Juan Carlos De Obeso
email: juancarlos.deobeso@ucalgary.ca

Peter B Kelemen

James M Leong

Manuel D Menzel

Craig E Manning

Marguerite Godard

Yue Cai

Louise Bolge

Project Phase Oman Drilling

Science Party

Juan Carlos

Emma Bennett

Dieter Garbe

Louise Koornneef

Chris Macleod

Tony Morris

Samuel Müller

Julie Noël

Daniel Nothaft

Laurent Brun

Gérard

Salim Al Amri

Salim Ahmed Alshahri

Saif Masoud Alhumaimi

Hamed Bader

Alwaeli

Andreas Beinlich

Mark Cloos

Matthew Cooper

Joëlle D ' Andres

Luke Deamer

Jeremy Deans

Rebecca Greenberger

Andrew Horst

Takashi Hoshide

Kevin Johnson

Jürgen Koepke

Kentaro Kondo

Alissa Kotowski

Catriona Menzies

Tomoaki Morishita

Khac Du

Nguyen

Suzanne Picazo

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

Completely carbonated peridotites represent a window to study reactions of carbon-rich fluids with mantle rocks. Here we present details on the carbonation history of listvenites close to the basal thrust in the Samail ophiolite. We use samples from Oman Drilling Project Hole BT1B, which provides a continuous record of lithologic transitions, as well as outcrop samples from listvenites, metasediments and metamafics below the basal thrust of the ophiolite. 87 Sr/ 86 Sr of listvenites and serpentinites, ranging from 0.7090 to 0.7145, are significantly more radiogenic than mantle values, Cretaceous seawater, and other peridotite hosted carbonates in Oman. The Hawasina sediments that underlie the ophiolite, on the other hand, show higher 87 Sr/ 86 Sr values of up to 0.7241. d 13 C values of total carbon in the listvenites and serpentinites range from -10.6‰ to 1.92‰. We also identified a small organic carbon component with d 13 C as low as -27‰. Based on these results, we propose that during subduction at temperatures above >400°C, carbon-rich fluids derived from decarbonation of the underlying sediments migrated updip and generated the radiogenic 87 Sr/ 86 Sr signature and the fractionated d 13 C values of the serpentinites and listvenites in core BT1B.

Plain Language Summary

Samples from Oman Drilling Project Hole BT1B provide a record of interactions of fluids rich in carbon dioxide with mantle rocks. This interactions lead to the formation of listvenites, rocks composed mainly by magnesite and quartz. Here we describe the formation of listvenites in the Oman ophiolite using Strontium and Carbon isotopes to characterize the source and nature of the fluid that pervasively transform the mantle rocks that now store vast amounts of carbon dioxide.

Introduction

Hydration and carbonation of ultramafic rocks are important processes in the carbon and water cycle of our planet [START_REF] Alt | The role of serpentinites in cycling of carbon and sulfur: Seafloor serpentinization and subduction metamorphism[END_REF][START_REF] Fruh-Green | Serpentinization of oceanic peridotites: Implications for geochemical cycles and biological activity[END_REF]. These alteration reactions are sinks of water and carbon where peridotites are exposed on the seafloor forming alteration minerals like serpentine and carbonates [START_REF] Alt | The role of serpentinites in cycling of carbon and sulfur: Seafloor serpentinization and subduction metamorphism[END_REF][START_REF] Klein | Brucite formation and dissolution in oceanic serpentinite[END_REF][START_REF] Macdonald | Rate of serpentinization in seafloor environments[END_REF][START_REF] Paulick | Geochemistry of abyssal peridotites (Mid-Atlantic Ridge, 15°20′N, ODP Leg 209): Implications for fluid/rock interaction in slow spreading environments[END_REF] which are carried back into the mantle in convergent margins. Fluids derived from the subducted slab can migrate and interact with the mantle wedge in subduction zones, so that the "leading edge of the mantle wedge" aka the "cold nose", can be partially hydrated and carbonated [START_REF] Blakely | Subduction-zone magnetic anomalies and implications for hydrated forearc mantle[END_REF][START_REF] Hyndman | Serpentinization of the forearc mantle[END_REF][START_REF] Kelemen | Reevaluating carbon fluxes in subduction zones, what goes down, mostly comes up[END_REF]. This is usually inferred from seismic data (e.g. [START_REF] Deshon | Evidence for serpentinization of the forearc mantle wedge along the Nicoya Peninsula, Costa Rica[END_REF][START_REF] Kamiya | Seismological evidence for the existence of serpentinized wedge mantle[END_REF][START_REF] Tibi | Seismic evidence for widespread serpentinized forearc mantle along the Mariana convergence margin[END_REF][START_REF] Tsuji | Tomographic evidence for hydrated oceanic crust of the Pacific slab beneath northeastern Japan: Implications for water transportation in subduction zones[END_REF]. Understanding the interaction of carbon-bearing hydrous fluids with peridotites is important to supplement and constrain geophysical observations. Fully carbonated peridotites, also known as listvenites [START_REF] Halls | Listvenite and related rocks: perspectives on terminology and mineralogy with reference to an occurrence at Cregganbaun, Co. Mayo, Republic of Ireland[END_REF], provide a window into the alteration processes that occur in the "cold nose" of the mantle wedge above subduction zones, where mantle peridotite reacts with hydrous and carbonated fluids likely derived from the subducting slab at moderate temperatures and pressures [START_REF] Beinlich | Massive serpentinite carbonation at Linnajavri, N-Norway[END_REF][START_REF] Boskabadi | Carbonate alteration of ophiolitic rocks in the Arabian-Nubian Shield of Egypt: sources and compositions of the carbonating fluid and implications for the formation of Au deposits[END_REF][START_REF] Boskabadi | Carbonation of ophiolitic ultramafic rocks: Listvenite formation in the Late Cretaceous ophiolites of eastern Iran[END_REF][START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF][START_REF] Menzel | Carbonation of mantle peridotite by CO2-rich fluids: the formation of listvenites in the Advocate ophiolite complex (Newfoundland, Canada)[END_REF]. Formation of listvenites appears to be restricted to particular conditions requiring high carbon concentrations in the fluid [START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF][START_REF] Hansen | Carbonated Serpentinite (Listwanite) At Atlin, British Columbia: a Geological Analogue To Carbon Dioxide Sequestration[END_REF][START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF][START_REF] Menzel | Carbonation of mantle peridotite by CO2-rich fluids: the formation of listvenites in the Advocate ophiolite complex (Newfoundland, Canada)[END_REF]. For example, complete carbonation of peridotites to form listvenites is not observed near the surface in ophiolites (e.g. [START_REF] Clark | Paleoclimatic reconstruction in northern Oman based on carbonates from hyperalkaline groundwaters[END_REF]de Obeso andKelemen, 2020, 2018;[START_REF] Del Real | Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks[END_REF][START_REF] Kelemen | In situ carbonation of peridotite for CO2 storage[END_REF][START_REF] Noël | Evidence of polygenetic carbon trapping in the Oman Ophiolite: Petro-structural, geochemical, and carbon and oxygen isotope study of the Wadi Dima harzburgite-hosted carbonates (Wadi Tayin massif, Sultanate of Oman)[END_REF][START_REF] Quesnel | Paired stable isotopes (O, C) and clumped isotope thermometry of magnesite and silica veins in the New Caledonia Peridotite Nappe[END_REF][START_REF] Schwarzenbach | Sulfur and carbon geochemistry of the Santa Elena peridotites: Comparing oceanic and continental processes during peridotite alteration[END_REF]. It is also not observed near the seafloor, where serpentinization and formation of carbonate veins are common (e.g [START_REF] Bach | Carbonate veins trace seawater circulation during exhumation and uplift of mantle rock: Results from ODP Leg 209[END_REF][START_REF] Delacour | Carbon geochemistry of serpentinites in the Lost City Hydrothermal System (30°N, MAR)[END_REF][START_REF] Schwarzenbach | Serpentinization and carbon sequestration: A study of two ancient peridotite-hosted hydrothermal systems[END_REF]. Fluid sources for complete carbonation have been associated with subduction in different listvenite localities. [START_REF] Menzel | Carbonation of mantle peridotite by CO2-rich fluids: the formation of listvenites in the Advocate ophiolite complex (Newfoundland, Canada)[END_REF] attributed carbonation of harzburgite in the Advocate ophiolite (Canada) to fluxing by slab-derived, CO2-rich fluids. Isotopic data (d 13 C, d 18 O and 87 Sr/ 86 Sr) of listvenites in the Late Cretaceous ophiolites of eastern Iran point to carbon-bearing fluids derived from subducted sedimentary units as the source of carbon [START_REF] Boskabadi | Carbonation of ophiolitic ultramafic rocks: Listvenite formation in the Late Cretaceous ophiolites of eastern Iran[END_REF].

