The recent Isla San Luis volcanic centre: Petrology of a rift-related volcanic suite in the northern Gulf of California, Mexico

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Abstract

Isla San Luis, one of the most recent eruptive centres in the Gulf of California, presents a complete magma evolution trend from basaltic andesites to rhyolites. The less-evolved lavas are palagonite tuffs, related to Surtseyan-type activity which characterized the emergent stage of the island. Subaerial lava flows and later high-energy hydromagmatic eruptions are dacites which make up the tuff rings of the southeastern corner of the island. Rhyolites are the latest erupted products and the development of the younger dome in the centre of the island was preceded by ash and pumice fallout containing quenched bombs with an obsidian crust and a pumiceous core. Basaltic andesites contain olivine (Fo(87-80)), calcium-rich plagioclase and sparse clinopyroxene microphenocrysts; the typical mineralogy of dacitic and rhyolitic lavas is plagioclase + two-pyroxenes. Major and trace elements vary regularly with MgO taken as a differentiation index. Isla San Luis lavas are enriched in LILE and depleted in Nb, Ta and Ti. Their characteristics are intermediate between tholeiitic and calc-alkaline lavas. They are also LREE enriched and the [(La/Yb)(n)] ratios steepen slightly with differentiation. Such an evolution is better explained by combined fractional crystallization and assimilation processes.

Original languageEnglish
Pages (from-to)31-52
Number of pages22
JournalJournal of Volcanology and Geothermal Research
Volume93
Issue number1-2
DOIs
StatePublished - 15 Nov 1999

Keywords

  • AFC process
  • Gulf of California
  • Hydromagmatism
  • Petrology
  • Volcanic island
  • Volcanology

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