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Seismic parameters of hcp‐Fe alloyed with Ni and Si in the Earth's inner core
Author(s) -
Liu Jin,
Lin JungFu,
Alatas Ahmet,
Hu Michael Y.,
Zhao Jiyong,
Dubrovinsky Leonid
Publication year - 2016
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2015jb012625
Subject(s) - inner core , alloy , materials science , earth (classical element) , core (optical fiber) , shear (geology) , metallurgy , analytical chemistry (journal) , chemistry , composite material , physics , mathematical physics , chromatography
Iron alloyed with Ni and Si has been suggested to be a major component of the Earth's inner core. High‐pressure results on the combined alloying effects of Ni and Si on seismic parameters of iron are thus essential for establishing satisfactory geophysical and geochemical models of the region. Here we have investigated the compressional ( V P ) and shear ( Vs ) wave velocity‐density ( ρ ) relations, Poisson's ratio ( ν ), and seismic heterogeneity ratios ( dlnρ / dlnV P , dlnρ / dlnV S , and dlnV P / dlnV S ) of hcp‐Fe and hcp‐Fe 86.8 Ni 8.6 Si 4.6 alloy up to 206 GPa and 136 GPa, respectively, using multiple complementary techniques. Compared with the literature velocity values for hcp‐Fe and Fe‐Ni‐Si alloys, our results show that the combined addition of 9.0 wt % Ni and 2.3 wt % Si slightly increases the V P but significantly decreases the V S of hcp‐Fe at a given density relevant to the inner core. Such distinct alloying effects on velocities of hcp‐Fe produce a high ν of about 0.40 for the alloy at inner core densities, which is approximately 20% higher than that for hcp‐Fe. Analysis of the literature high P‐T results on V P and V S of Fe alloyed with light elements shows that high temperature can further enhance the ν of hcp‐Fe alloyed with Ni and Si. Most significantly, the derived seismic heterogeneity ratios of this hcp alloy present a better match with global seismic observations. Our results provide a multifactored geophysical constraint on the compositional model of the inner core which is consistent with silicon being a major light element alloyed with Fe and 5 wt % Ni.