OBDUCCIóN Y METAMORFISMO DE OFIOLITAS TRIáSICAS EN EL FLANCO OCCIDENTAL DEL TERRENO TAHAMí, ORDILLERACENTRAL DE COLOMBIA

the dunites and metabasic rocks that compose the aburrá ophiolite were formed during late triassic times in a general supra-subduction zone that probably included a nascient arc and backarc and forearc basins. the arc and the associated basins must have been located somewhere in the pacific ocean, being displaced gradually to the south american continental margin to finally collide with it and be obducted over the western side of the tahamí terrane. the collision took place between late triassic and early cretaceous times, being more probable the first age. all these rocks underwent metamorphism in amphibolite facies during the overthrusting, although in some of them igneous relict gabbroic textures were preserved. the basic rocks were converted to metagabbros and several types of amphibolites. the amphibolites that underlie the dunite, forming a metamorphic sole, herein called la espadera-chupadero amphibolites, are very similar in their mineralogy and microstructures to the santa elena amphibolites of the ayurá-montebello group, but they show some differences in the composition of major, minor and trace elements. the protholith of the santa elena amphibolites, probably metamorphosed during permian or earlier times, seems to have been an n-morb oceanic crust, while the la espadera-chupadero amphibolites in part were formed as a nascient island arc as well as backarc basin basalts. rocks of similar age and tectonic setting could have been accreted to the northern andes in other places of colombia and ecuador, particularly in el oro complex of southern ecuador.