High‐Resolution Magnetic‐Geochemical Mapping of the Serpentinized and Carbonated Atlin Ophiolite, British Columbia: Toward Establishing Magnetometry as a Monitoring Tool for In Situ Mineral Carbonation. (10th April 2023)

• Record Type: Journal Article
• Authors: Tominaga, Masako; Beinlich, Andreas; Lima, Eduardo A.; Pruett, Paiden; Vento, Noah R.; Weiss, Benjamin P.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 24:Number 4(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-04-10
• Subjects: rock magnetism -- fluid‐rock interaction -- carbonation -- oceanic lithosphere -- ophiolite; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2022GC010730
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: We address in situ serpentinization and mineral carbonation processes in oceanic lithosphere using integrated field magnetic measurements, rock magnetic analyses, superconducting quantum interference device (SQUID) microscopy, microtextural observations, and energy dispersive spectroscopy phase mapping. A representative suite of ultramafic rock samples were collected, within the Atlin ophiolite, along a 100‐m long transect across a continuous outcrop of mantle harzburgite with several alteration fronts: serpentinite, soapstone (magnesite + talc), and listvenite (magnesite + quartz). Strong correlations between changes in magnetic signal strengths and amount of alteration are shown with distinctive contrasts between serpentinite, transitional soapstone, and listvenite that are linked to the formation and breakdown of magnetite. While previous observations of the Linnajavri ultramafic complex indicated that the breakdown of magnetite occurred during listvenite formation from the precursor soapstone (Tominaga et al., 2017, https://doi.org/10.1038/s41467-017-01610-4 ), results from our study suggest that magnetite destabilization already occurred during the replacement of serpentinite by soapstone (i.e., at lower fluid CO2 concentrations). This difference is attributed to fracture‐controlled flow of sulfur‐bearing alteration fluid at Atlin, causing reductive magnetite dissolution in thin soapstone zones separating serpentinite from sulfide‐mineralized listvenite. We argue that magnetite growth or breakdown in soapstone provides insight into the mode of fluid flow and the composition, which control the scale and extent of carbonation. This conclusion enables us to use magnetometry as a viable tool for monitoring the reaction progress from serpentinite to carbonate‐bearing assemblages in space and time with a caution that the three‐dimensionality of magnetic sources impacts the scalability of measurements. Plain Language Summary: Magnetic remote sensing has been used in unlocking otherwise inaccessible information about geodynamic processes. Here, we expand and use magnetometry to monitor in situ mineral carbonation processes in mantle peridotite, one of the major rock formations that compose this planet Earth. We conducted integrative magnetometry‐geochemistry observations in the field and lab using magnetic measurements, rock magnetic analyses, superconducting quantum interference device microscopy, microtextural observations, and energy dispersive spectroscopy phase mapping. Based on results from this integrative approach, we observe a correlation between magnetic signal and in situ carbonation process. This observation supports the idea that magnetic measurements can delineate carbonation extent and degree in peridotite alteration processes. We also observe that fluid chemistry and flow mode impact the magnetic signal of incipient carbonation. Altogether, our study enables us to further use magnetometry results in monitoring in situ peridotite carbonation, and possibly, the mode of fluid flows during the chemical process. Key Points: Magnetic measurements delineate carbonation processes and extent in peridotite We observe a correlation between magnetic signal and in situ carbonation process Fluid chemistry and flow mode impact magnetic signal of incipient carbonation