S41: Fluid-rock interaction and fluid loss during high-pressure metamorphism in subduction zones

Conveners:	Reiner Klemd	(reiner.klemd@mail.uni-wuerzburg.de)
	Haakon Austrheim	(hakon .austrheim @geologi.uio.no)
Keynote:	Timm John	(Kiel)

Metamorphic devolatilisation occurring among the different lithologies during subduction is important in terms of volatile recycling, transport of major and trace elements from the slab into the overlying mantle wedge, and the initiation of intraslab earthquakes. Fluids liberated from subducting slabs during dehydration at sub-arc depths are commonly thought to be responsible for these processes. Little is known about the nature, composition and flow behaviour of such fluids. We encourage contributions which address the characterisation of prograde and retrograde fluids involved in exhumed natural (ultra) high-pressure metamorphic samples, and numerical simulations of heat and mass transfer in subduction zones. Furthermore, submissions of experimental and natural studies are invited which contribute to understanding fluid loss processes during high-pressure metamorphism in subduction zones.

S42: Isotopic connections between metamorphism and magmatism in subduction zones

Conveners:	Horst Marschall	(Horst.Marschall@bristol.ac.uk)
	Robert L. King	(rlking@wsu.edu)
Keynote speaker:	Jeff Ryan	(Tampa, USA)

Conventional models for slab-mantle material transfer are based on geochemical signatures in volcanic rocks erupted on the overriding plate. Models of this type may successfully explain observed chemical and isotopic signatures, but are unrealistic in that they fail to address metamorphic and metasomatic processes occurring within the subducted slab and mantle wedge. This session invites papers that seek to improve connections between metamorphic and magmatic processes associated with subduction from the perspective of the geochemical evolution of slab metamorphism, metasomatism along the slab/mantle interface and within the mantle wedge, which may then be compared to arc volcanic signatures. We especially encourage submissions that address fractionation and recycling during subduction from stable isotopic records (e.g., Li, B) and radiogenic isotope tracers of exhumed subduction-related rocks (e.g., Sr, Nd, Hf, Pb).

S43: Experimental studies of the role of fluids in subduction processes

Conveners:	Jörg Hermann	(joerg.hermann@anu.edu.au)
	Roland Stalder	(rstalde@gwdg.de)
Keynote:	Max Schmidt	(ETH, Zürich)
	Craig Manning	(UCLA)

Fluid phases act as a trigger for partial melting and are considered important metasomatic agents during subduction zone processes. In recent years new experimental strategies have been developed and considerable progress has been made with respect to our knowledge of the physical properties and chemical behaviour of fluid phases at crustal and upper mantle conditions. This session will focus on experimental constraints on the role of water-dominated fluid phases during subduction processes and will cover a range of topics such as trace element partitioning, isotope fractionation, fluid-melt miscibility and fluid speciation. Furthermore, contributions involving physical properties such as viscosity, density and wetting behaviour are welcome, as well as in-situ spectroscopic studies and presentations on relevant novel experimental techniques, strategies and instrumentation.

S44: Mantle heterogeneity induced via ancient subduction

Conveners:	Steve Shirey	(shirey@dtm.ciw.edu)
	Ivan Savov	(savov@dtm.ciw.edu)
	Stephen Foley	(foley@uni-mainz.de)
Keynote:	Elisabeth Widom	(Miami, USA)

Increasing numbers of studies suggest that subduction processes on Earth have been active for more than 2.5 billion years. The recycling of oceanic lithosphere +/- sediments that must have accompanied all ancient convergent margins exerted a profound influence on the mantle by introducing subducted components, especially if ancient convergent margins evolved faster than those today. Recognition of the effects of past versus current subduction contributions to the convecting mantle has been difficult because of the similar geochemical imprints that ancient and modern subduction zones leave. Additional complexities arise from uncertainties in the composition of Proterozoic subducted sediments and crust, as well as unmodified mantle. We encourage submissions from the fields of petrology, geochemistry, geodynamics and mantle tomography which could help link ancient subduction zone processes with the compositional, rheological and density heterogeneities in the modern mantle. This could include a range of studies from those documenting subduction in Archean-Proterozoic terranes to those detailing the nature and distribution of heterogeneity in the mantle of any age. Particularly encouraged are submissions using a combination of radiogenic isotopes (Re-Os, U-Pb, Sm-Nd, Lu-Hf) and elemental and isotope slab tracers (B, Be, Li, C, N, O, H).

S45: Volcanic processes and volatiles in island arcs

Conveners:	Alison Shaw	(ashaw@whoi.edu)
	Gerhard Wörner	(gwoerne@gwdg.de)
Keynotes:	John Blundy	(Bristol, England)
	Paul Wallace	(Eugene, USA)

Various factors influence how materials are transferred through volcanic arc systems; these include primary volatile contents, magmatic differentiation, crystallization, degassing and magma ascent rates. This symposium will focus on the mass transfer of magmas and volatiles in subduction zones - from the zone of arc magma generation through to eruption at the surface. Arc magmas span a wide compositional range reflecting varying degrees of fractional crystallisation and magmatic differentiation. Their composition plays an important role in determining how they evolve during ascent or residence within crustal reservoirs. Silica and volatile contents in particular will control physical constraints on the mode of magma movement within the crust as well as the eruption style (e.g., effusive vs. explosive). Rates of cooling and degassing during ascent will also strongly affect the magma's physical parameters through enhanced rates of crystallisation. Finally, subsurface exsolution, fumarolic degassing and volatile release during eruption are all important processes of subduction zone magmatism. We welcome all contributions that address questions related to mass transfer in subduction zone systems, considering all possible scales from melt inclusions to global mass transfer budgets.

S46: Magmatic differentiation in subduction zone volcanoes (University of Waikato, New Zealand)

Conveners:	John Gamble	(J.Gamble@ucc.ie)
	Ralf Gertisser	(r.gertisser@esci.keele.ac.uk)
	Valentin Troll	(trollv@mail.tcd.ie)
Keynote:	Richard C. Price	(University of Waikato, New Zealand)

Magmas provide one of the most important probes of the interior of the Earth. Chemical information locked in plutonic or volcanic rocks can, in principle, be used to ascertain the compositions of the source from which the magma was originally formed and to unravel the physical conditions of melt generation. However, in all but a few cases, the compositions of magmas change as they ascend through the lithosphere in response to differentiation processes such as fractional crystallisation, decompression, crustal contamination and mixing and mingling with other magmas. Recognising that the melt phase and crystalline cargo in volcanic rocks (eg phenocryst assemblage in andesites) represent an aggregate of these multistage differentiation events, we can apply, modern in-situ trace element and isotopic analytical techniques to unravel the differentiation history of plutons and volcanoes. This not only gives us a means of accounting for the effects of differentiation and constraining the nature of the original magma source(s), but also gives us a way of quantifying these processes and associated elemental fluxes in subduction systems. This session seeks to bring together researchers that aim to unravel differentiation processes in subduction settings by applying methodologies such as crystal isotope stratigraphy, classical and experimental petrology, geochronology and geochemistry to quantify contributions from the slab, the mantle wedge and from magma-crust interaction during final ascent and shallow-level magma storage.