EVOLUTION OF THE YELLOWSTONE HOTSPOT TRACK: RETROSPECTIVE AND CURRENT IDEAS (Invited Presentation)

The long history of interdisciplinary research on the Yellowstone hotspot (YHS) has benefitted from the work of Ken Pierce, honoree of this session. Of particular acclaim is the paper Pierce and Morgan (1992), a ground-breaking analysis of the YHS track that provided a framework for later investigations. Many studies have supported or modified their fundamental conclusions, that the YHS is underlain by a deep-mantle plume responsible for the initiation of Columbia River flood-basalt (CRB) volcanism from ~17-15 Ma, followed by a transition from plume-head to plume-tail melting from 15-10 Ma, and the development of a well-defined hotspot track consistent with plate motion from 10 Ma to the present. There have been many competing ideas on the age, origin, length, and orientation of the YHS track since the publication of Pierce and Morgan (1992). Here, I summarize current ideas on the YHS track as it evolved evolved along a fixed hotspot path parallel to the trend of North American plate motion.

Many workers have embraced the notion of plume arrival at ~17-16 Ma, but since 2013 a growing volume of evidence supports a much older age to account for offshore volcanism and the accretion of the Siletzia oceanic plateau from 56-49 Ma, followed by overriding of the YHS by the North American plate from 42-34 Ma (Wells et al., 2014). Shielding of the YHS by the Farallon slab is marked by the lack of a geochemical plume signature in eruption products from 34-17 Ma. Instead, these back-arc eruptions are consistent with progressive thermomechanical erosion of the slab, associated with dehydration-melting and the melting of Farallon crust to produce an ENE-trending belt of adakite volcanism above the hotspot trend from 30-20 Ma (Camp et al., 2017). Seismic studies resolve a truncated Juan de Fuca plate at ~300 km depth and a large slab hole beneath the adakite/YHS trend (e.g., Obrebski et al., 2010) consistent with this period of slab disassociation. After a short volcanic hiatus, slab rupture resulted in the rapid rise and ponding of voluminous plume-modified mantle beneath the North American plate and eruption of the main phase of tholeiitic CRB from 17-15 Ma. This event was followed by a transition to age-progressive volcanism along the Yellowstone/Snake River Plain trend from 14 Ma to the present, modified by magmatism from plume-flux back-filling to the WSW.