Search for: All records

To explore controls on megathrust behavior and its connection with forearc deformation, we studied the Andreanof segment of the Aleutian Subduction Zone (offshore Alaska, USA), which has a simple geological history as a relatively young intra-oceanic subduction zone. Here, the forearc shows greater uplift and compression in the strongly coupled Adak region compared to the weakly coupled Atka region. Using multichannel seismic reflection data, we found that the incoming plate in both regions exhibits similar characteristics along the segment, suggesting that its properties do not account for the varying megathrust behavior and forearc deformation. Instead, differences between the Atka and Adak regions in the thickness of the methane hydrate stability zone, as marked by a bottom-simulating reflector, suggest more heat advection, and thus dewatering, in the Adak region, where the more developed fault network may enable fluid drainage, thereby lowering pore pressure at the megathrust and promoting coupling. Higher coupling allows for seismic and stress cycling that would sustain forearc permeability by faulting. Our results suggest a feedback between deformation and coupling that may be active or latent in other more complex subduction zones but in concert with or masked by other factors. 

Abstract Geological processes in Southern Patagonia are affected by the Patagonian slab window, formed by the subduction of the Chile Ridge and subsequent northward migration of the Chile Triple Junction. Using shear wave splitting analysis, we observe strong splitting of up to 2.5 s with an E‐W fast direction just south of the triple junction and the edge of the subducting Nazca slab. This region of strong anisotropy is coincident with low uppermost mantle shear velocities and an absence of mantle lithosphere, indicating that the mantle flow occurs in a warm, low‐viscosity, 200–300 km wide shallow mantle channel just to the south of the Nazca slab. The region of flow corresponds to a volcanic gap caused by depleted mantle compositions and absence of slab‐derived water. In most of Patagonia to the south of this channel, splitting fast directions trend NE‐SW consistent with large‐scale asthenospheric flow. 

Abstract The Patagonian slab window has been proposed to enhance the solid Earth response to ice mass load changes in the overlying Northern and Southern Patagonian Icefields (NPI and SPI, respectively). Here, we present the first regional seismic velocity model covering the entire north‐south extent of the slab window. A slow velocity anomaly in the uppermost mantle indicates warm mantle temperature, low viscosity, and possibly partial melt. Low velocities just below the Moho suggest that the lithospheric mantle has been thermally eroded over the youngest part of the slab window. The slowest part of the anomaly is north of 49°S, implying that the NPI and the northern SPI overlie lower viscosity mantle than the southern SPI. This comprehensive seismic mapping of the slab window provides key evidence supporting the previously hypothesized connection between post‐Little Ice Age anthropogenic ice mass loss and rapid geodetically observed glacial isostatic uplift (≥4 cm/yr).