The volcanic/plutonic ratio in space and time, on Earth and beyond; How efficiently do magmas reach the surface during planetary evolution?

Abstract

With the recognition of multiple crustal cross sections on our planet, the advent of high-precision geochronology, and the ever-increasing application of geophysical imaging beneath volcanoes, we now know that volcanic rocks are the tip of a magmatic “heat”berg, overlying a significant igneous plumbing system that leaves many types of plutonic rocks in the crust. The ratio of volcanic to plutonic rocks in a given magmatic province (the V/P ratio) varies in space and in time as a function of several parameters controlled by the tectonic setting, geological age of the magmatic province, duration of magmatic activity, rheology of the crust, physical properties of the magma and state of the magma reservoirs. This contribution intends to explore these different parameters, in order to better constrain how the V/P ratios evolve in space and time in the course of planetary crust evolution. In particular, we stress that the efficiency of phase separation (in particular crystal / melt separation) in crustal magma reservoirs, fundamental to igneous differentiation and crust formation, is a key factor in controlling the V/P ratios. This efficiency, in turns, depends on parameters such as magma fluxes (“mantle productivity”) and chemical compositions (including volatile content), as well as the mechanical properties of the multi-phase magma and of its the crustal container. The emergence of thermo-mechanical modeling tools coupling the magma reservoir with its surrounding wall-rocks is paving the way to a more quantitative understanding of the fundamental processes that control the fate of magmas traversing through planetary crusts.