The Alps contain records of deeply subducted oceanic lithosphere that detached at high-pressure (HP) conditions and later exhumed to the surface. 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 some Alpine ophiolites represent complete oceanic lithospheric sections that remained coherent during subduction and exhumation. Thus, Alpine ophiolites like Monviso 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 further test models of tectonic slicing, samples of various HP metamorphic rocks were collected from the well-studied Monviso Ophiolite, Italy. Here we focused on dry mafic eclogite bodies hosted within a hydrated chlorite-rich shear zone because of their pristine preservation of the HP mineral assemblage. A sample of dry HP eclogite was sectioned and analyzed by optical microscopy and scanning electron microscopy (SEM). High-resolution backscatter electron maps (3072×2304) and semi-quantitative chemical maps (1024×786) were collected using a Zeiss Supra 35 VP FEG SEM with a Bruker Quantax 100 Energy Dispersive x-ray microanalysis system at Miami University. Subtle shear fabrics within the dry eclogite sample indicate incomplete strain localization within the weak hydrated shear zone—providing insights into the nature of tectonic slicing inferred for similar HP ophiolites.
Author(s): Dwight Sims, Geology Major
Advisor(s): Buchanan Kerswell, Department of Geology & Environmental Earth Science
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