Natural equivalents of thermal gradient experiments

Abstract

Crystallization experiments using the intrinsic thermal gradient in 10mm length capsules loaded in piston-cylinder assemblies were used to investigate silicic magma crystallization. The application of experimental results to natural environments requires the scaling of physical parameters of petrological interest. Therefore, we propose here a comparative study between thermal gradients and numerical simulations of natural magma chambers. We use the Finite Element method to calculate thermal profiles across a cooling silicic magma chamber. These numerical profiles are compared with the intrinsic thermal structure of half-inch, piston-cylinder assemblies at 500MPa. It is concluded that a set of varied magma chamber geometries and/or distinct stages of their cooling history can approach the intrinsic thermal structure of laboratory experiments. Once the thermal properties for magma and its host rock are fixed, the experimental–numerical approach is mostly dependent on the volume and aspect ratio of the magma chamber. Our results indicate, for instance, that a 10mm length capsule with a thermal gradient of 40°C/mm (from 1100 to 700°C) may represent a 150–1100m wide portion of a cooling magma chamber of 10–20km diameter and 2–10km height, emplaced at a depth of 18km. Additional possible scenarios are represented by larger magma chambers, up to 30km diameter, in which the experimental thermal gradient can represent a 150–3700m-thin-section of the large igneous bodies.