Magmatic differentiation and bimodality in oceanic island settings - implications for the petrogenesis of magma in Tenerife, Spain

Abstract

The Tenerife post-Icod-collapse succession, comprised of the Teide-Pico Viejo central complex and its adjacent rift zones, marks the latest eruptive cycle on Tenerife (200-0 ka) that broadly evolved from primitive lavas to differentiated and partly explosive volcanism. At the same time, primitive lavas continued to erupt from dyke complexes in the rift zones, while intermediate lavas effused in the geographical transition from rift zone to central complex. To constrain the magmatic processes, that gave rise to the observed temporal and spatial patterns, several types of geochemical analyses of these rocks were applied and results embedded into a detailed, pre-existing framework of radiometric ages and whole-rock data. A case study of the composite lava flow of Montana Reventada allowed to investigate magma mixing as one potential mechanism to generate intermediate magma on Tenerife. The two end-members were a basanite and a phonolite, which erupted one after another, the basanite before the phonolite. The phonolite carries a considerable amount of mafic enclaves. Based on field evidence, the magma mixing event was constrained to a short interval before the eruption. A detailed geochemical dataset was used to confirm the mixed nature of the inclusions and to determine mixing ratios. Not all elements and oxides could be modelled, which is explained by observed crystal exchange between basanite and phonolite and by interdiffusion of trace elements between enclaves and phonolite. It thus appears that intermediate magma may form by magma mixing on Tenerife.