滇西马厂箐煌斑岩成因:地球化学、年代学及Sr-Nd-Pb-Hf同位素约束  

Genesis of lamprophyres from Machangqing, western Yunnan: Constraints from geochemistry, geochronology and Sr-Nd-Pb-Hf isotopes

作　　者：贾丽琼[1,2] 莫宣学[1,2] 董国臣[1,2] 徐文艺[3] 王梁[1,4] 郭晓东[4] 王治华[1,4] 韦少港[1,2] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [3]中国地质科学院矿产资源研究所,北京100037 [4]武警黄金地质研究所,廊坊065000

出　　处：《岩石学报》2013年第4期1247-1260,共14页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2009CB421002);111计划项目(B07011);长江学者和创新团队发展计划(IRT1083);中国地质调查局研究项目(1212011220920)联合资助

摘　　要：滇西马厂箐煌斑岩脉分为早晚两期,早期为云斜煌岩,晚期为云煌岩。对煌斑岩样品进行锆石LA-MC-ICP-MSU-Pb定年,获得33.77±0.11Ma的岩浆侵位年龄,表明马厂箐煌斑岩为马厂箐复式杂岩体中期岩浆结晶作用的产物,也是金沙江-哀牢山断裂带新生代早期岩浆活动的产物。岩石地球化学分析表明马厂箐煌斑岩高钾(K2O/Na2O=2.88～4.60)、富碱(K2O+Na2O=6.40%～7.55%)、高Mg#(74.3～76.9),富集大离子亲石元素(LILE)(K、Rb、Ba)和轻稀土元素(LREE),亏损高场强元素(HFSE)(Nb、Zr、P)和重稀土元素。同位素以高(87Sr/86Sr)i(0.707406～0.706506),低εNd(t)(-1.78～-7.64),富集放射性Pb(208Pb/204Pb=38.87～39.35,207Pb/204Pb=15.6390～15.6431,206Pb/204Pb=18.6579～18.8093)为特征。176Hf/177Hf为0.282712～0.282864,εHf(t)为-1.4～4.0,εNd(t)与εHf(t)存在Nd-Hf同位素解耦。根据岩石地球化学和同位素特征以及区域构造演化历史分析,马厂箐煌斑岩起源于金沙江洋壳俯冲交代作用形成的富集地幔,区域上软流圈物质上涌可能促使EMII的部分熔融形成煌斑岩岩浆,而金沙江-哀牢山断裂及其与其他断裂的交汇处则为岩浆上侵提供了良好的通道。Lamprophyres occur as early and late dykes in Machangqing, western Yunnan. The early lamprophyres are mostly kersantons and the late are minettes. Zircon LA-MC-ICP-MS U-Pb dating yields an age of 33.77±0.11Ma, which indicate lamprophyres are the product of middle stage magmatic process of Machangqing complex and early pulse of Cenozoic magmatism in the Jinshajiang-Ailaoshan fault belt. Geochemically, the lamprophyres have high values of potassium （K2O/Na2O=2.88-4.60）, alkaline （K2O＋Na2O=6.40%-7.55%） and Mg#（74.3-76.9） and are enriched in large ion lithophile elements （K, Rb, Ba） and LREEs and depleted in the high field strength elements （Nb, Zr, P） and HREEs. The isotopes of lamprophyres are characterized by high （87Sr/86Sr）i （0.707406-0.706506） , low εNd（t） （-1.78--7.64） but enriched radioactive Pb （208Pb/204Pb=38.87-39.35, 207Pb/204Pb=15.6390-15.6431, 206Pb/204Pb=18.6579-18.8093） . The ratios of 176Hf/177Hf range from 0.282712 to 0.282864, with εHf（t） values varying from -1.4 to 4.0. The εNd（t） and εHf（t） values show a Nd-Hf decoupling feature. Based on the geochemistry, isotopes and the regional tectonic evolution history, the lamprophyres were derived from EMII produced by an interaction between the Jinshajiang oceanic crust and the mantle peridotite while the heat was provided by the upwelling asthenosphere. The Jinshajiang-Ailaoshan fault belt is likely to act as migration channels for magmatic emplacement.

关 键 词：煌斑岩 地球化学 年代学 Sr-Nd-Pb-Hf同位素 岩石成因 马厂箐 

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