| 小兴安岭东安金矿区细粒正长花岗岩U-Pb年龄、岩石地球化学、Hf同位素组成及地质意义 |
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| 引用本文： | 李碧乐,孙永刚,陈广俊,郗爱华,支宇博,常景娟,彭勃.小兴安岭东安金矿区细粒正长花岗岩U-Pb年龄、岩石地球化学、Hf同位素组成及地质意义[J].地球科学,2016,41(1):1-16. |
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| 作者姓名： | 李碧乐 孙永刚 陈广俊 郗爱华 支宇博 常景娟 彭勃 |
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| 作者单位： | 1.吉林大学地球科学学院，吉林长春 130061 |
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| 基金项目： | 中国地质调查局地质大调查项目12120111086020吉林省科技发展计划重点项目20100445国家自然科学基金项目41272093国家自然科学基金项目41272095 |
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| 摘 要： | 东安金矿区细粒正长花岗岩是小兴安岭燕山早期与吉黑东部斑岩型-矽卡岩型钼多金属矿床有关的花岗岩带组成岩体之一.为了解区域燕山早期岩浆演化和大规模钼多金属热液的成矿作用，进一步提升东安金矿成矿地质背景的研究程度，对该花岗岩进行了岩石地球化学、锆石U-Pb年龄和Hf同位素研究，讨论了岩石成因、岩浆源区和构造背景.获得细粒正长花岗岩锆石LA-ICP-MS U-Pb定年结果184±2 Ma，MSWD=1.2，为早侏罗世.岩石富硅和钾(K2O/Na2O值为1.46~1.81)，低钙、镁和Mg#(Mg#=12.79~23.52)，A/CNK=1.05~1.14，属高钾钙碱性、弱过铝质系列岩石.岩石富集大离子亲石元素(Rb、K)和不相容元素(Th、U)，亏损高场强不相容元素(Nb、Ti等)，轻、重稀土元素分馏强烈，轻微负Eu异常(Eu/Eu*=0.76~0.92).综合岩石地球化学特征、Harker图解、Ce-SiO2和(K2O+Na2O)/CaO-(Zr+Nb+Ce+Y)判别图解确定岩石为高分异I型花岗岩.锆石的176Hf /177Hf值为0.282 588~0.282 775，εHf(t)值为-2.35~+3.94，二阶段模式年龄TDM2为973~1 386 Ma，岩浆源区应主要为起源于亏损地幔的中新元古代新增生陆壳的部分熔融，有硅铝质地壳物质的加入.研究表明，岩石形成于古太平洋板块俯冲引起大陆弧后伸展和岩石圈减薄的构造背景，幔源岩浆底侵为地壳熔融提供了热动力.燕山早期伸展体制下大陆岩浆弧环境的中-浅成、高钾钙碱性花岗质小侵入体是吉黑东部斑岩型-矽卡岩型钼多金属矿床找矿的主要目标.
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| 关 键 词： | 小兴安岭 东安金矿 细粒正长花岗岩 岩石地球化学 锆石U-Pb年龄 Hf同位素 |
| 收稿时间： | 2015-11-01 |
Zircon U-Pb Geochronology,Geochemistry and Hf Isotopic Composition and Its Geological Implication of the Fine-Grained Syenogranite in Dong’an Goldfield from the Lesser Xing’an Mountains |
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| Abstract: | The fine-grained syenogranite in the Dong'an goldfield is the early Yanshanian granite body in the Lesser Xing'an Mountains, it is one of the granite bodys of the granite belt which is related to porphyry and skarn-type molybdenum-polymetallic deposits in the east Jilin-Heilongjiang Province. In order to understand regional magmatic evolution in the early Yanshanian and cosmical molybdenum-polymetallic hydrothermal mineralization, thus further promote the research degree of the metallogenic background in the Dong'an goldfield. This paper presents geochemisty, zircon U-Pb geochronology, and Hf-isotopic data of these rocks, their petrogenesis, sources and tectonic implications have been investigated. The granitic rocks yield an average zircon LA-ICP-MS U-Pb age of 184±2 Ma (MSWD=1.2), i.e., the Early Jurassic. The granites have high SiO2 (75.39%-78.84%) and K2O (K2O/Na2O: 1.46~1.81), low CaO, MgO and Mg# (12.79-23.52), with A/CNK values of 1.05-1.14, indicating high potassium calc-alkaline, weakly peraluminous granites. The granites are enriched in large ion lithosphile elements (Rb, K) and incompatibale elements (Th, U), and depleted in high field-strength element (Nb, Ti). They have strong fractionation between LREE and HREE, as well as slightly negative Eu anomalies (Eu/Eu*=0.76-0.92). It was shown that these granitic rocks belong to highly fractionated I-type granites according to lithogeochemical constituents, Harker plots, the discrimination diagrams of Ce vs. SiO2 and (K2O+Na2O)/CaO vs. Zr+Nb+Ce+Y. All zircons in the granites have 176Hf/177Hf ratios ranging from 0.282 588 to 0.282 775, εHf(t) values ranging from -2.35 to +3.94, and two-stage Hf model ages (TDM2) ranging from 973 to 1 386 Ma. It was indicated that the magma was originated from the partial melting of Meso-Neoproterozoic juvenile accreted lower crust that was derived from the depleted mantle, with addition of ancient sialic crustal materials. The results show that the granites were generated from the extensional and lithospheric thinning environment due to the subduction of the Paleo-Pacific plate, and underplating of the mantle-derived magma provided the thermodynamic power for the partial melting of the crust. The small scale hypabyssal-middle high potassium calc-alkaline granitic intrusive bodies that were generated in the continental arc extension setting in the early Yanshanian are main targets for the prospecting of porphyry and skarn-type molybdenum-polymetallic deposits in the east Jilin-Heilongjiang Province. |
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