摘要
牛头山玄武岩分为亚碱性、过渡性和碱性三类。微量和稀土元素及同位素组成表明它们是活动大陆边缘的钠质玄武岩类。从亚碱性到碱性玄武岩,M值减小,K、Ce、Rb、Sr增加。^(37)Sr/^(36)Sr和1/^(36)Sr相关分析表明本区母岩浆及分离结晶产物均未遭受壳层放射成因锶的混染。定量模拟计算表明本区橄榄拉斑玄武岩母岩浆是上地幔石榴石二辉橄榄岩7％部分熔融的产物。
Analyses of major elements, REE, Rb Sr and Rb-, St- isotopes show that the Niutoushan basalts of Fujian, China belong to subalkaline volcanic rock series of active continental margins. Predominated by subalkaline basalt in association with minor amouts of alkaline basalt, this volcanic cone was well differentiated. The tholeiite in this area contains abundant mantle-source xenoliths and features a high Mg/Fe ratio. In addition, its Rb/Sr(0.0358), ^(87)Rb/^(86)Sr(0.101) and ^(87)Sr/^(86)Sr(0.7038) ratios are very close to those typical of pyrolite. It is thus believed to be the parent magma of the basaltic rocks in this area. The subalkaline and alkaline basalts have similar ^(87)Sr/^(86)Sr ratios, the initial ^(87)Sr/^(86)Sr ratio being 0.7039±0.0004. Batch melting model calculations on trace elements indicate that the olivine tholeiitic magma was derived from 7% partial melting of garnet lherzolite from upper mantle. From a simulated calculation on REE it is inferred that garnet was the residual phase during the upper mantle melting. Calculation on Rb, Sr fractional crystallization model indicates that the alkaline basalt was the residual melt formed after the fractional crystallization of either 67～42% gabbro or 43～25% anorthosite cumulates.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1990年第1期36-45,共10页
Acta Petrologica Sinica
关键词
玄武岩
铷
锶
稀土元素
地球化学
Basalt
Rb-Sr isotopes
REE geochemistry
Fractional crystallization
