德兴花岗闪长斑岩SHRIMP锆石U-Pb年代学和Nd-Sr同位素地球化学  

SHRIMP zircon geochronology and Nd-Sr isotopic geochemistry of the Dexing granodiorite porphyries.

作　　者：王强[1] 赵振华[1] 简平[2] 许继峰[1] 包志伟[1] 马金龙[1] 

机构地区：[1]中国科学院广州地球化学研究所,广州510640 [2]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2004年第2期315-324,共10页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40273019;40172028);中国科学院知识创新项目(KZCX3-SW-122;KZCX2-SW-117;KZCX2-102);国家重点基础研究发展规划项目(G1999043202)的资助。

摘　　要：德兴斑岩铜矿区的成矿斑岩的形成时代一直存在争议。本文对铜厂、富家钨花岗闪长斑岩进行了SHRIMP锆石U-Pb年代学研究。研究结果显示:(1)铜厂花岗闪长斑岩样品中锆石15个分析点的206Pb/238U年龄为165～177Ma.206Pb/238U年龄的加权平均值为171±3 Ma;(2)富家钨花岗闪长斑岩样品中锆石15个分析点的206Pb/238U年龄为166-177Ma,206Pb/238U年龄的加权平均值也为171±3 Ma。因此,德兴花岗闪长斑岩形成于中侏罗世(171±3 Ma)。该年龄与德兴斑岩铜矿区辉钼矿的Re-Os同位素年龄(173 Ma)在误差范围内一致,暗示了成岩成矿的一致性。德兴花岗闪长斑岩的形成时代与华南地区许多A型花岗岩,双峰式或板内火成岩和矿床的形成时代也大致一致,同时也与赣-杭裂谷带的活动时间一致,表 明德兴斑岩铜矿和花岗闪长斑岩形成于一个伸展的动力学背景下。另外,德兴花岗闪长斑岩很少有老的继承锆石以及其高的εNd(t)(-1.14-+1.80)和极低的初始87St/86Sr比值(0.7044-0.7047),暗示古老的地壳物质对其贡献并不明显,地幔物质可能在德兴花岗闪长斑岩的成因中发挥了重要作用。再结合其具有的埃达克质岩的元素地球化学特征。本文认为德兴花岗闪长斑岩很可能由拆沉下地壳物质的熔融形成。The formation time of ore-forming porphyries associated with the Dexing porphyry copper deposit has been disputed for a long time. This paper presents the data of the Sensitive High-Resolution Ion Microprobe ( SHRIMP- Ⅱ ) zircons geochronology data from the Tongchang and Fujiawu granodiorite porphyries. The results show that; (1) for the zircons from the Tongchang granodiorite porphyry, all 15 analyses give concordant 206Pb/238U ages in a narrow range of 165 - 177Ma, which correspond to a single age population with a weighted mean 206Pb/238U age of 171±3 Ma; and (2) for the zircons from the Fujiawu granodiorite porphyry, all 15 analyses give concordant 206Pb/238U ages in a narrow range of 166 ~ 177Ma, which correspond to a single age population with a weighted mean 206Pb/238U age of 171±3 Ma. This age (171±3 Ma) is interpreted as the formation time of the Dexing granodiorite porphyries, and is approximately consistent with the activity of Gan-Hang rift, A-type granites, bimodal or within-plate igneous rocks or ore deposit in South China. Therefore, the Dexing porphyry copper deposit and associated granodiorite porphyries were likely formed in an extensional setting. In addition, the Dexing granodiorite porphyries have few inherited zircons, and exhibit high εNd(t)( - 1. 14 to + 1. 80) and very low initial 87Sr/86Sr ratios (0. 7044 -0. 7047) , which indicate that old crustal materials probably played little role in their petrogenesis but mantle-derived new materials likely played an important role. Connected with their elemental geochemical characteristics of adakites, the Dexing granodiorite porphyries were considered to possibly originate from partial melting of delaminated lower crust.

关 键 词：SHRIMP锆石U-PB年代学 埃达克岩 拆沉 斑岩铜矿 构造背景 德兴 华南 

分 类 号：P597.3[天文地球—地球化学] P588.13[天文地球—地质学]