摘要
在壳幔作用道程中,壳幔源岩浆常会发生一定程度的混合,而它们Sr含量的差异会对混合岩浆的Sr同位素组成产生重大影响。本文简要介绍壳幔源岩浆的Sr含量差异对形成大陆型等同位素组成的双峰式火山岩的制约、幔源基性岩浆岩高(87Sr/86Sr)i的可能成因、岩浆混合程度的定量汁算及壳幔相互作用的一些最新的观点与研究成果,并讨论东南沿海白垩纪等同位素组成的双峰式火山岩的成因.指出基性端员玄武岩起源于上地幔楔.其高的Sr含量和高(87Sr/86Sr)i归因于地幔源区受到了俯冲板决的深海沉积物的参与,而酸性端员流纹岩岩浆由古老变质基底部分熔融生成的初始熔体与少量(5~6%)玄武质岩浆混合而成,并由于后者Sr含量近高于前者而使混合成因的流纹岩岩浆之(87Sr/86Sr)i明显低于古老变质基底而接近于玄武岩。
Crust - and mantle - derived magmas mix frequntly during crust - mantle interaction, and their various Sr contents exert important inf1uence on Sr isotope of mixed magma. This paper intmduces briefly the constraint of Sr contents to equi - isotope bimodal volcanics and high initial Sr isotope ratio of mantle - derived mafic rocks, quantitative calculation of magmatic mixing degree and new views as well as outcomes about crust - mantle interaction.Besides, it also discusses the petrogenesis of Cretaceous equi - isotope bimodal volcanics in the coastal region of southeastern China, advances that mafic and feIsic rocks came from mantle and crust (old metamorphic basement), respectively. It is concluded that high (87 Sr/86 Sr) i of basalts mainly ascribes to their derivation from enriched upper mantle wedge involved by sub-ducted - slab's pelagic sediments, and the mixing of a few(5 - 6 % ) basaltic and dominant rhyolitic magmas had nearly no effect on Sr isotope of basalts, but resulted in significant Sr isotope change of rhyolites, to which the key factor is the large disparity of their Sr contents.
出处
《火山地质与矿产》
1998年第1期24-33,共10页
Volcanology & Mineral Resources
关键词
壳幔作用
锶
同位素组成
岩浆岩
火山岩
Sr isotope Sr content crust-mantle interaction genesis of vol-canics southeastern coast of China