Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B

Abstract

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Deep Sourced Fluids for Peridotite Carbonation in the Shallow Mantle Wedge of a Fossil Subduction Zone: Sr and C Isotope Profiles of OmanDP Hole BT1B

“…To the first order, alteration of peridotite to form serpentinite and listvenite in Hole BT1B was nearly isochemical except for the addition of H 2 O and CO 2 . Average bulk rock Mg/Si, Fe/Si, Al/Si, Fe/Mg, and Cr/Al ratios in serpentinite and listvenite are close to the average composition of the Samail peridotite (Godard et al., 2021; Kelemen et al., 2020a; Kelemen et al., 2020b; Kelemen et al., 2021) and similar to the composition of previously studied listvenites from the outcrops extending north and northeast from the drill site (Falk & Kelemen, 2015). The core provides a unique record of the interaction between peridotites in the leading edge of the mantle wedge and hydrous fluids rich in CO 2 .…”

“…Drill core samples encompass all the identified lithologies from Hole BT1B. Major element compositions for Hole BT1B samples were reported in the Proceedings of the Oman Drilling Project with the exception of samples in the 181-186m depth interval which are reported by Godard et al (2021). Trace element compositions of Hole BT1B samples can be found in Godard et al (2021).…”

“…Major element compositions for Hole BT1B samples were reported in the Proceedings of the Oman Drilling Project with the exception of samples in the 181-186m depth interval which are reported by Godard et al (2021). Trace element compositions of Hole BT1B samples can be found in Godard et al (2021). Trace element compositions and loss on ignition for Hawasina formation outcrop samples were analyzed at Lamont Doherty Earth Observatory (LDEO).…”

“…This correction gives the lowest possible 87 Sr/ 86 Sr for all the samples based on reported ages. For the corrections, we used Sr and Rb concentrations reported by Godard et al (2021) for Hole BT1B and our analyses of Hawasina metasediments. While Rb/Sr is low in most BT1B samples and thus age corrections are small, this correction removes some of the apparent trends observed in measured 87 Sr/ 86 Sr versus depth.…”

“…The upper 6 m are composed of alluvial gravels followed by an ultramafic sequence comprised of listvenites (carbonated peridotites) interlayered with two serpentinite bands (80–100 m depth and 181–186 m depth). A thick (0.42 m) layer of gray‐green fault gouge at 196.6–197.1 m depth separates the ultramafic units from the metamorphic sole composed of fine‐grained metabasalts (Godard et al., 2021; Kelemen et al., 2020a; Kelemen et al., 2020b; Kelemen et al., 2021). To the first order, alteration of peridotite to form serpentinite and listvenite in Hole BT1B was nearly isochemical except for the addition of H 2 O and CO 2 .…”