江西武山铜矿区花岗闪长斑岩的地球化学和Sr-Nd-Hf同位素组成及成因探讨  

Geochemical and Sr-Nd-Hf isotopic compositions of granodiorite from the Wushan copper deposit,Jiangxi Province and their implications for petrogenesis

作　　者：蒋少涌[1] 李亮[1] 朱碧[1] 丁昕[1] 姜耀辉[1] 顾连兴[1] 倪培[1] 

机构地区：[1]南京大学地球科学系成矿作用国家重点实验室,南京210093

出　　处：《岩石学报》2008年第8期1679-1690,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金(40221301);科技部十一五支撑计划课题(2006BAB01B06);江苏省自然科学基金(BK2008026)联合资助

摘　　要：武山铜矿床是位于长江中下游地区九瑞矿集区中的一个大型铜矿床。本文对该矿床中与成矿关系密切的花岗闪长斑岩进行了详细的矿物化学、主量元素、微量元素、Sr-Nd-Hf 同位素研究。结果表明,岩体中黑云母富镁,为金云母,其 Fe^(3+)/Fe^(2+)组成表明岩浆氧逸度很高;角闪石具有 Mg/(Mg+Fe)高而 Si 低的特征,为阳起石和镁质角闪石,角闪石压力计计算表明岩体具有超浅成侵位特征。花岗闪长斑岩具有埃达克岩地球化学特征。岩石具有相对较高的 SiO_2(64.9%～68.62%,平均66.52%)和 Al_2O_3(14.0%～15.3%,平均14.8%)含量,同时岩石的 Mg~#很高(0.53～0.71),并具有相对较高的相容元素含量;岩石富集轻稀土((La/Yb)_N=27.8～64.5),Eu 负异常不明显,岩石同时富集大离子亲石元素,亏损高场强元素,具有较高的 Sr/Y 比值(35.0～68.2)。岩石的初始^(87)Sr/^(86)Sr 比值为0.7067～0.7075,ε_(Nd)(t)值为-4.08～-4.44,锆石的ε _(Hf)(t)值为-2.1～-7.0。详尽的元素和同位素地球化学特征表明武山花岗闪长斑岩是强烈壳幔相互作用的产物,很有可能是由拆沉的加厚下地壳发生部分熔融,并在其上升过程中与地幔橄榄石发生相互作用而形成的。Wushan deposit is a large copper deposit located in the Jiu-Rui mineralization concentrated area in the Middle and Lower Yangtze Reaches, south China. In this study, we report mineral chemistry, major, trace elements, and Sr-Nd-Hf isotopic compositions of the ore-related granodiorite at Wushan. The biotites are Mg-riched and belong to phlogopite, which Fe^3＋/Fe^2＋ ratios indicating a high oxygen fugacity （fO2） for the magma. The amphiboles show high Mg/（ Mg ＋ Fe） and low Si, and belong to actinolite and magnesiohornblende. The hornblende geobarometer indicates an ultra-shallow emplacement of the granodiorite. The rocks show geochemical characteristics of adakitic affinity with high SiO2 （64.9% - 68.62%, average 66.52% ） and A12 03 （ 14.0% - 15.3% , average 14.8% ）, and high Mg^# （0.53 - 0.71 ）. The trace elements are characterized by enrichment of K, Rb, Ba and Th, depletion of Nb, Ta, and Ti, high Sr, low Y, Sr/Y ratios of 35.0 - 68.2, and higher contents of V, Cr, Co and Ni. The REE characteristics are LREE enriched with （La/Yb） N ratio of 27.8 - 64.5, and lack any significant negative Eu anomaly. The initial ^87Sr/^86Sr ratios are low from 0.7067 to 0.7075, and the εNd （t） values are high at - 4.08 to - 4.44. The zircon Hf isotope analysis shows εNf （t） values of -2.1 to -7.0. These data suggested that the Wushan granodiorite was produced by strong crust-mantle interaction with very high proportion of mantle component, and was most likely derived from partial melting of delaminated lower crust at around 145 Ma. During its ascent, the magma may possibly have reacted with surrounding mantle peridotites.

关 键 词：武山铜矿 花岗闪长斑岩 地球化学特征 Sr-Nd—Hf同位素组成 壳幔相互作用 

分 类 号：P618.41[天文地球—矿床学] P588.132[天文地球—地质学]