In Oman, listvenites occur along the basal thrust of the ophiolite [START_REF] Nasir | Mineralogical and geochemical characterization of listwaenite from the Semail Ophiolite, Oman[END_REF][START_REF] Wilde | Preliminary study of tertiary hydrothermal alteration and platinum deposition in the Oman ophiolite[END_REF]. Previous studies have investigated their formation conditions and the nature of the carbonation fluids without reaching conclusive answers on the source of the fluids [START_REF] Beinlich | Ultramafic Rock Carbonation: Constraints From Listvenite Core BT1B, Oman Drilling Project[END_REF][START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF][START_REF] Nasir | Mineralogical and geochemical characterization of listwaenite from the Semail Ophiolite, Oman[END_REF][START_REF] Stanger | Silicified serpentinite in the Semail nappe of Oman[END_REF]. In this paper, we present 87 Sr/ 86 Sr and d 13 C data on samples from Oman Drilling Project Hole BT1B and the underlying sediments of the Hawasina Formation. We show that devolatization of the subducting sediments similar to the Hawasina Formation likely generated the carbonation fluids which reacted with the mantle wedge in this fossil subduction zone to form listvenites. These processes probably operate in subduction zones worldwide, where fluids migrate updip along the slab mantle interface, and then react with hanging wall peridotites storing large amounts of carbon.

Geological setting

The Samail ophiolite

The Samail ophiolite, along the northeast coast of Oman and the United Arab Emirates (UAE), is one of the best-exposed block of oceanic crust and its underlying mantle in the world. It was thrust over adjacent oceanic lithosphere soon after magmatic formation, and then onto the margin of the Arabian subcontinent in the late Cretaceous. The mantle section of the ophiolite is mainly composed of highly depleted, residual mantle peridotites (mostly harzburgites, e.g. [START_REF] Godard | Relationships between geochemistry and structure beneath a palaeo-spreading centre: a study of the mantle section in the Oman manuscript submitted to JGR: Solid Earth ophiolite[END_REF][START_REF] Hanghøj | Composition and Genesis of Depleted Mantle Peridotites from the Wadi Tayin Massif, Oman Ophiolite; Major and Trace Element Geochemistry, and Os Isotope and PGE Systematics[END_REF][START_REF] Monnier | Along-ridge petrological segmentation of the mantle in the Oman ophiolite[END_REF], together with 5 to 15% dunite [START_REF] Braun | Petrologic and Microstructural Constraints on Focused Melt Transport in Dunites and Rheology of the Shallow Mantle[END_REF][START_REF] Braun | Dunite distribution in the Oman Ophiolite: Implications for melt flux through porous dunite conduits[END_REF][START_REF] Collier | Spatial-Statistical Properties of Geochemical Variability as Constraints on Magma Transport and Evolution Processes at Ocean Ridges[END_REF]. Near the basal thrust, interlayered dunites and refertilized harzburgites comprise the distinctive "Banded Unit" [START_REF] Khedr | Chemical variations of abyssal peridotites in the central Oman ophiolite: Evidence of oceanic mantle heterogeneity[END_REF]. The peridotites are pervasively serpentinized, with serpentine (± brucite) making up ~ 30-100 wt% of "fresh" rock [START_REF] Godard | Relationships between geochemistry and structure beneath a palaeo-spreading centre: a study of the mantle section in the Oman manuscript submitted to JGR: Solid Earth ophiolite[END_REF][START_REF] Hanghøj | Composition and Genesis of Depleted Mantle Peridotites from the Wadi Tayin Massif, Oman Ophiolite; Major and Trace Element Geochemistry, and Os Isotope and PGE Systematics[END_REF][START_REF] Monnier | Along-ridge petrological segmentation of the mantle in the Oman ophiolite[END_REF] and/or completely carbonated to form listvenites [START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF][START_REF] Nasir | Mineralogical and geochemical characterization of listwaenite from the Semail Ophiolite, Oman[END_REF][START_REF] Stanger | Silicified serpentinite in the Semail nappe of Oman[END_REF][START_REF] Wilde | Preliminary study of tertiary hydrothermal alteration and platinum deposition in the Oman ophiolite[END_REF]. The listvenites only occur within a few km of the basal thrust of the ophiolite, and manuscript submitted to JGR: Solid Earth within the tectonic melanges with a serpentine matrix just below the base of the ophiolite [START_REF] Nasir | Mineralogical and geochemical characterization of listwaenite from the Semail Ophiolite, Oman[END_REF][START_REF] Stanger | Silicified serpentinite in the Semail nappe of Oman[END_REF].

