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Late Triassic to Jurassic Magmatism in Colombia: Implications for the Evolution of Northern Margin of South America
By Julián Andrés LÓPEZ–ISAZA and Carlos Augusto ZULUAGA
Volcanic and plutonic rocks that compose the Late Triassic to Jurassic magmatic belt in Colombia result from partial melting of lower crustal rocks mixed with mantle melts in a continental margin setting. Lithologies include quartz monzonites, monzogranites and syenogranites (locally leucocratic), granodiorites, tonalites, diorites, gabbros, and volcanoclastic successions intersected by porphyritic hypabyssal rocks of andesitic, dacitic and latitic compositions. The elongated geometry of plutons suggests that the accommodation space of magmatic pulses was related to transtensional environments in a supra–subduction tectonic framework with mantle interaction, melting of sediments of the slab and crustal contamination. The nature of magmatism resulted from the interaction between crustal and mantle–derived magmas in a continental margin setting that progressively changed from a Late Triassic post–collisional extensional setting (associated with orogenic collapse?) to a predominantly Late Jurassic volcanic arc setting developed in a supra–subduction regime; the evolution of the magmatic belt is marked spatially from east to west and temporally in a time span of approximately 60 my. The sources of the Late Triassic to Jurassic magmatic belt are varied, and are associated with melting of supra–subduction mantle wedge, with differentiation of tholeiitic or midly calc–alkaline basalts and intermediate rocks, and includes partial melting of pelitic rocks, tonalites and granodiorites, tholeiites, and high–aluminum basalts or andesites.
Keywords: high–potassium calc–alkaline rocks, shoshonitic magmatism, active continental margin, post–collisional magmatism, oblique subduction.