δ60Ni and δ13C Composition of Serpentinites and Carbonates of the Tekirova Ophiolite, Turkey, and Meatiq Ophiolite, Egypt

Anna Neubeck,Arjen Boosman,Dogacan Özcan,Arman Boskabadi,Hakan Hosgörmez,Magnus Ivarsson,Olivier Rouxel

doi:10.3389/feart.2021.651967

Abstract

Nickel isotope fractionation patterns in continental ultramafic environments generally show a depletion of δ60Ni in weathered rocks and an enrichment in bedrock samples. The present study focuses on stable Ni isotope fractionation patterns in carbonate-rich, ultramafic ophiolite samples with concomitant fluids at an active serpentinization site in southwestern Turkey, with a comparison to results from an inactive serpentinization site in the Eastern Desert of Egypt with carbonate-rich samples. All solid phase data from the inactive serpentinization area are consistent with previously reported values from serpentinites, whereas the solid precipitates in the active area (SW Turkey) give values slightly heavier than previously reported data. However, the Ni isotopic signatures in the active serpentinization system likely reflect the scavenging of light Ni by iron oxide and carbonate precipitation, as has been previously demonstrated in laboratory coprecipitation experiments. It is also possible that the active system results resemble previous laboratory experimental results that show a relatively strong initial fractionation between fluids and solids, which then diminishes with time due to aging of the precipitates.

Highlights

Several studies have investigated stable Ni isotope compositions in ultramafic/mafic rocks to better understand the geochemical cycling of Ni in natural environments (Cameron et al, 2009; Gueguen et al, 2013; Ratié et al, 2015; Spivak-Birndorf et al, 2018)
The BFE sample was dominated by brucite and hydromagnesite with minor amounts of carbonates (Supplementary Figure S2), whereas the BF1 and BF2 samples were almost completely dominated by carbonates (Supplementary Figure S3)
The IR, FG1, and FG2 samples consisted of loose sediments; IR and FG2 consisted of iron oxides and carbonates (Supplementary Figures S4, S5), while FG1 consisted purely of carbonates (Supplementary Figure S6)

Summary

Introduction

Several studies have investigated stable Ni isotope compositions in ultramafic/mafic rocks to better understand the geochemical cycling of Ni in natural environments (Cameron et al, 2009; Gueguen et al, 2013; Ratié et al, 2015; Spivak-Birndorf et al, 2018). The Ni isotopic composition of unweathered mafic and ultramafic rocks (such as gabbro, basalt, peridotite, dunite, and serpentinized varieties) falls within a relatively narrow range of −0.13–+0.32‰ (Gall et al, 2013; Gueguen et al, 2013; Ratié et al, 2015; Spivak-Birndorf et al, 2018).

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