Magma diversity reflects recharge regime and thermal structure of the crust

Abstract

The chemistry of magmas erupted by volcanoes is a message from deep within the Earth's crust, which if decrypted, can provide essential information on magmatic processes occurring at inaccessible depths. While some volcanoes are prone to erupt magmas of a wide compositional variety, others sample rather monotonous chemistries through time. Whether such differences are a consequence of physical filtering or reflect intrinsic properties of different magmatic systems remains unclear. Here we show, using thermal and petrological modelling, that magma flux and the thermal structure of the crust modulate diversity and temporal evolution of magma chemistry in mid to deep crustal reservoirs. Our analysis shows that constant rates of magma input leads to eruptible magma compositions that tend to evolve from felsic to more mafic in time. Low magma injection rates into hot or deep crust produces less chemical variability of eruptible magma compared to the injection of large batches in colder or shallower crust. Our calculations predict a correlation between magma fluxes and compositional diversity that resembles trends observed in volcanic deposits. Our approach allows retrieval of quantitative information about magma input and the thermal architecture of magmatic systems from the chemical diversity and temporal evolution of volcanic products.

Geochemical variability as an indicator for large volume eruptions in volcanic arcs

“…Caldera-forming eruptions require the accumulation of large magma volumes, suggesting that the conditions favouring this also result in wide ranges of erupted bulk-rock compositions (Fig S4,Data Repository). Due to the coupling between melt temperature and chemistry (e.g., Sisson et al 2005;Ulmer et al, 2018), we suggest that geochemical variability is related to thermal heterogeneity in spatially extensive magmatic plumbing systems (Weber et al, 2020a).…”

“…3). Such close spatial association of compositionally monotonous and highly variable volcanic systems emphasises the important role of local differences in crustal magma fluxes (Kent, 2013;Wörner et al 2017;Till et al, 2019;Weber et al, 2020a).…”

“…At present, available geophysical imaging studies have not identified a particular volcano with large, interconnected melt volumes in the shallow crust, capable of producing a massive caldera-forming eruption. Although crustal magma bodies have accumulation histories that span hundreds of thousands to millions of years (Cooper, 2019;Frey et al, 2018;Weber et al, 2020a;Liu et al, 2021), diffusion studies indicate that the final melt mobilisation process may operate over timescales of years to centuries for large and smaller eruptions alike (Costa et al, 2020;Cooper et al, 2017;Druitt et al, 2012). This disparity between accumulation and mobilisation timescales may impede the long-term identification of candidate volcanoes by geophysical means.…”

“…To anticipate volcanoes that could produce large eruptions in the future Newhall et al (2018) developed and applied six criteria, including high rates of magma supply from the lower to upper crust. Such rates of magma transfer are inherently difficult to assess but recent progress in thermochemical modelling of magmatic systems indicates that the chemical diversity of volcanic rocks provides a record of crustal magma fluxes (Weber et al 2020a). Here we further explore this hypothesis, starting from a data perspective and show that larger volcanic systems produce a greater variety of erupted bulk-rock compositions.…”

Determining the current size and state of subvolcanic magma reservoirs

“…The rationale behind these approaches is to integrate geological, geochemical, and/or geophysical records with the results of thermal modeling to identify fundamental parameters controlling the temporal evolution of magmatic systems [24][25][26][27][28][29][30] . The comparison between models highlights that the thermal evolution of plumbing systems, and the volumes of eruptible magma they contain, depends strongly on the average rate of magma input and on the thermal state of the crust 3,[31][32][33][34] . Variations of the modality of magma injection and of the geometry of the magmatic system, or magma convection play a minor role 3,24,33 .…”