4 Results
4.1 Western Alaska Range Arc
We compiled 179 bedrock ages and 422 single grain U-Pb zircon ages from
the Western Alaska Range Arc (Figures 2, 3, 4, 5, 6, 7; references in
supplemental S1). The swath of arc magmatism along the Western Alaska
Range Arc proceeds from ca. 100 Ma to 25 Ma with re-initiation of the
arc since ca. 1 Ma, based on the compilation of both bedrock and
detrital geochronology datasets (Herriott et al., 2014; Lease et al.,
2016; Jones et al., 2021; Cameron et al., 2022). Periods of peak
magmatism are ca. 98 Ma, 60 Ma, throughout the Oligocene and since ca. 1
Ma (Figure 3). There are no substantial East-West or North-South trends
with time besides a) a jump trenchward in magmatism from
~87 Ma to ~75 Ma and b) the modern
Denali magmatic gap (Rondenay et al., 2010) between Hayes Volcano and
Jumbo Dome-Buzzard Maar to the northeast (Figures 1 and 2).
4.2 Central Alaska Range Arc
We compiled 83 bedrock ages and 1325 single grain U-Pb zircon ages from
the Central Alaska Range Arc (Figures 2, 3, 4, 5, 6, 7; references in
supplemental S2). The swath of arc magmatism along the ARSZpulses from ca. 100 Ma to 25 Ma, with re-initiation of the arc since ca.
1 Ma based on the compilation of both bedrock and detrital geochronology
datasets (Athey et al., 2006; Andronikov et al., 2010; Lease et al.,
2016; Regan et al., 2020; 2021; Fasulo and Ridgway, 2021; Benowitz et
al., 2022; Brueseke et al., 2023) with a focus along the Denali Fault
system. Overall, there is minimal magmatism north of the Denali Fault
system with Jumbo Dome (Cameron et al., 2015) and Buzzard Maar
(Andronikov et al., 2010) being historical volcanos ~575
km from the modern trench (Fig. 1). Similar to the Western Alaska Range
Arc, periods of peak magmatism are ca. 95 Ma, ca. 60 Ma, and ca. 40 Ma
(Figure 3). There are no substantial East-West or North-South trends
with time except a gap in magmatism from ~87 Ma to
~75 Ma when it shifted outboard to the Talkeetna
Mountains and the southern Western Alaska Range (Figure 2).
4.3 Talkeetna Mountains
We compiled 86 bedrock ages and 2817 single grain U-Pb zircon ages from
the Talkeetna Mountains (Figures 2, 3, 4, 5, 6, 7; references in
supplemental S3). The Talkeetna Mountains have periods of peak magmatism
of ca. 80 Ma, ca. 58 Ma, and ca. 45 Ma (Figure 3) (e.g., Terhune et al.,
2019; Finzel et al., 2019). This area is mostly south of theARSZ, but is shown for completeness. The ca. 80 Ma magmatic peak
occurs during a period when magmatism ceases in the Central Alaska Range
Arc (ca. 87 Ma to 75 Ma) (Figure 2). The ca. 58 Ma and ca. 45 Ma
magmatic peaks in the Talkeetna mountains reflect the slab window and
relict slab window magmatism (Cole et al., 2006; Cole et al., 2007).