Lithologies below the Samail ophiolite nappe

Beneath the mantle section of the Samail ophiolite is a locally preserved "metamorphic sole". This sole is exposed discontinuously along the basal thrust, juxtaposed with the overlying Banded Unit at the base of the Samail mantle section. It records peak metamorphic temperatures of 700-900°C and imprecise peak pressures of 0.8 to 1.4 GPa [START_REF] Cowan | Structure of the metamorphic sole to the Oman Ophiolite, Sumeini Window and Wadi Tayyin: Implications for ophiolite obduction processes[END_REF]Hacker & Mosenfelder, 1996;[START_REF] Searle | Subduction zone metamorphism during formation and emplacement of the Semail ophiolite in the Oman Mountains[END_REF][START_REF] Searle | Structure and metamorphism of rocks beneath the Semail ophiolite of Oman and their significance in ophiolite obduction[END_REF][START_REF] Soret | Petrological evidence for stepwise accretion of metamorphic soles during subduction infancy (Semail ophiolite, Oman and UAE)[END_REF]. A lower temperature unit (∼450-550°C) with similar peak pressures (0.8 to 1.2 GPa) has also been identified from the metamorphic section of Oman DP Hole BT1B [START_REF] Kotowski | Structural and thermal evolution of an infant subduction shear zone: Insights from sub-ophiolite metamorphic rocks recovered from Oman Drilling Project Site BT-1B. Earth and Space Science Open Archive[END_REF]. The base of the sole is in fault contact with low grade allochthonous sediments of the Hawasina formation, which is composed of pelagic clastic units interlayered with limestones [START_REF] Bechennec | The Hawasina Basin: A fragment of a starved passive continental margin, thrust over the Arabian Platform during obduction of the Sumail Nappe[END_REF][START_REF] Bechennec | The Hawasina Nappes: Stratigraphy, palaeogeography and structural evolution of a fragment of the south-Tethyan passive continental margin[END_REF] deposited from the late Permian to the Cretaceous. The Hawasina sedimentary units were thrusted over autochthonous Mesozoic to Proterozoic platform sediments of the Arabian continental margin, forming nappes between the autochton and the ophiolite.

OmanDP Hole BT1B and Oman Listvenites

Hole BT1B was drilled in March 2017 in Wadi Mansah (23.364374°N, 58.182693°E), which yielded a total length of 300.1 m with 100% recovery [START_REF] Kelemen | Site BT1: fluid and mass exchange on a subduction zone plate boundary[END_REF]. The upper 6 meters 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 to 186 m depth). A thick (0.42 m) layer of grey-green fault gouge at 196.6 m-197.1 m depth separates the ultramafic units from the metamorphic sole composed of fine-grained metabasalts [START_REF] Godard | Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B. Earth and Space Science Open Archive[END_REF][START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF]2020). To the first order, alteration of peridotite to form serpentinite and listvenite in Hole BT1B was nearly isochemical except for the addition of H2O and CO2. 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 [START_REF] Kelemen | Site BT1: fluid and mass exchange on a subduction zone plate boundary[END_REF][START_REF] Zeko | Carbonation of the Oman ophiolite during subduction and emplacement[END_REF], Godard et al. 2021) and similar to the composition of previously studied listvenites from the outcrops extending north and northeast from the drill site [START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF]. The core provides a unique record of the interaction between peridotites in the leading edge of the mantle wedge and hydrous fluids rich in CO2. For an expanded version of the geology of Oman DP Hole BT1B and MoD mountain we refer the reader to the Proceedings of the Oman Drilling Project [START_REF] Kelemen | Site BT1: fluid and mass exchange on a subduction zone plate boundary[END_REF] and [START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF].

Materials and Methods

Samples analyzed for this study comprise a suite of drill core samples from OmanDP Hole BT1B (listvenites n=50, serpentinites n=14, metamorphic sole rocks n=11) and hand samples of the Hawasina formation (n=18) and metamorphic sole sediments (n=2). Location of Oman DP Hole BT1B and Hawasina samples are shown in Figure 1. 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 [START_REF] Kelemen | Site BT1: fluid and mass exchange on a subduction zone plate boundary[END_REF] with the exception of samples in the 181-186m depth interval which are reported by [START_REF] Godard | Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B. Earth and Space Science Open Archive[END_REF]. Trace element compositions of Hole BT1B samples can be found in [START_REF] Godard | Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B. Earth and Space Science Open Archive[END_REF]. Trace element compositions and loss on ignition for Hawasina formation outcrop samples were analyzed at Lamont Doherty Earth Observatory (LDEO). Rb and Sr concentrations were analyzed using a VG PlasmaQuad ExCell quadrupole ICP-MS following HNO3-HF digestion. Major element compositions of the Hawasina samples are available in supplementary table 1. Additional Sr isotopes were measured on samples from outcrops northeast of Hole BT1B [START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF]. [START_REF] Villey | Geological Map of Fanjah[END_REF], Google Earth and field observations. Hand samples collected for this study are marked with red circles with number of samples collected per location in black.

For Sr isotope analysis, bulk rock powder was fully digested in a HNO3-HF mixture overnight and redissolved in 3N HNO3 prior to column chemistry using the Eichrom® Sr resin. Purified Sr were analyzed for isotopic compositions interspersed with US National Institute of Standards and Technology (NIST) SRM 987 on a Thermo Scientific Neptune multi-collector ICP-MS at LDEO. In-run mass fractionations were normalized to 86 Sr/ 88 Sr=0.1194. Unknowns were normalized to SRM 987 87 Sr/ 86 Sr value of 0.701248. International standards BHVO-2 yielded 87 Sr/ 86 Sr value of 0.703509±41 (2s, n = 3) and BCR-2 yielded 0.705046±34 (2s, n = 3), which agree with published values from [START_REF] Weis | High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS[END_REF].

Total Carbon (TC) was measured from the same bulk rock powder splits as for Strontium isotopes. Total Organic Carbon (TOC, or reduced carbon) was measured from the residual rock powder after the removal of Inorganic Carbon (carbonate carbon) through reaction with dilute (3 N) HCl for at least 3 days, followed by washing with Millipore® water. Concentrations and d 13 C ratios of Total Carbon (TC) and Total Organic Carbon (TOC), were determined using a Costech element analyzer coupled with a Thermo Scientific Delta V plus mass spectrometer at LDEO. Sample runs were calibrated using Acetanilide for carbon contents (R 2 =0.9998). For d 13 C we used USGS40 (d 13 C =-26.77±0.16‰ V-PDB, n=4), USGS41 (d 13 C =37.63±0.12‰ V-PDB, n=4) and USGS24 (d 13 C =-16.04±0.13‰ V-PDB, n=4). All measured values of d 13 C standards agree with accepted values reported by the United States Geological Survey (USGS). Inorganic carbon contents and d 13 C of total inorganic carbon (TIC) were estimated by mass balance between TC and TOC.

Results

Depth profiles of 87 Sr/ 86 Sr, Sr and Rb concentrations, carbon concentrations, Total Carbon and Total carbon d 13 C are shown in Figure 2 and Table 1 and2 87 Sr/ 86 Sr range of MORB (Average ± 2s) [START_REF] Gale | The mean composition of ocean ridge basalts[END_REF][START_REF] Hofmann | Sampling Mantle Heterogeneity through Oceanic Basalts: Isotopes and Trace Elements[END_REF], Sr and Rb concentration range of Oman harzburgite (Average ± 2s) [START_REF] Godard | Relationships between geochemistry and structure beneath a palaeo-spreading centre: a study of the mantle section in the Oman manuscript submitted to JGR: Solid Earth ophiolite[END_REF][START_REF] Hanghøj | Composition and Genesis of Depleted Mantle Peridotites from the Wadi Tayin Massif, Oman Ophiolite; Major and Trace Element Geochemistry, and Os Isotope and PGE Systematics[END_REF][START_REF] Monnier | Along-ridge petrological segmentation of the mantle in the Oman ophiolite[END_REF], total carbon content of Oman harzburgite (Average ± 2s) [START_REF] Kelemen | Reevaluating carbon fluxes in subduction zones, what goes down, mostly comes up[END_REF] and mantle d 13 C (Average ± 2s) [START_REF] Deines | The carbon isotope geochemistry of mantle xenoliths[END_REF]. The distance from the basal thrust for the Hawasina metasediments is measured as the horizontal distance to the closest mapped metamorphic sole/ultramafic contact.

