Catastrophic gravity sliding during growth of the Cenozoic Marysvale volcanic field, southwest Utah, USA

The Cenozoic Marysvale volcanic field (MVF) contains at least three documented mega-scale gravity slides resulting from the southward collapse of the field. Slide masses form an overlapping contiguous complex covering an area >8000 km², with the largest slide (Markagunt gravity slide) being >3000 km². New age constraints show sliding events progressed from oldest on the east and youngest on the west (Sevier gravity slide ca. 25 Ma, Markagunt gravity slide ca. 23 Ma, and Black Mountains gravity slide ca. 21.5 Ma) as continuous growth of the MVF between 30 Ma and 21 Ma was punctuated intermittently by rapid inflation of batholithic intrusions to produce the necessary unstable slopes for volcanic field collapses. Catastrophic emplacement of each slide is indicated by features such as basal layers of sandstone-conglomerate-like material, injectites (clastic dikes) of the same material, highly brecciated and cataclastically deformed rocks, pseudotachylytes (friction induced melt), and a variety of stratigraphic and structural relationships. On this field trip, we will visit sites accessible by car and with minimal hiking within the three gravity slides with distinctive deformation features related to their scale, emplacement age, mechanism(s), and origin.