4.4 Wrangel Arc
We compiled 246 bedrock ages and 4347 single grain ages (U-Pb zircon
zircon and 40Ar/39Ar lithic grain
ages) from the Wrangell Arc (Figures 3, 4, 5, 6, 7; references in
supplemental S4). The swath of Wrangell Arc magmatism along theARSZ proceeds from ca. 100 Ma to Recent based on the compilation
of both bedrock and detrital geochronology datasets (Richter et al.,
1990; Berklehammer et al., 2019; Brueseke et al., 2019; Trop et al.,
2022). The detrital dataset is more diverse than the bedrock dataset,
which may reflect detrital grains being sourced from metamorphic and
sedimentary sources, or more likely reflects preferential bedrock
sampling of Wrangell aged lavas. Wrangell Arc periods of peak magmatism
are ca. 60 Ma and ca. 30 Ma to Recent (Figure 3). Wrangell Arc magmatism
occurs south of the Denali Fault for the entirety of its existence, but
shifts slightly with time generally from north (ca. 30 Ma to 18 Ma) to
east (ca. 18 Ma to 13 Ma), to west (ca. 13 Ma to 16 Ma), and finally to
a distinct northwest trend 6 Ma to 1 Ma slightly (see Trop et al.,
2022). From 30 Ma to 6 Ma magmatism is also focused along the Totschunda
and Duke River Faults with limited magmatism along the Totschunda Fault
6 Ma to Recent (Trop et al., 2022).
4.5 Compiled Alaska suture zone magmatic history
The combined datasets show peak periods of magmatism along theARSZ at ca. 95 Ma, ca. 60 Ma, ca. 40 Ma and Recent (Figure
3). The Wrangell Arc area has a slightly different history,
reflecting the shutting off of the western and eastern Alaska Range Arcs
at ca. 25 Ma (Trop et al., 2019; Jones et al., 2021; Benowitz et al.,
2022) and the initiation of the Wrangell Arc at ca. 30 Ma (Trop et al.,
2022).
4.6 Geophysics Compilation
The Western Alaska Range Arc generally follows the ARSZ which has
an east-west crustal thickness step (Figure 6) (Gama et al., 2022) and a
strong magnetic signature gradient (Saltus and Hudson, 2022). The
Central Alaska Range Arc is located primarily south of the Hines Creek
Fault and borders both sides of the Denali Fault system in theARSZ (Figure 5). There is a crustal thickness step across both
the Denali (Allam et al., 2017) and Hines Creek Faults (Brennan et al.,
2011, Allam et al., 2017) (Figure 6), and a strong magnetic signature
break across the Talkeetna Fault (Saltus and Hudson, 2022). The Wrangell
Arc is located in the ARSZ where there also is a crustal
thickness step (Figure 6) (Allam et al., 2017) and a magnetic signature
break (Saltus and Hudson, 2022).
The modern Yakutat slab has a shallow dip of ~5° for
nearly 200-km inboard of the trench and is in direct contact with the
overriding crust until it reaches the Chugach-Prince William
Terrane-Wrangellia Terrane boundary (Kim et al., 2014; Mann et al.,
2022). Once the subducting slab reaches roughly the Talkeetna Fault, its
dip increases to ~20° (Ferris et al., 2003; Rondenay et
al., 2010); near the Denali fault it begins steeply dipping into the
mantle (Jiang et al., 2018; Yang et al., this issue ). The
overriding plate crust has a northward-thickening wedge shape from
roughly 10 to 40 km thick under the Chugach-Prince William terrane, and
is at 35-55 km under the Wrangellia composite Terrane, 35-40 km under
the ARZS , 25 km under the Yukon Tanana Terrane, 35-40 km thick
north of the Tintina Fault and almost 50-km thick north of the Kobuk
Fault under the Arctic Plate (Veenstra et al., 2006; Rossi et al., 2006;
Brennan et al., 2011, Miller et al., 2018; Mann et al., 2022; Gama et
al., 2022; Yang et al., this issue ). There are Moho offsets
across each of these tectono-boundaries The upper-plate lithosphere is
absent or extends to ~50-km depth beneath the
Chugach-Prince William terrane, Wrangellia composite terrane, andARZS ; is 65-125 km thick beneath the Yukon Tanana terrane,
125-145 km thick beneath the region the north of the Tintina fault, and
up to 200-km thick north of the Kobuk Fault under the Arctic Plate
(O’Driscoll and Miller, 2015; Miller et al., 2018; Jiang et al. 2018;
Gama et al., 2022).