DEFORMATION OF DRY HIGH-PRESSURE ECLOGITES DURING TECTONIC SLICING OF SUBDUCTED OCEANIC LITHOSPHERE: A CASE STUDY FROM THE MONVISO OPHIOLITE, ITALY

The Alps contain records of deeply subducted oceanic lithosphere that were detached from the subducting plate at high-pressure (HP) conditions. These HP ophiolite bodies are key to understanding important geodynamics processes occurring along the plate-interface within subduction zones, yet the nature of their detachment and recovery is not well-understood. For example, HP ophiolites from other localities typically exhibit a mélange or mixed block-in-matrix structure, while Alpine ophiolites represent regular oceanic lithospheric sections that remained coherent during subduction and exhumation. Thus, Alpine ophiolites present a different model for heterogeneous deformation in subduction zone settings: strain must be highly localized along discrete shear zones (slicing) rather than widely distributed within the plate-interface (mélange). To place new constraints on models of tectonic slicing, samples of various HP metamorphic rocks were collected from the well-studied Monviso Ophiolite, Italy. We focus on the weak serpentinzed unit at the base of the ophiolite because it is the natural shearing point for tectonic slicing. Multiple samples of HP serpentinites with various amounts of finite strain were sectioned and analyzed by optical microscopy and scanning electron microscopy (SEM). High-resolution electron backscatter diffraction (EBSD) maps (up to 1024x1024µm) were collected using a Zeiss Supra 35 VP FEG SEM with a HKL Channel 5 EBSD system at Miami University. Raw EBSD maps were analyzed with the MTEX toolbox to quantify and compare dynamically recrystallized grains to non-recrystallized grains. Our results quantify the distribution and extent of strain localization at the base of the Monviso Ophiolite—providing insights into the nature of tectonic slicing inferred for similar HP ophiolites.