TY - JOUR
T1 - Silicate diffusion in alkali-carbonatite and hydrous melts at 16.5 and 24GPa
T2 - Implication for the melt transport by dissolution-precipitation in the transition zone and uppermost lower mantle
AU - Shatskiy, Anton
AU - Litasov, Konstantin D.
AU - Borzdov, Yuriy M.
AU - Katsura, Tomoo
AU - Yamazaki, Daisuke
AU - Ohtani, Eiji
N1 - Funding Information:
We greatly thank reviewers for a thorough reviews and constructive suggestions, K. Hirose for editorial handling and comments, N.V. Sobolev, I.S. Sharygin, and V.S. Shatsky for useful discussion. This study was conducted as a part of the 21st Century COE program at Okayama University and the Global Center-of-Excellence program at Tohoku University. This work was also supported by the Ministry of Education and Science of Russia (Project Nos. 14.B37.21.0601 and 14.B25.31.0032) and by the Russian Foundation for Basic Research (Project Nos. 12-05-01167 and 12-05-33008).
PY - 2013/12
Y1 - 2013/12
N2 - The diffusivity of dissolved Mg2SiO4 in wadsleyite saturated KMC melt (K2Mg(CO3)2+25.7wt.% MgSiO3) at 16.5GPa and 1700°C, MgSiO3 diffusivity in perovskite saturated KMCH (K2Mg(CO3)2×2H2O+31.7wt.% MgSiO3) and HM (H2O+75.7wt.% MgSiO3) melts at 24GPa and 1500°C were determined experimentally using a scaled-up version of a Kawai-type multi-anvil apparatus. During a diffusion experiment, silicate saturation was maintained at different levels in the two temperature regions by placing the diffusion cell in the thermal gradient of 20°C/mm. The diffusivity was computed from the total mass of silicate transported from "hot" to the "cold" region during the course of an experiment. At given conditions silicate diffusivities were estimated to be DKMCMg2SiO4=2×10-9m2/s, DKMCHMgSiO3=4×10-9m2/s, and DHMMgSiO3=5×10-8m2/s.Using obtained diffusivities we estimated possible migration rates of dispersed melt inclusion in the deep mantle by means of dissolution-precipitation considering different driving forces. The rates of melt migration driven by the lateral thermal gradient of 1°C/km in the mantle plume range from 4×10-8 to 8×10-7m/year. This means that during plume ascent time of about 50Ma, the melt can be moved by 2-40m. These values clearly demonstrate that the thermal gradient is very weak driving force in terms of melt segregation in the deep mantle. On the other hand, at typical mantle stress of 1MPa and droplet size of 100μm the migration rates of the HM, KMCH and KMC melts are estimated to be 22.5, 0.9 and 0.2m/year, respectively, which are 2-3 orders of magnitude faster than ascent rate of the mantle plume. This implies that all melt droplets on the way of ascending plume would be entrapped by the stressed zone in front of plume and accumulated in the plume head. This mechanism may explain segregation of mantle magmas with the source regions deeper than 150-250km, such as kimberlites.
AB - The diffusivity of dissolved Mg2SiO4 in wadsleyite saturated KMC melt (K2Mg(CO3)2+25.7wt.% MgSiO3) at 16.5GPa and 1700°C, MgSiO3 diffusivity in perovskite saturated KMCH (K2Mg(CO3)2×2H2O+31.7wt.% MgSiO3) and HM (H2O+75.7wt.% MgSiO3) melts at 24GPa and 1500°C were determined experimentally using a scaled-up version of a Kawai-type multi-anvil apparatus. During a diffusion experiment, silicate saturation was maintained at different levels in the two temperature regions by placing the diffusion cell in the thermal gradient of 20°C/mm. The diffusivity was computed from the total mass of silicate transported from "hot" to the "cold" region during the course of an experiment. At given conditions silicate diffusivities were estimated to be DKMCMg2SiO4=2×10-9m2/s, DKMCHMgSiO3=4×10-9m2/s, and DHMMgSiO3=5×10-8m2/s.Using obtained diffusivities we estimated possible migration rates of dispersed melt inclusion in the deep mantle by means of dissolution-precipitation considering different driving forces. The rates of melt migration driven by the lateral thermal gradient of 1°C/km in the mantle plume range from 4×10-8 to 8×10-7m/year. This means that during plume ascent time of about 50Ma, the melt can be moved by 2-40m. These values clearly demonstrate that the thermal gradient is very weak driving force in terms of melt segregation in the deep mantle. On the other hand, at typical mantle stress of 1MPa and droplet size of 100μm the migration rates of the HM, KMCH and KMC melts are estimated to be 22.5, 0.9 and 0.2m/year, respectively, which are 2-3 orders of magnitude faster than ascent rate of the mantle plume. This implies that all melt droplets on the way of ascending plume would be entrapped by the stressed zone in front of plume and accumulated in the plume head. This mechanism may explain segregation of mantle magmas with the source regions deeper than 150-250km, such as kimberlites.
KW - Carbonatite
KW - Diffusion
KW - Dissolution-precipitation
KW - Earth's mantle
KW - Hydrous melt
KW - Kimberlite
KW - Melt percolation
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U2 - 10.1016/j.pepi.2013.09.004
DO - 10.1016/j.pepi.2013.09.004
M3 - Article
AN - SCOPUS:84888298973
SN - 0031-9201
VL - 225
SP - 1
EP - 11
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
ER -