洋岛和洋底高原玄武岩数据挖掘:地球化学特征及其与MORB的对比

摘要

本文集合了GEOROC和PetDB两个数据库的资料,对全球洋岛玄武岩(Ocean Island Basalt,OIB)和洋底高原玄武岩(Ocean Plateau Basalt,OPB)数据进行分析研究.OIB和OPB是板内岩浆活动的产物,其形成一般与地幔柱(热点)有关.OPB通常指示地幔柱的头部,温度相对较低;OIB代表地幔柱的尾部,温度较高.我们对OIB的数据研究表明,OIB中的不相容元素并非像先前认为的那么富集,在构造判别图中,OIB和洋中脊玄武岩(Mid Ocean Ridge Basalt,MORB)有很大一部分是重叠的,揭示OIB源区既有强烈富集不相容元素的,也有明显亏损的,甚至还有强烈亏损类似岛弧玄武岩(Island Arc Basalt,IAB)的.OPB是指发育在海洋和大陆边缘的来自地幔的巨量玄武岩,虽然与OIB同属于板内环境,但OPB的地球化学性质更接近富集型洋中脊玄武岩(Enrich Mid Ocean Ridge Basalt,E-MORB),可能具有OIB和MORB之间过渡的特征.研究表明,OIB和OPB的源区除了来自下地幔以外(地幔柱),部分可能来自上地幔,有些还可能与板块消减带物质的再循环作用有关.因此,OIB和OPB的成因不可能只用地幔柱一种模式予以解释,还应当考虑板块活动中其他因素(洋壳再循环、古老陆壳再循环、消减带物质以及水的加入,部分熔融程度、岩浆混合作用、不同地幔端元混合等)的影响.%This study carried out the analysis for global data of OIB (Ocean Island Basalt) and OPB (Ocean Plateau Basalt) through compilation of the data of GEOROC and PetDB.Both OIB and OPB are the product of intraplate magmatic activity,which is generally related to mantle plume or hot spot.In the common sense,OPB stands for the head section of mantle plume with relatively low temperature while OIB for the tail section of mantle plume with relatively higher temperature.Our research of OIB in this paper suggests that the source region in OIB can be divided into three types:a strong enrichment type,an apparent defect type and the IAB-like type.This conclusion hints the large overlap part in OIB and MORB after tectonic discrimination diagrams analysis.OPB stands for the large amount of mantle-derived basalt developed in ocean and continental margin;despite belonging to the intraplate environment as OIB does,OPB's geochemical property is muck close to E-MORB's,suggesting that OPB has the transition features between OIB and MORB.This study suggests that except the lower mantle (mantle plume) and upper mantle,the source region of OIB and OPB also relate to the recycle effect of the matter from plate subduction zone.As a result,the genesis of OIB and OPB will not be explained just by the single pattern of mantle plume,and some other factors,such as recycling of oceanic crust and old continental crust,subduction material and water addition,partial melting,magma mixing,and different end member mix of mantle,etc.should be taken into consideration.