Heterogeneity of phonolitic pumice deposits from Tenerife, Canary Islands

International Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980.The island of Tenerife has an extensive Quaternary phonolitic pyroclastic series, comprising plinian pumice-fall deposits, ignimbrites, and pyroclastic surges. The dominant petro­logical feature of these pumice deposits is their geochemical and petrographical heterogeneity. Evidence is presented for three causes of heterogeneity: assimilation of roof-rock by the magma, resulting in less evolved compositions of the first erupted pumice; zonation of the magma chamber, causing a change to intermediate compositions among the last products of an eruption; and magma mixing, where mafic and banded tephra are distributed more or less randomly through a particular pumice deposit.