Strontium Isotopes

Measured 87 Sr/ 86 Sr values in Oman DP Hole BT1B lithologies show clear differences between (a) the metamorphic sole and (b) the listvenites and serpentinites. The listvenites and serpentinites vary from a minimum value of 0.709 in the upper serpentinite band to a maximum of 0.715 in some listvenites. 87 Sr/ 86 Sr values in the listvenites increase with depth from the surface to 150 m while the serpentinite band between 80-100 m have lower values. Below 150 m, 87 Sr/ 86 Sr values are relatively constant with increasing depth, until the second serpentine band at 181-186 m. Below the basal thrust, 87 Sr/ 86 Sr values are significantly lower in the metamorphic sole from 0.704 to 0.706, followed by lower 87 Sr/ 86 Sr values with greater depths (Figure 2). Although the metamorphic sole contains meta-basalts [START_REF] Godard | Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B. Earth and Space Science Open Archive[END_REF][START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF][START_REF] Kotowski | Structural and thermal evolution of an infant subduction shear zone: Insights from sub-ophiolite metamorphic rocks recovered from Oman Drilling Project Site BT-1B. Earth and Space Science Open Archive[END_REF][START_REF] Searle | Structure and metamorphism of rocks beneath the Semail ophiolite of Oman and their significance in ophiolite obduction[END_REF], all of the samples have higher 87 Sr/ 86 Sr than typical mid-ocean ridge basalts (MORB) [START_REF] Gale | The mean composition of ocean ridge basalts[END_REF][START_REF] Hofmann | Sampling Mantle Heterogeneity through Oceanic Basalts: Isotopes and Trace Elements[END_REF]. The Sr isotope values of the listvenite and serpentinite samples from BT1B are similar to those of listvenites in nearby outcrops (Falk and Kelemen, 2015, Figure 2), which are significantly more radiogenic than 87 Sr/ 86 Sr values of Oman peridotites [START_REF] Gerbert-Gaillard | Caractérisation Géochimique des Péridotites de l'ophiolite d'Oman : processus magmatiques aux limites lithosphère/asthenosphère[END_REF][START_REF] Lanphere | Sr isotopic tracer study of the Samail Ophiolite, Oman[END_REF][START_REF] Mcculloch | Sm-Nd, Rb-Sr, and18O/16O isotopic systematics in an oceanic crustal section: evidence from the Samail ophiolite[END_REF] and Cretaceous to modern seawater (McArthur et al. 2001), but less radiogenic than some Hawasina and autochthonous sediments [START_REF] Weyhenmeyer | Origin and evolution of groundwater in the alluvial aquifer of the Eastern Batinah Coastal Plain, Sultanate of Oman : a hydrogeochemical approach[END_REF]. Our serpentinites and listvenites are enriched in Sr and more radiogenic than similar litologhies in the Birjand ophiolite in eastern Iran [START_REF] Boskabadi | Carbonation of ophiolitic ultramafic rocks: Listvenite formation in the Late Cretaceous ophiolites of eastern Iran[END_REF]. Our samples of the Hawasina metasediments, and those collected from the same region by [START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF] have 87 Sr/ 86 Sr values ranging from 0.7082 to 0.7241. Six of these Hawasina samples are more radiogenic than any of the samples from Hole BT1B (Figure 3).

Carbon concentrations and d 13 C

Total Carbon

The carbon contents of samples from Hole BT1B are highly dependent on lithology (Figure 2). All samples of ultramafic origin contain some carbon, mainly as Mg-rich carbonates, with serpentinites containing 0.2 to 5 wt% carbon, and listvenites containing 6 to 12 wt%. Samples from the metamorphic sole below 200 m depth contain 0.02 to 0.27 wt% carbon. In contrast, the Hawasina metasediments have highly variable carbon contents. Some are almost pure metamorphosed limestones and dolomites with carbon contents of up to 11 wt%, while some have less than 0.05 wt% carbon. d 13 C in the upper 200m of Hole BT1B varies significantly between serpentinites and listvenites (Figure 2). Serpentinites contain significantly lighter carbon than listvenites, as manuscript submitted to JGR: Solid Earth observed in the depth profile (Figure 2). The lower serpentinite band contains two samples (74-2 0.0-5.0 cm and 74-3 42.0-47.0 cm) that contain significantly lighter carbon than any serpentinite in the upper band. In general, carbon concentrations correlate positively with d 13 C values in the upper 200 m (Figure 4). Metamorphic sole samples in the bottom 100 m have low carbon contents and did not yield enough CO2 for isotopic analysis. Total carbon d 13 C values in the Hawasina nappes range from -5.52‰ to 3.69‰, which almost encompasses the entire range of variation observed in Hole BT1B and appears to decrease with lower carbon contents.

Organic carbon

Graphitic carbon was identified in the core both at the drill site and during core inspection aboard the D/V Chikyu [START_REF] Kelemen | Site BT1: fluid and mass exchange on a subduction zone plate boundary[END_REF], Kelemen et al. 2021). This organic component has a characteristic low d 13 C signature in listvenites and serpentinites from Hole BT1B, which extends to a minimum of -27.04‰, representing 0.05wt% of total carbon in the sample from 74-1 56.0-64.0cm (Figure 4). In some cases, the intermediate values likely represent mixtures of organic and inorganic carbon, as some of the magnesite in the listvenites is very resistant to 3N HCl attack and remain undissolved even after 5 days of leaching. The observed light isotopic compositions are similar to those observed in other ultramafic localities such as Cerro de Almirez and Liguria [START_REF] Alt | The role of serpentinites in cycling of carbon and sulfur: Seafloor serpentinization and subduction metamorphism[END_REF]. These data confirm the presence of organic carbon in Hole BT1B, which was observed during drilling operations, core description aboard D/V Chikyu and via Raman spectroscopy [START_REF] Kelemen | Site BT1: fluid and mass exchange on a subduction zone plate boundary[END_REF], Kelemen et al. 2021). , 2016). The pressure of listvenite formation is very poorly constrained due to the lack of pressure-sensitive assemblages and the small size of fluid inclusions. A minimum pressure of 0.3 GPa is provided by the P-T conditions recorded by the Arabian carbonate platform during ophiolite obduction [START_REF] Grobe | Tectono-Thermal evolution of Oman's Mesozoic passive continental margin under the obducting Semail Ophiolite: A case study of Jebel Akhdar, Oman[END_REF]. For the upper limit, the listvenites must have formed at a pressure below the manuscript submitted to JGR: Solid Earth maximum pressure reported for the metamorphic sole (~ 1.4 GPa) [START_REF] Cowan | Structure of the metamorphic sole to the Oman Ophiolite, Sumeini Window and Wadi Tayyin: Implications for ophiolite obduction processes[END_REF][START_REF] Searle | Subduction zone metamorphism during formation and emplacement of the Semail ophiolite in the Oman Mountains[END_REF].

