Figure 7. Schematics of four distinct periods (100 Ma to 60) of
Central Alaska Range Arc magmatism. Translation along the Tintina and
Denali Faults not shown nor is rotations of the incoming slab during
plate vector changes discussed in the text. Mantle flow into the mantle
wedge, enhanced by trench advancement of the thick-cold lithosphere of
interior Western USA/Western Canada and the Arctic Plate (>
150 kms; O’Driscoll and Miller 2015; Tikoff et al., 2022) likely leads
to lower pressure and upper plate suction (e.g. Manea et al., 2012). a)
After the mid-Cretaceous docking of the Wrangellia Composite Terrane off
the coast of the Western USA/Western Canada (e.g. Trop et al., 2020;
Tikoff et al., 2022) there was a long period of “normal” subduction
from ca. 100 Ma to 60 Ma with arc magmatism focused in the ARZSwith minor magmatism north of the Border Ranges Fault (Bleick et al.,
2012). During this time period the ARZS underwent shorting (e.g.
Trop et al., 2019). There was a short period of steeper slab subduction
when the arc moved outboard towards the trench between ca.87 Ma and 75
Ma (Figure 1) that is not given its own schematic. b) The Alaska
convergent margin was likely a transform system from ca. 60 Ma to 50 Ma
after break off of the Kula slab (Terhune et al., 2019). During this
time period 44° ± 11° counter-clock wise oroclinal bending was occurring
(Coe et al., 1989; Gillis et al., 2022) and slab window magmatism in theARZS and to the south along the hinge of the orocline (Cole et
al., 2006; e.g. Terhune et al., 2019). This time period was also the
timing of rapid slip along the Border Ranges Fault (Smart et al., 1996)
and the Tintina Faults (Saltus et al., 2007). c) After accretion of the
Chugach-Prince William Terrane (Garver and Davidson, 2015) and a Pacific
plate motion change at ca. 50 Ma (Sharp and Clague, 2006) subduction
reinitiated and the trench jumped outboard about ~200
km. This time period was the start of rapid slip along the Denali Fault
system (Waldien et al., 2021). There was minor post-slab window
magmatism north of the Border Ranges Fault (e.g. Terhune et al., 2019)
with magmatism once again focused in the ARZS. At ca. 30 Ma the
Yakutat oceanic plateau (Worthington et al., 2012) started to subduct
under Alaska (Brueseke et al., 2019), but magmatism continued in theARZS till ca. 25 Ma (Trop et al., 2019). d) The shallow
subduction of the Yakutat oceanic plateau continued till ca. 1 Ma when
collision and slab segmentation initiated (Brueseke et al., 2023). This
slab segmentation led to the rejuvenation of the central Alaska Range
arc. Crustal thickness variations compiled from Veenstra et al. (2006),
Brennan (2011), Miller et al. (2018), and Mann et al., 2021. Lithosphere
thickness variations compiled from O’Driscoll and Miller (2015), Jiang
et al. (2018) and Gamma et al. (2022). Recent mantle flow and surface
velocity directions from McConeghy et al. (2022) and are inferred to be
similar during past subduction regimes. AT: Arctic Plate; UT:
Unidentified Terranes; YTT: Yukon Tanana Terrane; ARZS: Alaska Range
Suture Zone; WCT: Wrangellia Composite Terrane; CPWT: Chugach-Prince
William Terrane; KF: Kobuk Fault; TF: Tintina Fault; HF: Hines Creek
Fault; DF: Denali Fault; TaF: Talkeetna Fault; BRF: Border Ranges Fault.
Scale bar approximate. North Arrow rotates with paleo-location of the
Wrangell composite terrane (e.g. Terhune et al., 2019; e.g. Tikoff et
al., 2022).
5.3 Other examples of long-lived arc localization
Globally, there are many past and present examples of localized arc
magmatism. The Gangdese arc of southern Tibet was broadly localized ca.
100 Ma to 45 Ma (Ma et al., 2022). Magmatism has been localized and
focused along an inherited lithospheric-scale boundary in Iran from
Eocene to late Miocene times (Rabiee et al., 2020). Magmatism was
localized along the Burma plate during Cretaceous and Eo-Oligocene arc
magmatic events while the plate was being translated >2000
km and undergoing different subduction orientations/slab configurations
(Westerweel et al., 2019; Licht et al., 2020).
The Cascade Arc has been emplaced along the same general region of crust
since ca. 45 Ma (Humphreys and Grunder, 2022), with Eocene, Oligocene,
Miocene, Pliocene, and Pleistocene magmatic products intruded next to
and through one another. Even classic examples of long-lived arcs such
as the northern Andes (Ducea et al., 2015) appear to be emplaced along
pre-existing suture zones. About 70 million years of arc magmatism in
South America has generally been emplaced along the Peletec suture zone
in Ecuador with no Cenozoic arc magmatic products emplaced to the east
into the South American craton (Chiaradia et al., 2004; Glazner, 2022).
Our results in Alaska suggest that these and other regions of long-lived
arc localization reflect the geodynamic influence of upper-plate
hydrodynamic “suction” on underlying slab geometry.