Elemental mixing systematics and Sr–Nd isotope geochemistry of mélange formation: Obstacles to identification of fluid sources to arc volcanics

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

“…This similarity in the Sr-Nd isotope signature is also a strong argument against inheritance from the zoisite eclogites' precursor rock. Instead, the metasomatic formation of zoisite in the eclogites by the vein-forming fluids is the cause for the Sr-Nd isotope homogenization, because zoisite is the main carrier of both Sr (up to ~8000 ppm) and Nd (up to ~600 ppm) (Herms et al, submitted (King et al, 2006).…”

“…Without fluids, isotopic resetting is kinetically locked or restricted to sluggish intermineral diffusion. In general, the modification of pre-subduction isotopic compositions by fluid-rock interaction at HP conditions is a common feature (Bebout, 2007;Berger et al, 2010;King et al, 2006). During exhumation, HP subducted rocks can be incorporated into the subduction channel, i.e.…”

“…The direct examination of subduction zone metamorphic rocks provides insight of how mass is redistributed during metamorphism (e.g., Bebout, 1991;Beinlich et al, 2010;Gao et al, 2007;John et al, 2008;King et al, 2004;Sorensen and Grossman, 1989;Spandler et al, 2003Spandler et al, , 2004, about the nature of slab-derived agents added to arc lava sources and about chemical changes in subducting rocks potentially contributing to the geochemical heterogeneity of the upper mantle (e.g., Bebout, 2007;Breeding et al, 2004, John et al, 2004. Increasing attention has been directed towards metasomatic processes within subducted rocks because metasomatic rocks can constitute new bulk compositions that can influence the redistribution of major and trace elements (Bebout, 2007;King et al, 2006King et al, , 2007Scambelluri et al, 2006;Zack and John, 2007). Metasomatic rocks can also affect the composition of slab fluids as they may contain mineral assemblages that are able to transport water to great depths in the subduction zone (e.g., Schmidt and Poli, 1998).…”

“…The Rb-Sr system has been applied to provide constraints on sources and nature of fluids at depth (e.g., Glodny et al, 2003), and Sr isotopes can indicate the presence of a metamorphic fluid in mélange rocks (King et al, 2006) or previous seafloor alteration (Miller et al, 1988).…”

Fluid-metapelite interaction in an ultramafic mélange: implications for mass transfer along the slab-mantle interface in subduction zones

“…Recent studies of subduction zone mélanges have revealed that significant fluid flow and fluid-rock interaction took place along the slab-mantle interface (Bebout and Barton 1989, 2002Grossman 1989, 1993;King et al 2003King et al , 2006King et al , 2007Breeding et al 2004;Marschall et al 2006;Spandler et al 2008;Miller et al 2009;Penniston-Dorland et al 2010, 2012. The mélanges represent tectonic and metasomatic mixing of sedimentary, mafic, and ultramafic rocks along the interface region at the contact between the subducting slab and the mantle wedge.…”