壳幔岩浆混合作用与陆内环境高Sr/Y斑岩的形成及成矿：实例与探讨  

Crust-mantle magma mixing and implications for the formation of high Sr/Y ore-bearing porphyries in non-arc environments:A case study and discussion

作　　者：马星华 王志强[2] 王超[2] 鄢雪龙[2] 

机构地区：[1]国土资源部成矿作用与资源评价重点实验室、中国地质科学院矿产资源研究所,北京100037 [2]造山带与地壳演化教育部重点实验室、北京大学地球与空间科学学院,北京100871

出　　处：《岩石学报》2014年第7期2020-2030,共11页Acta Petrologica Sinica

基　　金：国家“973”项目(2013CB429804);国家青年科学基金项目(41202033)联合资助

摘　　要：产于陆内环境的含矿斑岩往往具有高Sr/Y特征,多数学者认为与岩浆起源于加厚或拆沉的下地壳有关。然而,目前这一模式仍存在较大争议。本文以敖仑花斑岩矿床为例,新报道了矿区内不成矿岩体的岩石学和地球化学特征,与同期成矿岩体进行对比,探讨含矿斑岩高Sr/Y原因及控制是否成矿的可能因素。相对于含矿斑岩,敖仑花贫矿黑云母花岗岩具有高SiO2（74%~78%）、低MgO（〈0.2%）和CaO（0.2%~1.1%）、贫Sr（30×10^-6~251×10^-6）和Cr（1×10^-6~6×10^-6）的特征,显示准铝质到过铝质性质（A/CNK=0.9~1.2）,Mg#值（2~30）与玄武岩实验熔体成份相似,说明岩浆可能主要来自基性下地壳源区的部分熔融。而已有的研究表明含矿斑岩为壳幔岩浆混合成因,富集地幔起源的偏基性岩浆的加入提升了寄主长英质岩浆的Mg#值、大离子亲石元素（Sr、La等）含量及其氧逸度（fO2）。我们认为幔源岩浆的混合可能是导致陆内环境含矿斑岩高Sr/Y及有利成矿的根本原因;相反,来自纯壳源的花岗质熔体因缺乏富水、高fO2幔源岩浆的参与而不利于形成斑岩Cu±Au±Mo矿床。A Ore-bearing porphyries formed in non-arc environments （such as continental collision zones and intra-continents） often have high Sr/Y ratios. Most researchers advocate that intermediate to felsic magmas for these ore-bearing porphyries originated from a thickened or delaminated continental lower crust source. However, this model is still under discussion. Here we report a case study to provide new insights into this issue and give a different interpretation. The Aolunhua porphyry Mo-Cu deposit from the eastern Central Asian Orogenic Belt formed in an intra-continental extensional setting during the Early Cretaceous. Two types of granitic intrusions have been recognized in the mining area. One is the fertile monzogranite-porphyry （formed at 132Ma by zircon U-Pb dating）, and the other one is the barren biotite granite （formed at 126Ma by zircon U-Pb dating）. In this paper, we present new petrological and geochemical data of the barren biotite granite, and compare these data with that of the fertile monzogranite-porphyry reported by previous studies. Our results show that the barren biotite granite has relatively high SiO2 （74.4% -78. 3% ）, K2O （4. 3% -4. 9% ）, Y （ 18.4 × 10^-6 -27.6×10^-6） andYb （2.4×10^-6 -3.0×10^-6）, but lowMgO （〈0.2%）, CaO （0.2% -1.1%）, Sr （30×10^-6 -251× 10^-6） and Cr （1.1 × 10^-6- 5.8× 10^-6） contents, and Mg# values （2 - 30）. They are metaluminous to peraluminous （A/CNK = 0. 9 - 1.2 ）, and show relatively flat REE patterns and pronounced negative Eu anomalies （ Eu/Eu＊ = 0. 05 - 0. 2 ） . These compositions are comparative to those of metabasaltic experimental melts （1-4.0GPa）, suggesting that magmas of the biotite granite probably derived from partial melting of a lower crust source. In contrast, the fertile monzogranite-porphyry contains plenty of mafic microgranular enclaves （ MMEs）, and is enriched in St, Ba, LREE and other LILE. They show concave REE patterns with negligible Eu anomalies, and have high Sr and La,

关 键 词：斑岩矿床 埃达克岩 壳幔岩浆混合 陆内环境 

分 类 号：P588.13[天文地球—岩石学] P611[天文地球—地质学]