High-pressure single crystal X-ray diffraction and FT-IR observation of natural chondrodite and synthetic OH-chondrodite

Abstract

High pressure single crystal X ray diffraction studies of a natural chondrodite, Mg 4.76 Fe 0.22 Ti 0.02 Si 1.99 O 8 (OH 1.26 F 0.74 ), and a synthetic OH chondrodite, Mg 4.98 Si 2.01 H 2.00 O 10 , were performed using a diamond anvil cell (DAC) up to 7.3 and 5.9 GPa, respectively and at room temperature. FT IR spectra of the natural chondrodite under high pressure conditions up to 9.9 GPa was also observed using a DAC. The axial linear compressibilities of these samples are calculated as βa = 1.69(4) × 10 ) for the synthetic OH chondrodite. The isothermal bulk moduli of these samples were calculated as K T = 124.1(4) GPa for the natural chondrodite and K T = 117(2) GPa for the OH chondrodite, by using the Birch Murnaghan equation of state assuming K = 4. The bulk moduli of total void space in each sample, assuming K = 4, were calculated to be K = 116(2) GPa for the natural chondrodite and K = 113(4) GPa for the OH chondrodite. The plots of bulk modulus versus the summation of the filling factor of polyhedral sites show a good correlation between the humite minerals. This relationship can be explained by the replacement of 4O 2− + Si 4 + 4(F, OH) − + generated in the humite homologous series. In the FT IR spectra of the natural chondrodite, four OH stretching vibrational peaks were observed at 3688, 3566, 3558 and 3383 cm −1 under ambient conditions. The pressure dependences of the frequency of these peaks up to 9.9 GPa are 2.8(3), 3.9(3), 4.0(3) and −2.1(2) (cm), respectively. With increasing pressure up to 9.9 GPa, the 3383 cm −1 peak shifts to lower frequency positions, whereas the other peaks shift to higher frequency positions. The shortening of the O5⋅ ⋅ ⋅ O5 distance, which is not the shared edge between M3 octahedra, related to hydrogen bonding with increasing pressure causes the negative pressure dependence of the 3383 cm −1 peak. The positive pressure dependence of the remaining IR peaks is due to the compression of the O5 H bond, and not related to hydrogen bonding with increasing pressure.

Hydration effects on crystal structures and equations of state for silicate minerals in the subducting slabs and mantle transition zone

“…Gibbs et al, 1970;Robinson et al, 1973;Yamamoto, 1977;Fujino and Takuchi, 1978;Ottolini et al, 2000;James, 2001, 2002;Friedrich et al, 2001Friedrich et al, , 2002Kuribayashi et al, 2004;Kunz et al, 2006;Ye et al, 2013Ye et al, , 2015. Natural chondrodite and clinohumite samples have been found in metamorphosed limestones and dolomites (Friedrich et al, 2002), as well as in serpentinized wehrlite .…”

“…Such discrepancy mostly comes from the selection of fitting methods for the EoS. For chondrodite, F -typically increases K T , compared with the F-free samples (Ross and Crichton, 2001;Friedrich et al, 2002;Kuribayashi et al, 2004). F  =(OH)  substitution could decrease the water content, while increase the density and the bulk modulus.…”

“…Yusa and Inoue, 1997;Yusa et al, 2000;Ross and Crichton, 2001;Crichton and Ross, 2002;Kudoh et al, 2002;Kuribayashi et al, 2003Kuribayashi et al, , 2004Kuribayashi et al, , 2008Smyth et al, 2004;Manghnani et al, 2005Manghnani et al, , 2013Holl et al, 2006Holl et al, , 2008Ganskow et al, 2010; al., 2010, 2012). On the other hand, some studies have been conducted for the P-V-T EoS of anhydrous forsterite, wadsleyite, and ringwoodite (Meng et al, 1993(Meng et al, , 1994Guyot et al, 1996;Li et al, 2001;Katsura et al, 2004Katsura et al, , 2009aKatsura et al, , 2009bCouvy et al, 2010).…”

“…Brucite: Duffy et al (1995), Catti et al (1995); Phase A: Kudoh et al (2002), Crichton and Ross (2002), Kuribayashi et al (2003), Holl et al (2006); norbergite: Kurbayashi et al (2008); chondrodite: Crichton (2001), Friedrich et al (2002), Kuribayashi et al (2004); clinohumite: Crichton and Ross (2002); olivine: Kudoh and Takéuchi (1985), Down et al (1996), Abramson et al (1997), Manghnani et al (2013); wadsleyite: Yusa and Inoue (1997), Hazen et al (2000), Holl et al (2008), Ye et al (2013); ringwoodite: Hazen (1993), Meng et al (1994), Yusa et al (2000), Smyth et al (2004), Manghnani et al (2005), Ganskow et al (2010), Ye et al (2012). It is noted that the number after "Fo" is the forsterite (Mg) content.…”

“…F  =(OH)  substitution could decrease the water content, while increase the density and the bulk modulus. The sample from Crichton and Ross (2002) is F-free, whereas that from Kuribayashi et al (2004) is F-rich (F  /(F  +OH  )= 85 mol.%, which decreases the water content to 1.4 wt.%. The water content in the olivine sample from Manghnani et al (2013) is very low (≤0.8 wt.%), and the K T0 value shows no significant difference from those of anhydrous samples (Kudoh and Takéuchi, 1985;Down et al, 1996).…”