Interaction of mantle-derived magma with island crust? Trace element and oxygen isotope data from the Diego Hernandez Formation, Las Canadas, Tenerife

The Quaternary Diego Hernandez Formation consists of interbedded phonolitic pyroclastics and basanite lavas and scoria beds. Most of the phonolites ar e mingled-magma units that contain a minor mafic component. The phonolites fall into two stratigraphically bounded groups, based on major and trace el ement abundances. Nh contents are especially distinctive due to a varying r ole for titanite during petrogenesis. Nepheline syenite xenoliths. which ar e plentiful in some of the phonolitic ignimbrites. fall into the same two c ompositional groupings hut are typically more strongly differentiated. Majo r and trace element variations during evolution of the phonolites can be mo delled by fractional crystallization, by melting of syenite, or bq some com bination of the two such as AFC. Trace element variations among the basanit es require the addition of a highly fractionated felsic component, either p honolitic magma or nepheline syenite. delta O-18 values of phonolites vary across twice the range of the basanites, inconsistent with an origin by pur e fractional crystallization of a basanitic parent. We conclude that recycl ing of differentiated rocks within the Tenerife island edifice has played a significant role in Quaternary magmatism on Tenerife. (C) 2000 Elsevier Sc ience B.V. All rights reserved.