Comparative Rhyolite Systems: Inferences From Vent Patterns and Eruptive Episodicities: Eastern California and Laguna del Maule

Abstract

The Pliocene-to-Holocene volcanic field surrounding Laguna del Maule covers 500-km 2 along the Andean crest in central Chile. The Pliocene-to-Holocene volcanic field at Long Valley covers a 1,000-km 2 area that straddles the Sierra Nevada-Basin and Range transition in California. Both fields have recurrently erupted large volumes of rhyolite-Long Valley throughout the Quaternary (since 2.2 Ma) and Laguna del Maule episodically since the Pliocene (3.7-0.04 Ma) and with extraordinary frequency in postglacial time (after 17 ka). Both are currently undergoing impressive geodetic and seismic unrest that has attracted intensive monitoring and scientific investigation. Because of an abundance of postglacial rhyolite eruptions in both areas, including many in the last few thousand years, the likelihood is high that similar activity will recur at both. The present contribution summarizes the rhyolites of the two volcanic fields and compares their respective vent distributions, compositions, volumes, and eruptive episodicities. The Pleistocene rhyolites of the Coso volcanic field, 200 km south of Long Valley, are also discussed as an additional comparator.The paper proceeds with brief overviews of each volcanic field, a background summary of preferred models of silicic magmatism, and then the presentation of the essential features of each of seven rhyolite eruptive sequences. Comparison of the California examples with Laguna del Maule is followed by a discussion of vent distributions and spacing, batch volumes, and eruptive episodicities. Finally, inferences are drawn about transcrustal processes that eventuated in large upper-crustal crystal-rich magma reservoirs and about the episodic extraction and eruption of numerous batches of crystal-poor rhyolitic melt from them. MethodsLaguna del Maule volcanic field was mapped on foot over the course of 10 austral summers (1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000) by the author, accompanied in various years by Estanislao Godoy, Judy Fierstein, Brad Singer, and Bob Drake (Hildreth et al., 2010). Fierstein (2017, 2018 subsequently led a team that documented the copious and complex tephra deposits around the volcanic field and far downwind in Argentina; and Singer concurrently spearheaded a team that investigated the field geochemically and geophysically.

Multi-scale, open-system magmatic and sub-solidus processes contribute to the chemical and isotopic characteristics of the Jurassic Guadalupe Igneous Complex, Sierra Nevada, California, USA

“…Sustained elevated temperatures supplied by basaltic, mantle-derived melts to the lower crust support the formation of lower-crustal MASH zones (i.e., zones of intensive melting, assimilation, storage, and homogenization: Hildreth and Moorbath, 1988; or deep crustal hot zones: Annen et al, 2006) as primary magma storage and differentiation sites in arcs. However, recent geophysical, petrological, and numerical modeling studies indicate that magma storage and differentiation can occur throughout the arc crust (e.g., Cashman et al, 2017;Delph et al, 2021;Barnes et al, 2021;Hildreth, 2021). Considerable debate still exists as to the extent to which differentiation processes may operate in the shallow crust (e.g., Bachmann and Huber, 2016).…”

Geochemistry, Magmatic Processes and Timescales of Recent Rhyolitic Eruptives of the Ōkataina Volcanic Centre, Taupō Volcanic Zone, Aotearoa/New Zealand

“…These eruptives have highly variable geochemical and isotopic characteristics resulting from a range of petrogenetic processes (e.g. Hervig and Dunbar 1992;Simon et al 2014;Wolff et al 2020;Hildreth 2021).…”