Timing of listvenite formation

Falk and Kelemen (2015) used Rb/Sr and 87 Sr/ 86 Sr data on mineral separates to produce an imprecise isochron age of 97±29Ma for a listvenite sample. This age is broadly consistent with the ~96 Ma age of formation of igneous crust in the ophiolite, along with the same age of metamorphism for the underlying metamorphic sole just beneath the basal thrust of the ophiolite [START_REF] Hacker | Rapid Emplacement of Young Oceanic Lithosphere: Argon Geochronology of the Oman Ophiolite[END_REF]Hacker et al., 1996;[START_REF] Rioux | Tectonic development of the Samail ophiolite: High-precision U-Pb zircon geochronology and Sm-Nd isotopic constraints on crustal growth and emplacement[END_REF][START_REF] Rioux | Synchronous formation of the metamorphic sole and igneous crust of the Semail ophiolite: New constraints on the tectonic evolution during ophiolite formation from highprecision U-Pb zircon geochronology[END_REF]. Moreover, listvenites are found in and near the basal thrust, from the UAE near the northwestern end of the ophiolite outcrop to the area around Hole BT1B, near the southeastern end of the ophiolite outcrop in Oman [START_REF] Nasir | Mineralogical and geochemical characterization of listwaenite from the Semail Ophiolite, Oman[END_REF][START_REF] Stanger | Silicified serpentinite in the Semail nappe of Oman[END_REF]. The extensive outcrop NE of Hole BT1B, known informally as MoD Mountain, exposes the Banded Horizon, a peridotite unit found at the base of the ophiolite mantle section composed of alternating 1-to 10-meter scale bands of dunite, harzburgite, and minor lherzolite. This unit has distinct geochemical characteristics, with higher Al and middle rare-earth-elements, compared to the residual mantle harzburgites that comprise most of the mantle section of the ophiolite [START_REF] Boudier | Shear zones, thrusts and related magmatism in the Oman ophiolite: Initiation of thrusting on an oceanic ridge[END_REF][START_REF] Godard | Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B. Earth and Space Science Open Archive[END_REF][START_REF] Khedr | Chemical variations of abyssal peridotites in the central Oman ophiolite: Evidence of oceanic mantle heterogeneity[END_REF][START_REF] Prigent | Mantle Wedge manuscript submitted to JGR: Solid Earth (De)formation During Subduction Infancy: Evidence from the Base of the Semail Ophiolitic Mantle[END_REF][START_REF] Yoshikawa | Melt extraction and metasomatism recorded in basal peridotites above the metamorphic sole of the northern Fizh massif, Oman ophiolite[END_REF]. The BT1B listvenites have compositions suggesting that they were formed after basal peridotites from the Banded Horizon [START_REF] Godard | Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B. Earth and Space Science Open Archive[END_REF].

Throughout this region, the contacts of listvenite bands within and at the base of the Banded Unit are broadly parallel to banding in the peridotite, and to the contacts between listvenite, peridotite, metamorphic sole, and the Hawasina nappe. These data are consistent with our hypothesis that most of the listvenites formed by alteration of mantle peridotite during the subduction of the underlying sediments via intra-oceanic thrusting and/or later emplacement of the ophiolite onto the Arabian continental margin.

On the basis of steep, fault-bounded contacts of listvenite with young, post-emplacement conglomerates, several workers have inferred that the listvenites formed during later uplift and extension [START_REF] Nasir | Mineralogical and geochemical characterization of listwaenite from the Semail Ophiolite, Oman[END_REF][START_REF] Stanger | Silicified serpentinite in the Semail nappe of Oman[END_REF][START_REF] Wilde | Preliminary study of tertiary hydrothermal alteration and platinum deposition in the Oman ophiolite[END_REF]. Recently, Scharf et al. (2020) reported 60 ± 16 Ma and 58 ± 6 Ma U/Pb ages for two carbonate veins that cut listvenite, and structural observations indicating a top-down sense of shear along some faulted listveniteperidotite and listvenite-sole contacts. Following prior interpretations, they interpret these ages as formation ages of the listvenites after ophiolite emplacement during uplift of the nearby Jebel Akdar and Saih Hatat anticlinoria. We find that their interpretation is inconsistent with the field observations reported above and evidence of a multistage tectonic overprint after peridotite carbonation and listvenite formation as reported by [START_REF] Menzel | Brittle Deformation of Carbonated Peridotite-Insights From Listvenites of the Samail Ophiolite (Oman Drilling Project Hole BT1B)[END_REF] and [START_REF] Kelemen | Site BT1: fluid and mass exchange on a subduction zone plate boundary[END_REF].

We have age-corrected our 87 Sr/ 86 Sr to the 96 Ma age reported by [START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF]. 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 [START_REF] Godard | Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B. Earth and Space Science Open Archive[END_REF] 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 age corrections particularly affect listvenites with relatively abundant chromian mica (fuchsite-muscovite solid solutions, Falk & Kelemen 2015, supplement) in the 115-163 m depth interval, as these micas host abundant Rb (Godard et al. 2021). The age correction also affects the estimated 87 Sr/ 86 Sr values of the metamorphic sole of BT1B and some of the Hawasina metasediments as their Sr and Rb concentrations are heterogeneous, ranging from 9 to 638 ppm for Sr and 0.4 to 97.7 ppm for Rb. Regardless, the age-corrected 87 Sr/ 86 Sr values of the listvenites are much higher than those of the mantle and Cretaceous seawater.

Fluid source for carbonation of peridotites in Oman DP Hole BT1B

87 Sr/ 86 Sr and d 13 C data on MoD Mountain listvenites and Hole BT1B samples suggest that replacement of peridotite by serpentinite and listvenite resulted from reaction with a single fluid along a reaction path [START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF]. The initial fluid was far from equilibrium with peridotite, which converted olivine and serpentine in the protolith to carbonates + quartz and approached equilibrium with serpentinite at higher extents of reaction progress and lower integrated water/rock ratios [START_REF] Beinlich | Ultramafic Rock Carbonation: Constraints From Listvenite Core BT1B, Oman Drilling Project[END_REF], Kelemen et al., 2021). Mg isotope data from a set of samples studied by [START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF] show significant differences between dolomite and magnesite listvenites. Dolomite listvenites (average δ 26 Mg ~ -1.33‰) are lighter in Mg isotopes than magnesite listvenites (average δ 26 Mg ~-0.33‰) (de Obeso et al., 2021), which suggests magnesite dissolution and dolomite formation. This is consistent with the modelled evolution of listvenites during fluid-rock reaction, with dolomite replacing magnesite at increasing water/rock ratios [START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF]. The process of formation of dolomite veins at the expense of magnesite has been documented in other Cretaceous ophiolites [START_REF] Boskabadi | Carbonation of ophiolitic ultramafic rocks: Listvenite formation in the Late Cretaceous ophiolites of eastern Iran[END_REF].

