| 塔里木巴楚小海子正长岩杂岩体的岩石成因探讨 |
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| 引用本文： | 位荀,徐义刚.塔里木巴楚小海子正长岩杂岩体的岩石成因探讨[J].岩石学报,2011,27(10):2984-3004. |
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| 作者姓名： | 位荀 徐义刚 |
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| 作者单位： | 1. 中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广州510640;中国科学院研究生院,北京100049
2. 中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广州510640 |
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| 基金项目： | 本文受国家973项目(2011CB808906)和中国科学院国际合作海外团队项目联合资助. |
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| 摘 要： | 巴楚小海子正长岩杂岩体是二叠纪塔里木大火成岩省的重要组成部分.SIMS锆石U-Pb定年显示其形成于279.7±2.0Ma,与本区辉绿岩脉和石英正长斑岩岩脉近于同时侵位.根据矿物学特征,小海子正长岩体可分为铁橄榄石正长岩和角闪正长岩两类.前者主要由碱性长石、铁橄榄石、单斜辉石、角闪石和少量石英、斜长石组成,后者主要由碱性长石、角闪石、黑云母和少量的石英、斜长石组成.小海子正长岩体为铁质、碱性系列,轻稀土相对富集,重稀土亏损,具有明显的Eu正异常,无Nb、Ta负异常,相对低的(87Sr/86Sr)；(0.7033 ～0.7038)和正的εNd(t)值(+3.1～+3.8),暗示它们来自亏损的地幔源区,没有地壳物质的加入.主微量和同位素地球化学分析,暗示巴楚小海子正长岩的母岩浆为碱性的幔源玄武质岩浆经橄榄石、单斜辉石分离结晶后的残余熔体,并且含有堆晶的碱性长石.这种含有碱性长石堆晶的熔体,在相对还原的条件下结晶,形成铁橄榄石正长岩；在相对氧化的条件下结晶,并经过不同程度斜长石的分离结晶形成角闪正长岩.
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| 关 键 词： | 正长杂岩体 锆石定年 碱性玄武质岩石 分离结晶 小海子 巴楚 塔里木大火成岩省 |
| 收稿时间： | 6/1/2011 12:00:00 AM |
| 修稿时间： | 2011/8/30 0:00:00 |
Petrogenesis of Xiaohaizi syenite complex from Bachu area,Tarim |
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| WEI Xun and XU YiGang.Petrogenesis of Xiaohaizi syenite complex from Bachu area,Tarim[J].Acta Petrologica Sinica,2011,27(10):2984-3004. |
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| Authors: | WEI Xun and XU YiGang |
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| Institution: | State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;Graduate University of Chinese Academy of Sciences, Beijing 100049, China;State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China |
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| Abstract: | Xiaohaizi syenite complex located within Tarim basin is an important part of Permian Tarim Large Igneous Provinces (LIPs). SIMS zircon U-Pb analysis yields Early Permian age of 279.7±2.0Ma, and coeval with diabase and quartz syenite porphyry dikes in the same area. Based on mineralogical composition, it can be categorized into fayalite syenite and amphibole syenite. The former consists mainly of alkali feldspar, fayalite, clinopyroxene, amphibole with minor quartz and plagioclase, and the latter contains mainly alkali feldspar, amphibole, biotite with minor quartz and plagioclase. Xiaohaizi syenites are ferroan, alkaline series and enriched in LREEs relative to HREEs with pronounced positive Eu anomalies, but no negative Nb and Ta anomalies. Geochemical and Sr-Nd isotopic compositions indicate that they were derived from a depleted mantle source without crustal assimilation. Major and trace elements and Sr-Nd isotopic compositions suggest that the parental magma of Xiaohaizi syenites were residual melt left by olivine and clinopyroxene fractional crystallization of mantle-derived alkaline basaltic magma. They crystallized as fayalite syenite under relatively reduced condition, and as amphibole syenite under relatively oxidized environment accompanied by variable degree of plagioclase fractionation. |
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| Keywords: | Syenite complex SIMS zircon dating Alkaline basaltic magma Fractional crystallization Xiaohaizi Bachu Tarim LIPs |
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