Petrology of Subducted Slabs

Abstract

Key Words phase diagram, experiment, peridotite, basalt, sediment s Abstract The subducted lithosphere is composed of a complex pattern of chemical systems that undergo continuous and discontinuous phase transformation, through pressure and temperature variations. Volatile recycling plays a major geodynamic role in triggering mass transfer, melting, and volcanism. Although buoyancy forces are controlled by modal amounts of the most abundant phases, usually volatile-free, petrogenesis and chemical differentiation are controlled by the occurrence of minor phases, most of them volatile-bearing. Devolatilization of the subducted lithosphere is a continuous process distributed over more than 300 km of the slab-mantle interface. Melting of the subducted crust, if any, along sufficiently hot P-T paths, is governed by fluid-absent reactions, even though the difference between fluid and melt vanishes at pressures above the second critical end point. The density distribution at a depth of 660 km suggests episodic penetration in space and time of subducted slabs into the lower mantle and sinking down to the D region at the core-mantle boundary.

Thermal and mechanical controls on the evolution of archean crustal deformation: Examples from Western Australia

“…Within the realm of low-volume partial melting appropriate to the thermal regimes considered in this study, our formulation corresponds most closely to the viscosity-melt fraction relationship proposed by Rosenberg and Handy [2004]. We used the pressure-temperature (P-T) loci for the wet solidus and dry liquidus (Figure 5a) fitted by Gerya and Yuen [2003] to the experimental data of Johannes [1985], Schmidt and Poli [1998], and Poli and Schmidt [2002], to estimate M as a function of temperature. The effective viscosity of the partially melted crust (0 < M < 1) was then estimated by using the equation derived by Gay et al [1969] for high-concentration suspensions [see also Pinkerton and Stevenson, 1992]: (14) where η liq is the effective viscosity of granitic liquid.…”

Earthquake behavior and structure of oceanic transform faults

“…[18] We incorporate the effects of mechanical weakening associated with serpentinization by modifying equation (9) when two conditions are met: (1) deformation occurs brittlely (77fr < 77creep) and (2) serpentine or tale is stable based on the stability fields of Poli and Schmidt [2002] for watersaturated peridotites. For a hydrous lherzolite composition, serpentine is stable at temperatures below 540 0 C and talc is stable for temperatures between approximately 540'C-640 0 C at a depth of 10 km (pressures of -300 MPa) [Poli and Schmidt, 2002].…”

“…For a hydrous lherzolite composition, serpentine is stable at temperatures below 540 0 C and talc is stable for temperatures between approximately 540'C-640 0 C at a depth of 10 km (pressures of -300 MPa) [Poli and Schmidt, 2002]. In serpentinized regions, the coefficient of friction (pt) in equations (6)-(9) is adjusted from the unaltered olivine value of 0.85 to 0.1, the lower labderived value appropriate for lizardite, chrysotile, and talc [Reinen et al, 1994;.…”

“…Incorporating hydrothermal cooling further increases the depth of brittle deformation. In Figure 10 we show the calculated stability of antigorite and talc [Poli and Schmidt, 2002] at a depth of 10 km for a slow slipping transform fault. Figure 10 illustrates the enhanced hydration surrounding the transform fault [36] Hydrated peridotite is capable of transporting significant amounts of water to the arc melting region and postarc depths in subduction zones [Hacker, 2008].…”

P–T and structural constraints of lawsonite and epidote blueschists from Liberty Creek and Seldovia: Tectonic implications for early stages of subduction along the southern Alaska convergent margin

“…Several studies have also demonstrated that the transformation of lawsonite, a high-density hydrous mineral with ca. 11 wt% H 2 0 which is stable at high pressure and low temperature, from the lawsonite-stability to epidote-stability fields leads to the release of water in the subduction channel (e.g., Poli and Schmidt, 2002;Tsujimori et al, 2006). The presence of free water in the subduction channel triggers the partial melting of the mantle wedge above the subduction 60' 55 ' ".…”