Stability of dense hydrous magnesium silicate phases in the systems Mg 2 SiO 4 -H 2 O and MgSiO 3 -H 2 O at pressures up to 27 GPa

Thermal, hydrous, and mechanical states of the mantle transition zone beneath southern Africa

“…The south African cratons were formed rapidly in the presence of subduction zones [5,6] and subducting lithosphere may supply water to the transition zone [42,43]. A cold transition zone would be a particularly likely place for accumulation of excess water due to higher water solubility than in ambient mantle [44,45], especially during the Archaean. Water exsolution below 660 km and heavy melts above the 410-km discontinuity could prevent convective mixing of water throughout the mantle over time [46].…”

“…Other constants are b (0.14 km per percent of water saturation [34,35]), c (36U10 35 l/K [49]), and d (30.038 per percent of water saturation [47,48]). Two simpli¢cations in the equation require further experimental constraints: the change in the depth of the phase transition is likely a non-linear function of water content [33] ; and water solubility is a function of temperature [44,45]. Assumptions in tomographic inversions (e.g.…”

Elasticity of phase D and implication for the degree of hydration of deep subducted slabs

“…The full dataset of acoustic velocities for each composition were inverted together with calculated phonon directions to determine the six independent C ij using a weighted least-square minimization procedure to solve the Christoffel equation [Musgrave, 1970]. The final fit model yields the elastic constants listed in Table 1 with an average deviation of the velocities of 0.2% for Mg-phD and 1% for the AlFe-phD.…”

“…Seismic anomalies identified at various depths in subduction zones, including low velocity zones (LVZ) and high shear wave splitting [Abers, 2000[Abers, , 2005Gu et al, 2001;Chen and Brudzinski, 2003;Wookey et al, 2002] have been often related to the plausible presence of hydrous phases [Mainprice and Ildefonse, 2009;Hacker et al, 2003]. Among the candidate hydrous phases, phase D (ideal formula MgSi 2 H 2 O 6 , 10-18 wt.% H 2 O) has been proposed in petrological studies as the ultimate water carrier along cold slab geotherms [Kanzaki, 1991;Ohtani et al, 2000Ohtani et al, , 2001 and could account for more than 50 vol.% of very hydrous subducted peridotites from 700 to 1250 km depth [Iwamori, 2004]. Additionally, water released during the breakdown of phase D in the uppermost lower mantle (1100-1400 km depth [Shieh et al, 1998]) may provide a mechanism for the rehydration of the overlaying mantle, triggering changes in the viscosity of the mantle with important consequences for mantle convection [Lawrence and Wysession, 2006].…”

Multianvil techniques in conjunction with synchrotron radiation at Deutsches ElektronenSYnchrotron (DESY) – HAmburger SYnchrotron LABor (HASYLAB)

“…Understanding and modeling of mantle dynamics require more detailed insights into the structural and physical properties of materials relevant for great depths. Ultradeep subduction, penetrating into the lower mantle , and the interpretation of slab recycling in plumes require a fundamental understanding of the water and energy budget of our planet Earth (Bolfan-Casanova et al, 1997Kohlstedt, 1994aKohlstedt, , 1994bKohlstedt, , 1996Kohlstedt et al, 1994Kohlstedt et al, , 1996Litasov et al, 2003Litasov et al, , 2004Litasov and Ohtani, 2003a, 2003b, 2005Ohtani and Maeda, 2001;Ohtani et al, 2000Ohtani et al, , 2001aOhtani et al, , 2001bOhtani et al, , 2003Ohtani et al, , 2004Rubie and Ross-II, 1994;Rubie et al, 1990;Suzuki et al, 2001). Following this line, the transition zone and the core-mantle boundary are regions of special interest.…”