新疆博格达东缘色皮口地区晚石炭世裂谷火山岩地球化学、锆石U-Pb年代学及Hf同位素研究  

Geochemistry,zircon U-Pb age and Hf isotopes of Late Carboniferous rift volcanic in the Sepikou region,eastern Bogda,Xinjiang

作　　者：高景刚[1,2] 李文渊[1] 刘建朝[2] 高云霞[2] 郭新成[3] 周义[2] 范庭宾[3] 

机构地区：[1]西安地质矿产研究所,西安710054 [2]长安大学地球科学与资源学院,西部矿产资源与地质工程教育部重点实验室,西安710054 [3]新疆维吾尔自治区地质矿产勘查开发局第十一地质大队,乌鲁木齐833000

出　　处：《岩石学报》2014年第12期3539-3552,共14页Acta Petrologica Sinica

基　　金：国家重点基础研究计划(2009CB421005);中国地质调查局项目(1212011121092;12120113078200);新疆维吾尔自治区1:5万区域地质矿产调查项目(XJQDZ2008-05);中央高校基本科研业务费专项资金(CHD2010JC128);长安大学基础研究支持计划专项基金联合资助

摘　　要：新疆色皮口地区位于博格达造山带东段北部,区域内的上石炭统柳树沟组火山岩为玄武岩-玄武安山岩、角斑岩-石英角斑岩和流纹岩,组成双峰式火山岩建造。岩石SiO 2含量为48.07%~77.62%,赖特碱度率（AR）为1.35~4.7,Na2O＋K2O含量为3.74%~9.02%,K2O/Na2O值为0.04~1.04,为低钾高钠钙碱性-碱性岩石。玄武岩、玄武安山岩TiO 2=0.86%~1.7%,较高的Al、低Mg,以及低K2O/TiO 2和K2O/P2O5比值（分别为0.13~1.81、0.36~6.00）,反映了在岩浆演化过程中发生了不明显的分离结晶作用。玄武岩、玄武安山岩、角斑岩不相容元素K、Rb、Th、Ba强富集,高场强元素Nb、Ta、Zr、Hf无富集,Ti亏损不明显,玄武岩（Th/Nb）N值为1.36~6.55,Nb/La值为0.29~0.44,具有较低的Nb/Zr比值（0.03~0.05）。由玄武岩到石英角斑岩,稀土元素组成略右倾平行曲线簇,倾斜度（轻重稀土分异度）略增大,铕负异常趋于明显（δEu=0.81~1.17）。流纹岩不相容元素K、Rb、Th、Ba富集,高场强元素Nb、Ta、Zr、Hf富集,流纹岩稀土总量增高,轻重稀土分异增大,明显铕负异常（δEu=0.27~0.50）,显示后期较强的岩浆分异作用。石英角斑岩的锆石LA-ICP-MS U-Pb定年结果为314.9±1.2Ma（n=16,MSWD=0.4,Th/U比值在0.56~1.21之间）,这表明石英角斑岩形成时代为晚石炭世。石英角斑岩中锆石的176Hf/177Hf比值均分布在0.282897~0.283097之间,并具有较高的正εHf值（11~18）,平均值为14,Hf的模式年龄tDM2介于180~628Ma。所有锆石的176Hf/177Hf比值和εHf值位于亏损地幔演化线与下地壳之间,并靠近亏损地幔演化线。上述特点反映晚石炭世火山岩形成于板内裂谷环境,下部玄武岩与角斑岩-石英角斑岩具有同源特征,暗示岩浆源区来源于亏损地幔,并受地壳混染。The Upper Carboniferous Liushugou Formation bimodal volcaric rocks, consisting of basalt, basaltic andesite, keratophyre-quartz keratophyre and rhyolite, are widely distributed in Sepikou ea which is located in the eastern margin of Bogda Mountain, Xinjiang. The rocks in the studied area have low-K （K20 =0. 17% 4. 07% ） and high-Na （Na20 =3.09% 6. 47% ） ; SiO2 contents between 48.07% and 77.62% ; AR exponent between 1.35 and 4.7 ; Na20 ＋ K20 contents between 3.74% and 9. 02% ; the low K20/Na20 ratios （0. 04 1.04） ; these data shows that it belongs to calc-alkalic alkalic rocks. The basahs, basaltic andesites have slight high-A1, low-Mg, low K20/TiO2 and K20/P205 radios （the values are 0. 13 1.81, 0. 36 -6. 00）, indicating that fractional crystallization is not clear. The basalt, basaltic andesite, keratophyre are characterized by high abundance K, Rb, Th, Ba; and depletion in HFSE （Nb, Ta, Zr, Hf）, and slightly depletion in Ti. The basalts are characterized by （Th/Nb）N = 1.36 6. 55 ratios, and Nb/La = 0. 29 0.44 ratios, and low Nb/Zr = 0. 03 0. 05 ratios, Chondrite-normalized REE patterns for basalts- keratophyre is slight-leaning parallel curve clusters, together with slight enrichment in LREE contents and low HREE/LREE ratios, the keratophyre exhibits slightly negative Eu anomalies （SEu = 0. 81 1.17 ）. The rhyolite is characterized by high abundance K, Rb, Th, Ba, and high abundance in HFSE （Nb, Ta, Zr, Hf）, high rhyolite Y.REE contents, low HREE/LREE ratios, They also exhibit that the fractionated REE patterns with prominent negative Eu anomalies （ 8Eu = O. 27 0. 50 ）, suggesting stronger crystallization differentiation of magma. In situ U-Pb ages and Hf isotopes of quartz keratophyre were analyzed on the basis of micro area studies upon zircon. Zircon U-Pb ages of the quartz keratophyre are 314. 9 ＋ 1.2Ma （n = 16, MSWD =0. 4）, respectively with their Th/U ratio of 0. 56 1.21. The quartz keratophyre zircons, with their 176Hf/177Hf ratios varying in 0. 282897

关 键 词：博格达裂谷 柳树沟组 双峰式火山岩 HF同位素 新疆 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]