汉诺坝幔源单斜辉石巨晶氢同位素组成的离子探针分析:微尺度不均一性

摘要

Hydrogen isotopic compositions of three mantlederived clinopyroxene megacrysts from Cenozoic basalts at Hannuoba have been measured by ion microprobe. Heterogeneity occurs in a single grain, δD variation is up to 60‰ on the scale of 2mm. No correlation exists between δD values and hydrogen contents and chemical compositions are homogeneous, so the hydrogen isotope variations are considered to be inherited from parent magma. We suggest that the δD scatter of the parent magma could be related to D/H fractionations between vapor and melt during magma degassing. Shortly after the formation of clinopyroxene megacrysts, they are brought to the surface by the host magma and underwent quenching.%运用离子探针技术测定了河北汉诺坝新生代玄武岩中3个单斜辉石巨晶的氢同位素组成,结果显示同一颗粒内部表现出微尺度的不均一性,2mm范围内δD的变化达到60‰。δD和氢含量之间不存在同步的变化,巨晶内部的化学成分均一,因此我们认为巨晶的氢同位素不均一性继承自母岩浆。母岩浆的氢同位素变化可能是去气过程中气相与熔体之间的分馏引起的。单斜辉石巨晶形成后很短的时间内即被寄主岩浆带至地表并经历了快速淬火。