Pressure-induced Pbca–P21/c phase transition of natural orthoenstatite: The effect of high temperature and its geophysical implications

摘要: Abstract In-situ high-pressure (P) high-temperature (T) Raman spectroscopy has been used to investigate the effect of temperature on phase transition Mg-rich orthoenstatite (OEN) a newly-discovered P21/c (HPCEN2) up 673 K and 18.2(10) GPa. Two natural samples were in this study: near end-member Mg (Zabargad Island, Egypt), Al + Fe-bearing (San Carlos, Arizona). For San Carlos OEN (SC-OEN), experiment was performed at room temperature, 373, 573 673 K; Zabargad Island (Zabg OEN), experiments 673 K. The three phases OEN, HPCEN2, another with space group C2/c (denoted by HPCEN) are readily distinguished characteristic doublet, triplet, or singlet, respectively, 660–680 cm−1 range. Similarly, splitting peak 1100 cm−1 is indicative an OEN → HPCEN2 transition. both samples, no other than HPCEN2 observed within investigated P–T recovered products after slow cooling for over 24 h from 16.6(9) GPa OEN. Clapeyron slope (dP/dT) bracketed between +0.020 −0.0026 GPa/K Zabg-OEN, +0.0023 −0.0049 GPa/K SC-OEN. Our results suggest possible stability field bottom upper mantle.