斜长石中人工合成流体包裹体的实验研究

doi:10.19657/j.geoscience.1000-8527.2023.036

摘要/Abstract

摘要：

天然斜长石流体包裹体被广泛应用于揭示各种地质作用及地质过程的研究,但关于这类包裹体的捕获机制及捕获后的变化、地质温压计等研究需要基于斜长石的人工合成流体包裹体研究的验证或修正。目前,以斜长石为寄主矿物的人工合成流体包裹体技术尚未见诸报道。本文基于传统的寄主矿物裂隙愈合方法,通过在寄主矿物的预处理、囊组装等方面的适当改进,在1~1.5 GPa、800~900 ℃ 的条件下,模拟俯冲带中玄武质洋壳发生脱挥发分反应的实验中,以斜长石为寄主矿物的流体包裹体被成功地合成。对合成的包裹体进行了详细的岩相学观察、激光拉曼光谱分析和显微测温分析,以及尝试性的单个流体包裹体的激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)分析,结果显示斜长石捕获了常温下呈富碳液相+富水液相的两相流体包裹体,捕获的流体具有H₂O+CO₂±CH₄±N₂的组成,流体盐度因加入初始标液不同而有变化,有Cu、Mo等被活化进入到流体中。实验展示了基于斜长石的人工合成流体包裹体技术在二氧化硅不饱和体系的高温高压模拟实验中的成功运用,其在地质流体和实验地球化学等地学研究领域有广阔的应用前景。

关键词: 人工合成流体包裹体, 斜长石, 高温高压, 实验研究, 实验地球化学

Abstract:

Natural fluid inclusions hosted by plagioclase are widely used to reveal mechanism under various geo-logical processes and phenomena.However, the capturing mechanism and subsequent changes, as well as geothermobarometer of such inclusions require validation or modification based on the study of artificially synthesized fluid inclusions in plagioclase.There are no available reports on the technology for fluid inclusion synthesis with host mineral like plagioclase.According to the conventional host mineral fracture healing method, the fluid inclusions were successfully synthesized in host plagioclase through improving the pretreatment of the plagioclase, and capsule assembly in experiments simulating the devolatilization reaction of basaltic crust in the subduction zone under 1-1.5 GPa and 800-900 ℃.Detailed petrographic observations, laser Raman spectroscopic analysis, microthermometric analysis, and preliminary laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of individual fluid inclusions were performed on the synthesized inclusions.We revealed that the plagioclase captured two-phase fluid inclusions with a carbon-rich liquid phase and a water-rich liquid phase at room temperature.The captured fluids have compositions of H₂O+CO₂±CH₄±N₂, with varying salinity depending on the initial fluid used.Additionally, elements such as Cu and Mo were activated and entered the fluid.The plagioclase-based synthesis technology was demonstrated by the successful application in the high-temperature and high-pressure simulation experiments of silica-undersaturated systems.We suggest that the technology of fluid inclusion synthesis in plagioclase bear broad applications in geoscience fields such as geo-fluids and experimental geochemistry in future.

Key words: synthetic fluid inclusion, plagioclase, high temperature-pressure, experimental study, experimental geochemistry

中图分类号:

P579
P599

杜俊, 刘洪微, 常洪伦. 斜长石中人工合成流体包裹体的实验研究[J]. 现代地质, 2023, 37(06): 1634-1643.

DU Jun, LIU Hongwei, CHANG Honglun. Experimental Study on Fluid Inclusion Synthesis in Plagioclase[J]. Geoscience, 2023, 37(06): 1634-1643.

图/表 7

图1 样品组装(a)及实验囊(b)

Fig.1 Schematic diagrams of the sample assembly (a) and the capsule (b)

表1 实验条件和主要参数

Table 1 Experimental conditions and main parameters in this study

实验编号	温度 (℃ )	压力 (GPa)	囊尺寸 (mm)	斜长石质量(mg)	初始物质量(mg)			退火时间(h)
实验编号	温度 (℃ )	压力 (GPa)	囊尺寸 (mm)	斜长石质量(mg)	变玄武岩	标液		退火时间(h)
D4	900	1.0	5/7/12	37.2	285.8	/		48
D7	800	1.0	5/7/12	42.5	266.2	/	48
D9	800	1.0	5/7/12	35.3	230.8	16.0^a	48
D10	900	1.2	10/12/17	47.6	2333.2	100.0^a	48
D11	800	1.5	10/12/17	44.4	2129.0	100.0^a	72
D12	900	1.0	5/7/12	47.9	334.0	12.0^a	48
D13	900	1.0	5/7/12	31.0	334.2	12.0^b	48
D15	900	1.0	6/8/12	42.4	545.4	12.0^b	48
D16	900	1.0	6/8/12	46.7	511.2	12.0^b	72
D17	800	1.0	6/8/12	47.5	586.8	12.0^b	48

图2 典型的合成斜长石流体包裹体透射光下显微照片 (a)实验D4包裹体;(b)实验D9包裹体;(c)实验D10包裹体;(d)实验D11包裹体

Fig.2 Micrographs of the typical synthesized fluid inclusions in plagioclase by transmitted light

图3 合成流体包裹体拉曼光谱 (a)包裹体来自实验D4;(b)包裹体来自实验D10

Fig.3 Raman spectra of the synthesized fluid inclusions

表2 合成流体包裹体的显微测温分析结果

Table 2 Microthermometric parameters of the synthesized fluid inclusions

实验编号	包裹体个数	尺寸(μm )	富碳相体积比(% )	T_m-car(℃ )	T_m-clath(℃ )	T_h-car^*(℃ )	T_h-total^**(℃ )
D4	10	5~20	70~80	-58.0~-59.3	7.0~10.5	2.8~10.8	352~385
D9	10	5~15	36~56	-59.0~-63.5	12.0~14.6	4.9~9.5	300~346
D10	5	5~15	40~62	-58.0~-62.3	11.9~13.3	1.5~8.4	301~330
D11	6	5~15	44~51	-58.1~-65.5	10.6~15.5	-6.8~10.5	180~190^***

图4 合成斜长石流体包裹体显微测温照片(D10) (a)常温下两相流体包裹体;(b)降温后,在富碳液相中出现气泡相;(c)显示笼形水合物融化;(d)包裹体完全均一至临界相,水相和富碳相体积变化不大,二者之间界面逐渐模糊并消失;圆圈中包裹体较为典型

Fig.4 Microthermometrical photographs of the synthesized fluid inclusions in plagioclase

图5 实验D13的流体包裹体LA-ICP-MS瞬时信号

Fig.5 Representative LA-ICP-MS time-resolved signal profile of a fluid inclusion from experiment D13

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