Petrotectonic characteristics, geochemistry, and U-Pb geochronology of Jurassic plutons in the Upper Magdalena Valley-Colombia: Implications on the evolution of magmatic arcs in the NW Andes

Field, petrographic, and geochemical characterization along with U-Pb zircon geochronology of the Jurassic plutons exposed in the Upper Magdalena Valley (Colombia) allowed recognizing distinct western and eastern suites formed in at least three magmatic pulses. The western plutons crop out between the eastern flank of the Central Cordillera and the Las Minas range, being limited by the Avirama and the Betania-El Agrado faults. The western suite comprises a quartz monzonite quartz monzodiorite quartz diorite series and subordinate monzogranites. Chemically, the rocks are high-K calc-alkaline I type granitoids (some reaching the shoshonitic series) with metaluminous of magnesium affinity. Trace element tectonic discrimination is consistent with magmatism in a continental arc environment. Most rocks of this suite crystallized between 195 and 186 Ma (Early Jurassic, Pliensbachian), but locally some plutons yielded younger ages between 182 and 179 Ma (Early Jurassic, Toarcian). The eastern suite crops out in the eastern margin of the Upper Magdalena Valley, east of the Betania El Agrado fault. Plutons of this unit belong to the monzogranite series with rock types ranging between syenogranites and granodiorites. They are high-K calc-alkaline continental granitoids, some metaluminous and some peraluminous, related to I-type granites generated in a volcanic arc. Crystallization of the suite was between 173 and 169 Ma (Middle Jurassic, Aalenian-Bajocian), but locally these rocks contain zircon with earlier inherited ages related to the magmatic pulse of the western suite between 182 and 179 Ma (Early Jurassic, Toarcian). The evolution of the Jurassic plutons in the Upper Magdalena Valley is best explained by onset or increase in subduction erosion of the accretionary prism. This explains the eastward migration of the arc away from the trench. Subduction of prism sediments increased the water flux from the subducting slab, decreasing solidus temperatures, therefore increasing the volume of magma and the amount of crustal melts involved in the magma. This is explains the crystallization of older and more primitive quartzmonzodiorite stocks in the west and the later crystallization of granitic bodies with batholitic dimensions in the east. (C) 2017 Elsevier Ltd. All rights reserved.