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1. Assessing the Role of Water in Alaskan Flat‐Slab Subduction

   https://doi.org/10.1029/2021GC009734  

   Petersen, Sarah E.; Hoisch, Thomas D.; Porter, Ryan C. (May 2021, Geochemistry, Geophysics, Geosystems)

   Abstract Low‐angle subduction has been shown to have a profound impact on subduction processes. However, the mechanisms that initiate, drive, and sustain flat‐slab subduction are debated. Within all subduction zone systems, metamorphic dehydration reactions within the down‐going slab have been hypothesized to produce seismicity, and to produce water that fluxes melting of the asthenospheric wedge leading to arc magmatism. In this work, we examine the role hydration plays in influencing slab buoyancy and the geometry of the downgoing oceanic plate. When water is introduced to the oceanic lithosphere, it is incorporated into hydrous phases, which results in lowered rock densities. The net effect of this process is an increase in the buoyancy of the downgoing oceanic lithosphere. To better understand the role of water in low‐angle subduction settings, we model flat‐slab subduction in Alaska, where the thickened oceanic lithosphere of the Yakutat oceanic plateau is subducting beneath the continental lithosphere. In this work, we calculate the thermal conditions and stable mineral assemblages in the slab crust and mantle in order to assess the role that water plays in altering the density of the subducting slab. Our slab density results show that a moderate amount of hydration (1–1.5 wt% H₂O) in the subducting crust and upper lithospheric mantle reduces slab density by 0.5%–0.8% relative to an anhydrous slab, and is sufficient to maintain slab buoyancy to 300–400 km from the trench. These models show that water is a viable factor in influencing the subduction geometry in Alaska, and is likely important globally. 

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2. Lithospheric Foundering in Progress Imaged Under an Extinct Continental Arc

   https://doi.org/10.1029/2024GL111290  

   Schulte‐Pelkum, Vera; Kilb, Deborah (December 2024, Geophysical Research Letters)

   Abstract A long‐standing question is how felsic continental crust is differentiated from its mafic parent mantle magmas. One currently proposed fundamental mechanism is lithospheric foundering and loss of dense material into the mantle. A type locality is the young extinct arc forming the Sierra Nevada, California. Here, we image a distinct anisotropic shear layer below the crust‐mantle boundary using receiver functions. The sense of shear is consistent with west‐ to southwestward removal of lithosphere. The shear signal is strongest in the southern Sierra, where lithospheric foundering was proposed to have concluded several million years ago, and is deeper and less pronounced in the central Sierra, where ongoing lithospheric foundering is corroborated by a band of unusually deep (40+ km) seismicity along the western foothills. Our observations provide progressive snapshots of a lithospheric foundering process spanning several million years and hundreds of kilometers, illuminating a fundamental differentiation process by which continents are built. 

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3. Water transport to the core–mantle boundary

   https://doi.org/10.1093/nsr/nwab007  

   Walter, Michael J (January 2021, National Science Review)

   null (Ed.)

   Abstract Water is transported to Earth's interior in lithospheric slabs at subduction zones. Shallow dehydration fuels hydrous island arc magmatism but some water is transported deeper in cool slab mantle. Further dehydration at ∼700 km may limit deeper transport but hydrated phases in slab crust have considerable capacity for transporting water to the core-mantle boundary. Quantifying how much remains the challenge. 

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4. Genesis of Intermediate‐Depth and Deep Intraslab Earthquakes beneath Japan Constrained by Seismic Tomography, Seismicity, and Thermal Modeling

   https://doi.org/10.1029/2018GL080025  

   Chen, Min; Manea, Vlad Constantin; Niu, Fenglin; Wei, S. Shawn; Kiser, Eric (February 2019, Geophysical Research Letters)

   Abstract The distribution of intermediate‐depth and deep intraslab earthquakes with respect to subducting slabs offers a unique insight into seismogenesis at high pressures and temperatures that should inhibit brittle failure. This study constrains the surface of the subducting Pacific Plate beneath Japan at depths between 100 and 380 km based on a previous continental‐scale adjoint tomography model. Earthquake distributions relative to the slab surface reveal double seismic zones located within the top 60 km of the Pacific Plate. Thermal modeling suggests that the lower‐plane seismicity corresponds to temperatures between 400 and 900 °C. The seismogenic pressure and temperature conditions correlate approximately with the conditions of dehydration reactions of several hydrous minerals, that is, antigorite (serpentine) and chlorite at depths between 100 and 200 km and phase A at greater depths between 200 and 380 km. These correlations indicate that at these depths water released from dehydration processes may facilitate triggering slab mantle earthquakes. 

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5. Comprehensive High‐Precision Relocation of Seismicity on the Island of Hawai‘i 1986–2018

   https://doi.org/10.1029/2020EA001253  

   Matoza, Robin S.; Okubo, Paul G.; Shearer, Peter M. (January 2021, Earth and Space Science)

   Abstract Abundant seismicity beneath the Island of Hawai‘i from mantle depths to the surface plays a central role in understanding how volcanoes work, grow, and evolve at this intraplate oceanic hotspot. We perform systematic waveform cross‐correlation, cluster analysis, and relative relocation of 347,445 events representing 32 years of seismicity on and around the island from 1986 to 2018. We successfully relocate 275,009 (79%) events using ∼1.7 billion differential times (PandS) from ∼128 million similar‐event pairs. The results reveal a dramatic sharpening of seismicity along faults, streaks, rings, rift zones, magma pathways, and mantle fault zones; seismicity delineating crustal detachments on the flanks of Kīlauea and Mauna Loa is particularly well‐resolved. The resulting high‐precision spatio‐temporal image of seismicity captures almost the entire 1983–2018 Pu‘u ‘Ō‘ō‐Kūpaianaha eruption of Kīlauea with its numerous distinct episodes and wide‐ranging activity, culminating in the 2018 lower East Rift Zone eruption and summit collapse. 

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