ON THE ORIGIN AND EVOLUTION OF INTRAPLATE VOLCANISM: THE CASE FOR YELLOWSTONE (Invited Presentation)

Intraplate volcanism differs from that along subduction zones in that the former sometimes displays age-progressive tracks resembling typical hotspots like Hawaii. While hotspots occurring far from plate boundaries are often considered a direct result of plume-induced shallow melting, the Yellowstone volcanic province (YVP), with two tracks moving in opposing directions, has inevitably been affected by the subduction of the Farallon/Juan de Fuca plate below the west coast. It is therefore unclear how much shallow vs deep mantle materials feeds into the YVP.

In order to address this question, we simultaneously evaluate the Cenozoic subduction history and its interaction with other mantle structures including the recently imaged Yellowstone plume. Our forward subduction model suggests that the various fast seismic anomalies below the western U.S. represent highly segmented Farallon slab (Liu & Stegman, EPSL, 2011), with the initial slab tear corresponding to the formation of the mid-Miocene Columbia River flood basalt (Liu & Stegman, Nature, 2012). We find that the ascending trajectory of the plume is largely blocked by the sinking slab (Leonard & Liu, GRL, 2016), implying that the imaged voluminous slow seismic anomalies below the Snake River Plain and the Yellowstone caldera should not have originated from the YS plume. Our recent inverse convection model demonstrates that the heat fueling the YVP was mostly derived from eastward migrating hot Pacific asthenosphere through the central tear and around the edges of the downgoing slab (Zhou et al., Nature Geoscience, 2018). This model also best reproduces the unique seismic anisotropy pattern within the western U.S., further confirming the eastward intruding hot mantle (Zhou et al., EPSL, in review). This heat source was reconstructed back to below the Pacific-Juan de Fuca spreading center at ~20 Ma, distant from the newly imaged root of the YS plume. Our studies, therefore, provide new insights, along with new questions, on the thermal interaction between the deep mantle and the surface.