Geochemical Profiles Across the Listvenite‐Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results From Drilling at OmanDP Hole BT1B

Abstract

Listvenites (or listwaenites) are produced by CO 2 -metasomatism of mantle-derived ultramafic rocks (Falk & Kelemen, 2015;Halls & Zhao, 1995). They are composed mainly of quartz and carbonate (magnesite and/or dolomite, ±Cr-or Mg-rich micas ± chlorite) and are often associated with serpentinites, ophicarbonates and/ or talc. Since their first description in the literature (Rose, 1837), they have been investigated for one of their main characteristics: the occurrence of mineralizations concentrating economically valuable metals, such as

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

“…Major element compositions for Hole BT1B samples were reported in the Proceedings of the Oman Drilling Project (Kelemen et al, 2020a;Kelemen et al, 2020b) with the exception of samples in the 181-186 m 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).…”

Listvenite Formation During Mass Transfer into the Leading Edge of the Mantle Wedge: Initial Results from Oman Drilling Project Hole BT1B

“…This observation suggests that both Sr and Ca were added during low temperature alteration, along with H 2 O and CO 2 . These topics are discussed further by Godard et al (2021).…”

“…Additional constraints on, and discussion of, the solid volume increases during formation of the MoD Mountain listvenites are provided by Godard et al (2021). Because porosities in peridotite, serpentinite and listvenite rarely if ever exceed 5%, all of these solid volume changes must be accommodated mainly by expansion of the entire rock volume.…”

“…The sole contains metasediments and meta‐volcanic rocks—including submarine pillow lavas—with the major element compositions of mid‐ocean ridge basalts (MORB) as well as alkali basalts and more evolved andesites and dacites (Alabaster et al., 1982; Ernewein et al., 1988; MacLeod et al., 2013; Pearce et al., 1981; Searle et al., 1980). In core from BT1B, alkaline metabasalt compositions in the sole (Godard et al., 2021; Kelemen, Matter, et al., 2020) are unlike the magmas that formed the crust of the Samail ophiolite. In the ophiolite, the structurally lowest, “Geotimes” or “V1” lavas are similar to normal mid‐ocean ridge basalts, though they probably were hydrous and they contain a hint of an arc trace element signature (Alabaster et al., 1982; Ernewein et al., 1988; MacLeod et al., 2013; Pearce et al., 1981).…”

“…However, in this paper we informally group the Haybi Formation into an undifferentiated metamorphic sole unit. In the sole sampled by drill core from Hole BT1B, metasediments are clearly distinguishable from the metabasalts based on texture, but some of them are compositionally similar to the metabasalts, perhaps reflecting a volcanoclastic origin, whereas others grade into somewhat odd, low‐SiO 2 , muscovite‐bearing lithologies (Godard et al., 2021; Kelemen, Matter, et al., 2020; Kotowski et al., 2021).…”