新疆萨惹什克锡矿与萨北碱性A型花岗岩成因关系的年代学制约  

Genetic connection of Sareshike tin deposit with the alkaline A-type granites of Sabei body in Xinjiang:constraint from isotopic ages.

作　　者：唐红峰[1] 屈文俊[2] 苏玉平[1] 侯广顺[1] 杜安道[2] 丛峰[1] 

机构地区：[1]中国科学院地球化学研究所地球深部物质与流体作用地球化学研究室,贵阳550002 [2]国家地质实验测试中心,北京100037

出　　处：《岩石学报》2007年第8期1989-1997,共9页Acta Petrologica Sinica

基　　金：国家自然科学基金项目;国家重点基础研究发展规划项目(2001CB409805)资助.

摘　　要：新疆东准噶尔地区的萨惹什克锡矿呈脉状产于萨北花岗岩体中。对于这种脉状矿床,成岩和成矿近时性的时间制约是证明矿床与围岩有成因关系的首要证据。萨北岩体由含碱性铁铁矿物的碱性花岗岩组成,全岩地球化学结果显示,碱性花岗岩具高碱、低 Ca,明显富集稀土元素、高场强元素(Zr,Hf,Nb,Ta,Y)和大离子亲石元素(Rb,Th,U),而强烈亏损Sr,Ba,Eu,属于典型的碱性 A 型花岗岩。锡矿脉由占绝对优势的锡石和石英组成,受北东和近东西向的断裂破碎带控制。原有研究证实,形成该锡矿床的成矿流体属于具高温、低盐度和低密度的岩浆水。据此并结合锡矿体的围岩性质,前人认为锡矿床与碱性花岗岩有成因联系。但是,由于分析技术和样品选择上的制约,萨北岩体成岩和萨惹什克锡矿成矿的确切时代一直没有得到合理的解决。本文报道了我们最近获得的碱性花岗岩锆石 LA-ICP-MS U—Pb 和锡矿石辉钼矿 Re-Os 同位素年龄(分别为306±3Ma 和307±11Ma)。上述结果表明,萨北碱性花岗岩和萨惹什克锡矿石属于同期地质事件的产物,从而为两者具有密切成因联系提供了重要的年代学制约。此外,根据碱性花岗岩的ε_(Nd)(t)(≈+5.0)低于研究区亏损地幔4.5个ε单位,我们认为形成萨北岩体的花岗岩浆不是直接来源于亏损地幔玄武质岩浆结晶分异作用的产物,而更可能是起源于本区年轻洋壳和陆源沉积物的部分熔融。Abstract Sareshike tin deposit occurs as veins within Sabei granitic body in East Junggar, Xinjiang. For such vein deposit, the temporal constraint from nearly simultaneous mineralization with emplacement is the most important evidence for confirming the genetic connection between the ore-body and its direct wall rock. Sabei body is composed of alkalin granites with the development of alkaline ferromagnesian. The granites have high alkali but low Ca contents, obvious enrichment in REE, HFSE （Zr, Hf, Nb, Ta, Y） and LILE （ Rb, Th, U）, and strong depletion of Sr, Ba, Eu. They are defined as typical alkaline A-type. The ore veins are predominately composed of cassiterite and quartz, and their occurrence is controlled by faults in NE and nearly EW trend. Previous investigation has shown that the ore-forming fluid is magmatic water with high temperature but low salinity and density. Based on these features together with the wall rock of ore veins, it was suggested that the tin deposit has genetic link with the alkaline granites. However, appropriate isotopic ages, for both the granites and tin deposit, have not previously been obtained due to the limits from analytic method and sample selection. In this paper, LA-ICP-MS U-Pb age of zircons from the alkaline granite and Re-Os age for molybdenites from the deposit are reported, which are 306 ± 3Ma and 307± 11Ma, respectively. These ages imply that the alkaline granites and tin deposit are resulted from a simultaneous geological process, and provide important chronological constraint for the closely genetic connection of Sareshike tin deposit with the alkaline granites of Sabei body. In addition, from the БNd（t） （=＋5.0） of the alkaline granites, 4.5 epsilon units lower than that of the depleted mantle under the studied region, we consider that the granitic magma forming Sabei body was not originated by crystallization differentiation of basaltic magma directly from depleted mantle, but probably by partial melting of young oceanic crust and continent-d

关 键 词：锆石IA-ICP-MS U-PB年龄 辉钼矿Re-0s年龄 萨惹什克锡矿 碱性A型花岗岩 东准噶尔 新疆 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]