新疆阿尔泰库吉尔特伟晶岩海蓝宝石矿物化学研究
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P578.953;P574.2

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国家自然科学基金(41963003);云南省“兴滇人才”项目


Mineral chemistry of aquamarine from Kujierte pegmatite in Altay, Xinjiang
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    摘要:

    海蓝宝石属绿柱石族矿物,产出于花岗伟晶岩中,其结晶过程可贯穿于伟晶质岩浆演化的不同阶段,同时也是岩浆熔体和流体包裹体的重要宿主矿物。库吉尔特伟晶岩是新疆阿尔泰可可托海地区众多伟晶岩脉中产出高质量海蓝宝石的LCT型伟晶岩。本文对库吉尔特伟晶岩中产出的海蓝宝石进行了主、微量元素和流体包裹体研究。流体包裹体岩相学显示,在海蓝宝石中熔体/熔体-流体包裹体(MI/M-FI)和流体包裹体(FI)分布呈现一定的规律, MI/M-FI主要集中在晶体的根部至中部,而FI则富集在边缘区域,说明该海蓝宝石的结晶过程经历了较为完整的伟晶岩岩浆演化阶段。测温结果显示,M-FI的均一温度>550℃,FI的均一温度范围为220~400℃,盐度介于0~14%之间,密度为0.6~0.9 g/cm2,流体属于中-高温、中-低盐度的H2O-NaCl-CO2体系。在结晶学和流体包裹体岩相学基础上确定出海蓝宝石晶体代表岩浆-热液过渡阶段和岩浆期后热液阶段的部位,进行电子探针(EPMA)和激光剥蚀电感耦合等离子体质谱分析(LA-ICP-MS),结果显示海蓝宝石为Fe元素主导致色,在海蓝宝石生长过程中Fe2+以Na++Fe2+→Al3+的通道-八面体替代模式进入矿物晶格使其呈现蓝色。在伟晶岩演化早-中期,海蓝宝石中碱金属(Li、Na、K、Cs)与过渡族金属元素(Fe、Mg、Mn)含量变化稳定,进入晚期这些金属元素含量陡增。结合该地区板块运动长期处于挤压俯冲环境,推测库吉尔特伟晶岩岩浆演化过程处于非封闭的状态,晚期仍然有深部岩浆房富集Fe、Mg、Mn的流体呈脉动式注入,导致原始热液流体成分发生波动。

    Abstract:

    Aquamarine belongs to the beryl group minerals and is produced in granite pegmatites. Its crystallization process can run through different stages of the evolution of pegmatitic magma, and it is also an important host mineral for magma melts and fluid inclusions. Kujierte pegmatite is an LCT type pegmatite that can produce high-quality aquamarine among numerous pegmatite veins in the Koktokay area of Altay, Xinjiang. This article investigates the main, trace elements, and fluid inclusions of aquamarine produced in Kujierte pegmatite. Fluid inclusion petrology shows that the distribution of melt/melt fluid inclusions (MI/M-FI) and fluid inclusions (FI) in aquamarine exhibits a certain pattern: MI/M-FIs are mainly concentrated from the root to the middle of the crystal, while FIs are enriched in the edge region, indicating that the crystallization process of the aquamarine has undergone a relatively complete stage of pegmatite magmatic evolution. The temperature measurement results show that the homoge-nization temperature of M-FIs is >550℃, and the homogenization temperature range of FIs is 220~400℃, with salinity ranging from 0 to 14% and density ranging from 0.6 to 0.9 g/cm2. The fluid belongs to H2O-NaCl-CO2 system with the medium high temperature and medium low salinity. Based on the orientation of crystal crystallization and the distribution of fluid inclusions, the magma hydrothermal transition stage and post magmatic hydrothermal stage were divided. Electron probe analysis (EPMA) and laser ablation plasma mass spectrometry (LA-ICP-MS) analysis results showed that Fe element dominated the coloration of aquamarine. During the growth process of aquamarine, Fe2+ entered the mineral lattice in a channel octahedral substitution mode of Na++Fe2+→ Al3+, resulting in a light blue coloration. In the early to middle stages of the evolution of pegmatites, the content of alkali metals (Li, Na, K, Cs) and transition metal (Fe, Mg, Mn) elements in aquamarine remained stable, and in the late stage, the content of these metal elements increased sharply. Combined with the long-term compression and subduction of plate in the region, which has led to the overflow of deep material in the earth, and the evolution of pegmatite magma in an unclosed system, it is believed that the fluid enriched with Fe, Mg, and Mn in the deep magma chamber was injected in a pulsating manner in the late stage, resulting in a fluctuating change in the composition of the original hydrothermal fluid.

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丁志丹,邹妤,王蝶, 2024. 新疆阿尔泰库吉尔特伟晶岩海蓝宝石矿物化学研究[J]. 岩石矿物学杂志, 43(3):575~591.
DING Zhi-dan, ZOU Yu, WANG Die, 2024. Mineral chemistry of aquamarine from Kujierte pegmatite in Altay, Xinjiang[J]. Acta Petrologica et Mineralogica, 43(3): 575~591.

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  • 收稿日期:2024-01-24
  • 最后修改日期:2024-03-15
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  • 在线发布日期: 2024-05-23
  • 出版日期: 2024-05-25