西天山尼勒克水泥厂大哈拉军山组形成时代与构造背景  

Geochrpnology and Tectonic Setting of Dahalajunshan Volcanic Rocks from Nileke Cement Plant,North Margin of Yili Basin,Western Tianshan

作　　者：高山林 李云新[2] 

机构地区：[1]中国石油化工股份有限公司石油勘探开发研究院,北京100083 [2]中国石油化工股份有限公司胜利油田录井公司,山东东营257200

出　　处：《新疆地质》2015年第4期440-448,共9页Xinjiang Geology

基　　金：国家重大专项(2011ZX05005-004)资助

摘　　要：西天山伊犁盆地北部尼勒克水泥厂剖面大哈拉军山组火山岩以凝灰岩为主,夹有厚度不等的流纹岩、英安岩等酸性喷发岩。大哈拉军山组与下古生界志留系呈角度不整合接触,与上覆下石炭统阿克沙克组呈平行或低角度不整合接触。剖面下部流纹岩的SHRIMP锆石U-Pb年龄为（367±3）Ma。岩石Si O2为68.05%-71.97%,富碱、高钾,低钙镁、低钛,A/CNK=1.0-1.67,为高钾钙碱性过铝质酸性岩。样品稀土元素总量较高,为186.56×10^-6-294.40×10^-6,轻稀土相对富集,具显著的负Eu异常,分布曲线呈典型右倾＂海鸥型＂。微量元素显示大离子亲石元素（LILE）K,Rb,U,Th等相对富集,Sr,Ba呈明显负异常,亏损Nb,Ta,P和Ti等高场强元素,Nb/Ta、Zr/Hf、Th/Y比值及低Mg^#等地球化学特征表明其可能为上地壳部分熔融产物。大哈拉军山组碎屑岩沉积物源来自再循环造山带,沉积地层发育序列及同沉积正断层显示伸展盆地沉积特征,因此,我们认为伊犁盆地大哈拉军山组是晚泥盆—早石炭世早期区域性造山后伸展盆地发育的产物。The volcanic rocks of＂Dahalajunshan＂Formation was found at the cement plant of Nileke county, north margin of the Yili basin,western Tianshan,mainly consist of tuff, intercalated different thickness rhyolite,dacite. Zircon SHRIMP U-Pb dating results of the rhyolite show ages of 367±3Ma,corresponding to the Late Devonian. Petrogeochemistry analyses suggest that the rhyolite belong to calc-alkaline peraluminous rhyolitic rocks characterized with high potassium,silica and alkaline,low magnesium, calcium and titanium,and A/CNK=1.0-1.67. Meanwhile they have relatively high total Rare Earth Element（ REE） content（∑REE =186.56- 294.40×10^- 6） with LREE-rich patterns. The rocks are marked by a＂sea- gull＂right dipping curves of REE distribution showing relatively strong negative Eu anomalies. The large ion lithophile elements such as Rb,Th and U are relatively enriched, whereas Sr,Ba have obvious negative anomalies and high strength field elements such as Nb,Ta and Ti,are relatively depleted. Geochemical characteristics of incompatible elements ratios such as Nb/Ta, Zr / Hf, Th/Y and lower Mg^#indicate that the rocks may be partial melting of the younger upper crust within plate. Regional angular unconformity between＂Dahalajunshan＂Formation and lower Paleozoic strata, provenance of the sandstone from recycling orogenic belt and syndepositional normal faults combination indicate extensional basin setting within plate. So we suggest the＂Dahalajunshan＂Formation is response to post- orogenic intra-continental regional extension of the central Tianshan area during Late Devonian-Early Carboniferous Period.

关 键 词：伊犁盆地 大哈拉军山组 晚泥盆—早石炭世 造山后伸展 

分 类 号：P542[天文地球—构造地质学]