Journal article

Ollo de Sapo Cambro-Ordovician volcanics from the Central Iberian basement—A multiphase evolution

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  • Terra Nova. - 2018, vol. 30, no. 5, p. 350–358
English The Cambro-Ordovician rhyodacitic to dacitic volcanics from the Central Iberian basement, currently known as Ollo de Sapo (toads eye), have been reported as a specific group of felsic porphyritic rocks with blue quartz and large phenocrysts of K- feldspar, in a partly vitreous or fine-grained matrix. Interpreted to form Cambro- Ordovician volcanic domes, they are accompanied by tuffs, ignimbrites and products of reworking in a near-surface environment. The coarse- to fine-grained rocks exhibit rather large K-feldspar phenocrysts, plagioclase and rounded blue quartz, representing former corroded phenocrysts. Their colouration indicates unmixing of TiO2 at around 900°C during cooling from relatively high crystallisation temperatures, indicating their origin at hot lower crustal conditions. We propose at least a two-step evolution (1) starting around 495 Ma in the lower crust of a collapsing cordillera, generating a phenocryst-rich mush and adiabatic melting of the lower crustal protolith to produce the spectacular Ollo de Sapo porphyrites, before (2) magma ascent and crustal extension leading to a different thermal regime around 483 Ma.
Faculté des sciences et de médecine
Département de Géosciences
  • English
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