Resumo

PARDO VILLAVECE, Natalia; JARAMILLO, José María  e  CEPEDA, Héctor. THE PAIPA VOLCANO, EASTERN CORDILLERA OF COLOMBIA , SOUTH AMERICA (PART II): PETROGRAPHY AND MAJOR ELEMENTS PETROLOGY . Earth Sci. Res. J. [online]. 2005, vol.9, n.2, pp.148-164. ISSN 1794-6190.

Paipa volcano products are mainly pyroclastic pumice and ash flow tuffs, lava domes and pyroclastic block and ash flow tuffs. They are classified as alkaline rhyolites and trachytes and high-K calcalkaline rhyolites . Chemical data show SiO2 values between 68 and 72%, and alkalis (Na2O+K2O) content of 7%-10%. Essential minerals are phenocrysts and glomerocrysts of anorthoclase , sanidine up to 1 ,5 cm and anorthoclase -mantled plagioclase; accessory minerals are red biotite , and hastingsite while trace minerals are augite , zircon, sphene and magnetite. Crystals have disequilibrium textures, such as dissolution embayments , corrosion and reabsortion borders, normal, inverse, oscillating and patchy zonation , together with fibrous borders intercalated with euhedral borders. In correlation with published data of Iza volcanic rocks, Paipa rocks chemical composition confirms that acid and alkaline magmas that have erupted in the Eastern Cordillera of Colombia during the Neogene are strongly different from the calc-alkaline magmas that erupt in the westward active arc (Central Cordillera). Detailed structural, geochemical and geophysical research has to be done in future research to establish the geodynamic framework that governs the volcanism of the Eastern Cordillera .

Palavras-chave : Bubble-wall texture; CIPW norm; ignimbrites; lava-domes; phreatomagmatic eruptions; pyroclastic flows; modal compositions; normal composition; shards.

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