Lawsonite blueschist, Sivrihisar, Turkey

(field of view = 4 mm)

Omphacite-bearing lawsonite blueschist, Sivrihisar, Turkey (field of view = 4 mm)

Subduction Petrofabrics

The rheology of subducted crust strongly influences the geophysical and geochemical evolution of convergent plate boundaries, including the interaction of deformation, metamorphism, and fluid-rock reaction during subduction and exhumation, and the rates of processes such as exhumation of high-pressure rocks. This NSF-funded research addresses questions of the mechanisms of large-magnitude transport (exhumation) of high-pressure rocks in subduction zones by characterizing the kinematics of deformation from the map scale to the grain-scale using syn-kinematic high-pressure index minerals. Microstructural, petrologic, and stable isotope analyses are used to determine deformation mechanisms, flow laws, and fluid-rock interaction in the context of high-pressure conditions.

The focus of this investigation is the Sivrihisar Massif, Turkey: an exhumed subduction complex with pervasive, syn-kinematic high-pressure assemblages preserved in metasedimentary (marble, quartzite) and metabasaltic (eclogite, blueschist) rocks.

In particular, we are studying columnar marble (calcite pseudomorphs after aragonite), glaucophane-bearing quartzite, and lawsonite-bearing blueschist and eclogite. Lawsonite fabrics such as the one in the figure to the left (top) are particularly useful for kinematic analysis (Teyssier et al., 2010, Geology).

This project also involves research on the transition from high-pressure/low-temperature subduction fabrics and assemblages to lower-pressure/higher-temperature (Barrovian) fabrics and assemblages. An apparently structurally continuous transition is preserved in the Sivrihisar Massif, from blueschist/eclogite to sillimanite zone rocks (Whitney, 2002; Seaton et al., 2009; Whitney et al., 2011).

People: Erkan Toraman, Nick Seaton, Christian Teyssier, Donna Whitney, Peter Davis (PhD 2008)