Regional crustal and lithospheric thickness model for Alaska, the Chukchi shelf, and the inner and outer bering shelves

Abstract

SUMMARY This study presents for the first time an integrated image of the crust and lithospheric mantle of Alaska and its adjacent western shelves of the Chukchi and Bering seas based on joint modelling of potential field data constrained by thermal analysis and seismic data. We also perform 3-D forward modelling and inversion of Bouguer anomalies to analyse density heterogeneities at the crustal level. The obtained crustal model shows northwest-directed long wavelength thickening (32–36 km), with additional 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 predicted 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 north to above 30 km to the south. This sharp crustal thickness gradient agrees with the presence of a crustal tectonic buttress guiding block motion west and south towards the subduction zone. The average crustal density is 2810 kg m−3. The denser crust, up to 2910 kg m−3, is found south of the Denali Fault likely related to the oceanic nature of the Wrangellia Composite Terrane rocks. Offshore, less dense crust (<2800 kg m−3) is found along the sedimentary basins of the Chukchi and Beaufort shelves. At LAB levels, there is a regional SE–NW trend that coincides with the current Pacific Plate motion, with a lithospheric root underneath the Brooks Range, Northern Slope, and Chuckchi Sea, that may correspond to a relic of the Chukotka-Artic Alaska microplate. The obtained lithospheric root (above 180 km) agrees with the presence of a boundary of cold, strong lithosphere that deflects the strain towards 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.

Variations of Crustal Thickness in Alaska and Northwestern Canada: Implications for Crustal Modification and Accretion of Tectonic Units

“…Schulte-Pelkum et al (2020) analyze the RFs in Alaska and northwestern Canada and provide a map of the crustal anisotropy and dipping structures. Torne et al (2020) estimate the average crustal density across Alaska and suggest that the crust is denser to the south of the Denali Fault than to its north. Some studies focus on the regional scale on parts of the Alaska and northwestern Canada.…”

“…Torne et al. (2020) estimate the average crustal density across Alaska and suggest that the crust is denser to the south of the Denali Fault than to its north.…”

“…The density of the seismic station coverage in Alaska and northwestern Canada has significantly increased with the deployment of the EarthScope USArray since 2014. Numerous models exist for this region in both continental and regional scales, which provide constraints on the lithospheric structure (e.g., Berg et al., 2020; Feng, 2021; Feng & Ritzwoller, 2019; Gama et al., 2021; Gou et al., 2019; Martin‐Short et al., 2018; Nayak et al., 2020; Ward & Lin, 2018; Yang & Gao, 2020), the thickness variations of the crust and lithosphere (e.g., Allam et al., 2017; Audet et al., 2020; Miller et al., 2018; Miller & Moresi, 2018; Torne et al., 2020; Zhang et al., 2019), and the topography of the mantle transitional zone (e.g., Dahm et al., 2017; Van Stiphout et al., 2019).…”

Synthesis of the Seismic Structure of the Greater Alaska Region: Continental Lithosphere

“…These constraints will be useful for lithospheric-scale (e.g., Finzel et al, 2015;McConeghy, Flesch, & Elliott, 2022) and mantle-scale (e.g., Jadamec & Billen, 2010, 2012Jadamec et al, 2013;Haynie & Jadamec, 2017) geodynamical models of subduction in Alaska and its impact on the overriding continental lithosphere. The crustal seismic velocities and thickness constraints synthesized in this study could also help to better design representative models of upper plate dynamics (Torne et al, 2019) and models of plateau subduction to examine the effects of plateau subduction-collision on long-term plate boundary evolution (e.g., Koons et -27-manuscript submitted to AGU Monograph al., 2010;Haynie, 2019;Moresi et al, 2014) and the role of eclogitization of the subducting plateau with depth (Arrial & Billen, 2013).…”

Towards a Digital Twin of the Earth System: Geo-Soft-CoRe, a Geoscientific Software & Code Repository

“…Geoid-elevation inversion is a code to simultaneously invert lithospheric geoid anomalies and surface elevation for the 1D crustal and lithospheric thickness coupled with temperature and density distributions (Fullea et al, 2006;Fullea et al, 2007). This software has been applied to map the crust-mantle boundary and the lithosphere-asthenosphere boundary in the Gibraltar Arc System, Atlas Mountains and adjacent areas (Fullea et al, 2007), the Iberian Peninsula (Torne et al, 2015), the Arabia-Eurasia collision zone in Iran (Jiménez-Munt et al, 2012), central Eurasia (Robert et al, 2017), the African mainland (Globig et al, 2016), and in Alaska and surroundings shelves (Torne et al, 2020).…”