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