Calderas of the Marysvale Volcanic Field, west central Utah

摘要: Five calderas (Three Creeks, Big John, Monroe Peak, Mount Belknap, and Red Hills) have been identified a sixth (Lion Flat) tentatively in the middle Tertiary Marysvale volcanic field of western Utah. The are manifestations separate magma bodies that worked their way to shallow depths between 27 19 Ma. No coherent ash flow exists field; instead, units interleaved at different places general sequence. chambers vented flows collapsed as formed discrete high-level plutons; they probably underlain by deep composite batholith consisting many individual plutons from two distinct petrogenetic types, calc-alkalic bimodal (mafic-silicic). four largest can be separated into groups contrasting structural behavior. Three Creeks John broad faulted downwarps sagged relatively whose roofs were sufficiently strong inhibit development ring faults. In contrast, Peak Belknap subcircular with thin roofs, so easily breached large volumes lava erupted within calderas. Neither type shows postcollapse resurgence; above deeper too uplifted, those weak contain magmatic pressures.