As noted above, after the magnesite and dolomite listvenites formed they were cataclastically deformed, and then cut by late Ca-rich carbonate veins [START_REF] Menzel | Brittle Deformation of Carbonated Peridotite-Insights From Listvenites of the Samail Ophiolite (Oman Drilling Project Hole BT1B)[END_REF]). Thus, one might expect the veins to have formed from a later, geochemically distinctive fluid as suggested by variable clumped isotope (D47) derived temperatures [START_REF] Beinlich | Ultramafic Rock Carbonation: Constraints From Listvenite Core BT1B, Oman Drilling Project[END_REF] and changes in geochemical signatures in dolomite-dominated intervals [START_REF] Godard | Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B. Earth and Space Science Open Archive[END_REF]). This can be further addressed in future studies via careful sampling of the post-cataclastic veins and dolomite-rich domains.

Returning attention to the source of the fluid that formed the bulk of the listvenites, assuming that Sr and CO2 were derived from the same fluid, Sr isotopes can be used to constrain the source of the carbonating fluids that formed the serpentinites and listvenites. [START_REF] Falk | Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement[END_REF] proposed three possible sources of fluids for carbonation: (1) compaction of pore waters from underlying Hawasina metasediments, (2) low temperature dehydration of opal and clay minerals in calcite-bearing Hawasina metasediments, and (3) higher-grade metamorphic devolatilization reactions involving subducted sediments similar to the Hawasina metasediments coupled with fluid that migrated up the subduction zone.

Unlike younger, mantle-peridotite-hosted carbonates, the listvenites do not contain a significant fraction of seawater-or groundwater-derived Sr [START_REF] Gerbert-Gaillard | Caractérisation Géochimique des Péridotites de l'ophiolite d'Oman : processus magmatiques aux limites lithosphère/asthenosphère[END_REF][START_REF] Kelemen | Rates and Mechanisms of Mineral Carbonation in Peridotite: Natural Processes and Recipes for Enhanced, in situ CO 2 Capture and Storage[END_REF][START_REF] De Obeso | Fluid rock interactions on residual mantle peridotites overlain by shallow oceanic limestones: Insights from Wadi Fins, Sultanate of Oman[END_REF][START_REF] Weyhenmeyer | Origin and evolution of groundwater in the alluvial aquifer of the Eastern Batinah Coastal Plain, Sultanate of Oman : a hydrogeochemical approach[END_REF]. The listvenites have 87 Sr/ 86 Sr ratios that are distinct from recent, low-temperature carbonate veins and travertine in the mantle section of the ophiolite [START_REF] Kelemen | Rates and Mechanisms of Mineral Carbonation in Peridotite: Natural Processes and Recipes for Enhanced, in situ CO 2 Capture and Storage[END_REF][START_REF] De Obeso | Fluid rock interactions on residual mantle peridotites overlain by shallow oceanic limestones: Insights from Wadi Fins, Sultanate of Oman[END_REF][START_REF] Weyhenmeyer | Origin and evolution of groundwater in the alluvial aquifer of the Eastern Batinah Coastal Plain, Sultanate of Oman : a hydrogeochemical approach[END_REF]. Almost all of the listvenites and associated serpentinites from BT1B core and MoD Mountain outcrops have 87 Sr/ 86 Sr ratios at 96 Ma higher than Cretaceous seawater (Falk & Kelemen 2015, and this paper). In contrast, young, peridotite-hosted carbonate veins and travertines in the Samail ophiolite consistently have 87 Sr/ 86 Sr lower than 0.709 and appear to contain mixtures of Sr derived from seawater or groundwater and the mantle [START_REF] Gerbert-Gaillard | Caractérisation Géochimique des Péridotites de l'ophiolite d'Oman : processus magmatiques aux limites lithosphère/asthenosphère[END_REF][START_REF] Kelemen | Rates and Mechanisms of Mineral Carbonation in Peridotite: Natural Processes and Recipes for Enhanced, in situ CO 2 Capture and Storage[END_REF][START_REF] De Obeso | Fluid rock interactions on residual mantle peridotites overlain by shallow oceanic limestones: Insights from Wadi Fins, Sultanate of Oman[END_REF][START_REF] Weyhenmeyer | Origin and evolution of groundwater in the alluvial aquifer of the Eastern Batinah Coastal Plain, Sultanate of Oman : a hydrogeochemical approach[END_REF].

Core samples of the sole have 87 Sr/ 86 Sr ratios that are similar to Indian Ocean MORB and near-ridge Pacific seamounts [START_REF] Hofmann | Sampling Mantle Heterogeneity through Oceanic Basalts: Isotopes and Trace Elements[END_REF], which are systematically lower than the Sr isotope ratios of the listvenites. Perhaps the metamorphic sole metabasalts are remnants of a subducted seamount, similar to accreted seamounts along the Cascadia margin of North America (e.g., Duncan, 1982), which derived from the enriched mantle source of some Indian Ocean MORB. Alternatively, the 87 Sr/ 86 Sr ratios may have increased during alteration. The stark difference in 87 Sr/ 86 Sr between the metamorphic sole and the listvenites indicates that fluids derived from the sole are not responsible of the 87 Sr/ 86 Sr enrichment observed in the ultramafic lithologies in Wadi Mansah.

In contrast, age-corrected Sr isotope ratios for Hawasina metasediments underlying the ophiolite and the metamorphic sole, north and northeast of Hole BT1B, have 87 Sr/ 86 Sr up to 0.7134 at 96 Ma (Figure 2). The samples with the most radiogenic 87 Sr/ 86 Sr are clastic sediments containing minor amounts of carbonates. Hawasina limestones, on the other hand, have lower 87 Sr/ 86 Sr values, which is consistent with calcite precipitated from seawater that incorporated a minor, radiogenic clastic component. Based on these observations, the most likely source of the fluids that formed the listvenites are derived from the Hawasina metasediments.

