Timescales of mingling in shallow magmatic reservoirs
Published:January 01, 2015
C. P. Montagna, P. Papale, A. Longo, 2015. "Timescales of mingling in shallow magmatic reservoirs", Chemical, Physical and Temporal Evolution of Magmatic Systems, L. Caricchi, J. D. Blundy
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Arrival of magma from depth into shallow reservoirs has been documented as one of the possible processes leading to eruption. Magma intruding and rising to the surface interacts with the already emplaced, degassed magmas residing at shallower depths, leaving chemical signatures in the erupted products. We performed two-dimensional numerical simulations of the arrival of gas-rich magmas into shallow reservoirs. We solve the fluid dynamics for the two interacting magmas, evaluating the space–time evolution of the physical properties of the mixture.
Convection and mingling develop quickly into the chamber and feeding conduit/dyke, leading on longer timescales to a density stratification with the lighter, gas-richer magma, mixed with different proportions of the resident magma, rising to the top of the chamber due to buoyancy. Over timescales of hours, the magmas in the reservoir appear to have mingled throughout, and convective patterns become harder to identify.
Our simulations have been performed changing the geometry of the shallow reservoir and the gas content of the initial end-member magmas. Horizontally elongated magma chambers, as well as higher density contrasts between the two magmas, cause faster ascent velocities and also increase the mixing efficiency.
Videos showing the evolution of magma composition with time in the shallow chamber for simulations 1–4 are available at www.geolsoc.org.uk/SUP18819
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Chemical, Physical and Temporal Evolution of Magmatic Systems
Our understanding of the physical and chemical processes that regulate the evolution of magmatic systems has improved tremendously since the foundations were laid down 100 years ago by Bowen. The concept of crustal magma chambers has progressively evolved from molten-rock vats to thermally, chemically and physically heterogeneous reservoirs that are kept active by the periodic injection of magma. This new model, while more complex, provides a better framework to interpret volcanic activity and decipher the information contained in intrusive and extrusive rocks.
Igneous/metamorphic petrology, geochemistry, geochronology and numerical modelling all contributed towards this new picture of crustal magmatic systems. This book provides an overview of the wide range of approaches that can nowadays be used to understand the chemical, physical and temporal evolution of magmatic and volcanic systems.
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