The Behaviour and Influence of Fluids in Subduction Zones

Unique among the terrestrial planets, the Earth has a substantial hydrosphere, which has had an extraordinary influence on the way the planet has evolved. Whereas volcanic activity is the main route by which fluids escape from depth to reach the atmosphere/hydrosphere, the dominant route by which fluids may enter the deeper levels of the Earth is via subduction zones. How deep can these fluids penetrate? More importantly, what influence do fluids have in controlling geological processes at depth? This volume contains the proceedings of the Discussion Meeting, held at the Royal Society in November 1990, which tried to assess the role of fluids in the subduction environment, first at shallow levels where material is entering the subjuction system, but then following processes down to progressively deeper levels in the Earth's mantle, to the zone of melting and beyond. These processes include the formation of accretionary sedimentary prisms, which represent important lateral additions to the continental crust at island arcs and continental margins, and whether subduction zones represent the important interface across which some of the major chemical reservoirs in the Earth are formed. This collection of papers serves as both a review or synthesis of what recent research in geophysics, oceanography, sedimentology, tectonics, geochemistry, mineralogy, petrology and thermal modelling has achieved in recent years and points to the direction of future investigations.

Table of Contents:
Geophysical evidence for the role of fluids in accretionary wedge tectonics, G.K.Westbrook; fluids in convergent margins - what do we know about their composition, origin, role in diagenesis and importance for oceanic chemical fluxes?, M.Kastner, H.Elderfield and J.B.Martin; the microstructural evolution of fluid flow paths in semi-lithified sediments from subduction complexes, R.J.Knipe, S.M.Agar and D.J.Prior; plumbing accretionary prisms - effects of permeability variations, J.C.Moore, K.M. Brown, et al; sediment deformation and fluid activity in the Nakai, Izu-Bonin and Japan forearc slopes and trenches, A.Taira and K.T. Pickering; water budgets in accretionary wedges - a comparison, X.Le Picon, P.Henry and the Kaiko=Nankai scientific crew; fluid expulsion from the Cascadia accretionary prism - evidence from porosity distribution, direct measurements and GLORIA imagery, B.Carson, M.L.Holmes, et al; numerical simulation of subjuction zone pressure-temperature-time paths - constraints on fluid production and arc magmatism, S.M.Peacock; a physical model for the volume and composition of melt produced by hydrous fluxing above subduction zones, J.H.Davies and M.J.Bickle; solubility of apatite, zircon and rutile in supercritical aqueous fluids with implications for subduction zone geochemistry, J.C.Ayers and E.B.Watson; fluid influence on the trace element compositions of subduction zone magmas, A.D.Saunders, M.J.Norry and J.Tarney; element fluxes associated with subduction-related magmatism, C.J.Hawkesworth, et al; partial melting of subducted oceanic crust and isolation of its residual eclogitic lithology, W.F.McDonough.