TY - JOUR

T1 - In situ observation of the pyroxene-majorite transition in Na2MgSi5O12 using synchrotron radiation and Raman spectroscopy of Na-majorite

AU - Dymshits, Anna

AU - Sharygin, Igor

AU - Litasov, Konstantin

AU - Shatskiy, Anton

AU - Gavryushkin, Pavel

AU - Ohtani, Eiji

AU - Suzuki, Akio

AU - Funakoshi, Kenichi

PY - 2015/2/1

Y1 - 2015/2/1

N2 - In situ X-ray diffraction study of the pyroxene to majorite transition in Na2MgSi5O12 was carried out in Kawai-type high-pressure apparatus coupled with synchrotron radiation. The phase boundary between Na-pyroxene and Na-majorite was determined over the temperature interval of 1073-1973 K and was described by a linear equation P (GPa) = 12.39 + 0.0018×T (K). The Clapeyron slope (dP/ dT) determined in this study is similar to the one predicted by computer simulations (Vinograd et al. 2011) but smoother than the one obtained by quenched experiments (Dymshits et al. 2010). The presence of sodium in the system lowers the pressure of pyroxene-to-majorite transformation. For the first time Na-majorite was characterized using Raman spectroscopy. Raman peaks of Na-majorite are broader than pyrope due to the substitution of Mg2+ for Na+ at the X site. Both Si-O symmetric stretching (A1g-n1) and O-Si-O symmetric bending (A1g-n2) modes of Na-majorite are significantly shifted to higher frequencies relative to corresponding bands of pyrope. In contrast the A1g-R (SiO4) mode of Na-majorite (342 cm-1) displays a lower frequency than that of pyrope (365 cm-1). Our results enable further understanding of the mechanisms responsible for phase transformations in the Earth's transition zone and lower mantle.

AB - In situ X-ray diffraction study of the pyroxene to majorite transition in Na2MgSi5O12 was carried out in Kawai-type high-pressure apparatus coupled with synchrotron radiation. The phase boundary between Na-pyroxene and Na-majorite was determined over the temperature interval of 1073-1973 K and was described by a linear equation P (GPa) = 12.39 + 0.0018×T (K). The Clapeyron slope (dP/ dT) determined in this study is similar to the one predicted by computer simulations (Vinograd et al. 2011) but smoother than the one obtained by quenched experiments (Dymshits et al. 2010). The presence of sodium in the system lowers the pressure of pyroxene-to-majorite transformation. For the first time Na-majorite was characterized using Raman spectroscopy. Raman peaks of Na-majorite are broader than pyrope due to the substitution of Mg2+ for Na+ at the X site. Both Si-O symmetric stretching (A1g-n1) and O-Si-O symmetric bending (A1g-n2) modes of Na-majorite are significantly shifted to higher frequencies relative to corresponding bands of pyrope. In contrast the A1g-R (SiO4) mode of Na-majorite (342 cm-1) displays a lower frequency than that of pyrope (365 cm-1). Our results enable further understanding of the mechanisms responsible for phase transformations in the Earth's transition zone and lower mantle.

KW - diamond

KW - in situ experiment

KW - mantle

KW - Na-majorite

KW - Na-pyroxene

KW - phase transition

UR - http://www.scopus.com/inward/record.url?scp=84923677643&partnerID=8YFLogxK

U2 - 10.2138/am-2015-4801

DO - 10.2138/am-2015-4801

M3 - Article

AN - SCOPUS:84923677643

VL - 100

SP - 378

EP - 384

JO - American Mineralogist

JF - American Mineralogist

SN - 0003-004X

IS - 2-3

ER -