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Abstract In their article entitled “Trapdoor Fault Activation:A Step Toward Caldera Collapse at Sierra Negra,Galapagos,Ecuador” Shreve and Delgado (2023,https://doi.org/10.1029/2023jb026437) examine co‐eruptive deformation during the 2018 eruption of Sierra Negra Volcano. One of their major conclusions is that the 2018 eruption, and specifically co‐eruptive faulting, represents the initial stages of caldera collapse. They reach this conclusion because they focus their analysis solely on co‐eruptive deformation, and do not investigate the total (net) deformation for the 2005 to 2018 eruption cycle. Bell, La Famina, et al. (2021,https://doi.org/10.1038/s41467‐021‐21596‐4) investigated both the pre‐ and co‐eruptive phases of the 2018 eruption and showed that net deformation was one of caldera resurgence, not subsidence. In this comment, we demonstrate that the conclusion of collapse, or even initiation of collapse, is attributable to not accounting for pre‐eruptive deformation on the intra‐caldera Trapdoor Fault system and incorrectly assuming that the volcano‐tectonic dynamics of Sierra Negra mimic those of other basaltic calderas.
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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
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 CO2concentrations). 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.
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- Award ID(s):
- 2153786
- PAR ID:
- 10406151
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 24
- Issue:
- 4
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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