Influence of faulting on magma propagation during volcano-tectonic events (Iceland) using structural data and analogue modelling.

Abstract:

Volcano-tectonic events are found in various geological settings, included extensional environments. Understanding how magma propagates in the crust and eventually where it will erupt is one of the key challenges in volcanology research.

Classical models of magma propagation assume Earth’s upper crust as homogeneous and fully elastic and they do not account for pre-fractured medium. However, in volcano-tectonically active systems, inherited structures exist and may not be optimally oriented with the current stress field.

This study analyses the role of pre-existing crustal structure and their reactivation on the propagation of magma in extensional environments.

Iceland counts several recent rifting episodes in its volcanic systems, which involve reactivation of pre-existing structures. Literature on the Icelandic rifting events and their return periods suggest a cyclic nature of strain deficit loading and subsequent release. These cycles at divergent plates boundaries are expressed as a steady ~2cm/yr average extension rate in the far-field and as discrete, stepwise opening in the near-field.

Based on the strain deficit concept, we mapped representative structures in the North Volcanic Zone with a fixed-wing UAV.

The processing of the drone images resulted in a DEM (2-3 cm/px) and an orthomosaic (1-2 cm/px) of the fieldwork area. On this imagery, we performed a detailed morphological and structural analysis, looking at the shape of the overall graben structures and the effect of the topography on the faulting processes. Results show two sets of orientations: a main one, striking N-S, and a younger set oriented NE-SW, (which fits better with current geodetic data) highlighting oblique interactions. We will further look at fractures and potential kinematic indicators to reconstruct the paleostress history of this area of the plate boundary.

Parallel and based on the results of the field observations, we are building up an analogue experiment setup. The experiments will include extension, representing the long-term tectonic deformation, and injection tests, representing the short-term magmatic intrusions, to analyse the role of the structure’s presence and reactivation during magma propagation.