TY - JOUR
T1 - Elastic Moduli of Jadeite-Enstatite Majorite
AU - Reichmann, Hans J.
AU - Sinogeikin, Stanislav V.
AU - Bass, Jay D.
AU - Gasparik, Tibor
N1 - Publisher Copyright:
© Copyright 2002 by the American Geophysical Union.
PY - 2002/10/1
Y1 - 2002/10/1
N2 - The adiabatic bulk (KS) and shear (G) moduli of a polycrystalline majorite-garnet solid solution with composition (Na0.92Mg2.08)(Mg0.02Al1.06Si0.92)Si3O12 were measured at ambient conditions by Brillouin spectroscopy. KS and G were found to be 171.6 (3.5) GPa and 103.5 (2.0) GPa, respectively. Assuming a linear dependence of the elastic moduli on composition for the Mg2Si2O6 (enstatite-majorite, En-Mj) - NaAlSi2O6 (jadeite-majorite, Jd-Mj) join, the calculated KS and G of the fictive Jd-Mj end-member are 178 and 125 GPa, respectively. At ambient conditions, the shear velocity change associated with the pyroxene to majorite transition increases dramatically with increasing Na content in the system. In contrast, there is virtually no shear velocity increase associated with the pyroxene to majorite transition in MgSiO3. If this relationship holds at high pressures and temperatures, it suggests that for mineral assemblages containing an abundance of large radius cations such as Ca and Na, the pyroxene→garnet reaction will produce higher shear velocity gradients than assemblages that are relatively deficient in these elements. Such chemical effects could play a significant role in explaining high seismic velocity gradients in the transition zone.
AB - The adiabatic bulk (KS) and shear (G) moduli of a polycrystalline majorite-garnet solid solution with composition (Na0.92Mg2.08)(Mg0.02Al1.06Si0.92)Si3O12 were measured at ambient conditions by Brillouin spectroscopy. KS and G were found to be 171.6 (3.5) GPa and 103.5 (2.0) GPa, respectively. Assuming a linear dependence of the elastic moduli on composition for the Mg2Si2O6 (enstatite-majorite, En-Mj) - NaAlSi2O6 (jadeite-majorite, Jd-Mj) join, the calculated KS and G of the fictive Jd-Mj end-member are 178 and 125 GPa, respectively. At ambient conditions, the shear velocity change associated with the pyroxene to majorite transition increases dramatically with increasing Na content in the system. In contrast, there is virtually no shear velocity increase associated with the pyroxene to majorite transition in MgSiO3. If this relationship holds at high pressures and temperatures, it suggests that for mineral assemblages containing an abundance of large radius cations such as Ca and Na, the pyroxene→garnet reaction will produce higher shear velocity gradients than assemblages that are relatively deficient in these elements. Such chemical effects could play a significant role in explaining high seismic velocity gradients in the transition zone.
UR - http://www.scopus.com/inward/record.url?scp=0036820606&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0036820606&partnerID=8YFLogxK
U2 - 10.1029/2002GL015106
DO - 10.1029/2002GL015106
M3 - Article
AN - SCOPUS:0036820606
SN - 0094-8276
VL - 29
JO - Geophysical Research Letters
JF - Geophysical Research Letters
IS - 19
M1 - 1936
ER -