Thermodynamic modeling of fluid-rock reactions [START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF] shows that the characteristic listvenite mineral assemblages -magnesite + quartz -are attained from fluids with ~20,000 ppm dissolved C for listvenite formation at 100-300 °C and 0.5 to 1 GPa, similar to the assemblages modeled by Klein and Garrido (2011) at lower pressures. Such high dissolved carbon contents are impossible to attain by congruent dissolution of pure calcite in aqueous fluids at these P-T conditions [START_REF] Kelemen | Reevaluating carbon fluxes in subduction zones, what goes down, mostly comes up[END_REF], which rules out silicate-poor limestones such as those from the continental margin as a carbon source. On the other hand, metamorphic devolatilization of rocks composed of silicate-carbonate mixtures can produce Crich fluids at temperatures above 400 °C and low to moderate pressures, depending on the rock composition. Thus, we infer that the fluids that formed the listvenites derived from devolatilization of subducting metasediments. During prograde subduction metamorphism, calcsilicate rocks, containing both clastic and carbonate components, undergo extensive devolatilization at 2-3 GPa and 500 to 700°C [START_REF] Gorman | Modeling open system metamorphic decarbonation of subducting slabs[END_REF][START_REF] Stewart | Pervasive subduction zone devolatilization recycles CO2 into the forearc[END_REF] and lose significant amounts of their CO2 in this PT range due to reactions similar to the simplified reaction:

CaMg(CO3)2 (dolomite) + CaMgSi2O6 (diopside) + 2 CaAl2Si2O7(OH)2•H2O (lawsonite) = 2 Ca2MgAl2Si3O12 (garnet) + 4 H2O + 2 CO2
In contrast, carbonate-rich compositions (limestone, dolomite, marble) are predicted to retain most of their CO2 during subduction (e.g, [START_REF] Kerrick | Metamorphic devolatilization of subducted marine sediments and the transport of volatiles into the Earth's mantle[END_REF][START_REF] Stewart | Pervasive subduction zone devolatilization recycles CO2 into the forearc[END_REF].

These decarbonation reactions are possible for both the metamorphic sole and Hawasina sediments. The modelling approach of [START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF] suggests that fluids derived from the sole and clastic Hawasina metasediments will have enough dissolved carbon to react with peridotite and result in magnesite-quartz rocks, the characteristic listvenite assamblage. However, if fluids derived from the sole are the source of the carbon, admixing of a different fluid derived from Hawasina metasediments is required to explain the 87 Sr/ 86 Sr measured in the listvenites. On the other hand, Kelemen et al. show that fluids derived from a rock with composition analogous to Hawasina OM20-17 contain enough dissolved carbon for serpentinization and carbonation of peridotite with increasing water/rock (W/R) ratios. This, combined with the radiogenic 87 Sr/ 86 Sr composition of OM20-17, suggests that a single fluid could be responsible for carbonation of the peridotites. We test this scenario using the reaction path proposed by [START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF]. Their model generates a fluid with ~14,000 ppm carbon at 400°C and 1GPa from decarbonation of a rock with composition such as OM20-17. Under these modelled conditions (400 °C, 1 GPa) a lithology like OM20-17 will lose ~65% of its carbon, other Hawasina samples require less decarbonation to produce fluids capable of carbonating the peridotites. If this fluid is then cooled to 200°C and depressurized to 0.5GPa without losing much of its carbon before reacting with peridotites, listvenites are predicted to form at water/rock (W/R)~100.

At temperatures greater than ~ 300°C, dissolved CO2 in aqueous fluids have d 13 C values that are higher than those of co-existing calcite and dolomite [START_REF] Chacko | Oxygen and carbon manuscript submitted to JGR: Solid Earth isotope fractionations between CO2 and calcite[END_REF][START_REF] Deines | Carbon isotope effects in carbonate systems[END_REF][START_REF] Horita | Oxygen and carbon isotope fractionation in the system dolomite-water-CO2 to elevated temperatures[END_REF]). Thus, for example, fluid in equilibrium with calcite with d 13 C between -5.5‰ to -3.5‰ (as in Hawasina clastic metasediments) would contain dissolved CO2 with d 13 C of -1.9‰ to 0.1‰ at 400°C. At lower temperatures, like those estimated for listvenite formation in the Samail ophiolite, calcite and dolomite have d 13 C higher than co-existing fluids. Thus, dolomite and magnesite in equilibrium with fluids with d 13 C of -1.9‰ to 0.1‰ would have d 13 C in the range of -0.2‰ to 1.8‰, similar to the d 13 C observed in the listvenites from Hole BT1B and the surrounding outcrops.

Figure 5a illustrates that the listvenites and serpentinites from Hole BT1B lie along the reaction path used by [START_REF] Kelemen | Mass transfer into the leading edge of the mantle wedge: Initial results from Oman Drilling Project Hole BT1B. Earth and Space Science Open Archive[END_REF]. In our calculations, we assume that reacting fluids enriched in Sr (250 ppm), with 87 Sr/ 86 Sr values at 96 Ma that are similar to those of clastic Hawasina metasediments (0.7110 to 0.7135), reacted with the peridotite with mantle-like 87 Sr/ 86 Sr (0.7027±0.0011). In the model serpentinites plot at low W/R between 1 to 5 while listvenites require significantly more fluid at W/R between 5-100. The listvenites and serpentinites follow a mixing trend (Figure 5b) between mantle peridotite like compositions (Sr=1.5 ppm, 87 Sr/ 86 Sr=0.7027±0.0011, C=680ppm and d 13 C=-6.0±2.0‰) and low temperature carbonates that crystallized from a fluid produced by high-pressure, high-temperature devolatilization with Sr isotope ratios in the range of the Hawasina clastic metasediments (Sr=250ppm, 87 Sr/ 86 Sr~0.7100 to 0.7135) and fractionate carbon isotopes as described above. These trends together suggest that the CO2-bearing aqueous fluids that formed the listvenites from Hole BT1B and surrounding outcrops were derived by devolatilization of calc-silicate metasediments, with 87 Sr/ 86 Sr and d 13 C similar to clastic sediments in the Hawasina Formation along a subduction zone geotherm. These fluids migrated updip to lower pressures and temperatures to form the listvenites.

Conclusions

Listvenites and spatially associated serpentinites from Hole BT1B and surrounding outcrops that replace residual mantle peridotites from the base of the Samail ophiolite have Sr isotope ratios that are more radiogenic than their peridotite protoliths, Cretaceous seawater, modern seawater, groundwater in the ophiolite, and the underlying metamorphic sole. We suggest that the radiogenic Sr isotope component was transported via carbon-rich aqueous fluid that reacted with the peridotite to form the listvenites and serpentinites. The 87 Sr/ 86 Sr values of manuscript submitted to JGR: Solid Earth this component resemble those of calcite-bearing clastic sediments in the Hawasina Formation underlying the ophiolite. However, the fluid must have contained higher dissolved carbon contents than feasible for congruent dissolution of pure calcite at < 2 GPa and/or < 550°C. Thus, we hypothesize that this fluid was derived by devolatilization of carbonate-and silicate bearing meta-sediments akin to the Hawasina clastic metasediments at 0.5 to 2.3 GPa and 400 to 700°C in the subduction zone [START_REF] Searle | Structure and metamorphism of blueschist-eclogite facies rocks from the northeastern Oman Mountains[END_REF]. This fluid then migrated updip to react with hanging wall peridotite at <1 GPa and <250°C, forming the listvenites and serpentinites. Carbon isotope fractionation during high temperature devolatilization followed by low temperature carbonate precipitation during the reaction with peridotite likely controlled the isotopic characteristics of the listvenites and the serpentinites with d 13 C from -10.6‰ to 1.92‰ and 87 Sr/ 86 Sr from 0.7090 to 0.7145.

Figure 1 .

 1 Figure 1. Simplified geologic map of Wadi Mansah and vicinity of Oman DP Hole BT1B compiled after Villey et al. (1986), Google Earth and field observations. Hand samples collected for this study are marked with red circles with number of samples collected per location in black.

