The Central Alaska Hot Springs Belt (CAHSB), extending from eastern Alaska west to the Seward Peninsula, includes Pilgrim Hot Springs located 70 km north of Nome. The CAHSB continues west across Bering Strait to Chukotka, Russia, where over 30 more geothermal sites are known (Polyak et al., 2010; 2013). The faults and tectonic setting that control these geothermal resources are poorly known. We review the geologic and tectonic setting of geothermal sites nearest to the Bering Straits: the Pilgrim Hot Springs, Serpentine Hot Springs, those near the Kigluaik and Bendeleben Mountains, and the Lorino Hot Springs in Russia. Active faults close to these hot springs appear to re-activate older normal structures in today’s N-S extensional stress field. Limited young displacement occurs on these faults, but at their time of formation in the Late Cretaceous to Eocene, larger displacements occurred, making them re-activated zones of weakness today. Active faults on the Seward Peninsula include the E-W trending Kigluaik and Bendeleben normal faults that extend for 175 km with associated hot springs, including Pilgrim Springs. These faults uplift metamorphosed and intruded rocks and bound Cenozoic to Recent basins in their hanging wall. The parallel Bering Strait, Port Clarence and Norton Sound faults are active offshore. In Chukotka, the NW trending Kolyuchin-Mechigmen zone is likely a reactivated Cretaceous fault system that juxtaposed granitic and metamorphic rocks to the north with supracrustal rocks to the south (Bering Strait Geologic Field Party, 1997). First motions show normal and strike-slip and hot springs have variable isotopic evidence for mantle-derived He (Polyak et al., 2010; 2013). The Bering Sea basalt province (BSBP) lavas range from 6 Ma to Recent and are similar in composition to those erupted in intraplate settings, oceanic islands, continental rifts and transtensional systems (Wirth et al., 2002; Akinin et al., 1997; Andronikov and Mukasa, 2007). Mantle sources are deep ( greater than 1.5 GPa, greater than 50 km) and lavas erupted with little or no residence time in shallower magma chambers (Wirth et al., 2002; Akinin et al., 1997). Although spatially associated with the westernmost CAHSB, only the Russian hot springs have evidence for mantle-derived helium. Seismic data and studies of crust and mantle xenoliths in basalts of the BSBP indicate highly extended 30-35 km thick crust beneath the Bering Shelf intruded by calc-alkaline magmas in the Cretaceous to Paleocene (Klemperer et al., 2002; Akinin et al., 2009; 2013). Faults bounding basins offshore Seward Peninsula were most active in the Paleocene-Eocene. Contemporary deformation and eruption of basalts in the Bering Strait region suggests renewed onset of extension in the last 6 Ma. Alaska represents a complex tectonic setting in terms of its contemporary deformation, driven by high convergence rates and shallow subduction in southern Alaska that results in N-S shortening extending north to the Arctic margin. A review of deformation across Alaska compared to the Bering Strait region shows pronounced differences through time to the present-day. Eastern Alaska has undergone significant shortening that migrated north with time, while the Bering Shelf region underwent extensional deformation leading to quiescence after about 40-50 Ma. Today, western Alaska appears to be in the process of decoupling as it moves relatively S and W (e.g. Elliott and Freymueller, 2020) and has begun to extend again. Exploration for geothermal resources should focus on the Seward Peninsula-Chukotka region characterized by earthquakes that indicate N-S extension and eruption of mantle derived basalts. Blind geothermal systems should be considered in northern Seward Peninsula in the region of the Kotzebue Basin and Selawik Trough, which are pre-existing E-W trending structures that cut deep into the crust and are likely to be reactivated in the present-day stress field.

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