摘要
印度尼西亚克拉卡托火山安山岩的各类矿物斑晶中含大量岩浆包裹体。根据岩浆包裹体均—温度和化学成分,可以建立如下斑晶矿物结晶顺序(由早至晚):斜长石中心相(An83—72)、橄榄石→斜长石过渡相(An61)、单斜辉石、钛磁铁矿→斜长石边缘相(An 54—42)。斜长石斑晶中心部分在5 kb压力的岩浆深处结晶。高压环境和高钛含量,有利于早期斜长石斑晶所含岩浆包裹体中发生硅酸盐液体不混溶作用。这是板块构造消减带中安山质熔岩的特点。
Sequence of crystallization is established for the magmatic inclusion phenocrystals on the basis of thermometeical and chemical studies: 1) The eentral phase of plagioelase phenoerystals (An 83.2-72.6) containiing type A inclusions, divine. 2) intermediate phase of plagioelase phenocrystals (An 61.3) containing type B inclusions, clinopyroxe-ne, titanomagnetite. 3) peripheral phase of plagioclase phenocrystals (An 54.4-42.6) with type G inclusions. This sequence is accompanied by:a) a progressive drop in ho-mogenization temperature of magmatic inclusions; b) the host plagioelase changes pro-gressively from bytownite to andesine; and c) trapped silicate liquids vary in a progres-sive manner from andesitic to dacitic.Thermobarometrical studies permit us to consider that the crystallization of the central phase of plagioclase crystals trapping type A inclusions took place at about 5 kb. The absence of immiscibility in the magmatic inclusions of intermediate and peri-pheral zones of plagioclase phenocrystals may be interpreted as that iinmiscibillity is fa-vored only by high pressures. The high titanium contents in type A inclusions favor also the separation of immiscible fluids.This type of evolution of magmatic inclusions and especially the presence of liquid immiscibility in the magmatic inclusions of early plagioelase phenocrysts is typical of many andesitic lavas generated in subduction regions.
出处
《地球化学》
CAS
1986年第1期1-12,i003,共13页
Geochimica
