峨眉山大火成岩省赋Nb-Ta-Zr矿化正长岩脉的形成时代和锆石Hf同位素组成  

Zircon U-Pb ages and Lu-Hf isotopic compositions of the Nb-Ta-Zrbearing syenitic dikes in the Emeishan large igneous province

作　　者：王汾连[1,2] 赵太平[1] 陈伟[3] 王焰[1] 

机构地区：[1]中国科学院广州地球化学研究所,广州510640 [2]中国科学院大学,北京100049 [3]香港大学地球科学系

出　　处：《岩石学报》2013年第10期3519-3532,共14页Acta Petrologica Sinica

基　　金：国家基础研究发展计划(973项目)(2011CB808903)资助

摘　　要：攀西地区广泛发育Nb-Ta-Zr矿正长岩脉,它们在空间上与峨眉山大火成岩省的玄武岩、辉长岩及长英质岩体(正长岩和花岗岩)共生,但是否有成因联系并不清楚。本文对攀西地区炉库和白草两个Nb-Ta-Zr矿区中的正长岩体、无矿及含矿正长岩脉进行了锆石LA-ICPMS法U-Pb定年和Lu-Hf同位素研究。研究表明,炉库矿区正长岩体和无矿正长岩脉锆石UPb年龄为255.6±2.0Ma和255.6±1.5Ma,含矿正长岩脉为256.7±4.4Ma;白草矿区正长岩体和含矿正长岩脉形成时间为257.9±2.3Ma和257.8±1.3Ma。这些年龄结果均显示攀西地区Nb-Ta-Zr矿化的形成时代与正长岩体一致,说明Nb-Ta-Zr矿化的形成与峨眉山大火成岩省紧密相关,为地幔柱成矿系统的一部分。两个矿区含矿正长岩脉的锆石εHf(t)值分别为+0.1^+9.5(多数集中于+2^+6,炉库矿区)和-0.2^+7.7(白草矿区),与正长岩体相似(炉库矿区为+1.0^+6.6,白草矿区为+2.1^+6.2),说明含矿岩脉与正长岩体有紧密成因联系。结合锆石年龄和Hf同位素研究初步认为,正长岩体和正长岩脉是峨眉山地幔柱岩浆底侵到下地壳底部的基性岩再次部分熔融的结果。Both Nb-Ta-Zr-bearing and Nb-Ta-Zr-barren syenitic dikes of the Luku and Baicao ore districts in the Panxi region （SW China） are spatially associated with basalts, gabbreic and felsic （granitic and syenitic） intrusions of the ～260Ma Emeishan large igneous province （ELIP）. The syenitic plutons, barren and mineralized dikes at Luku were dated to be 255.6 ± 2. OMa, 255. 6 ± 1.5Ma and 256. 7 ±4. 4Ma, respectively. The syenitic pluton and mineralized dikes at Baicao were dated to be 257. 9 ± 2. 3Ma and 257. 8 ± 1.3Ma, respectively. These age data indicated that the Nb-Ta-Zr mineralization hosted in the syenitic dikes are part of the ELIP. Mineralized dikes at Euku and Baicao have zircon εnf （t） values ranging mostly from ＋ 2 to ＋ 6 and -0. 2 ～ ＋ 7.7, comparable to those of the spatially closely associated syenitic plutons （ ＋ 1.0 ～ ＋ 6. 6 in Luku and ＋ 2. 1 ～ ＋ 6. 2 in Baicao）, implying that the mineralized dikes may have evolved from the syenitic magma. This is important for regional exploration of Nb-Ta-Zr deposits. We consider that the syenitic plutons and dikes may be the products of partial melting of underplated mafic cumulates.

关 键 词：Nb-Ta-Zr矿 锆石U-PB年龄和HF同位素 正长岩脉 攀西地区 峨眉大火成岩省 

分 类 号：P588.133[天文地球—岩石学] P597.3[天文地球—地质学]