Thermomechanical Modeling of the Formation of a Multilevel, Crustal‐Scale Magmatic System by the Yellowstone Plume

Abstract

Geophysical imaging of the Yellowstone supervolcano shows a broad zone of partial melt interrupted by an amagmatic gap at depths of 15-20 km. We reproduce this structure through a series of regional-scale magmatic-thermomechanical forward models which assume that magmatic dikes stall at rheologic discontinuities in the crust. We find that basaltic magmas accumulate at the Moho and at the brittle-ductile transition, which naturally forms at depths of 5-10 km. This leads to the development of a 10-to 15-km thick midcrustal sill complex with a top at a depth of approximately 10 km, consistent with geophysical observations of the pre-Yellowstone hot spot track. We show a linear relationship between melting rates in the mantle and rhyolite eruption rates along the hot spot track. Finally, melt production rates from our models suggest that the Yellowstone plume is~175°C hotter than the surrounding mantle and that the thickness of the overlying lithosphere is~80 km. Plain Language SummaryWe present a series of supercomputer models which we use to investigate the origins of the two-level magmatic system revealed by recent geophysical observations of the Yellowstone supervolcano. We show that the distribution of melt which matches these observations arises when we assume that rising magmas preferentially accumulate at depths where there are strong contrasts in the ratio of melt overpressure to the effective viscosity of the surrounding crust. Melt accumulates at the major rock strength discontinuities which occur at the base of the crust and at the brittle-ductile transition which forms above the developing magmatic system at approximately 10-km depth. This second boundary captures the considerable majority of the melt and produces a basaltic sill complex which resides between depths of 10 and 25 km and which provides heat which melts the surrounding crust. This sill complex cools and solidifies and separates the partially molten crust above and below it into the two magmatic systems seen in the geophysical images. Finally, we are able to constrain the temperature of the Yellowstone mantle plume to be 175°C hotter than the surrounding mantle and the thickness of the overlying lithosphere to be approximately 80 km. Model SetupWe performed several dozen 2-D numerical experiments exploring a broad parameter space using a 1,000 × 300-km finite difference grid with a resolution of 2 km, with 16 or more Lagrangian markers per cell, a time step of 5 kyr, and a total duration of 7-8 Myr. We are interested in the behavior of the crustal magmatic system which develops over a relatively stable mantle plume tail, rather than over the plume head which is COLÓN ET AL. 3873

High‐Resolution Numerical Modeling of Heat and Volatile Transfer from Basalt to Wall Rock: Application to the Crustal Column beneath Long Valley Caldera, CA

“…Among the parameters explored in this study, three exert the strongest control: (1) random versus fixed emplacement of sills, (2) the initial depth range of sill emplacement, and (3) the time interval over which a thickness of basalt is emplaced. These results are broadly consistent with previous work in the literature (e.g., Annen et al, ; Colón et al, ; Dufek & Bergantz, ; Karakas & Dufek, ; Leeman et al, ). An important factor additionally explored in this study is the development of a mixed crustal lithology as the crust is gradually heated through the periodic and random emplacement of basaltic sills.…”

“…Several previous studies have addressed the origin of silicic melts by modeling the thermal evolution of the crust as a function of basalt influx (e.g., Shaw, 1980;Huppert & Sparks, 1988;Petford & Gallagher, 2001;Jackson et al, 2003;Dufek & Bergantz, 2005;Annen et al, 2006;Leeman et al, 2008;Karakas & Dufek, 2015;Colón et al, 2018). These studies examined how different rates of basalt emplacement heat the crust, leading to the onset of crustal melting, and over what spatial and temporal scales this process might occur.…”

Isotopic and Petrologic Investigation, and a Thermomechanical Model of Genesis of Large-Volume Rhyolites in Arc Environments: Karymshina Volcanic Complex, Kamchatka, Russia

“…DeCelles et al (2009) argue against this latter model, pointing out that magmas associated with flareups tend to have lower ε Nd values, indicating that crustal melting was disproportionately responsible for producing the silicic intrusions relative to the differentiation of a greater volume of mantle-derived basalts. However, Colón et al (2018a) pointed out that greater magmatic fluxes from the mantle actually serve to increase the proportion of crustal melt in the resulting rhyolites, as the greater heat allows more crust to melt at a slightly faster rate than it allows for more basalts to be differentiated to rhyolite, a result which we replicate here.…”

“…Unlike in the Colón et al (2018a) model, the lithosphere is fixed relative to the ascending plume, and the plume is much cooler and weaker than in the Yellowstone model, to more accurately reproduce a typical subduction flux for the arc (e.g., Jicha and Jagoutz, 2015). The plume advects from the base of the model at a rate of ∼3,700 km 2 /Myr, as in Colón et al (2018a), but has a much lower potential temperature of 1,475 • C (compared to a background value of 1,350 • C) to produce the desired amount of mantle melting. We also begin the model with only a 50 km thick lithosphere (compared to 80 km for the Yellowstone study).…”

“…To further investigate the origins of the huge volumes of magma produced in a relatively short time at Karymshina, we used a slight modification of the 2D model used for the Yellowstone hotspot in Colón et al (2018a), which is in turn a modification of the original large scale thermomechanical code developed by Gerya and Yuen (2003). The model setup that we use for Kamchatka, where the crust is 30-38 km thick (Figures 1, 2) is identical to what is described in the Colón et al (2018a) study, with a few key exceptions.…”