RIFT ZONE REORGANIZATION THROUGH FLANK INSTABILITY IN OCEAN ISLAND VOLCANOES: AN EXAMPLE FROM TENERIFE, CANARY ISLANDS

Abstract

The relationship between rift zones and flankinstability in ocean island volcanoes is often inferred butrarely documented. Our field data, aerial image analysis,and40Ar/39Ar chronology from Anaga basaltic shieldvolcano on Tenerife, Canary Islands, support a rift zone—flank instability relationship. A single rift zone dominatedthe early stage of the Anaga edifice (~6–4.5 Ma).Destabilization of the northern sector led to partial sea-ward collapse at about ~4.5 Ma, resulting in a giantlandslide. The remnant highly fractured northern flank ispart of the destabilized sector. A curved rift zone devel-oped within and around this unstable sector between 4.5and 3.5 Ma. Induced by the dilatation of the curved rift, afurther rift-arm developed to the south, generating a three-armed rift system. This evolutionary sequence is sup-ported by elastic dislocation models that illustrate how acurved rift zone accelerates flank instability on one sideof a rift, and facilitates dike intrusions on the oppositeside. Our study demonstrates a feedback relationship be-tween flank instability and intrusive development, a sce-nario probably common in ocean island volcanoes. Wetherefore propose that ocean island rift zones representgeologically unsteady structures that migrate and reor-ganize in response to volcano flank instability.