Determining the rates and conditions of subduction initiation beneath the Samail Ophiolite

Subduction zones are the primary loci of chemical exchange between the surface and the deep Earth. Understanding how subduction initiates and evolves is important for characterizing the nature of this exchange. The geological record contains a rich archive of subduction initiation in the form of ophiolites, which are pieces of oceanic crust and mantle emplaced on continents.

These ophiolites often contain a thin veneer of rocks smeared out and welded to their base (“metamorphic soles”) that are thought to represent the first increments of subducted material in a newly formed subduction zone, i.e., when a plate first begins to sink. This proposal seeks to characterize the thermal and chemical record of these earliest subducted rocks along the base of Samail Ophiolite (Oman/UAE) to determine the rates and conditions at which subduction started in the Samail system.

These data will be critically tested against geodynamic models to understand the tectonic settings and physical parameters leading to subduction initiation. The data will also be used to trace the earliest phases of subduction-related chemical exchange between the surface and the deep Earth. The project is spearheaded by two early career scientists; supports the educational, technical, and professional development of two undergraduate students; and funds the development of a virtual museum exhibit about ophiolites for the general public.

The research is expected to identify: i) the duration of high-T metamorphism in the Samail sole, ii) metamorphic conditions and mass flow paths (P-T-t) in the sole, and iii) variations in (i) and (ii) along the length of the ophiolite. Analytical work will be performed on garnet amphibolites previously collected from the Samail metamorphic sole. We will collect garnet, clinopyroxene, and Ti-phase trace-element spots and maps (LA-ICPMS); quantitative garnet and clinopyroxene major-element maps (EPMA); bulk-rock major and trace-element data (XRF, ICPMS); and Raman spectra on strained quartz and zircon inclusions in garnet.

These data will be used for conventional, single-element (e.g., Zr-in-titanite), and elastic thermobarometry to characterize P-T paths experienced by each of the studied samples, as well as diffusion modelling of trace- and major-element profiles in garnet and clinopyroxene to constrain T-t histories. These data will also be used to test between order-of-magnitude differences in metamorphic timescales from different geochronological techniques, potentially supporting either long-term “forced” subduction initiation or shorter-term “spontaneous” subduction initiation.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.