T216 Late Cretaceous to Early Paleogene Tectonic Development of the North American Cordillera II

Tuesday, 24 September 2019
1:30 PM - 5:30 PM
Room 231ABC, North Building

RAISING THE RESURRECTION PLATE BY STRUCTURALLY RESTORING SUBDUCTED SLABS BELOW THE NW CORDILLERA

Paper number: T216-6
Program: Technical Sessions
Time: 2:50 PM – 3:05 PM

Authors

Abstract

Subduction of the now-vanished “Resurrection” plate, and two bounding mid-ocean ridges, has been proposed from two coeval belts of Paleocene to Miocene near-trench magmatism in Alaska and Oregon. We test the presence of this cryptic plate with a plate reconstruction since 50 Ma, constrained by unfolded (i.e. structurally restored) Farallon and Pacific-Kula slabs from four recent global and local mantle tomographies including MITP16 and UUP07. Our 3-D slab mapping reveals a steeply-dipping (>45°) Aleutian slab that is flattened across the uppermost lower mantle. East of Anchorage, this slab becomes shallowly-dipping (<45º). Below Vancouver Island, the Cascadia slab has a ~45° dip. This slab becomes shallowly-dipping to the south, where it extends to the longitude of Illinois and is flattened across the uppermost lower mantle. We also mapped localized high-velocity anomalies below western Yukon at ~500-600 km depth. Slab unfolding from six transects across Alaska and the Aleutian Islands reveals pre-subduction slab lengths of ~1,500 to 6,300 km (east to west). When reconstructed within a global plate model, the Aleutian slabs account for ~50 Ma of Pacific-Kula subduction west of Anchorage but only ~30 Ma to the east, forming an apparent gap in restorable oceanic lithosphere below southeast Alaska. Similarly, seven transects across the western United States reveal pre-subduction slab lengths of ~1,500 to 6,000 km (north to south) that account for only ~25 Ma of Farallon subduction below Vancouver Island (i.e. a second gap) and ~80 Ma near southern California. Intersection of the bounding edges of these apparent gaps with North America since ~50 Ma show close correspondence with the Coast Range Basalt Province (northwest USA), Sanak-Baranof belt (Alaska), and younger near-trench magmatism between the two. Thus, we suggest that our reconstructed gaps between the Kula and Farallon plates are slab windows that constrain the locations of the Kula-Resurrection and Resurrection-Farallon ridges since at least 50 Ma. The localized high-velocity tomographic anomalies below western Yukon fit within our plate reconstruction as a “Resurrection plate”. Our slab reconstruction provides new, independent spatiotemporal constraints on the lost Resurrection plate and NW Cordillera plate tectonics since early Eocene time.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-339144

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