Subduction zones are fundamental locations of mass recycling and chemical exchanges between the surface and the interior of the earth. Extensive, and at times explosive, volcanism results from these exchanges. Arc volcanoes display strikingMoreSubduction zones are fundamental locations of mass recycling and chemical exchanges between the surface and the interior of the earth. Extensive, and at times explosive, volcanism results from these exchanges. Arc volcanoes display striking characteristics.
They are aligned along a sharp front and cluster in regularly spaced groups parallel to the convergent margin. Furthermore, arc lavas with widely different compositions are erupted close to one another in both space and lime. The goal of this thesis is to understand the processes occurring in the wedge which cause these surface characteristics.-Numerical models of buoyant porous fluid migration and wet melt production are formulated in Chapter 1.
The effects of solid flow, slab dip, wedge thermal structure and grain-size on melt production are investigated. We find that melting is localized along a sharp melting front and that the height of the melting column is only of secondary importance. Solid flow determines the rate at which both hydrous fluids and fertile mantle material are brought into the melting region, thereby controlling melt production rates. These models are applied to the Aleutian subduction zone in Chapter 2.
We find that variations in subduction parameters such as convergence rate and slab dip exert an overarching controlling influence on melt production and cause a decrease in melt production westward along the Aleutian arc.-Chapter 3 and 4 investigate models of both stable trace element and U-series isotopes exchange in the wedge taking into account the effects of fluid migration and diffusion on trace element systematics. We find that both highly and moderately incompatible elements need to be incorporated in slab-derived fluids in order to agree with observed arc lava trace element patterns.
U-series show that melts produced along the melting front need to be extracted to the surface with little chemical exchange with the surrounding mantle material, thereby necessitating channelized flow. Furthermore, linear trends on U-Th isochron plots do not yield ages which correlate with processes occurring in the wedge. These ages should consequently not be used to estimate fluid migration time scales in the wedge.