RAISING THE RESURRECTION PLATE FROM AN UNFOLDED-SLAB PLATE TECTONIC RECONSTRUCTION OF NORTHWESTERN NORTH AMERICA SINCE EARLY CENOZOIC TIME

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. Here we summarize results of a recent paper by Fuston and Wu (2021) published in GSA Bulletin that mapped in 3D and unfolded (i.e. structurally restored) Farallon and Pacific-Kula slabs from multiple mantle tomographies, and restored these plates within a global plate model. We found 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. The Cascadia slab accounts for only ~25 Ma of Farallon subduction below Vancouver Island (i.e., a second gap) and ~80 Ma near southern California. We also mapped localized high-velocity anomalies below western Yukon at ~500-600 km depths that we call the ‘Yukon slab’. Within a quantitative plate model, intersection of the bounding edges of these apparent slab gaps with North America since ~50 Ma show close correspondence to the Coast Range Basalt Province (northwest USA), Sanak-Baranof belt (Alaska), and younger near-trench magmatism between the two, even when terrane translation is considered. 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”-like plate, providing new geophysical evidence of its existence. Our reconstructions support a northern option Farallon ridge geometry that allows up to ~1200 km of Chugach terrane translation since the Paleocene, providing a new ‘tomographic piercing point’ for the Baja-BC terrane translation debate.