Replenishment and crystallization in epicontinental silicic magma chambers: evidence from the Bandelier magmatic system
The Cerro Toledo Rhyolite (Jemez volcanic field, New Mexico) records the volcanism that occurred after the eruption of the Lower Bandelier Tuff ignimbrite, which formed Toledo caldera at 1.51 +/- 0.03 Ma. Pumice samples from the top of this ignimbrite and from the base of the Cerro Toledo Rhyolite tephra sequence are stratigraphically and geochemically distinct from younger Cerro Toledo Rhyolite tephras that overlie this basal suite. All samples exhibit decreasing La/Lu with increasing Lu concentrations. For a given Lu content, however, the Lower Bandelier Tuff and basal member Cerro Toledo Rhyolites have higher La/Lu compared to overlying Cerro Toledo Rhyolites. This difference can be explained either by (1) differentiation of a single batch of magma in which trace mineral solubilities increased with time due to higher volatile contents, or (2) replenishment of the magma chamber by an input of silicic magma after caldera collapse at 1.51 Ma. Large-scale replenishment of epicontinental silicic magma chambers may be restricted to timescales of 10 5 years.
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