西准噶尔克拉玛依OIB型枕状玄武岩地球化学及其地质意义研究  

Geochemistry and tectonic significance of OIB-type pillow basalts in western Mrs. of Karamay city (western Junggar), NW China.

作　　者：朱永峰[1] 徐新[2] 魏少妮[1] 宋彪[3] 郭璇[1] 

机构地区：[1]北京大学地球与空间科学学院造山带与地壳演化教育部重点实验室,北京100871 [2]国家305项目办公室新疆资源环境中心,乌鲁木齐830000 [3]北京离子探针中心中国地质科学院,北京100037

出　　处：《岩石学报》2007年第7期1739-1748,共10页Acta Petrologica Sinica

基　　金：国家自然科学基金资助(批准号:40572033).

摘　　要：克拉玛依西山的枕状玄武岩与浊积岩-凝灰岩共生,厚度大于400米的枕状玄武岩层被火山角砾岩-安山岩-硅质岩-凝灰岩覆盖,岩枕之间充填着硅质泥岩。锆石 SHRIMP 定年结果表明,枕状玄武岩可能在早寒武世形成(>517Ma,这套地层曾经一直被认为属于石炭系)。枕状玄武岩的稀土元素含量(117.4×10^(-6)～153.6×10^(-6))和配分模式与洋岛玄武岩(OIB)基本一致。枕状玄武岩中大离子亲石元素(Cs、Rb、Ba、K、Pb 和 Sr)的含量变化较大(明显偏离 OIB),高场强元素(Nb、Ta、Zr、Hf、Ti 和 P)相对 OIB 和原始地幔没有表现出明显异常[e.g.,(Nb/Ta)_(PM)=0.92～0.98,(Zr/Hf)_(PM)=1.08～1.18]。西准噶尔地区存在这套 OIB 型海相火山-沉积建造说明古亚洲洋在西准噶尔地区于寒武纪就已经存在。这套海相玄武岩岩枕中存在大量古元古代—新太古代(1883～2536Ma)岩浆锆石的事实说明,早古生代洋岛玄武岩岩浆源区存在古老大陆地壳物质。The pillow basalts in the western Mts. of Karamay city （western Junggar）, with 〉 400 meters in thickness, coexisting with turbidite-tuff, were covered by andesite, volcanic breccia, siliceous rocks and tuff. Silicalites filled the interspace of the pillows. The pillow basalts probably were formed at Early Cambrian （ 〉 517Ma） based on zircon SHRIMP dating （these rock unit was previously believed to be formed during the Carboniferous period）. The REE distribution patterns of these basahs are the same as the ocean island basalt （OIB）. Their Cs, Pb, Ba, K, Pb and Sr contents vary widely （away from OIB）. Relative to the Primary Mantle and OIB, no obvious anomalies of Nb, Ta, Zr, Hf, P, and Ti occur [ （Nb/Ta） PM = 0.92 - 0.98, （Zr/Hf） PM = 1.08 - 1.18 ]. The occurrence of these OIB-type pillow basalts indicates that there were oceanic islands in west Junggar （formed during Early Paleozoic）. The occurrence of Neoproterozoic- Neoarchean （ 1883 - 2536 Ma） magmatic zircons in these OIB-type pillow basalts suggests that old continental crust materials occurred in the OIB-type magma source and recycled in the Paleo-Asian Ocean during Early Paleozoic.

关 键 词：枕状玄武岩 微量元素 地球化学 洋岛玄武岩(OIB) 西准噶尔 

分 类 号：P588.145[天文地球—岩石学] P594[天文地球—地质学]