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Diverse Jurassic Magmatic Arcs of the Colombian Andes: Constraints from Petrography, Geochronology and Geochemistry
By Gabriel RODRÍGUEZ–GARCÍA, Ana María CORREA–MARTÍNEZ, Gilberto ZAPATA–GARCÍA, María Isabel ARANGO–MEJÍA, Gloria OBANDO–ERAZO, Juan Pablo ZAPATA–VILLADA and José Gilberto BERMÚDEZ
Manuscript accepted May 15, 2019
New field, petrographic, whole–rock geochemical and U–Pb zircon geochronological data obtained from Jurassic plutonic rocks of the Santander Massif (SM), plutonic and volcanic rocks in the Upper Magdalena Valley (UMV) and plutonic rocks in the northern block of the Ibagué Batholith (NBIB) provide evidence that the Jurassic igneous activity that is recorded in several blocks of the Colombian Andes began in the Late Triassic and ended in the Early Cretaceous. This magmatism developed in at least three different magmatic arcs, each during clearly defined time periods, over basements with different characteristics. The first stationary continental margin arc was active between the Late Triassic (ca. 214 Ma) and the Early Jurassic (ca. 184 Ma). It is located in the SM and is primarily represented by monzogranitic, peraluminous plutons generated by multiple magmatic pulses that involved varying degrees of crustal melting. This study proposes, for the first time, that most of the arc was emplaced into primarily Ordovician basement and that a small part was emplaced into early Neoproterozoic basement. The second arc, which is located in the UMV, developed between the Early Jurassic (ca. 197 Ma) and the Middle Jurassic (ca. 167 Ma) during at least three magmatic pulses related to arc migration, which is evidenced by compositional and temporal variations in which the plutons evolved from metaluminous monzodiorites to peraluminous granites, and the volcanic rocks evolved from andesites to rhyolites. This second arc was emplaced into Neoproterozoic metamorphic basement, Paleozoic sedimentary rocks, Permian igneous rocks and Triassic sedimentary rocks. The third continental margin arc, which is located in the NBIB, formed from the Late Jurassic (ca. 158 Ma) to the Early Cretaceous (ca. 138 Ma). It is characterized by at least two pulses that are represented by a western syntectonic pluton and an eastern post–tectonic pluton, both of which have calc–alkaline metaluminous tonalitic compositions, that are separated by a band of metamorphic basement rocks of Late Jurassic age, not Neoproterozoic or Permian – Triassic as was previously thought.
Keywords: continental arc magmatism, U–Pb zircon geochronoloy, metamorphic basement , peraluminous magmatism, metaluminous magmatism.