The temporal evolution of chemical and physical properties of magmatic systems

Abstract

Exactly 100 years ago the great Canadian-born petrologist N. L. Bowen published two seminal works on the chemical differentiation of magmas in which he posed the basis for a physicochemical understanding of the fractionation of crystals from melts in molten rock. A subsequent century of research and technological advances has enhanced our understanding of the physics and chemistry of magmatic systems and their temporal evolution. The image of sub-volcanic magmatic systems has evolved greatly in that time, from a simple 'boiling vat' concept of molten rock in which bubbles, crystals and melt separate gravitationally to a recognition that magma vats are relatively rare and that most magmatic systems spend much of their lifetime in a partially molten, or mushy, state. Real magmatic systems appear to be organized into a series of storage regions periodically connected by feeding structures transferring magma (and heat) at different fluxes. Magma fluxes between the different portions of this plumbing system, and the variation of the chemical and physical properties of magma as it rises through the crust, exert essential controls on the eruptive modalities of volcanoes and the geochemistry of their products. This book presents a collection of contributions that use petrology, geochemistry, geochronology and numerical modelling to identify the processes operating at different depths within magmatic systems and to characterize the fluxes of magma between them.

Estimates of Volume and Magma Input in Crustal Magmatic Systems from Zircon Geochronology: The Effect of Modeling Assumptions and System Variables

“…As a consequence, magma fluxes also control the time span over which residual melts of various compositions are present (in different relative proportions) within a reservoir. While we will not dwell long on this aspect, such results indicate that the rate of magma input in subvolcanic reservoirs affects the long-term probability of magmas of different compositions to be sampled during volcanic eruptions (Melekhova et al, 2013;Caricchi and Blundy, 2015b). On the other hand, in magmatic systems that are assembled extremely rapidly and cool over time, the probability of magma with a given composition to be present within the magma reservoir is exclusively controlled by the topology of the phase diagram (Marsh, 1981).…”

“…In periodically replenished magmatic reservoirs, the relative volume of magma and residual melt of various compositions change over hundreds of thousands to millions of years as a function of the average rate of magma injection, the thermal properties and chemistry of the wall rocks and the topology of the pertinent phase diagrams for magmas contained within the magmatic system (Spera and Bohrson, 2001;Annen et al, 2006;Glazner, 2007;Solano et al, 2012Solano et al, , 2014Melekhova et al, 2013;Caricchi et al, 2014;Nandedkar et al, 2014;Caricchi and Blundy, 2015a). The rate of magma transfer between the different portions of a magmatic system plays a pivotal role in controlling the physical and chemical evolution of magmas from the mantle to the surface, creating an intrinsic link between temperature evolution, crystallization, and variation of residual melt composition (Crisp, 1984;Annen et al, 2006;White et al, 2006;Glazner, 2007;Stolper and Asimow, 2007;Annen, 2009;Caricchi et al, 2014;Caricchi and Blundy, 2015b). Therefore, determining magma fluxes within the Earth's crust would allow us to establish links between the geochemistry of magmas erupted at the surface and the temporal evolution of the chemical and physical properties of magmatic reservoirs at depth.…”

Effects of chaotic advection on the timescales of cooling and crystallization of magma bodies at mid crustal levels

“…Recent works shed new light on the mechanisms acting during the growth of new magma bodies [ Annen ; Annen et al ., ]. In particular, it is now accepted that large igneous masses in the crust result from the accretion and/or amalgamation of smaller ones [ Lipman ; Annen et al ., ; Caricchi and Blundy , ].…”

“…Although largely studied, several key questions are still open regarding the thermal and chemical fate of these magmatic masses [ Caricchi and Blundy , ]. Among them: (1) what are the dynamics governing the development of these magmatic systems [e.g., Thorpe , ; Tatsumi and Kogiso , ; Zandt et al ., ; Bergantz et al ., ]?…”

“…Understanding the dynamics occurring during the thermochemical evolution of igneous bodies at mid to lower-crustal level is of crucial importance in both petrology and volcanology since the possible behaviors of a magmatic mass strongly depend on the development of thermal and compositional heterogeneities, which, in turn, can influence the way a magmatic mass differentiates and/or erupts [Bachmann and Bergantz, 2008;Cooper and Kent, 2014;Caricchi and Blundy, 2015;Laumonier et al, 2014].…”