伊宁地块特克斯达坂晚石炭世伊什基里克组双峰式火山岩地球化学特征  

Geochemical characteristics of the bimodal volcanic rocks in Upper Carboniferous Yishijilike Formation in Tekes Daban area of Yining landmass

作　　者：宁文涛 李永军[1,2] 汪振宇 王祚鹏[1] 李甘雨 NING Wen-tao;LI Yong-jun;WANG Zhen-yu;WANG Zuo-peng;LI Gan-yu(School of Earth Science and Resources,Chang'an University,Xi'an 710054,China;Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,MNR,Xi'an 710054,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]自然资源部岩浆作用成矿与找矿重点实验室,陕西西安710054

出　　处：《岩石矿物学杂志》2019年第1期1-20,共20页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金项目(41273033;41303027)~~

摘　　要：伊宁地块特克斯达坂一带出露的晚石炭世伊什基里克组双峰式火山岩主要由玄武岩、流纹岩两大端员组成,其Si O2含量为47. 13%～77. 72%,在53. 62%～72. 15%之间存在明显的间断,具有双峰式火山岩的特征。LAICP-MS锆石U-Pb定年获得流纹岩年龄为302. 8±3. 6 Ma,表明该套火山岩形成于晚石炭世。玄武岩Si O2含量为47. 13%～53. 62%,具有低Si O2、高Fe2O3(TFe2O3=10. 90%～17. 40%)、高MgO(3. 74%～10. 12%,平均为6. 48%)和高Na(Na2O=2. 84%～6. 69%)、低K(K2O=0. 48%～3. 77%)特征(Na2O/K2O=1. 21～12. 18),轻稀土元素富集而重稀土元素亏损[(La/Yb)N=1. 58～4. 94],具有弱的负Eu异常(δEu=0. 30～1. 10),亏损Ta、Nb、Th、Sr等不相容元素。流纹岩Si O2含量为72. 15%～77. 72%,具有高Si O2、高K(K2O=6. 12%～9. 48%)、低Na(Na2O=0. 40%～2. 39%)特征(Na2O/K2O=0. 04～0. 36),K、Rb和LREE显著富集[(La/Yb)N=2. 46～10. 48],相对亏损Ba、Sr、P、Ti,且有基本一致的强负Eu异常(δEu=0. 18～0. 44),具有A2型花岗岩地球化学特征。此外,玄武岩具有相对高的Mg#值和Co、Cr、Ni含量,其εNd(t)值为3. 45、3. 55,表明玄武岩来自于亏损地幔的部分熔融;而流纹岩具有低Mg#和正εHf(t)值,暗示其形成与玄武质岩浆底侵过程中的地壳熔融有关。结合二阶段锆石Hf模式年龄,认为源区可能与元古宙的变质结晶基底重熔有关。根据上述地球化学特征并结合构造判别图解,认为特克斯达坂一带伊什基里克组双峰式火山岩形成于造山后伸展环境,具有板内成因特征。该套典型双峰式火山岩的发现为进一步探讨伊宁地块石炭纪构造演化提供了重要依据。The bimodal volcanic rocks of Upper Carboniferous Yishijilike Formation from the Tekes Daban area in Yining landmass consist mainly of basalts and rhyolites. Their SiO2 values range from 47. 13% to 77. 72%, and exhibit a gap of SiO2 between 53. 62% and 72. 15%, displaying a typical bimodal geochemical affinity. The LA-ICPMS zircon U-Pb ages of rhylites yielded an age of 302. 8 ± 3. 6 Ma, suggesting that these bimodal volcanic rocks were formed at the beginning of Late Carboniferous. Basalt samples have SiO2 values of 47. 13% ~ 53. 62%, with high Fe2O3(TFe2O3 being 10. 90% ~ 17. 40%) and Mg O(3. 74% ~ 10. 12%, 6. 48% on average), high Na(2. 84% ~ 6. 69%) and low K(0. 48% ~ 3. 77%) values. The basalts are obviously enriched in light rare earth elements and depleted in heavy rare earth elements [(La/Yb)N= 1. 58 ~ 4. 94]. In contrast, the rhyolites samples have Si O2 values of 72. 15% ~ 77. 72%, high K(6. 12% ~ 9. 48%) and low Na(0. 40% ~ 2. 39%) concentrations. Compared with the basalts of bimodal volcanic rocks, they show significant depletion of Ba, Sr, P, Ti elements, obvious enrichment of light rare earth elements and relative depletion of heavy rare earth elements. They exhibit strongly negative Eu anomaly(δEu = 0. 18 ~ 0. 44) and geochemical characteristics of A2 type granites. In addition, the basalts have high values of Mg^#, Co, Cr, Ni, with εNd(t) of basalt samples being 3. 45 and 3. 55.These features indicate that basaltic magmas were derived from partial melting of a depleted mantle source. The rhyolites of the Yishkilike Formation have low Mg^#and positive εHf(t) values, suggesting that their formation was related to crustal melting during the process of basaltic magma underplating. Combined with the two-stage Hf model ages, it is suggested that the rhyolite source may be related to the reworking of Proterozoic metamorphic basement.These geochemical characteristics together with structural tectonic discriminant diagrams show that the bimodal volcanic rocks of the Yishijilike Formation were formed in

关 键 词：双峰式火山岩 地球化学特征 伊什基里克组 特克斯达坂 伊宁地块 

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