Magma Mixing in the 1100 AD Montaña Reventada Composite Lava Flow : Interaction of Rift Zone and Central Complex Magmatism

• Zoned eruption deposits frequently show a lower felsic and an upper maficmember, thought to reflect eruption from a large, stratified magmachambers. In contrast, however, the Montaña Reventada composite flow inTenerife consists of a lower basanite and a much thicker upper phonolite. Asharp interface separates the basanite and phonolite, and a chilled margin atthis contact indicates the basanite was still hot upon emplacement of thephonolite, i.e. the two magmas erupted in very quick succession. Threetypes of mafic to intermediate inclusions are found in the phonolite, whichcomprise foamy quenched ones, inclusions with chilled margins and thosethat are physically mingled, reflecting progressive mixing with adecreasing temperature contrast between the end-member magmasinvolved. Analysis of basanite, phonolite and inclusions for majors, tracesand Sr, Nd and Pb isotopes show the inclusions to be derived from binarymixing of basanite and phonolite end-members in ratios of 2:1–4:1.Although basanite and phonolite magmas were erupted in quick succession, contrasting206Pb/204Pb ratios show them to be geneticallydistinct. The Montaña Reventada basanite and phonolite first came intocontact just prior to eruption and had seemingly limited interaction time.Montaña Reventada erupted from the transition zone between twoplumbing systems, the phonolitic Teide-Pico Viejo complex and thebasanitic Northwest rift zone. A rift zone basanite dyke most likelyintersected a previously emplaced phonolite magma pocket, leading toeruption of geochemically and texturally unaffected basanite, followed byinclusion-rich phonolite that exploited the already established conduit.

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NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Multidisciplinär geovetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geosciences, Multidisciplinary (hsv//eng)

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