岩浆到热液演化的包裹体记录——以骑田岭花岗岩体为例

摘要

Qitianling granite is a complex massif with multi-stage intrusions during the Early Yanshanian Period. Petrochemical data show that it belongs to alkali-rich and highly evolved A-type granite formed in tension setting within a plate. The centimetre- and metre-sized pegmatoid cystidium and miarolitic quartz widely occurred in the second stage medium-fine grain biotite granite, implying that it is resulted from differentiation of the oversaturated-volatile magma. In addition, the coexist of melt-fluid inclusions and fluid inclusions in quartz indicated that the pegmatoid cystidium and miarolitic quartz were produced in the transition stage from granite magmatic melt to hydrothermal solution. The data of micro-thermometry showed that the trapped temperatures of melt-fluid inclusions are over 530℃, the homogenization temperatures of fluid inclusions are between 172℃ and 454℃., indicating the temperature of fluids in hydrothermal stage, and the homogenization temperatures of fluid inclusions in sphalerite are between 285℃ and 417℃ , indicating the temperature and salinity of ore-forming fluid. Their evolution process from middle-fine grain biotite granite to pegmatoid cystidium to miarolitic quartz implied that magmatic and hydrothermal system underwent an evolution process: from volatile-rich fluid to melt and high salinity fluid to high salinity fluid to low salinity fluid and finally formed magmatic hydrothermal fluid in the CaCl2-NaCl-H2 O-CO2 system. Based on the data of petrography and Raman spectrum of fluid inclusions, the existence of feldspar, calcite, rutile and metallic oxides in the fluid and crystal-rich melt-fluid inclusions implies that the captured fluids have a competent ore-forming potentiality.%骑田岭花岗岩是燕山期花岗岩早期多阶段侵入复式岩体,岩石化学的研究表明它是富碱的、高分异的A型花岗 岩,形成于板内拉张的构造环境.在其第二阶段中细粒黑云母花岗岩内广泛发育着厘米级至米级似伟晶岩囊状体和石英晶洞,它们是富挥发份岩浆固结的产物,代表岩石形成过程经历了明显的岩浆-热液过渡阶段.包裹体显微岩相学研究在骑田岭黑云母花岗岩的石英中发现熔体-流体包裹体和流体包裹体共存,这一结果进一步证实骑田岭中细粒黑云母花岗岩中的似伟晶岩囊状体和石英晶洞是花岗质熔体在岩浆-热液过渡阶段的产物.显微测温结果显示,熔体-流体包裹体的捕获温度大于530℃,说明岩浆热液过渡阶段的温度不低于该温度;闪锌矿中流体包裹体的均一温度在285 ～ 417℃之间,盐度为11.7%NaCleqv,代表了成矿流体的温度和盐度;流体包裹体的均一温度为172 ～ 454℃,代表热液阶段流体的温度.从中细粒黑云母花岗岩到似伟晶岩囊状体再到石英晶洞,岩浆.热液体系经历了富挥份熔体一熔体+高盐度流体→高盐度流体→低盐度流体的完整演化过程,形成了CaC12-NaCI-H20-C02体系的岩浆热液流体.包裹体岩相学及激光拉曼探针分析结果显示,在流体包裹体和多晶熔体-流体包裹体中含有长石、方解石、金红石及金属氧化物等子矿物,暗示其所捕获的流体具有较强的成矿能力.