Magma Chamber Formation by Dike Accretion and Crustal Melting: 2D Thermo‐Compositional Model With Emphasis on Eruptions and Implication for Zircon Records

Abstract

We present a 2D thermo‐elastic model of a magma body formation in a granitic crust by injection of rhyolitic or basaltic dikes and sills. Elastic analytical solutions enable the computation of rock displacement in response to magma intrusion and evacuation during volcanic eruptions. Phase diagrams for magma and rocks govern melting/crystallization behavior and temperature evolution in 16 million computational cells. Calculated temperature histories are used to predict zircon crystallization/dissolution, their ages, and isotopic ratios within individual batches of magma and rocks. Incremental dike injection naturally generates magma batches of melt that form kilometer‐wide clusters appearing in different parts of the domain with diverse shapes, horizontal and vertical interconnectivity. The volume of eruptive melt strongly depends on magma influx rates Q, the width of the injection region W, and eruptions. For example, rhyolitic dike injection with Q = 0.125 m3/s with W = 5 km during 100 ka generates ∼50 km3 of eruptive melt while no significant melt forms if W = 10 km. Injection of basaltic dikes into the granitic crust generates comparable amounts of rhyolitic melt from dike‐residual and country rocks. High injection intensities produce magma reservoirs capable of large eruptions, while repetitive eruptions lead to shrinkage of magma bodies. High heat input causes host rock zircons to lose a significant portion of their old cores. Magmatic zircons in the periphery form quickly due to rapid cooling of intruded dikes while in the central part crystals can grow during several hundreds of ka. The model predicts highly heterogeneous O and Hf isotopic ratios recorded in zircons.

Comparison of Continuously Recorded Seismic Wavefields in Tectonic and Volcanic Environments Based on the Network Covariance Matrix

“…Such resonant sources would also generate narrow‐band signals and may explain the observed spectral lines. More specifically, parts of the volcanic interior where the magma is stored are believed to be formed by multiple injections of dykes and sills (e.g., Annen et al., 2005; Jaxybulatov et al., 2014; Melnik et al., 2021) which results in very heterogeneous structures and presence of many melted‐magma‐filled layers or pockets concentrated in relatively small volumes. Such fluid‐filled structures can act as “resonators” and generate signals with observed spectral peaks.…”

“…Our second hypothesis is that the broadening of the location spot of the volcanic tremor is due to the de‐focusing caused by strong scattering within the very heterogeneous parts of sub‐volcanic media. In particular, the vicinity of the plumbing systems might be strongly heterogeneous in terms of its elastic properties because of the irregular distribution of pockets of partially molten magma (e.g., Melnik et al., 2021). In general, the source of tremors is also believed to be located within the plumbing system (Chouet, 1996).…”