UNDERSTANDING THE SOURCES OF SEGMENTATION OF VOLCANIC CENTERS ALONG THE YELLOWSTONE HOTSPOT TRACK: INSIGHTS FROM HIGH RESOLUTION THERMOMECHANICAL MODELING

The bimodal hotspot track connecting the active volcanic center at Yellowstone National Park with the 17-15 Ma flood basalts of the Columbia River large igneous province is composed of a series of predominantly rhyolitic volcanic centers that were the site of numerous “supereruptions” of rhyolite ash flow tuffs that formed clusters of overlapping calderas. The youngest three of these centers, the 10.4-~6.5 Ma Picabo center, the 6.6 to ~4 Ma Heise center, and the 2.1-0 Ma Yellowstone center, were separated by significant spatial and/or temporal gaps in activity. We use high-resolution magmatic thermomechanical finite difference models to investigate the origin of these hiatuses and similar inferred spatial and temporal gaps between older volcanic centers on the hotspot track. These models differ from previous numerical studies of the interaction between a mantle plume and continental crust in that they include the production and transport of magmas in the mantle and the crust. They also include criteria that determine the height to which magmas ascend through the crust based on the buoyant forces driving magma ascent and the strength of the surrounding crustal rocks.

 

We find that the main control on the location of new intrusions into the upper crust are weak shear zones and faults in the crust that accommodate deformation caused by both the buoyant force of the plume on the base of the lithosphere as well as the loading of the crust by large ~10 km thick intrusions of basalt into the lower crust. These faults and shear zones provide pathways for rhyolitic melt to ascend into the upper crust under a new volcanic center where remelting of recently intruded or erupted magmas can occur. The spacing of these faults, which is influenced by the strength, thickness, and speed of the crust over the mantle plume, as well as the vigor of the plume itself, in turn strongly influence the volcanic spacing and the ultimate structure of the entire hotspot track.