18 Crossing Borders: Large-scale tectonic models of the North American Cordillera

This session focusses on the Phanerozoic evolution of the North American Cordillera, soliciting studies that address large-scale tectonic models associated with obliquely convergent and divergent movement along the margin.

Thursday, 23 April 2026
8:00 AM - 12:00 PM
LMH, Isla Carmen

Eastern Aleutians slab gap and its impact on Kula-Pacific tectonic reconstructions and Alaska geology

Paper number: 18-2
Program: Technical Sessions
Time: 8:25 AM – 8:45 AM

Authors

Abstract

Recent high-resolution seismic tomography from the Alaska Amphibious Community Seismic Experiment has revealed a low-velocity anomaly in the Alaska-eastern Aleutians slab beneath the Alaskan Peninsula at depths of 200 to 500 km, ranging from ~55.5 to 57.5°N in latitude and ~158.5°W to 168°W in longitude. This anomaly was interpreted as a slab tear by the tomographic study of Wang et al. (2025), but it was not reconstructed in detail.  We have mapped out the slab in three dimensions and unfolded (i.e., flattened) the slab to structurally restore it back to the Earth’s surface. This unfolded slab was then integrated into a quantitative plate reconstruction using GPlates software with global plate motion data from Matthews et al. (2016). We ‘unsubduct’ the Alaska slab and find that the slab tear matches the position of the Kula-Pacific spreading ridge at 43 Ma, the time the ridge went extinct.  Cenozoic plate models of the present-day northeastern Pacific are not fully constrained by seafloor isochrons, resulting in two possible timings for slab tear initiation (immediately following subduction, above a depth of 150 km, or much closer to the present day, below a depth of 150 km) and requiring inferences from upper plate geology to resolve. We reconstruct subduction of the extinct Kula-Pacific Ridge along the Alaska-eastern Aleutians trench between 10 and 5 Ma, sweeping across the eastern section of the trench from 56.8°N, 155.6°W to 52.2°N, 167.9°W. Using the published ages of magmatic events from the upper plate, we determine that slab tear initiation likely occurred when the subducted Kula-Pacific ridge was at a depth greater than 150 km, closer to the present-day and possibly coincident with Yakutat slab tearing to the east. Finally, we compare the Eastern Aleutians slab gap with other slab gaps formed by the subduction of extinct spreading ridges and examine how our unfolding and reconstruction of the subduction of the Kula-Pacific spreading ridge could affect plate reconstruction models.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410854

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