Abstract
The Soldier Meadow Tuff (SMT) consists mostly of a voluminous sheet of distinctive phenocryst-rich comendite ash-flow tuff distributed around the eastern to southern margin of the High Rock caldera (HRC), source of the 16.3 Ma Summit Lake Tuff. The SMT is a lithologically complex single cooling unit composed of several repetitions of planar and cross-bedded surges, lag-breccias, and massive lithofacies. Stratigraphic repetition of these deposits suggests the SMT erupted in several, closely-spaced pulses, each of which developed eruption columns and column collapses. The HRC is the likely source of the SMT, which erupted approximately 16.1 Ma. The ash-flow sheet of the SMT thins away from ring fracture vents, and pumice imbrications and surge deposits indicate southeast flow away from the HRC. Eruption of the SMT may have caused additional caldera collapse as indicated by aeromagnetic lows in the southeastern part of the HRC. Collinear trends of major element-oxides, trace elements, and rare earth elements genetically link Summit Lake Tuff, Soldier Meadow Tuff, Soldier Meadow lavas, and post-Soldier Meadow pyroclastic and lava units to a common magmatic source, likely a continental tholeitte. The magma evolved through typical crystal fractionation processes.