Effects of water on P-V-T equation of state of pyrope

Abstract

High-pressure single-crystal / powder synchrotron X-ray diffraction was carried out on a hydrous pure magnesium pyrope (Mg 3 Al 2 Si 3 O 12) containing 900 ppmw H 2 O, synthesized at 4.0 GPa and 1300 K. The pressure-volume (P-V) single-crystal data from room pressure to 9.81 GPa at ambient temperature were fitted by a third-order Birch-Murnaghan equation of state (BM-EoS) yielding a unit-cell volume of V 0 = 1505.14±0.38 Å 3 , an isothermal bulk modulus of K 0 = 160±3GPa and its pressure derivative K′ 0 = 5.2±0.4. When fixing K' 0 =4.0, the data yielded V 0 = 1504.58±0.32 Å 3 and K 0 = 166±2GPa. The pressure-volume-temperature (P-V-T) EoS of the synthetic hydrous pyrope was also measured at temperatures up to 900 K and pressures up to 16.75 GPa, using a diamond anvil cell in conjunction with in situ synchrotron angle-dispersive powder X-ray diffraction. The P-V data at room temperature and in a pressure range of 0.0001-14.81 GPa were then analyzed by a third-order BM-EoS and yielded V 0 = 1505.35±0.25 Å 3 , K 0 = 161±2 GPa, K′ 0 = 5.0±0.3. With K' 0 fixed to 4.0, we also obtained V 0 = 1505.04±0.29 Å 3 and K 0 = 167±1 GPa. Consequently, we fitted the P-V-T data with the high-temperature third-order BM-EoS approach and obtained the thermoelastic parameters of V 0 = 1505.4±0.3 Å 3 , K 0 =162±1 GPa, K′ 0 = 4.9±0.2, the temperature derivative of the bulk modulus (∂K 0 /∂T

Phase Transition of Enstatite‐Ferrosilite Solid Solutions at High Pressure and High Temperature: Constraints on Metastable Orthopyroxene in Cold Subduction

“…En 70 Fs 30 , En 44 Fs 56 , and Fs 100 have comparable values on (∂K T /∂ T ) P (−0.024(3) -−0.032(10) GPa/K) and α T (α 0 = 3.5(6)-4.1(5) ×10 −5 K −1 ). In addition, the thermal expansion coefficients of En 70 Fs 30 , En 44 Fs 56 , and Fs 100 are larger than those of anhydrous orthopyroxenes ( Figure S10; Sarver & Hummel, 1962; 10.1029/2020GL087363 Skinner, 1966;Frisillo & Barsch, 1972;Dietrich & Arndt, 1982;Jackson et al, 2003), which indicates that the incorporation of water enhances the thermal expansion of orthopyroxene, being consistent with previous studies of En 100 and other nominally anhydrous silicates (Fan et al, 2017;Xu et al, 2018;Ye, 2016). The thermal EoS parameters of the βand γ -opx phases were not successfully obtained due to the narrow data coverage (Figure 3).…”

“…Data were analyzed by GSE_ADA/RSV (Dera et al, 2013), APEX3 Crystallography Software Suite, and SHELXL package (Sheldrick, 2008). The details of sample synthesis, SCXRD experiments, and data processing are provided in Text S1 (Balan et al, 2013; Bell et al, 1995; Dera, Zhuravlev, et al, 2013; Dolomanov et al, 2009; Fan et al, 2017; Fei et al, 2007; Koch‐Müller et al, 2004; Momma & Izumi, 2011; Rauch & Keppler, 2002; Rivers et al, 2008; Sheldrick, 2008; Stalder et al, 2015; Xu et al, 2017; Xu et al, 2018; Xu et al, 2019; Zhang et al, 2017).…”

Phase Transitions in Orthoenstatite and Subduction Zone Dynamics: Effects of Water and Transition Metal Ions

“…In summary, oEn#1 and oEn#2, which have comparable estimated water contents, are very close in thermal expansion coefficients. Their α T values are significantly larger than reported in previous studies on synthetic oEn 100 , which is most likely a consequence of the incorporation of water, because water is known to enhance thermal expansion in olivine and pyrope (e.g., Fan et al, ; Suzuki et al, ; Trots et al, ; Ye et al, ). We conclude that the bulk modulus K T 0 of oEn is more sensitive to the variation of Ni content, while the thermal expansion α T changes in response to variations in the water content.…”

“…In general, thermal expansion changes with temperature. However, in view of the relatively low experimental temperature range and the limited high‐pressure and temperature data in this study, α T is often assumed to be constant over the temperature range, that is, α T = α 0 (e.g., Fan et al, , ; Nishihara et al, ; Xu et al, ). The V 0 , K T 0 , and K ′ T 0 values obtained by fitting the P ‐ V‐T data are in agreement with EoS fit at ambient temperature within the uncertainty (Table ).…”

Crystal-Chemical Properties of Synthetic Almandine-Pyrope Solid Solution by X-Ray Single-Crystal Diffraction and Raman Spectroscopy

“…Eleven 12 , and Pyr 100 ) used in this study were synthesized at high pressure and high temperature using a multi-anvil pressure apparatus (YJ-3000t) at the Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China. The sample assembles and synthesis process were similar to those used by Fan et al (2017) and Xu et al (2018) [12,13], and were briefly described here.…”