Sound velocities of Na0.4Mg0.6Al1.6Si0.4O4 NAL and CF phases to 73 GPa determined by Brillouin scattering method
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The sound velocities of two aluminum-rich phases in the lower mantle, hexagonal new Al-rich phase (NAL) and its corresponding high-pressure polymorph orthorhombic Ca-ferrite-type phase (CF), were determined with the Brillouin scattering method in a pressure range from 9 to 73 GPa at room temperature. Both NAL and CF samples have identical chemical composition of Na0.4Mg0.6Al1.6Si0.4O4 (40 % NaAlSiO4–60 % MgAl2O4). Infrared laser annealing in the diamond anvil cell was performed to minimize the stress state of the sample and obtain the high-quality Brillouin spectra. The results show shear modulus at zero pressure G 0 = 121.960 ± 0.087 GPa and its pressure derivative G’ = 1.961 ± 0.009 for the NAL phase, and G 0 = 129.653 ± 0.059 GPa and G’ = 2.340 ± 0.004 for the CF phase. The zero-pressure shear velocities of the NAL and CF phases are obtained to be 5.601 ± 0.005 km/sec and 5.741 ± 0.001 km/sec, respectively. We also found that shear velocity increases by 2.5 % upon phase transition from NAL to CF at around 40 GPa.
KeywordsHigh pressure NAL phase CF phase MORB Sound velocity
We thank two anonymous reviewers and editor of Professor Masanori Matsui for their very constructive comments and suggestions in the reviewing process, which helped us greatly in improving the manuscript. The enlightening discussions were conducted with Professor Heping Li and Dr Shuangming Shan from Laboratory for High Temperature and High Pressure Study of the Earth’s Interior, Institute of Geochemistry, CAS. Dr Saori Imada provides the starting material. The X-ray diffraction measurements were conducted at BL10XU, SPring-8 (Proposal no. 2011B0087 and 2012A0087). This research was financially supported by the “135” Program of Institute of Geochemistry, CAS, the Knowledge-Innovation Key Orientation Project of CAS (KZCX2-YWQN110), NSF of China (41174079 and 40974051), and the Japan Society for the Promotion of Science.
- Hammersley AP (1998) Fit2d: V9.129 reference manual v3.1. Inter Rep ESRF98HA01, ESRF, GrenobleGoogle Scholar
- Miyajima N, Yagi T, Hirose K, Kondo T, Fujino K, Miura H (2001) Potential host phase of aluminum and potassium of the Earth’s lower mantle. Am Mineral 86:740–746Google Scholar
- Ricolleau A, Perrillat JP, Fiquet G, Daniel I, Matas J, Addad A, Menguy N, Cardon H, Mezouar M, Guignot N (2010) Phase relations and equation of state of a natural MORB: implications for the density profile of subducted oceanic crust in the Earth’s lower mantle. J Geophys Res 115:B08202. doi: 10.1029/2009JB006709 CrossRefGoogle Scholar