Abstract Peridotite carbonation represents a critical step within the long-term carbon cycle by sequestering volatile CO 2 in solid carbonate. This has been proposed as one potential pathway to mitigate the effects of greenhouse gas release. Most of our current understanding of reaction mechanisms is based on hand specimen and laboratory-scale analyses. Linking laboratory-scale observations to field scale processes remains challenging. Here we present the first geophysical characterization of serpentinite carbonation across scales ranging from km to sub-mm by combining aeromagnetic observations, outcrop- and thin section-scale magnetic mapping. At all scales, magnetic anomalies coherently change across reaction fronts separating assemblages indicative of incipient, intermittent, and final reaction progress. The abundance of magnetic minerals correlates with reaction progress, causing amplitude and wavelength variations in associated magnetic anomalies. This correlation represents a foundation for characterizing the extent and degree of in situ ultramafic rock carbonation in space and time.
A log‐based volcanic stratigraphy of Ocean Drilling Program Hole 1256D provides a vertical cross‐section view of in situ upper crust formed at the East Pacific Rise (EPR) with unprecedented resolution. This stratigraphy model comprises ten electrofacies, principally identified from formation microscanner images. In this study, we build a lava flow stratigraphy model for the extrusive section in Hole 1256D by correlating these electrofacies with observations of flow types from the modern EPR, such as sheet flows and breccias, and pillow lavas and their distribution. The resulting flow stratigraphy model for the Hole 1256D extrusive section represents the first realization of detailed in situ EPR upper oceanic crust construction processes that have been detected only indirectly from remote geophysical data. We correlated the flow stratigraphy model with surface geology observed from the southern EPR (14°S) by Shinkai 6500 dives in order to obtain the relationship between lava flow types and ridge axis‐ridge slope morphology. This dive information was also used to give a spatial‐time reference frame for modeling lava deposition history in Hole 1256D. In reconstructing the lava deposition history, we interpreted that the origins of the ∼100 m thick intervals with abundant pillow lavas in Hole 1256D are within the axial slope where pillow lavas were observed during the Shinkai 6500 dives and previous EPR surveys. This correlation could constrain the lava deposition history in Hole 1256D crust. Using the lateral scale of ridge axis–ridge slope topography from the Shinkai 6500 observations and assuming the paleospreading rate was constant, 50% of the extrusive rocks in Hole 1256D crust were formed within ∼2000 m of the ridge axis, whereas nearly all of the remaining extrusive section was formed within ∼3000 m of the ridge axis. These results are consistent with the upper crustal construction model previously suggested by seismic studies.
<p>Fluid&#8211;rock interactions link mass and energy transfer with large-scale tectonic deformation, drive the formation of mineral deposits, carbon sequestration, and rheological changes of the lithosphere. While spatial evidence indicates that fluid&#8211;rock interactions operate on length scales ranging from the grain boundary to tectonic plates, the timescales of regional fluid&#8211;rock interactions remain essentially unconstrained, despite being critically important for quantifying the duration of fundamental geodynamic processes. Here we show that reaction-induced transiently high permeability significantly facilitates fast fluid flow through low-permeability rock of the mid-crust. Using observations from an exceptionally well-exposed fossil hydrothermal system to inform a multi-element advective&#8211;diffusive&#8211;reactive transport model, we show that fluid-driven reaction fronts propagate with ~10 cm year<sup>-1</sup><sub>,</sub> equivalent to the fastest tectonic plate motion and mid-ocean ridge spreading rates. Consequently, in the presence of reactive fluids, large-scale fluid-mediated rock transformations in continental collision and subduction zones occur on timescales of tens of years, implying that natural carbon sequestration, ore deposit formation, and transient and long-term petrophysical changes of the crust proceed, from a geological perspective, instantaneously.</p>
