新疆北部库尔提蛇绿岩中角闪片岩的原岩恢复及其成因  

Protoliths reconstruction of amphibolites from Kuerti ophiolites in north Xinjiang and its petrogenesis.

作　　者：马林[1,2] 张海祥[1] 张伯友[1] 牛贺才[1] 

机构地区：[1]中国科学院广州地球化学研究所同位素年代学和地球化学重点实验室,广州510640 [2]中国科学院研究生院,北京100049

出　　处：《岩石学报》2008年第4期673-680,共8页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划(2007CB411303);国家自然基金(40672057,40473016)的联合资助。

摘　　要：库尔提角闪片岩产于库尔提蛇绿岩南部岩片中,与斜长花岗岩呈互层产出。这套角闪片岩的不相容微量元素组分显示了大洋中脊和岛弧玄武岩的双重特征,主要表现为大离子亲石元素(LILE)富集,高场强元素(HFSE)亏损以及平坦到亏损的轻稀土(LREE)配分模式。原岩恢复的结果表明,该角闪片岩的原岩为亚碱性的拉斑玄武岩类。库尔提角闪片岩亏损的LREE、高ε_(Nd)(t),以及关键元素比值(Th/Nb,La/Yb和Th/Yb)呈正相关都表明,其源区可能以MORB地幔为主,同时还伴有少量弧组分。因此,我们认为其形成于弧后盆地环境,同时推断该区弧后盆地存在一个二阶段的熔融演化模式:第一阶段,大约在晚古生代早期,古亚洲洋向西伯利亚板块发生北向俯冲,在会聚板块边界,弧火山岩被从含水的地幔楔中提取出来,留下一个亏损地幔;第二阶段,随着古亚洲洋板块持续消减,在中-晚泥盆世形成了库尔提弧后盆地,下部的亏损地幔发生了小比例的部分熔融形成了这套角闪片岩的原岩。Amphibolites form the southern slab of Kuerti ophiolite alternate with plagiogranites as dikes. They are characterized by LILE enrichment, HFSE depletion and flat to depleted LREE pattern that display the features both of MORB and Island Arc Basalt. The study of the protoliths of these amphibolites indicates that their protoliths are sub-alkalic tholeiites, which represents the lower intrusive rock section of ophiolites. Generally positive correlations of the elemental ratios （ e, g. , Th/Nb, La/Yb and Th/Yb）, depleted LREE and highεNd （t） values show the source of amphibolites might be the depleted MORB mantle with some arc component. Therefore, we propose a two-stage evolution model to interpret the compositional characteristics of the Kuerti amphibolites. First, during Early Devonian, arc basaltic melts were extracted from the hydrated arc mantle wedge beneath Kuerti by the northward subduction of the paleo-Asian Oceanic crust, leaving behind a depleted mantle source. Then, low degree partial melting of the depleted mantle source occurred and sub-alkalic tholeiites, which are the protoliths of Kuerti amphibolites, generated during seafloor spreading in the Kuerti backarc basin in middle Late Devonian.

关 键 词：新疆北部 库尔提蛇绿岩 原岩恢复 岩石成因 弧后盆地 

分 类 号：P588.125[天文地球—岩石学] P588.37[天文地球—地质学]