Calibration of high-temperature furnace assemblies for experiments between 200 and 600 MPa with end-loaded piston-cylinder apparatuses

Abstract We present pressure calibration results for piston-cylinder –” and 1” high temperature furnace assemblies in the 200-600 MPa range aiming to expand its applicability to simulate upper crustal conditions. The furnace assemblies were made up by crushable MgO, graphite heater, pyrex glass spacer, and NaCl sleeve. Twenty-one experiments were carried out over a range of pressures (200-600 MPa) and temperatures (870-945°C) to determine the liquidus curve of NaCl. The obtained curve slope fits that given by Siewert et al. (1998), but offsets by ~ -55 MPa, implying the need of a constant P upward correction in the 300-600 MPa and ca. 300-400 MPa pressure ranges for the 3/4” and 1” assemblies, respectively. However, if the NaCl melting points (918-920°C) obtained by Bohlen (1984) at 500 MPa are used as reference, no pressure correction is needed. Larger offsets (to -120 MPa) were obtained under pressure conditions around and lower than 300 MPa with the 1” assembly. Our results confirm the applicability of Bristol-type end-loaded piston-cylinders coupled with appropriate furnace assemblies in assessing relatively low-pressure conditions (down to ~ 200 MPa, ~ 7 km depth) found in the Earth’s upper crust, where important magmatic, hydrothermal and metamorphic processes occur.

摘要 本研究针对200–600 MPa区间内的3/4英寸与1英寸活塞圆筒（piston-cylinder）高温炉组件开展压力校准实验，旨在拓展其模拟地球上地壳条件的应用范围。该类高温炉组件由可压缩氧化镁（MgO）、石墨加热器、派热克斯（Pyrex）玻璃垫片与氯化钠（NaCl）套管构成。研究团队在200–600 MPa压力区间与870–945 ℃温度区间内完成21组实验，以测定氯化钠的液相线曲线。所得液相线曲线斜率与Siewert等人（1998）的研究结果吻合，但整体偏移量约为-55 MPa，这表明3/4英寸与1英寸组件分别需要在300–600 MPa和约300–400 MPa的压力区间内施加恒定的正向压力校正。不过，若以Bohlen（1984）在500 MPa下测得的氯化钠熔点（918–920 ℃）作为参照标准，则无需进行压力校正。但使用1英寸组件时，在300 MPa左右及更低压力条件下会出现更大的偏移（可达-120 MPa）。本研究结果证实，布里斯托尔型端部加载活塞圆筒（Bristol-type end-loaded piston-cylinders）装置搭配适配的高温炉组件，可有效用于评估地球上地壳中相对低压的环境条件（最低可达约200 MPa，对应约7 km埋深），而该区域正是重要的岩浆、热液与变质作用发生的场所。