Cartografía y Petrografía de las Migmatitas de las Minas, Cordillera Central de Colombia: Implicaciones en su evolución y caracterización del grado de fusión parcial.
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Bonilla Celis, Edinson Yesid | 2021-10-27
eng: The “Migmatitas de las Minas” are metamorphic rocks of Proterozoic age with NE-SW trending, which outcrop in the Minas Range, in the eastern flank of the Central Cordillera of Colombia. This unit is subdivided in two zones: to the south, with a lower degree of partial melting, stromatic and patch-type metatexites predominate, with an amount of leucosome of 0% - 20%, and to the north are mainly stromatic and nebulitic diatexites that reach 45% of leucosome, indicating an increase in the degree of partial melting from south to north. The neosome is segregated, which in situ, in source and vein-type leucosomes, with compositional variations between tonalite, granodiorite, and monzogranite, and residues are comprised of quartz-feldspar gneiss, quartz-biotite gneiss, and amphibolite. The anatectic event occurred in volcanoclastic protoliths and reached high temperature amphibolite facies, from 650 °C to 750 °C and pressures between 4 kbar to 8 kbar, as a result of dehydration reactions of muscovite, biotite and hornblende with H_2 O content. The prograde mineral assemblage defined by hornblende + plagioclase + biotite + ortose + augite + rutile, mark the metamorphic peak, at temperatures from 760 °C to 830 °C and pressures between 5.6 kbar to 8,5 kbar, corresponding to low temperature granulite facies, indicating very advanced stages or the end of partial melting. Later, a retrograde metamorphism occurred in greenschist facies, represented by actinolite + chlorite + clinozoisite + epidote mineral assemblage, at temperatures below 500 °C. Based on previous geochronological and paleomagnetic studies, it is established that the partial melting event registered in the “Migmatitas de las Minas” began in the Stenian due to the collision of the “Colombia-Oaxaquia” arc against the SE margin of Amazonia, and it continue until the Tonian due to collision of Amazonia against Baltica and the closure of the Mirovoi Ocean.
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