Ice Age Floods Institute

Puget Lobe Lecture: Jeff Tepper on the Initiation of the Cascade Arc
2025-11-17 19:00 - 20:30 (America/Los_Angeles) | Bellevue College Building T Room 117, 3000 Landerholm Cir SE, Bellevue, WA, 98007, United States
Dr. Jeff Tepper
The Cascade volcanic chain, the world’s youngest continental arc, was “born” shortly after accretion of the Siletzia oceanic terrane ~50 My ago. That collision, which led to formation of the Olympics, terminated the earlier subduction system and caused a portion of the subducting Farallon slab to break off. When Cascade magmatism began less than 5 My later, there was a new trench located outboard of Siletzia. In this talk I will present a new model, based on petrology, geochronology, plate motion reconstructions, and mantle tomography, that explains how subduction was initiated so quickly and in a setting where the slab was young and hot and in theory too buoyant to subduct.
