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High‐Resolution Numerical Modeling of Heat and Volatile Transfer from Basalt to Wall Rock: Application to the Crustal Column beneath Long Valley Caldera, CA
Author(s) -
Calogero M. A.,
Hetland E. A.,
Lange R. A.
Publication year - 2020
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2018jb016773
Subject(s) - sill , geology , basalt , partial melting , mafic , caldera , geochemistry , crust , dike , petrology , igneous rock , flood basalt , magma , geomorphology , volcano , volcanism , tectonics , seismology
We present a high‐resolution numerical model of the thermal evolution of the crustal column beneath Long Valley caldera, California, from which >800 km 3 rhyolite erupted over the last 2.2 Myr. We examine how randomly emplaced basaltic sills of variable thickness (10, 50, or 100 m) at various depth intervals (10–25 km) and at variable emplacement rates (5–50 m/kyr) gradually heat the crust and lead to a variably mixed crustal lithology (solidified mafic sills and preexisting granitoid). We additionally explore the time scales over which dissolved water (~3 wt%) in a newly emplaced basaltic sill exsolves during crystallization and is transferred to adjacent wall rock that is undergoing partial melting. We employ a finite‐difference‐based technique, with variable spatial (≥1 m to ≥10 km) and temporal (<100 and > 10 6 years) resolution, that enables dense analysis within and directly adjacent to a newly emplaced sill. Our results show that once ambient crustal temperatures reach ~500–600 °C, subsequent injections of basaltic sills lead to significant partial melting of adjacent wall rock (granitoid and solidified mafic sills) on time scales (10 1 –10 2 years) that match those of exsolution of H 2 O‐rich fluid from basaltic sills. Large volumes of fusion (>10%) during fluid‐undersaturated partial melting, combined with the preexisting occurrence of aplite dikes, facilitates the development of melt‐filled fractures that exceed the critical length for self‐propagation. The advection of wall‐rock partial melts (with a combined mantle‐derived and crustal geochemical signature) to shallower depths will alter both the thermal and compositional profile of the middle‐upper crust.