Rhyolites of the Mono-Inyo Chain
Rhyolites of the Mono-Inyo Chain
Holocene to late Pleistocene
A series of rhyolitic vents aligned approximately south from Panum Crater, just south of Mono Lake, to Deadman Creek lava flow just within the northwestern topographic boundary of Long Valley caldera. Composed of a series of >35 lava domes, coulees, explosion craters, and ejecta rings, with a variably extensive apron of pyroclastic flow and fall deposits, some reworked (apron mostly included in unit v-y; Hildreth, 2004). Lavas are predominantly sparsely porphyritic high-silica (~75-77% SiO2) rhyolite, lesser sparsely porphyritic lower-silica (~70-74% SiO2) rhyolite and uncommon coarsely porphyritic rhyodacite (e.g., Hildreth, 2004). Lava volume is ~4 km3 (Hildreth, 2004), but total erupted volume is greater and includes some additional volume of pyroclastic material, an unknown proportion of which may be buried, eroded, or deposited away from the chain.
Predominantly Holocene in age, with relatively few units as old as ~20 ka, and earliest eruption at ~42 ka (based on dating of domes), or possibly as early as 60-70 ka (based on dating of nearby tephra layers; Marcaida and others, 2019, and references therein). Several lava flows and pyroclastic flows and fall (some subplinian) were released most recently during a ~1345 CE episode on Mono Craters (Sieh and Bursik, 1986), and a ~1350 CE episode on Inyo Chain (Millar and others, 2006; Hildreth, 2004; Hildreth and Fierstein, 2016).
Included in unit v-y are Black Point on the north side of Mono Lake, volcanic rocks exposed as islands in the lake, and the Red Cones southwest of Mammoth Mountain, which Bailey (2004) includes in the Mono-Inyo chain. Bailey included Red Cones based on age, chemistry, and isotopic data. However, Hildreth (2004) notes that the northern rocks are compositionally distinct from the Mono Craters magmas.