海南岛新生代玄武岩中富硅熔体包裹体特征及成因  

Characteristics of Silicon-rich Melt Inclusions in the Cenozoic Basalts from Hainan Island and Their Genesis

作　　者：许鑫[1] 张立飞[1] 田伟[1] 朱金涛 何衍鑫 XU Xin;ZHANG Lifei;TIAN Wei;ZHU Jintao;HE Yanxin(School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]北京大学地球与空间科学学院,北京10087

出　　处：《现代地质》2025年第1期31-45,共15页Geoscience

基　　金：国家重点研发计划项目“俯冲带深部过程与非生物成气”(2019YFA0708503);中国石油天然气集团有限公司-北京大学基础研究项目“西太平洋板块俯冲对中国东部构造岩浆演化和无机天然气资源的影响”(8410103027)。

摘　　要：熔体包裹体记录了岩浆喷发前的演化、去气过程以及岩浆中挥发分等重要信息,是研究玄武质岩浆系统及其地幔源区强有力的工具,被广泛应用于探索地幔岩浆的起源和演化。然而,关于熔体包裹体均一化加热前后的玻璃成分差异目前研究较少。本文选择海南岛蓬莱地区新生代玄武岩橄榄石斑晶中熔体包裹体为研究对象,采用电子探针对熔体包裹体玻璃及其寄主矿物进行元素组成分析。结果显示,寄主矿物橄榄石的Fo值为70~85,CaO含量大于0.1%,为典型的橄榄石斑晶。室温下,熔体包裹体由熔体(玻璃)、气泡和子矿物(辉石、斜长石、钛铁矿)组成。熔体包裹体玻璃成分为英安质熔体。通过高温炉对含熔体包裹体的橄榄石进行均一化加热后,包裹体中未见子矿物,包裹体玻璃成分为玄武质、玄武安山质熔体,少数为安山质熔体,与海南岛蓬莱地区新生代玄武岩全岩成分相近。本文认为海南岛蓬莱地区新生代玄武岩橄榄石斑晶中存在富硅熔体包裹体的原因是包裹体被捕获后冷却速率缓慢导致熔体内部发生分离结晶,进而残余熔体不断向富硅方向演化而形成。因此,对熔体包裹体进行研究时首先观察熔体包裹体内部结构特征,必要时进行均一化加热实验。Melt inclusions record important information such as the evolution of pre-eruption,degassing process,and volatile budget in magma.Melt inclusions are powerful tools for studying basaltic magma systems and mantle source,and are widely used to study the origin and evolution of magma derived mantle.There are a large number of melt and fluid inclusions in the olivine phenocryst of the Cenozoic basalts in the Penglai area of Hainan Island.Using an electron microprobe to analyze the composition of melt inclusions and their host minerals.The host mineral olivines have Fo values ranging from 70 to 85,with CaO values exceeding 0.1%,which is typical phenocrysts rather than mantle xenocrysts.At room temperature conditions,the melt inclusions are composed of melt(glass),bubbles and sub-minerals(pyroxene,plagioclase and Ilmenite).The glass compositions in melt inclusions are dacite and trachyte.Olivines containing melt inclusions were heated in a high-temperature furnace.After homogenization melt inclusions,no sub-minerals were observed in the melt.The glass compositions of the melt inclusions are basalt and basaltic andesite,and a few are andesite.The compositions of homogenization melt inclusions are similar to those of the bulk Cenozoic basalts in the Penglai area,Hainan Island.This study suggests that the presence of Si-rich melt inclusions in the phenocrysts of the Cenozoic basaltic rocks in the Penglai area of Hainan Island are due to the slow cooling rate after the melt inclusions are trapped.The slow cooling rate in melt made fraction crystallization in the melt inclusions,leading to the continuous evolution of the residual liquids towards Si-rich direction.Therefore,before conducting research on melt inclusions,it is necessary to carefully observe the internal structural characteristics of the melt inclusions,and if necessary,conduct heating experiments.

关 键 词：海南岛 新生代玄武岩 橄榄石 斑晶 富硅熔体包裹体 成因 

分 类 号：P588.12[天文地球—岩石学]