Publication Date:
2022-05-26
Description:
Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(5), (2020): e2019JB018632, doi:10.1029/2019JB018632.
Description:
Carbonate‐altered peridotite are common in continental and oceanic settings and it has been suggested that peridotite‐hosted carbonate represent a significant component of the carbon‐cycle and provide an important link in the CO2 dynamics between the atmosphere, hydrosphere, and lithosphere. The ability to constrain the timing of carbonate and accessory phase growth is key to interpreting the mechanisms that contribute to carbonate alteration, veining, and mineralization in ultramafic rocks. Here we examine a mantle section of the Samail ophiolite exposed in Wadi Fins in southeastern Oman where the peridotite is unconformably overlain by Late Cretaceous‐Paleogene limestone and crosscut by an extensive network of carbonate veins and fracture‐controlled alteration. Three previous 87Sr/86Sr measurements on carbonate vein material in the peridotite produce results consistent with vein formation involving Cretaceous to Eocene seawater (de Obeso & Kelemen, 2018, https://doi.org/10.1098/rsta.2018.0433). We employ (U‐Th)/He chronometry to constrain the timing of hydrothermal magnetite in the calcite veins in the peridotite. Magnetite (U‐Th)/He ages of crystal sizes ranging from 1 cm to 200 μm record Miocene growth at 15 ± 4 Ma, which may indicate (1) fluid–rock interaction and carbonate precipitation in the Miocene, or (2) magnetite (re)crystallization within pre‐existing veins. Taken together with published Sr‐isotope values, these results suggest that carbonate veining at Wadi Fins started as early as the Cretaceous, and continued in the Miocene associated with magnetite growth. The timing of hydrothermal magnetite growth is coeval with Neogene shortening and faulting in southern Oman, which points to a tectonic driver for vein (re)opening and fluid‐rock alteration.
Description:
This research was supported by a National Science Foundation (NSF) Graduate Research Fellowship to E.H.G. Cooperdock, the UTChron Laboratory at The University of Texas at Austin, the Chevron (Gulf) Centennial Professorship to D.F. Stockli, and by a Sloan Foundation grant awarded to P.B. Kelemen. We are grateful to Desmond Patterson for assistance and training with He measurements and data reduction, to Jessie Maisano for technical support with the X‐Ray Computed Tomography. These data and images were produced at the High‐Resolution X‐ray Computed Tomography Facility of the University of Texas at Austin. EHGC is grateful to Jaime Barnes, Richard Ketcham, Frieder Klein and Othmar Müntener for helpful comments on an earlier version of this manuscript. Thank you to Fin Stuart and Uwe Ring for their helpful reviews, and Stephen Parman for feedback and editorial handling of the manuscript. The (U‐Th)/He data in this manuscript are available in the GeoChron repository (https://www.geochron.org) and sample IGSNs are in the SESAR database (http://www.geosamples.org).
Description:
2020-10-06
Keywords:
magnetite
;
U‐Th/He thermochronology
;
ophicarbonate
;
Oman
;
Wadi Fins
;
serpentinite
Repository Name:
Woods Hole Open Access Server
Type:
Article
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