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

We present a high‐resolution numerical model of the thermal evolution of the crustal column beneath Long Valley caldera, California, from which >800 km3 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 dept...

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Bibliographic Details
Published in:Journal of geophysical research. Solid earth 2020-03, Vol.125 (3), p.n/a
Main Authors: Calogero, M. A., Hetland, E. A., Lange, R. A.
Format: Article
Language:English
Subjects:
Advection
Basalt
Calderas
crustal evolution
Crystallization
Dikes
Embankments
Fractures
Geophysics
high‐resolution
Lithology
Magma
magma emplacement
Mathematical models
Melting
Numerical models
partial melting
Resolution
Rhyolite
Rhyolites
Rocks
Sills
Thermal evolution
thermal modeling
Time
Variable thickness
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Summary:We present a high‐resolution numerical model of the thermal evolution of the crustal column beneath Long Valley caldera, California, from which >800 km3 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 ( 106 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 (101–102 years) that match those of exsolution of H2O‐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. Key Points A new high‐resolution numerical thermal model is presented, operating over broad spatial (≥1 m to ≥10 km) and temporal scales (106 years) The time scale over which H2O‐rich fluid exsolves from a crystallizing basaltic sill matches that for transient heating of adjacent wall rock Once ambient crust is ~600 °C, large melt fractions in wall rock (granitoid and mafic sills) adjacent to new basaltic sills may form and advect
ISSN:2169-9313
2169-9356
DOI:10.1029/2018JB016773