1. Introduction
Convergent margins often accumulate long-lived lithospheric-scale
crustal weaknesses that result from the accretion and dismemberment of
terranes (e.g., Wilson, 1965). These mechanical weaknesses frequently
manifest as strike-slip faults in oblique convergent settings and slip
in response to changing plate boundary conditions (e.g., Powell, 1993;
Storti et al., 2003; Najman et al., 2022). The evolution of
transform-fault systems is a response, in part, to the orientation of
pre-existing faults with respect to variations in plate convergence
(e.g., Walcott 1998; McCaffrey et al., 2000). Thus, changes in the
orientation of convergence during major plate reconfigurations may
modify which faults accumulate strain through geologic time. As fault
splays are translated and rotated along a master strike-slip system they
can also become preferentially aligned for increased slip accommodation
(e.g., Riccio et al. 2014).
Strike slip faults typically have a dip slip component in
transpressional settings and thus, thermochronology is often used to
document rock cooling along strike slip systems (e.g., Fitzgerald et
al., 1995; Benowitz et al., 2014) which can be inferred to reflect
periods of partitioned horizontal slip. Exhumation related rapid cooling
can also be inferred from kinetic modelling of thermochronology data
from strike slip fault corridor sampling transects. Therefore, applying
geochronology and thermochronology to rock samples collected along the
Totschunda fault integrated with regional geologic constraints presents
an opportunity to improve our understanding of the slip distribution on
the Denali fault strike-slip fault system and also the mechanisms
responsible for slip distribution between the Totschunda and Eastern
Denali faults since ca. 52 Ma.
The intersecting Totschunda and Denali faults of Alaska are both
interpreted as Cretaceous strike-slip faults that developed across a
Mesozoic collisional suture zone with strike-slip reactivation of the
suture zone structures (e.g., Churkin et al., 1982; Ridgway et al. 2002;
Fitzgerald et al., 2014; Trop et al., 2019, 2020). While plate
convergence along the southern Alaska boundary continues, Late Miocene
clockwise rotation of the Pacific plate and attached Yakutat microplate
relative to North America has influenced tectonics extensively in
interior Alaska (e.g., Fitzgerald et al. 1993, 1995; Waldien et al.,
2019) and may have drastically modified which faults transfer stress
from the plate boundary into interior Alaska. Numerous studies suggest
that in response to the Late Miocene Pacific-Yakutat plate motion
change, the Eastern Denali fault (Figure 1) has played a diminished role
in the transfer of slip from the plate boundary to the continental
interior (Waldien et al., 2018; Choi et al., 2021; Allen et al., 2022;
Trop et al., 2022; Benowitz et al. 2022a, b). Herein we refer to the
Pacific and neighboring Yakutat microplate as the Pacific-Yakutat plate
when referencing how the Late Miocene Pacific plate vector change
affected Alaska plate boundary conditions.