Mammoth Mountain volcanic rocks
Mammoth Mountain volcanic rocks
late Pleistocene
Consists of a cluster of mostly silicic domes and flows that constructed the volcanic edifice of Mammoth Mountain and are centered on the southwestern topographic boundary of Long Valley caldera. This dome and flow cluster is composed predominantly of mildly alkaline porphyritic trachydacite, lesser phenocryst-poor alkalic rhyodacite, and one set of alkalic rhyodacite, pumice-lapilli, pyroclastic fall deposits (Hildreth, 2004; Hildreth and Fierstein, 2016). The oldest dated unit is 99 ± 7 ka and the youngest is 50 ± 3 ka (both Ar-Ar), although older extrusive units may be buried and undated (Hildreth and Fierstein, 2016).
These rocks represent a focus of silicic magmatism, which is surrounded by a field of genetically related mafic to intermediate composition monogenetic vents distributed within 5-9 km of Mammoth Mountain that is included within unit v-y (e.g., Hildreth and Fierstein, 2016).