摘要
西准噶尔西南部奥陶纪蛇绿岩中出露的火山岩包括枕状和块状熔岩、玄武安山岩和安山岩,并与超镁铁质岩紧密共生。岩石化学成分表明枕状玄武岩具有低钛和钾的特征,而块状玄武岩富 K_2O、P_2O_5和 TiO_2。与亏损型大洋中脊玄武岩(N-MORB)相比,唐巴勒枕状玄武岩表现为大离子亲石元素富集,亏损 Ti、Ni、Cr、Co 和 Zr。这些特点说明该建造属岛弧火山活动的产物。但它们的 Sr、Th、Ta、HREE 的丰度以及 Ti/V、La/Ta 值都与同等分离程度的 N-MORB 相近。这些岩石很可能是伏于消减带之上的富大离子亲石元素的上地幔楔部分熔融形成的。
Volcanic rocks exposed in the Middle Ordo vician ophiolites are distributed in the southwes-tern part of western Junggar.According to the petrochemical classification,they comprise ba-salts(pillow and massive lavas),basaltic andesites and andesites which are all closely associatedwith ultramafic bodies.More than 50% of the studied rock samples are subalkalic and therest are alkalic volcanics.In the subalkalic volcanics both tholeiitic and calc-alkalic seriesare existent.The basalts are mostly TiO_2-low island-arc tholeiites although the TiO_2-high tran-sitional type is present as well.Based on the major and trace element data and their relationships,it is evident that therocks were derived from partial melting of a LILE-rich mantle wedge overlying thesubduction zone.The pillow lavas were formed from about 15% partial melting while the mas-sive lavas seem to have formed from <10% partial melting.Therefore,the Tangbalt ophio-lites are considered to be the product of island-arc volcanic activity,and probably generated inthe fore-arc or back-arc tectonic settings other than on the mid-ocean ridges.
出处
《地球化学》
CAS
CSCD
北大核心
1993年第4期399-408,共10页
Geochimica
基金
中国科学院核分析技术开放实验室资助
