A Reference Section Through Fast‐Spread Lower Oceanic Crust, Wadi Gideah, Samail Ophiolite (Sultanate of Oman): Whole Rock Geochemistry

Abstract

Oceanic crust covers more than two-thirds of Earth's surface and 90% of Earth's volcanism is associated with the formation of oceanic lithosphere along a 60,000 km network of oceanic spreading ridges. The formation of oceanic crust is one of the dominant processes in the chemical differentiation and physical evolution of our planet exerting primary control on the transfer of material, heat, and volatiles from Earth's interior to its crust, oceans, and atmosphere. Knowledge of the composition of oceanic crust is a prerequisite for the calculation of their fluxes and for testing models of crustal accretion and magma differentiation at oceanic spreading ridges.

A Reference Section Through Fast‐Spread Lower Oceanic Crust, Wadi Gideah, Samail Ophiolite (Sultanate of Oman): Trace Element Systematics and REE Crystallization Temperatures—Implications for Hybrid Crustal Accretion

“…As this data set lacks HREE compositions for plagioclase and rotation is present, the resulting temperatures are about 50°C too heigh, showing that HREE/LREE temperature offsets are not a unique feature of Wadi Gideah gabbros. (b) Plagioclase fractional crystallization evolution lines for different water contents (dashed lines) of the Gideah Bulk Crust composition (Garbe‐Schönberg et al., 2022) modeled with MELTS at 2 kbar buffered by QFM (Ghiorso & Sack, 1995). The main result here is that the anorthite‐temperature trend of the Wadi Gideah gabbros (solid black line, equal to Figure 8a) can only be explained for a water content between 0.4 and 0.6 wt% H 2 O.…”

“…We studied the samples using a polarized light microscope to identify petrographic key parameters and to select regions of interest suitable for microanalytical measurements based on the following conditions: (a) crystals and clusters belong to the primary rock-forming assemblage and domain, (b) have sufficient size to place multiple large spots in the core region when performing LA-ICP-MS measurements (spot size plagioclase 120 μm, clinopyroxene 32-44 μm), (c) homogeneous and well crystallized with smooth surfaces and with as few as possible cleavage cracks and fractures, and (d) showing the least amount of primary . Separation between upper and lower sheeted dikes after Garbe-Schönberg et al (2022). Geological map modified after (Peters et al, 2008).…”

“…By focusing on primary magmatic features as a function of crustal depth, this work provides a direct link between the on‐axis thermal rock record and numerical models of crustal accretion. This paper is part of a series of manuscripts that deal with different aspects of the Wadi Gideah transect sample suite obtained from the Oman ophiolite, which provides a coherent section through fast‐spread oceanic crust (Garbe‐Schönberg et al., 2022; Koepke et al., 2022; Mock, Ildefonse, et al., 2021).…”

“…(height above the mantle‐crust transition zone, for calculation of h.a.M., see Section 2.1), Varitextured gabbros, VG, ∼4.1–5.0 km h.a.M., Upper foliated gabbros, UFG; ∼3.5–4.1 km h.a.M., Lower foliated gabbros, LFG, ∼2.6–3.5 km h.a.M., Layered gabbros, LG, ∼0.2–2.6 km h.a.M., mantle‐crust transition zone, MTZ, ∼0–0.2 km h.a.M. (for details see Figure 1b, Koepke et al., 2022; Garbe‐Schönberg et al., 2022; Mock, Ildefonse, et al., 2021). Varitextured gabbros outcrop north of the gabbro‐dike transition zone at several hills roughly exceeding a height of 50 m, being widespread in the lower wadi plain, which is heavily covered by Neogene debris (Figure 1a).…”

“…Separation between upper and lower sheeted dikes after Garbe‐Schönberg et al. (2022). Geological map modified after (Peters et al., 2008).…”