Abstract
The petrologic diversity of volcanic rocks reflects the dynamics of magma reservoirs and the temporal evolution of magma chemistry can provide valuable information for hazard assessment. While some stratovolcanoes monotonously produce intermediate magmas (55–68 wt% SiO2), dominantly erupted magma types (e.g., basaltic andesite, andesite or dacite) frequently differ even between neighboring volcanoes. If such differences arise due to thermal maturation processes over time or are predetermined by other properties of magmatic systems remains poorly understood. This study helps to elucidate the underlying factors modulating the chemistry of the magma preferentially erupted by Nevado de Toluca volcano in Central Mexico. We present a new dataset of bulk-rock and mineral chemistry spanning the entire 1.5 Million years of the volcanos’ eruptive history. The results reveal that Nevado de Toluca dacites and minor andesite originate in a stable configuration of pre-eruptive processes and plumbing system architecture by hybridization between an upper crustal silicic mush and deeper sourced basaltic andesite magmas. Yet, a subtle trend toward increasing silica content with time (2 wt% in 1.5 Ma) and episodicity in magma hybridization conditions are observed. We use thermal simulations of pulsed magma injection to probe the controlling variables on the temporal variation and compositional mode of magma geochemistry. The results show that the subtle temporal trend toward increasing bulk-rock SiO2 content is plausibly explained by slightly dropping recharge rates and continued upper crustal reservoir growth. Our modeling also shows that the dominant composition of eruptible magmas (“petrologic mode”) can shift as a function of magma flux, extrusive:intrusive ratio and temperature of the recharge magma. A comparison of SiO2 whole rock distributions for monotonous Mexican stratovolcanoes and their peripheral cones shows that their petrologic modes vary in concert, indicating that the recharge magma chemistry or temperature is a major control on the preferentially erupted magma composition for these volcanoes.
Highlights
IntroductionOver the last 30 years, combined geological mapping, dating and geochemical analyses have revealed that the range of erupted magma chemistry differs significantly for individual volcanic centers (Hildreth and Lanphere, 1994; Singer et al, 1997; Gertisser and Keller, 2003; Frey et al, 2004; Thouret et al, 2005; Bacon and Lanphere, 2006; Hildreth, 2007; Hora et al, 2007; Singer et al, 2008; Fierstein et al, 2011; Jicha et al, 2012; Walker et al, 2013; Muir et al, 2015; Rivera et al, 2017)
We present and analyze a combined dataset of 97 bulk rock major and trace element analysis for the long-term eruptive history of Nevado de Toluca volcano
The most mafic erupted bulk compositions with SiO2 contents around 55 wt% are observed in monogenetic cones, extending into the basaltic andesite field, in agreement with previous work on peripheral cones surrounding Nevado de Toluca (Martínez-Serrano et al, 2004; Torres-Orozco et al, 2017)
Summary
Over the last 30 years, combined geological mapping, dating and geochemical analyses have revealed that the range of erupted magma chemistry differs significantly for individual volcanic centers (Hildreth and Lanphere, 1994; Singer et al, 1997; Gertisser and Keller, 2003; Frey et al, 2004; Thouret et al, 2005; Bacon and Lanphere, 2006; Hildreth, 2007; Hora et al, 2007; Singer et al, 2008; Fierstein et al, 2011; Jicha et al, 2012; Walker et al, 2013; Muir et al, 2015; Rivera et al, 2017). The high viscosities of silica-rich magmas and the high densities of basaltic melts may act as physical barriers, preventing magma transport and inhibit volcanic eruptions of such compositions (Stolper and Walker, 1980; Marsh, 1981; Pinel and Jaupart, 2000; Moran et al, 2011) If such barriers are effective in preventing the eruption of very mafic and silicic magma compositions, they may be overcome by mixing/mingling processes induced by mafic magma recharge in crustal mush reservoirs and produce compositionally monotonous intermediate volcanoes (Reubi and Blundy, 2009; Kent et al, 2010; Kent, 2014). Magma properties such as the initial water content or nonlinearities in melt fraction-temperature relations can modulate the variety of compositions present in a magmatic system (Melekhova et al, 2013; Nandedkar et al, 2014; Caricchi and Blundy, 2015b; Hartung et al, 2019; Huber et al, 2019)
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