1 Introduction
The upper-plate location of continental arc magmatism is broadly
correlated with the geometry of the subducting slab, with melt
generation and individual volcanic centers generally positioned above
the subducting slab 100 ± 40 km depth contours (Isacks and Barazangi et
al., 1977; England et al., 2004; Syracuse and Abers, 2006). Numerous
factors can influence subducting slab geometry, including the age of the
incoming slab (Jarrard, 1986), buoyant topographic highs (e.g., oceanic
plateaus: Van Hunen et al., 2002, 2004; aseismic ridges: George et al.,
2022), the thickness of the overriding plate (e.g., Sharples et al.,
2014), trench shape and curvature (e.g., Chiao et al., 2002),
convergence rate (e.g., Billen and Hirth, 2007), and convergence
obliquity (e.g., Laurencin et al., 2018). Thus, overall arc localization
should be limited, given the dynamic nature of long-lived subduction
systems, wherein slabs can break off and active ridges can subduct, the
age of the incoming plate can change over time (Grow & Atwater, 1970),
incoming plate speed and direction can both vary with time (Stock &
Molnar, 1988; Richards & Lithgow-Bertelloni, 1996), and bathymetric
highs can be fully subducted (Gutscher et al., 1999) or accreted (Yang
et al., 2015). Thus, it is accepted that long-lived arcs should migrate
large trench-perpendicular distances as both slab and upper-plate
geometries morph over time (e.g. Gianni and Luján, 2021).
Hence, how arcs can be localized on 107-year time
scales, hundreds of kilometers inboard of a non-stationary trench
(Kirsch et al., 2016; Rabiee et al., 2020; Humphreys and Grunder, 2022;
Ma et al., 2022), remains an enigma. Furthermore, during periods of slip
activity, crustal blocks along strike-slip faults are translated to new
positions, intrinsically creating a natural struggle against a clear
geological record of arc localization (Alvarado et al., 2016; Trop et
al., 2022). Moreover, overriding plates themselves are always in
relative motion to the incoming slab (DeMets et al., 2015), and
trench-to-arc distance also can vary with time due to accretion (Hughes
and Pilatasig, 2002) and subduction erosion (Stern, 2011). Potential arc
localization is compounded further by the fact that fluids and hence
melt can be generated from a large area of a subducting slab and
channeled up-dip (Wilson et al., 2014).
In this work we document arc-localization inboard of the proto and
modern Pacific trench along the mobile Alaska Range Suture Zone
(ARZS; Ridgway et al., 2002; Trop et al., 2019) since ca.
100 Ma (Figure 1). Variability of incoming subducting slab
characteristics and convergent margin configurations—including both
normal oceanic plate and oceanic plateau subduction, plate vector
changes, oroclinal bending and reconfiguration of trench shape, terrane
accretion, long distance translation (>2000 km; e.g.,
Stamatakos et al., 2001; Tikoff et al., 2022) and a Paleocene slab break
off/slab window event—have not drastically affected ARSZ arc
location with time. These observations naturally lead to the deduction
that a) inherited upper-plate lithospheric thickness and temperature
contrasts across the ARSZ and northern Alaska (Miller et al.,
2018; Gama et al., 2022) and along the western-Northern Cordillera
(Clowes et al., 1995; Estève et al., 2020) have played a role in
subducting slab geometry under the Wrangell composite terrane of
southern Alaska, b) arc localization, since ca. 100 Ma has been in part
controlled by inferred upper-plate related hydrodynamic (viscous) mantle
wedge “suction” forces, c) upper-plate crustal heterogeneity
preferentially focuses magma ascent, perhaps through melt ponding at
Moho offsets and d) upper-plate lithospheric-scale strike-slip faults
can act as passive and active conduits for arc magmatism (e.g. Regan et
al., 2021).