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Oman drilling project

Two-thirds of Earth’s surface is made up of oceanic crust, which forms at mid-ocean ridges and is recycled into the mantle via subduction at convergent plate boundaries. During each phase of its 200 million year lifecycle the oceanic crust plays a key role in global geochemical cycles, including the carbon cycle. The inaccessibility of the present-day seafloor makes it logistically difficult to study. However, fragments of ancient oceanic lithosphere (crust + uppermost mantle) that have been tectonically emplaced on continental margins provide access to complete cross-sections of seafloor. These exposed sections of oceanic lithosphere are called ophiolites. The Samail Ophiolite, in Oman and the United Arab Emirates, is the largest, best-exposed section of oceanic lithosphere in the World.

The Oman Drilling Project is a comprehensive drilling program that aims to sample the whole ophiolite sequence, from crust through to upper mantle, in a series of diamond- and rotary-drilled boreholes. Data collection will include analysis of rock core, geophysical logging, fluid sampling, hydrological measurements and microbiological sampling. A large number of scientists from a broad spectrum of disciplines will use these new datasets to address a diverse range of scientific questions relating to the formation, hydrothermal alteration and biotic and abiotic weathering of oceanic lithosphere.

The overarching goal of scientific drilling in the Samail ophiolite is to understand the full spectrum of processes that create and modify oceanic crust and shallow mantle, involving mass and energy transfer between the mantle, the crust, the hydrosphere, the atmosphere and the biosphere over a range of temperatures from 1350 to 20°C, depths from the surface to 10 or 20 km below the paleo-seafloor, and tectonic settings from spreading ridges to the deep ocean to surficial weathering to subduction zones.

The Oman Drilling Project will address long-standing unresolved questions regarding formation of oceanic lithosphere at mid-ocean ridges, hydrothermal alteration of the sea floor and subsequent mass transfer between the crust and the oceans and recycling of volatile elements in subduction zones. Furthermore, the science team will undertake frontier exploration of subsurface weathering processes that lead to natural uptake of CO2 from surface waters and the atmosphere, and the nature of the subsurface biosphere in areas where these processes are occurring.

Drilling operations started on december 25, 2016, in Wadi Jidya. Three 400m-deep borehole have already been completed and cored with 100% recovery, in lower crust gabbros and in the the gabbro/sheeted dikes transition zone ; a fourth one is in progress, in the hydrated and carbonated mantle peridotites at the base of the ophiolite, and through the metamorphic sole. Other drill holes, without coring, are in progress in the serpentinized mantle section, first stage of a series of holes that will be later used for onsite experiments.

Members of Géosciences Montpellier who have participated and will participate one way or another are Marguerite Godard, Julie Noël, Delphine Roubinet, Laurent Brun, Bernard Célérier, Philippe Gouze, Gilles Henry, Benoit Ildefonse, Gérard Lods, Philippe Pezard, Émilien Oliot et Richard Leprovost.

photo : Rotary drilling in Batin, a region where Julie Noël works for her PhD. She completed a detailed mapping of the area with the help of Émilien Oliot. This borehole is one of the two test holes that will allow the OmanDP team to select the site for the active serpentinization study, in which several teams from GM are heavily involved.
© Marguerite Godard (2017)

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