  . The Hawasina metasediments are plotted as the horizontal map distance to the closest mapped metamorphic sole/ultramafic contact.

Figure 2 .

 2 Figure 2. Depth profiles of OmanDP Hole BT1B (top panels) and distance from basal thrust for Hawasina metasediments (bottom panels). From left to right 87 Sr/ 86 Sr (measured), 87 Sr/ 86 age corrected at 96 Ma, Sr concentrations, Rb concentrations, total carbon (TC) concentration, total carbon d 13 C, (squares in metamorphic sole from Zeko (2021). Black dashed line in top panels correspond to basal thrust. Green reference bands in all panels indicate, from left to right:87 Sr/ 86 Sr range of MORB (Average ± 2s)[START_REF] Gale | The mean composition of ocean ridge basalts[END_REF][START_REF] Hofmann | Sampling Mantle Heterogeneity through Oceanic Basalts: Isotopes and Trace Elements[END_REF], Sr and Rb concentration range of Oman harzburgite (Average ± 2s)[START_REF] Godard | Relationships between geochemistry and structure beneath a palaeo-spreading centre: a study of the mantle section in the Oman manuscript submitted to JGR: Solid Earth ophiolite[END_REF][START_REF] Hanghøj | Composition and Genesis of Depleted Mantle Peridotites from the Wadi Tayin Massif, Oman Ophiolite; Major and Trace Element Geochemistry, and Os Isotope and PGE Systematics[END_REF][START_REF] Monnier | Along-ridge petrological segmentation of the mantle in the Oman ophiolite[END_REF], total carbon content of Oman harzburgite (Average ± 2s)[START_REF] Kelemen | Reevaluating carbon fluxes in subduction zones, what goes down, mostly comes up[END_REF] and mantle d 13 C (Average ± 2s)[START_REF] Deines | The carbon isotope geochemistry of mantle xenoliths[END_REF]. The distance from the basal

Figure 3 .

 3 Figure 3. 87 Sr/ 86 Sr values, both measured (left) and age corrected to 96 Ma (right), plotted versus inverse Sr concentration for core samples from OmanDP Hole BT1B and other lithologies measured in Oman and Iran. Data from Falk and Kelemen (2015) for samples of the same lithologies as those documented here are shown as inverted triangles, employing the same color scheme as used for samples in this study. Data for Hawasina sediments are from this study and Falk and Kelemen (2015), those for Oman peridotites are from Gerbert-Gaillard (2002, leached samples only), those for autochthonous sediment samples are from Weyhenmeyer (2000) and those for Iran samples are from Boskabadi et al. (2020). Rb concentrations were not reported for the autochthonous clastic metasediments from Weyhenmeyer (2000), so we assume a Rb upper bound concentration of 200 ppm (twice the maximum measured in Hawasina metasediments). This Rb concentration was used with the measured 87 Sr/ 86 Sr and Sr concentration, to estimate a minimum Sr isotope ratio at 96 Ma for these samples. Seawater and Cretaceous seawater values from McArthur et al. (2001).

Figure 4 .

 4 Figure 4. Total Carbon (large circles) and Total Organic Carbon (small circles) versus d 13 C for listvenites, serpentinites and Hawasina metasediments.

Figure 5 .

 5 Figure 5. (left) Total carbon (wt%) vs. 87 Sr/ 86 Sr at 96 Ma. Black lines are reaction paths of carbon rich fluid reacting with peridotite at 200°C and 0.5GPa at variable water/rock (dashed tie lines) from Kelemen et al. (2021). The reacting fluid is assumed to have 87 Sr/ 86 Sr values of 0.7100 to 0.7135 like those of clastic Hawasina metasediments. (right) Inorganic carbon d 13 C vs. 87 Sr/ 86 Sr at 96 Ma. Black lines are mixing lines between mantle and carbonate minerals precipitated from a metamorphic fluid. The fluid has the same carbon concentration as the reaction path on the figure 5a and the d 13 C fractionation between the carbonate and the fluid are described in the body of the text, with values for high and low PT shown as red and blue boxes respectively. We assume that the fluid has the Sr isotope ratios of Hawasina clastic metasediments. 87 Sr/ 86 Sr values for the depleted mantle are from mid-ocean-ridge-basalt (MORB) from Hofmann (2013) . Mantle d 13 C is from Deines (2002).

Table 1 .

 1 Lithological information, depth, strontium, rubidium and carbon concentrations and Sr and C isotope ratios of samples from OmanDP Hole BT1B

	Table 1 attached as Excel spreadsheet
	Abbreviations SE= Standard error, TC= Total Carbon, TOC= Total Organic Carbon, V-PDB= Vienna Pee Dee
	Belemnite standard, n.d.=not determined

Table 2 .

 2 Lithological information, location, strontium, rubidium and carbon concentrations and Sr and C isotope data of samples for Hawasina and metamorphic sole samples Table 2 attached as Excel Spreadsheet

Abbreviations SE= Standard error, TC= Total Carbon, T V-PDB= Vienna Pee Dee Belemnite standard, n.a.= not available, n.d.=not determined

Acknowledgments and Data

JCO wants to thank Steven Goldstein for allowing early access to the laboratories in LDEO to complete isotope work soon after partial reopening following the first wave of the COVID-19 pandemic in New York. JCO work to complete this manuscript at UCalgary was in part funded from the Canada First Research Excellence Fund. Wei Huang is thanked for help with measurements of carbon concentrations and d 13 C. We thank Mark Dekkers for editorial handling. Constructive comments from an anonymous Associate Editor, Arman Boskabadi and an anonymous reviewer helped to improve an earlier versions of this manuscript. This research used samples and/or data provided by the Oman Drilling Project. The Oman Drilling Project (OmanDP) has been possible through co-mingled funds from the International Continental Scientific Drilling Project (ICDP; Kelemen, Matter, Teagle Lead PIs), the Sloan Foundation -Deep Carbon Observatory (Grant 2014-3-01, Kelemen PI), the National Science Foundation (NSF-EAR-1516300, Kelemen lead PI), NASA -Astrobiology Institute (NNA15BB02A, Templeton PI), the German Research Foundation (DFG: KO 1723/21-1, Koepke PI), the Japanese Society for the Promotion of Science (JSPS no:16H06347, Michibayashi PI; and KAKENHI 16H02742, Takazawa PI), the European Research Council (Adv: no.669972; Jamveit PI), the Swiss National Science Foundation (SNF:20FI21_163073, Früh-Green PI), JAMSTEC, the TAMU-JR Science Operator, and contributions from the Sultanate of Oman Ministry of Regional Municipalities and Water Resources, the Oman Public Authority of Mining, Sultan Qaboos University, CNRS-Univ. Montpellier, Columbia University of New York, and the University of Southampton.

Authors declare no conflict of interest.

All data is in the process of being approved by Pangea repository: https://issues.pangaea.de/browse/PDI-30281 and https://issues.pangaea.de/browse/PDI-30282