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陈井胜,刘淼,李斌,李伟,李崴崴,杨帆,汪岩.内蒙古翁牛特旗晚志留世二长花岗岩年代学及地球化学特征[J].地质通报,2017,(8):1359-1368.
内蒙古翁牛特旗晚志留世二长花岗岩年代学及地球化学特征    点此下载全文
陈井胜1  刘淼1  李斌1  李伟1  李崴崴2  杨帆1  汪岩1
1. 中国地质调查局沈阳地质调查中心, 辽宁 沈阳 110034;
2. 辽宁省地质矿产研究院, 辽宁 沈阳 110029
基金项目:中国地质调查局项目《内蒙古1:5万敖汉旗、捣各郎营子、新地、铁匠营子幅区域地质矿产调查》(编号:12120113053400)、《辽宁1:5万台吉、他拉皋、七道岭、十二台营子幅区域地质调查》(编号:DD20160048-05)、《内蒙古敖汉旗大黄花地区矿产地质调查》(编号:12120114055501)
DOI:
摘要:
      内蒙古翁牛特旗小营子地区铅锌矿周围分布有大面积花岗岩,野外地质调查及室内鉴定为二长花岗岩。通过LA-ICPMS锆石U-Pb同位素测试,确定其形成时代为419.3±9.2Ma,属于晚志留世。二长花岗岩中SiO2含量为74.41%~75.05%,K2O含量为3.05%~4.42%,K2O/Na2O值介于0.70~1.11之间,Al2O3含量为13.22%~14.02%,铝饱和指数(A/CNK)为0.99~1.1,Fe、Mg、Ti氧化物含量较低,这些特征显示二长花岗岩为富硅、略富铝、中高钾钙碱性I型花岗岩。轻、重稀土元素比值(LREE/HREE)在10.61~16.61之间,(La/Yb)N值在12.52~27.44之间,轻、重稀土元素分馏明显,δEu值为0.48~0.81,显示中等负Eu异常。富集大离子亲石元素Rb、Ba、U、K,相对亏损高场强元素Nb、Zr、Hf,具有低的Sr、Yb含量。地球化学特征显示,二长花岗岩形成于活动大陆边缘火山弧。结合区域地质资料推断,小营子二长花岗岩是在古亚洲洋向华北板块俯冲背景下白乃庙岛弧消亡过程中形成的。
关键词:翁牛特旗  二长花岗岩  锆石U-Pb测年  地球化学  白乃庙岛弧
Zircon U-Pb chronology and geochemical characteristics of Late Si-lurian monzogranite in Ongniud Bannar, Inner Mongolia    Download Fulltext
CHEN Jingsheng1  LIU Miao1  LI Bin1  LI Wei1  LI Weiwei2  YANG Fan1  WANG Yan1
1. Shenyang Center of China Geological Survey, Shenyang 110034, Liaoning, China;
2. Liaoning Institute of Geology and Mineral Resources, Shenyang 110029, Liaoning, China
Fund Project:
Abstract:
      The granite widely distributed in the Xiaoyingzi lead-zinc ore deposit of Ongniud Bannar, Inner Mongolia, consists of monzogranite as revealed by field geological survey and thin section identification. Zircon LA-ICP-MS U-Pb dating result shows that the monzogranite was formed in late Silurian (419.3±9.2Ma) rather than in Mesozoic as previously held. The values of SiO2, K2O, K2O/Na2O, Al2O3 are 74.41%~75.05%, 3.05%~4.42%, 0.70~1.11, 13.22%~14.02% respectively, the aluminum saturation index-es (A/CNK) range from 0.99 to 1.1, and the oxides of Fe, Mg, Ti are relatively low, which implies that the monzogranite is I-type granite. The ratios of light and heavy rare elements (LREE/HREE) are between 10.61 and 16.61, and the (La/Yb)N ratios are be-tween 12.52 and 27.44, suggesting obvious fractionation between light and heavy rare elements. The values of δEu are 0.48~0.81 with moderate negative europium anomaly. It is enriched in large ion lithophile elements (LILEs) Rb, Ba, U, K, depleted relatively in high field strength elements (HFSEs) Nb, Zr, Hf, and depleted relatively in Sr, Yb. All these geochemical characteristics show that the monzogranite is a product of volcanic arc on an active continental margin. The regional geological data reveal that the monzogranite was formed in the process of extinction of Bainaimiao island arc in the setting of subduction of the Paleo Asian Ocean to the North China craton.
Keywords:Ongniud Bannar  monzogranite  zircon U-Pb dating  geochemical  Bainaimiao island arc
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