摘要
东天山吐哈盆地北缘巴里坤煤矿一带发育一套拉斑系列玄武岩—安山岩,该套火山岩的LA-ICPMS锆石U-Pb年龄为366.1±1.7Ma,属晚泥盆世。全岩主微量分析显示其SiO_2含量集中于46.67%~52.18%,具有高铝(Al_2O_3=15.81%~17.74%)、相对低钛(TiO_2=0.99%~2.44%)以及贫钾富钠(Na_2O=2.82%~3.82%,K_2O=0.17%~1.62%)的特征。稀土总量在103.75×10^(-6)~137.26×10^(-6)之间,在球粒陨石标准化的配分曲线中表现出一致的轻稀土略富集而重稀土亏损的右倾模式,存在弱的负Eu异常。Ti/Yb-Zr/Nb、La/Nb-Sr协变图和Th/Ce等显示岩浆在源区和上升过程中基本没有俯冲沉积物参与和地壳混染。火山岩样品Mg#=54.46~64.34,Ni、Cr含量都低于幔源原生岩浆值,预示着岩浆经过了适度演化。原始地幔标准化的蛛网图和Nb、Th、U等微量元素比值显示其兼有IAT和N-MORB的性质,Th/Yb-Ta/Yb和Hf/3-Th-Ta构造环境判别图解显示其形成于与俯冲相关环境。结合该区域地质资料及本研究中火山岩年龄,认为吐哈盆地北缘巴里坤煤矿一带的火山岩是康古尔塔格洋向北俯冲的产物,其预示着博格达地区在晚泥盆世就已经进入了局部伸展环境,后期的侧向撕裂加快了博格达裂谷化的过程,是博格达地区从主动伸展到被动拉张的转变。
A set of tholeiitic volcanic rocks （basalt-andesite） was developed within Balikun colliery in the northern margin of Tuha basin, East Tianshan. The measured zircon U-Pb age（366.7±1.1Ma） by LA-ICP-MS shows that the volcanic rocks formed in Late Devonian. Their SiO2 contents change in a narrow limits（46.67%-52.18%） and they are featured with higher Al（Al2O3 =15.81%-17.74%）, lower Ti （TiO2 =0.99%-2.44%）, and being rich in Na（Na2O=2.82%-3.82%） and deficient in K（K2O=0.17%-1.62%）. Their REE abundance is from 103.75×10^-6-137.26×10^-6, with a rightly-oblique patterns type characterized by LREE enrichment and HREE depletion and a negative anomaly of Eu. Ti/Yb Zr/Nb diagram, La/Nb-Sr diagram and Th/Ce ratio indicate the magma was hardly effected by subduction sediment and crust. The samples＇ Mg^#（54.46-64.34）, Ni and Cr are lower than the primary magma from mantle source, which means the magma evoluted in some extent. Primitive mantle-normalized multi- elements spider diagram and Nb, Th, U ratio displays that the volcanic rocks possess the chemical characteristics of IAT and N-MORB, in Th/Yb-Ta/Yb and Hf/3-Th Ta discrimination diagrams, which imply they formed in subduction related environment. Combining this study with regional geology information, we think that the volcanic rocks in the northern margin of Tuha basin is the reflection of Kangguertage ocean subducting northerly, and it reveals that Bogda region had been in a partial stretch environment in the late Devonian, when the stretch environment of Bogda region transformed from initiative type into passive type, and then the lateral tear promoted the process of Bogda rift valley evolving.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2015年第8期1402-1416,共15页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号:41272089)
天山关键地区区域地质调查项目(编号:12120113042200)
西北基础地质调查成果集成与综合研究项目(编号:1212011220649)联合资助的成果
