What plutons tell us about the evolution of large silicic magma systems?
Monday, 8 January 2018
Salon Maule (Hotel Quinamavida)
Michel de De Saint Blanquat1, Catherine Annen2, Lukas P Baumgartner3, Mathieu Benoit1, Jon D Blundy4, Guillaume Delpech5, Sophie Demouy1, Damien Guillaume6, Michel Gregoire1, Francisco Herve7, Eric M Horsman8, Richard Derek Law9, Thierry Menand10, Sven S Morgan11, Othmar Müntener3, Jean-Louis Paquette6, Léandre Ponthus1, Benita Putlitz3, Alejandro Sanchez12, Anne Schöpa13, Basil Tikoff14 and Olivier Vanderhaeghe1, (1)CNRS, GET Toulouse, CNRS, IRD, CNRS, University of Toulouse, Toulouse, France, (2)University of Bristol, Bristol, United Kingdom, (3)University of Lausanne, Lausanne, Switzerland, (4)University of Bristol, School of Earth Sciences, Bristol, United Kingdom, (5)University of Paris-Sud 11, Orsay, France, (6)Laboratoire Magmas et Volcans, Clermont-Ferrand Cedex, France, (7)Andrés Bello University, Santiago, Chile, (8)East Carolina University, Greenville, NC, United States, (9)Virginia Tech, Blacksburg, VA, United States, (10)University Blaise Pascal Clermont-Ferrand II, Clermont-Ferrand, France, (11)Central Michigan Univ, Mount Pleasant, MI, United States, (12)University of Chile, Santioago, Chile, (13)Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany, (14)University of Wisconsin Madison, Geoscience, Madison, WI, United States
Abstract:
Intrusive rocks mainly occur as mappable bodies of various shapes and volumes called plutons. Recent studies showed that plutons form by localized injections of discrete magma pulses over variable periods of time, and that behind the concept of plutons is the observation of focused emplacement of magma in space and time, i.e. the existence of a “close in space - close in time” relationship. Furthermore, structural, textural and geochronological evidence do not support the concept of plutons as being fossil magma chambers, and chemical evidence indicate that plutons are not the restites or cumulates of magmas either. Thus, why and how plutons form is of primordial importance and central to our understanding of the evolution of large silicic magma system.
The first question we need to address is then "Why plutons?" or "Why and how magma is accumulated at a given locality during variable periods of time (thousands to millions of years) to form plutons?" The controlling processes can either be source-related, transport-related, emplacement-related, or a combination of these. We will examine this question by investigating the respective role of these three successive stages with the help of a quantitative evaluation of the different magma fluxes involved in magma transfer from deep hot zones to the surface.
The second question concerns the relationship between the intrusive and the effusive records: "Are plutons volcanic leftovers ? In other words, "Do we know how to structurally recognize a fossil magma chamber?" and "What is the plutonic record of an (super)eruption?" In fact, we do not know any pluton showing in its internal structures evidences for periodic infilling and emptying cycles, and deflated plutons have never been identified to date. Is it because we do not know how to recognize them? Is it because a pluton has to necessarily accumulate magma, even if it is connected to a volcanic system? Or, alternatively, is it because they do not really exist? We will present a structural review of the construction of plutons in various geodynamic (continental and oceanic, divergent and convergent) and magmatic systems (arc, collisional, intracontinental, intraoceanic), and discuss the consequences with regard to the relationships between plutonism and volcanism, which are critical for large silicic magma systems.
