摘要
大陆地壳或岩石圈的混染作用可以给出似消减带信号,并导致将受到混染的大陆玄武岩误判为岛弧玄武岩。没有受到混染的软流圈(或地幔柱)源大陆玄武质岩石通常是以(Th/Nb)N<1、Nb/La≥1、低87Sr/86Sr(t)比值、高εNd(t)值及La/Nb和La/Ba比值与洋岛玄武岩相似并以具有缺乏Nb、Ta、Ti负异常的“隆起”状多元素地幔标准化分配型式为特征。当在所研究的火山岩系中发现有未受到混染的软流圈(或地幔柱)源玄武质岩石存在,基本上就可以排除它们有属于岛弧或活动大陆边缘火山岩系的可能。对于那些具有消减带信号的基性熔岩,可以根据Zr含量和Zr/Y比值,或利用Zr/Y-Zr图解,判断它们是否真正是岛弧或活动大陆边缘玄武岩。
Contamination by continental crust or lithosphere can yield subduction-type signatures and lead to the misidentification of contaminated continental basalts as arc related ones. Uncontaminated asthenosphere （or plume） -generated continental basaltic rocks are normally characterized by （Th/Nb）N〈 1, Nb/La≥1, low ^87Sr/^86Sr（t） ratios, high eNd（t） values, similar La/Nb and La/Ba ratios to ocean island basalts （OIB） and ＂hump-shaped＂ mantle-normalized multi-element patterns without negative Nb, Ta and Ti anomalies. As the uncontaminated asthenosphere （or plume） -generated basaltic rocks have been found in the studied volcanic successions, the possibility can be basically excluded that they belong to island-arc or active continental margin volcanic rocks. For the basic lavas with subduction-type signatures, we can judge whether they are really island-arc or active continental margin basalts by studying Zr contents and Zr/Y ratios or Zr/Y - Zr diagram.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2007年第1期77-89,共13页
Acta Petrologica et Mineralogica
基金
国家自然科学基金资助项目(40472044)
中国地质调查局综合研究项目(1212010611804)