The objectives of International Ocean Discovery Program Expedition 398, Hellenic Arc Volcanic Field (11 December 2022 to 10 February 2023), were to study the volcanic record of the central Hellenic island arc; document the links and feedbacks between volcanism/magmatism, crustal tectonics, and sea level; investigate the processes and products of shallow submarine eruptions of silicic magma; and groundtruth the seismic stratigraphy of Santorini caldera.Reconstructing the subsidence history of the southern Aegean Sea and searching for deep life inside and outside of Santorini caldera were additional objectives.During the expedition, 10 primary and alternate sites that were originally proposed were drilled, in addition to 2 extra sites that were requested during the expedition.Outside of Santorini caldera, drilling penetrated the thick basin fills of the crustal rift system hosting the Christiana-Santorini-Kolumbo volcanic field, identifying numerous pumice and ash layers, some known from on land and others hitherto unknown, pushing back the onset of volcanism in the area into the Early Pleistocene or even Pliocene.Significant events of mass wasting into the basins, accompanied by very high sedimentation rates, were also documented.These basin sites served to groundtruth the seismic stratigraphy of the basins and open the way to unraveling relationships between volcanic activity and crustal rift pulses.Two sites of condensed sequences served to sample many volcanic layers within the detailed age-depth constraints provided mainly by biostratigraphy, as diagenetic effects complicated the magnetic reversal record significantly.Drilling penetrated the Alpine basement at three basin sites northeast of Santorini, whereas in the Christiana Basin to the southwest it penetrated a thick sequence of Messinian evaporites.Drilling inside Santorini caldera penetrated to ~120 meters below seafloor, less than planned due to hole instability issues but deep enough to groundtruth the seismic stratigraphy and sample the different layers.One intracaldera hole yielded a detailed tephra record of the history of the Kameni Islands, as well as possible evidence for deep bacterial colonies within the caldera.Despite variable recovery in the unstable pumice and ash deposits, the expedition was a significant success that may address almost all the scientific objectives once the laboratory work has been done. Plain language summaryAbout 800 million people are threatened by volcanic eruptions around the globe: high plumes of ash, ground-hugging flows of hot ash and rock, earthquakes, and associated tsunamis.The Christiana-Santorini-Kolumbo volcanic group in the Aegean Sea of Greece is particularly hazardous because the volcanoes have produced many eruptions in the past, and some were highly explo-
Abstract We conducted a novel study to capture the on‐going advancement of mineral weathering within a serpentinite formation by using an integrated approach of multi‐scale quantitative rock magnetic analyses and nano‐resolution geochemical imaging analyses. We studied a suite of rock samples from the Coast Range Ophiolite Microbial Observatory (CROMO) in California to conduct rock magnetic analyses enabling us to determine character of Fe‐bearing minerals and to predict locations of reaction boundaries among various stages of weathering. QEMSCAN® and other electron micro‐imagery analyses highlighted microstructural changes in amorphous minerals, and possible changes in porosity and coincides with the iron‐enrichment region. This iron enrichment indicates initiation of iron (‐oxides) nucleation, resulting in extremely fine gain magnetite formation. This is a newly documented mode of magnetite production in serpentinites and enhances the application of magnetite abundance as a proxy for the degree and extent of water‐rock interaction in mantle peridotite and serpentinite.
Abstract We find at fast‐ and intermediate‐spreading seafloor that their ridge‐parallel bathymetric profiles between two neighboring fracture zones, excluding the part of the seafloor inward to fracture zone (FZ) valley, are predominantly upward concave. The temporal evolution of the bathymetric profiles from the lithosphere formed at the Chile Rise is characterized by (a) the rapid growth of the middle deflection to about 200 m relative to the ends for the first few millions of years and (b) a steady state afterward. We show that these characteristics and the upward‐concave sense of bending can be reasonably explained as the flexure of a thin elastic plate contracting thermally from the top while cooling. The best‐fitting model needs only about 10% of the thermal bending moment based on the half‐space cooling model and the free‐end assumption. Our model is consistent with the recent observations that oceanic lithosphere is cut open at a FZ valley, which disprove the previous assumption that ocean floor is bent down forming the valley walls.
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