We present an integrated image of the lithosphere of Alaska and its western Chukchi and Bering seas shelves based on joint modeling of potential field data constrained by thermal analysis and seismic data. We also perform 3D forward modelling and inversion of Bouguer anomalies to analyze crustal density heterogeneities. The obtained crustal model shows NW regional thickening (32 to 36 km), with localized trends of thicker crust in the Brooks Range (40 km) and in the Alaska and St. Elias ranges (50 km). Offshore, 28–30 km thick crust is obtained near the Bearing slope break and 36–38 km in the northern Chukchi Shelf. In interior Alaska, the crustal thickness changes abruptly across the Denali fault, from 34-36 to the N to above 30 km to the S, that agrees with the presence of a crustal tectonic buttress guiding block motion W and S to the subduction zone. The average crustal density is 2810 kg∙m-3. Denser crust (2910 kg∙m-3) is found S of the Denali Fault related to the oceanic nature of the Wrangellia Composite Terrane rocks. Offshore, less dense crust (< 2800 kg∙m-3) is found along the basins of the Chukchi and Beaufort shelves. At LAB levels, there is a regional SE–NW trend that coincides with the Pacific plate motion, with a lithospheric root beneath the Brooks Range, Northern Slope, and Chuckchi Sea, that may be a relic of the Chukotka-Artic Alaska microplate. The lithospheric root (> 180 km) agrees with the presence of a boundary of cold, strong lithosphere that deflects the strain to the south. South of the Denali Fault the LAB topography is quite complex. East of 150 °W, below Wrangellia and the eastern side of Chugach terranes, the LAB is much shallower than it is west of this meridian. The NW trending limit separating thinner lithosphere in the East and thicker in the West agrees with the two–tiered slab shape of the subducting Pacific Plate. This research has been funded by the We–Me project (PIE–CSIC–201330E111), AGUR 2017–SGR–847, Alpimed (PIE-CSIC-201530E082), Subtetis (PIE-CSIC-201830E039) and funds from the University of Houston. This is a contribution within the PolarCSIC platform. Ref: M. Torne, I. Jiménez–Munt, J. Vergés, M. Fernàndez, A. Carballo, M. Jadamec. Geophysical Journal International, Volume 220, Issue 1, January 2020, Pages 522–540, https://doi.org/10.1093/gji/ggz424.

Lithospheric slab breakoff can occur in various styles including a horizontal ‘tearing’, where an initial weakness develops into tearing and laterally propagates along the slab. Slab tearing has been invoked to explain changes in plate kinematics in the Western Mediterranean and the tectonic uplift that led to the Messinian Salinity Crisis. However, this process remains debated regarding its surface signature and the physical parameters controlling its initiation and dynamics. Here, we use 3D thermo-mechanical modelling to investigate geodynamic parameters affecting the slab-tearing initiation and its lateral propagation, and to quantify the corresponding surface vertical motions. We find that an oblique convergence introduces an asymmetry that favors the initiation of one-sided slab tearing. The tectonic configuration of the overriding plate has little effect on the trench migration rate, and slab tearing can results purely from the negative buoyancy of the subducted slab. This force and the slab retreat it causes are enough to generate an arcuate plan-view shape to the orogen. The slab-tear propagation rate varies from 37-67 cm/yr. During propagation, the slab tearing depth increases along the subducting slab, with a shallow initial tear (80-150 km) and a deeper tear (170-200 km) on the opposite end. The time needed for the slab to detach completely is geologically fast (<2 Myr). The slab tearing can cause a prominent surface uplift of 0.5-1.5 km throughout the forearc region with an uplift rate of 0.23-2.16 mm/yr, which is consistent with the situation during the first stage of the Messinian Salinity Crisis.

Lithospheric slab tearing, the process by which a subducted lithospheric plate is torn apart and sinks into the Earth’s mantle, has been proposed as a cause for significant surface vertical motions. However, little is known about the mechanisms that help initiate slab tearing and the consequential topographic changes. This study aims to explore this process by means of 3D thermo-mechanical modelling. We use the Gibraltar Arc region (Betics Cordillera) as a reference scenario of continental collision where such tearing-uplift interaction has been proposed. Our results suggest that the obliquity of the continental passive margin (relative to the trench axis) is a major influence on the initiation of slab tearing because it promotes a laterally diachronous continental collision, which leads to earlier tearing inception in one end of the slab. As a result of this, the model results predict an east-to-west slab tearing (tearing velocity 37.6–67.6 cm/yr with the lower-mantle viscosity of up to 1e+22 Pa·s). While the fast slab tearing (<2 Myr over 600 km wide slab) and the lack of arcuate slab in our models limit a direct comparison with the Western Mediterranean, this approach provides a new insight into the link between slab tearing in the mantle and surface uplift. Our models yield uplift rates of 0.23–2.16 mm/yr in response to slab tearing. This range is compatible with the uplift rate needed to achieve an equilibrium between seaway-uplift and seaway-erosion, which could have led to the closure of marine gateways during the onset of the Messinian Salinity Crisis.