夏河—合作一带,在早印支期处于地壳和岩石圈加厚的陆缘弧环境,那扎岩体就是该阶段岩浆作用的产物。The lithology of Nazha pluton in Hezuo,Gansu Province is granite porphyry.Through the study of rock geology,LA-ICP-MS zircon U-Pb age,and rock geochemistry,the genetic mechanism and tectonic significance of the Nazha pluton are explored,providing new evidences for the tectonic evolution of the Indosinian period in this region.The rock geochemical analysis of granite porphyry shows that the content of SiO_(2) is 69.50%~73.48%,the content of TiO_(2) is 0.008%~0.084%,the content of CaO is 0.22%~2.07%,the content of Na_(2)O is 2.96%~3.40%,the content of K_(2)O is 4.38%~4.84%,the content of Al 2O 3 is 14.74%~16.19%,the aluminum saturation index A/CNK value is 1.49~1.91(>1.1),and the Rittman indexσis 1.88~2.27.The result indicates the granite belonging to high potassium calc alkaline peraluminous S-type granite.Total rare earth element(ΣREE)content is 42.82×10^(-6)~62.85×10^(-6),LREE/HREE value is 16.55~24.19,light rare earth element is relatively enriched,and theδEu value is 0.79~1.41.High field strength elements P and Ti are relatively deficient,the Nb and Ta are slightly deficient,and large ion lithophile elements and light rare earth elements Th,Rb and K are relatively enriched.The geochemical characteristics of rocks show that the Nazha pluton originated from the partial melting of metamorphic sandstones and mudstones,with the high Mg#value(67~77),and the low total rare earth element content,with some.The mantle-derived components added during diagenesis.LA-ICP-MS zircon U-Pb age(250.4±1.0 Ma)was obtained from granite porphyry and formed in Early Indosinian period.Combined with the regional geological background,the author believes that the Xiahe-Hezuo area in West Qinling region was in the continental margin arc environment of crustal and lithosphere thickening during the Early Indosinian period,and the Nazha pluton is the product of the magmatism in this stage.

关 键 词：锆石U-Pb年龄 花岗斑岩 早印支期 那扎岩体 地质调查工程 西秦岭 

分 类 号：P534.51[天文地球—古生物学与地层学] P588.11[天文地球—地质学] P597.3