LACK OF VOLCANIC LINEAMENTS AND ANISOTROPY IN VOLCANISM RELATED TO RIFTING IN EL HIERRO, CANARY ISLANDS - SPAIN

El Hierro is part of the Canary Island Seamount Province generated by mantle upwelling beneath the Atlantic Ocean lithosphere off the NW African continental lithosphere flank. It originates ~3800m below sea level and rises to a maximum altitude of 1502m. El Hierro is a <1.1 Ma shield volcano dissected by three large scale landslides revealing a series of overlapping volcanic buildings that have progressively developed and collapsed, and was later pierced by cinder cones. Seismic tomography identified an efficient fracture system that allows magma to rise to the surface. Gravity models indicate the basaltic volcanism of El Hierro is related to rifting episodes. Usually rift structures control the orientation of magmatic intrusions and in turn manifest as cone ellipticity and alignments. Previous research indicate the orientations of linear arrays and elongation of extrusive volcanic features can reflect the locations of subsurface feeder dikes that feed these structures, which lie parallel to the maximum elongation of these features (σ₁) and perpendicular to the tensile forces (σ₃).

In this study, over 300 pyroclastic cones are mapped on El Hierro using Lidar and Google Earth. Directional statistical tests are applied to establish whether the observed distribution is random, here indicating the lack of a predominant trend. High confidence features with a long/short axis ratio greater than 1.2 are considered good candidates to study ellipticity and are analysed with QGis Tool to obtain Minimum Boundary Geometry. A clear trend cannot be identified when plotted on a stereonet. Angles between nearest neighboring features, indicative of possible preferential lineaments, are calculated and plotted using ArcGIS Pro. These also display a wide range of orientations but no clear trends. These results indicate that although the magmatism at El Hierro has been related to rifting, the later stage of activity represented by the analysed pyroclastic cones are broadly isotropic.