中文摘要:文章对黔西南白层地区出露的燕山期超基性岩墙进行了单颗粒锆石SHRIMP U_Pb年龄和Hf同位素组成研究，获得A、B两组不同的锆石年龄。A组锆石呈不规则粒状，具不完整的宽大条带，12颗锆石的 SHRIMP U-Pb年龄加权平均值为（84±1）Ma，代表了超基性岩墙的侵位年龄；锆石Hf原位分析表明，176Hf/177Hf 从0.282561到0.282719，εHf（84 Ma）平均为-3.61，表明岩浆源区主要以富集地幔为主，并受到部分地壳物质的混染。B组锆石晶形完整，具典型的中酸性岩浆型振荡环带，3颗锆石的SHRIMP U-Pb模式年龄为409～450 Ma。176Hf/177Hf 从0.282379到0.282440，εHf(t)平均为-3.77，均低于A组锆石，属于捕获锆石。据此认为84 Ma左右由于华南岩石圈伸展，软流圈地幔上涌，导致岩石圈富集地幔部分熔融，熔体上升过程中与409～450 Ma左右形成的少量地壳岩石发生混染，随后快速侵位冷凝而形成基性_超基性岩墙。白层地区84 Ma的超基性岩浆活动是整个华南西部燕山晚期（80～90 Ma）岩浆活动的一部分。右江褶皱带周缘的燕山晚期岩浆活动主要与大规模的Sn、W、Ag、Cu、Pb、Zn等矿床有关，但右江褶皱带内部的燕山晚期岩浆活动是否与以卡林型金矿为代表的低温热液矿床有成因上的联系，尚需更多矿床年代学资料的证实。
Abstract:The Baiceng basic_ultrabasic dykes in southwest Guizhou constitute the large
st outcrop of Yanshanian basic_ultrabasic rocks in Youjiang fold belt. Two group
s of zircon (group A and B) were obtained in the rocks. Group A zircon grains as
sume the irregular granular form and incomplete broad bands. The SHRIMP U_Pb ana
lysis of 12 zircon grains gave a weighted mean 206Pb/238U age of (84±1)Ma, which is interpreted as the emplacement age of this intrusion. LA-MC-ICP-MS insitu Lu-Hf isotopic analysis of the same zircon grains gave 176Hf/177Hf ratios ranging from 0.282561 to 0.282719 and the average εHf(84 Ma) of -3.61, suggesting that their parental magmas were mainly derived from a enriched mantle and partly mixed with the lower continental crust rock. The other group of zircon grains (Group B) have a perfect crystal shape and typical oscillatory zoning. The SHRIMP U_Pb analysis of 3 zircon grains gave a 206Pb/238U model age of 409～450 Ma,176Hf/177Hf ratios ranging from 0.282379 to 0.282440, and average εHf（t）of -3.77, lower than the values of Group A. These data indicate that Group B zircon grains are captured ones. It is inferred that the Baiceng basic-ultrabasic pluton originated from a mixed melting between an enriched lithospheric mantle and the continental crust rock formed in 409～450 Ma, responding to an extension of lithosphere at 84 Ma or so. This induced the upwelling of asthenospheric mantle. The Baiceng basic_ultrabasic magma activity of 84 Ma was part of the Late Yanshanian magmatic activity in western South China. The Late Yanshanian magmatic activity on the margin of Youjiang folded belt was related to large-scale Sn, W, Ag, Cu, Pb, Zn mineralization. Nevertheless, the problem that whether the Carlin_type gold deposits are related to magmatic activity of this epoch inside the Youjiang fold belt is worthy of further discussion.
keywords:geochemistry, zircon U_Pb age,Hf isotopic composition, ultrabasic rock,Baicceng,southwestern Guizhou
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基金项目:中央级公益性科研院所基本科研业务费专项资金K2007_1_2）、国家重点基础研究发展计划（973计划）(2007CB411407)和中国博士后科学基金（20080430456）
引用文本：
陈懋弘,章 伟，杨宗喜,陆 刚,侯可军,刘建辉.2009.黔西南白层超基性岩墙锆石SHRIMP U-Pb年龄和Hf同位素组成研究[J].矿床地质,28(3):240~250Chen MaoHong,ZHANG Wei,YANG ZongXi,Lu Gang,Hou KeJun,LIU JianHui.2009.Zircon SHRIMP U-Pb age and Hf isotopic composition of Baiceng ultrabasic dykes in Zhenfeng Couty,southwestern Guizhou Province[J].Mineral Deposits28(3):240~250
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