Abstract
AbstractThe Fairweather fault (southeastern Alaska, USA) is Earth’s fastest-slipping intracontinental strike-slip fault, but its long-term role in localizing Yakutat–(Pacific–)North America plate motion is poorly constrained. This plate boundary fault transitions northward from pure strike slip to transpression where it comes onshore and undergoes a <25°, 30-km-long restraining double bend. To the east, apatite (U-Th)/He (AHe) ages indicate that North America exhumation rates increase stepwise from ∼0.7 to 1.7 km/m.y. across the bend. In contrast, to the west, AHe age-depth data indicate that extremely rapid 5–10 km/m.y. Yakutat exhumation rates are localized within the bend. Further northwest, Yakutat AHe and zircon (U-Th)/He (ZHe) ages gradually increase from 0.3 to 2.6 Ma over 150 km and depict an interval of extremely rapid >6–8 km/m.y. exhumation rates that increases in age away from the bend. We interpret this migration of rapid, transient exhumation to reflect prolonged advection of the Cenozoic–Cretaceous sedimentary cover of the eastern Yakutat microplate through a stationary restraining bend along the edge of the North America plate. Yakutat cooling ages imply a long-term strike-slip rate (54 ± 6 km/m.y.) that mimics the millennial (53 ± 5 m/k.y.) and decadal (46 mm/yr) rates. Fairweather fault slip can account for all Pacific–North America relative plate motion throughout Quaternary time and indicates stability of highly localized plate boundary strike slip on a single fault where extreme rock uplift rates are persistently localized within a restraining bend.
Highlights
Characterizing the evolution of plate boundary faults from earthquakes to orogenesis remains a fundamental challenge for illuminating seismic hazards, placing geodetic deformation into geologic context, and constraining tectonic models across different geologic domains
Dextral slip rates of 50–57 m/k.y. since 12–17 ka are constrained by 184 piercing points along the offshore Queen Charlotte fault (Brothers et al, 2020) and are consistent with estimated rates of 48–58 m/k.y. since 1 ka for the onshore Fairweather fault (Plafker et al, 1978; note mm/yr = m/k.y. = km/m.y.)
Decadal to millennial slip on the Queen Charlotte–Fairweather fault system can account for 85%–100% of the 48–53 km/m.y. of Pacific–North America relative plate motion (DeMets and Merkouriev, 2016), suggesting that plate boundary strain is highly localized on these time scales
Summary
Characterizing the evolution of plate boundary faults from earthquakes to orogenesis remains a fundamental challenge for illuminating seismic hazards, placing geodetic deformation into geologic context, and constraining tectonic models across different geologic domains. Decadal to millennial slip on the Queen Charlotte–Fairweather fault system can account for 85%–100% of the 48–53 km/m.y. of Pacific–North America relative plate motion (DeMets and Merkouriev, 2016), suggesting that plate boundary strain is highly localized on these time scales.
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