LISTVEIN: Multiscale structure evolution during peridotite carbonation and hydration in an oceanic subduction zone: a case study of listvenite in the Oman Ophiolite

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Listvenites in the Oman Ophiolite formed from oceanic mantle peridotite thrust over carbonate-bearing sediments in the hanging wall of a subduction zone. In this example of large scale peridotite hydration and carbonation processes, core BT1 of the ICDP Oman Drilling Project (OmDP) provides a unique sample. Although listvenites record carbon fluxes in oceanic subduction zones and are a possible natural analogue for carbon capture and storage via mineralization, the processes by which this carbonation occurs are not well understood, calling for work to understand the evolution of this natural example. We propose a micro- and macrostructural study of deformation and reaction structures in listvenite and serpentinized peridotite in Core BT1. Using optical and electron microscopy (ViP, CL, BIB-SEM, EDX, EBSD, QEMSCAN) integrated with our core description data and with the state of the art image data (core scans, X-ray CT, hyperspectral, XRF) collected by OmDP, we will focus on (i) the different generations of fault, cataclasite and fracture and vein structures modifying the listvenite microstructure, analyzing overprinting relationships and deformation mechanisms, (ii) the microstructure of listvenite, testing the presence of a ductile shear zone during carbonation, (iii) the microstructure of protolith serpentinites and partially altered peridotites, (iv) microstructures in syntaxial and antitaxial veins to distinguish reaction-induced- from tectonically and pore pressure-induced fracturing, and finally (v) on micro- and nano-porosity and its connectivity to constrain potential fluid pathways in the matrix.We aim to better understand the interplay of force of crystallization, tectonic stress and pore pressure during large scale hydration and carbonation processes in BT1 and test hypotheses on driving forces, structural evolution and fluid transport pathways in this system. More generally, we hope to contribute a process-oriented perspective to studies of mass transfer and element “recycling” in subduction zones, and to understand the effect of mass transfer and mineralogical transformation on plate-boundary deformation.