Mechanical fragmentation and thermal erosion of dyke adjacent host rocks induced by fluid-dynamic shear stress and latent heat release in response to turbulent magma flow

Abstract

We present a quantitative account of the thermodynamical and fluid-mechanical aspects of granitic host rock erosion related to dyke emplacement by considering the latent heat released from the dyke, subsequent thermal damage, and erosion processes. When these processes are coupled with the fluid-dynamic shear forces induced by magma turbulence, they provide the main driving force for mechanical fragmentation and xenolith entrainment. To make these inferences, we have estimated the Reynolds Number related to magma flow in a series of well-exposed dykes in Eastern India. We define the thresholds of turbulent to laminar flow based on Reynolds Numbers, where values over 2000 indicate that the magma had flowed turbulently. In these cases, both thermal erosion and fluid-dynamic shear stresses would have combined to fragment the adjacent host rock. Equations for the conservation of mass are derived and presented in order to quantify the complex interactions between magma and cold host rock. We further propose a novel linear integro-differential equation to determine xenolith size resulting from internal collisions and secondary fragmentation. Our model and results will be helpful in interpreting magma flow characteristics, magmatic evolution, and host rock entrainment processes in exposed outcrops of magmatic intrusions.