Thermal equation of state of majoritic knorringite and its significance for continental upper mantle

Abstract

The P-V-T equation of state (EoS) for majoritic knorringite Mg 3.19 Cr 1.60 Si 3.19 O 12 at pressures to 17 GPa and temperatures to 1673 K was obtained from in situ X-ray diffraction experiments using a Kawai-type multi-anvil apparatus. Fitting of the room-temperature P-V data to a third-order Birch-Murnaghan EoS yielded an isothermal bulk modulus, K 0,300 = 154 (4) GPa, and a pressure derivative, K′ 0,300 = 5.4 (1.2). When fitting a high-temperature Birch-Murnaghan EoS using all of the P-V-T data at a fixed V 0 = 1549.08 Å 3 ,we find that K 0,300 = 157 (2) GPa, K′ 0,T = 4.5 (6), (∂K 0,T /∂T) P = À0.019 (4) (GPa K À1 ), a = 3.00 (14) × 10 À5 K À1 , and b = 0.65 (24) × 10 À8 K À2 , where α = a + bT is the volumetric thermal expansion coefficient. Fitting the Mie-Grüneisen-Debye EoS with the present data with a Debye temperature fixed at θ 0 = 731 K yielded a Grüneisen parameter, γ 0 = 1.34 at q = 1.0 (fixed). The thermoelastic parameters of pure knorringite were estimated and were compared with the previous data on other garnet compositions. The presence of Cr 2 O 3 in pyrope garnets in the upper mantle decreases P-and S-velocities by 1.6% and the density increases by 1.7% (for 20 mol.% knorringite end member) compared to pure pyrope. The results show the importance of accounting knorringite end-member for accurate estimation of mantle garnet acoustic velocities.

High‐Pressure and High‐Temperature Single‐Crystal Elasticity of Cr‐Pyrope: Implications for the Density and Seismic Velocity of Subcontinental Lithospheric Mantle

“…To examine whether the elastic properties of Cr‐pyrope at high P and high T can be calculated using the end‐member component elastic properties, we calculated the elastic properties ( ρ , K S , G , V P , and V S ) of Prp‐Cr#12 at high P and high T using the directly measured elastic parameters (Table S4 in Supporting Information ) in this study and then compared the results to those calculated using the elastic parameters interpolated from linear mixing of end‐member elastic parameters (end‐member model; Table S5 in Supporting Information ; Angel et al., 2018; Arimoto et al., 2015; Bass, 1986, 1989; Cameron et al., 1973; Chantel et al., 2016; Dymshits et al., 2014; Faccincani et al., 2021; Fan et al., 2020; Gréaux & Yamada, 2019; Gwanmesia et al., 2014, 2006; Hao et al., 2020; Hugh‐Jones, 1997; Isaak et al., 1992; Jackson et al., 2007; Jacobsen et al., 2010; Jeanloz & Thompson, 1983; Klemme et al., 2005; Kroll et al., 2012; Li & Neuville, 2010; Ma et al., 2009; Z. Mao et al., 2015; Milani et al., 2015, 2017; Ohashi, 1984; Sang & Bass, 2014; Sinogeikin & Bass, 2000, 2002; Soga, 1967; Tribaudino et al., 2008; Wang & Ji, 2001; Xu et al., 2018, 2020, 2022; Yang & Ghose, 1994; Zhang & Bass, 2016a, 2016b; Zhang et al., 1998; Zhao et al., 1997, 1998; Zou, Gréaux, et al., 2012). We calculated the elastic properties at pressures of 3–8 GPa at 1000 and 1600 K, which are the lower and upper bound of typical SCLM P ‐ T conditions where garnet‐peridotite stabilizes.…”

Thermoelastic properties of chromium oxide Cr2O3 (eskolaite) at high pressures and temperatures

“…9). Thermoelastic parameters of En were taken from Shinmei et al (1999) and Knr and Mj 10 Knr 90 from Dymshits et al (2014a). The enthalpy, entropy and heat capacity of Knr and En from Holland and Powell (2011) and Esk from Gurevich et al (2009) were used.…”

“…Cr 2 O 3 was observed as an experimental product or reagent in different important reactions (Dymshits et al 2014a;Klemme 2004;Klemme et al 2000;Zou and Irifune 2012;Turkin and Sobolev 2009). The possible formation of Esk in association with Cr-rich garnet may occur during metasomatic interaction of mantle peridotites containing chromite with CO 2 (+H 2 O) fluid or the carbonate-silicate melt (Bataleva et al 2012).…”

Thermodynamic behavior of Na-majorite and knorringite-majorite garnet systems

“…In this work, we report the thermoelastic behavior and P -V -T equation of state of such two garnets i.e. Na-majorite [Na 2 MgSi 5 O 12 ] and knorringite [Mg 3 Cr 3 SiO 3 O 12 ] 0.80 [Mg 4 Si 4 O 12 ] 0.99 solids using thermodynamic approaches [Dymshits et al, 2014b]. These garnets are of significant as they are capable of crystallizing under the condition of deep mantle and transition zone [Dymshits et al, 2014b].…”

“…Na-majorite [Na 2 MgSi 5 O 12 ] and knorringite [Mg 3 Cr 3 SiO 3 O 12 ] 0.80 [Mg 4 Si 4 O 12 ] 0.99 solids using thermodynamic approaches [Dymshits et al, 2014b]. These garnets are of significant as they are capable of crystallizing under the condition of deep mantle and transition zone [Dymshits et al, 2014b]. This study of garnets at higher pressure is crucial as these garners comprise as much as half of earth transitions zone [Dymshits et al, 2014a].…”