Tectonic evolution of the Hellenic (Greece) and Otago (New Zealand) subduction wedges

This dissertation describes a multi-disciplinary study into the tectonic evolution of convergent margins, with particular emphasis on the modern Hellenic subduction wedge exposed in Crete, Greece. The thermal evolution of the wedge is constrained through several approaches. Metamorphic temperatures are measured using the Raman spectroscopy of carbonaceous material thermometer, which is refined and expanded for use at lower temperatures. Application to several basement units in Crete establishes peak metamorphic temperatures and documents a modest thermal offset across a major low-angle detachment fault. This result suggests that the high-pressure rocks in Crete were exhumed primarily by pervasive brittle thinning rather than slip on a single fault.; The cooling history of the high-pressure rocks in Crete is re-evaluated through the combination of published data and new thermochronologic results. This revision establishes an unsteady history with several drastic changes in the cooling rate. A correlation between the apparent cooling rate and the subduction velocity suggests that the rate of within-wedge deformation and exhumation is primarily controlled by the rate that material fluxes into the wedge.; The important role of accretion in driving deformation is further revealed through strain analysis, both from the Hellenic wedge as well as the Mesozoic subduction wedge exposed in the South Island, New Zealand. In both settings, the quantification of pressure solution strains documents spatial variation in the pattern of deformation. In the frontal parts of these systems, deformation is characterized by weak vertical stretching and subhorizontal shortening. The more interior parts of the wedges show co-axial vertical shortening and the development of a flat-lying foliation. Study of fault-slip kinematics from the high-pressure rocks in Crete establishes a similar geometry for brittle deformation, with co-axial vertical shortening and radial extension. These spatial changes in the nature of the deformation fabric are interpreted to reflect variation in the mode of accretion into the wedge. Offscraping in the front of a wedge may reduce its taper and drives vertical stretching. In contrast, underplating at the base of the wedge may destabilize a wedge, leading to vertical thinning and the development of a flat-lying foliation.