Understanding axial melt lens dynamics and lower crust accretion at fast-spreading mid-ocean ridges: new insights from drill cores obtained by the ICDP Oman Drilling Project

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In winter 2016/17, the ICDP drilling initiative "Oman Drilling Project" (OmanDP) successfully penetrated the lower paleocrust of the Oman ophiolite, the world’s largest, best-exposed, and most-studied section of subaerially exposed oceanic lithosphere. The cores are 400 m long and were recovered with a nearly 100 % success rate, making them a uniquely valuable resource for petrographical, petrological, geochemical and structural study and ensuring access to coherent sections throughout critical zones of a fast-spreading oceanic crust: the lowermost layered gabbros (core GT1), the layered to foliated gabbro transition (core GT2), and the gabbro/dike transition (core GT3). The drilled transects through the plutonic crust of the Oman paleocrust can be regarded as a Rosetta Stone for understanding the mode of accretion and cooling of fast-spread oceanic crust that covers about one third of our planet. The proposed project focuses on four main scientific targets: (1) exploring of axial melt lens dynamics at the gabbro/dike transition, (2) investigating the nature of the transition between layered and foliated gabbro in the mid-crust (3) understanding the mechanisms of layer-forming processes in the deep, layered crust, and (4) testing the hypothesis that amphibole-bearing patches/veins formed in the magmatic-metamorphic regime are the results of initial cooling of the deep crust. We plan to integrate petrographical, petrological, geochemical and micro-structural work (lattice preferred orientation using electron backscattering diffraction) on layered, foliated and varitextured gabbros. The results will establish the basis for a deep understanding of the magmatic and initial hydrothermal processes within the axial melt lens and surrounding crystal mush, which form the magma chambers at the end of the melting column beneath mid-ocean ridges.