[SCG56-01] Feedback between melt percolation and deformation at Oman crust-mantle transition zone: ICDP_ Exp. 807 Holes CM1A and CM2B
Keywords:Oman crust-mantle, Melt percolation , Olivine CPO , XRF,ICP-MS, LA-ICP-MS, Oman drilling project
Samples from holes CM1A and CM2B have a large petrological and chemical variability, mainly reflecting the different rock types, especially across the crust-mantle transition. CM1A and CM2B volatile element contents reflect extensive serpentinization linked to interaction with H2O-rich fluids, and abundant carbonate veins downhole, suggesting an association between CO2-rich fluids and serpentinization. Whole-rock and clinopyroxene trace element abundances are similar to Oman ophiolite compositions described in previous studies. All gabbroic domains display nearly parallel REE patterns with a strong depletion in HFSE relative to REE. Dunites and harzburgites display variable trace element contents and REE patterns, negative or positive anomalies in Eu and commonly moderate to strong positive anomalies in U, Pb, Sr and Ti. The variation of REE concentrations and patterns observed in Oman dunites could be explained by melt-rock reactions leading to dunite formation, after the dissolution of orthopyroxene in harzburgite and interaction with interstitial melt.
Another way to explore melt percolation and deformation feedback at Oman crust-mantle transition zone is the analysis of detailed olivine crystallographic preferred orientations (CPO) of 36 selected samples from hole CM1A (1 olivine gabbro, 10 dunites, and 8 harzburgites) and CM2B (6 dunites, and 12 harzburgites). Olivine CPO‘s indicates that all samples from the Oman crust-mantle transition zone display well-developed olivine CPO, the three classics high temperatures olivine CPO’s symmetries (axial-, axial- and orthorhombic) are present with an olivine J-index varying from 1.2 to 8.6. The geochemical investigations conducted onboard D/V Chikyu (Phase 2 Leg 3; July-Aug. 2018) together with the variabilities observed in olivine CPO types and strength within Oman crust-mantle transition could be explained by the localization of deformation during diffuse (crystals grains boundaries) and focused (veins, faults) melt percolation.