An integrated study of the magmatic products linked to the Cumbre Nueva Collapse, La Palma

Groom, Simon (2017) An integrated study of the magmatic products linked to the Cumbre Nueva Collapse, La Palma. Doctoral thesis, Birkbeck, University of London.

Abstract

The eruptive sequences linked to the Cumbre Nueva Collapse of La Palma’s Taburiente volcano provide ideal material for a study that integrates field volcanology, geochronology, lava petrology and whole rock magmatic geochemistry. Lavas exposed in Taburiente’s El Time region and on the post-collapse Bejenado volcano bracket the collapse and record this period’s magmatic processes. Their integrated study allows us to reconstruct how a collapse interacted with the magma supply system. By studying the same lava flows using multiple techniques that address successively deeper parts of the magma supply we present an unusually well-constrained interpretation of the processes at depth. Results of field and 40Ar/39Ar geochronological study indicate that the collapse (≈530 ka) ended a typical period of volcanic re-surfacing at Taburiente’s Paleo-Cumbre Nueva Rift. It was followed by focused volcanism within the collapse structure producing the Bejenado volcano. This was a major, rapid, volcanic episode that included explosive phreatomagmatic activity as well as of voluminous, effusive lava emplacement. Its physical volcanology was in part controlled by magmatic evolution, with products ranging from basanites to tephri-phonolites. Petrological study indicates that dynamic collapse-related processes took place within the magma reservoir system throughout this period, in reservoirs located in the lithospheric mantle. Reservoir processes included the disruption of cumulates, super-saturated crystallisation of feldspar and clinopyroxene, mixing between primitive and evolved magmas, and assimilation of amphibole-bearing lithologies. Whole rock elemental and isotope (Sr, Nd, Pb) geochemistry results indicate that most of Bejenado’s eruptive products were hybrids between two magma batches with contrasting source signatures in a major ongoing reservoir process. The more primitive of these batches had an unusually depleted isotope signature for La Palma lavas, while the more evolved, HIMU-dominated, magma had high incompatible element contents. The unusual depleted signature indicates that the collapse affected the deepest part of the magma-supply system.

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