PERMIAN-TRIASSIC OROGENESIS IN THE NORTHERN ANDES: A RECORD OF ARC MAGMATISM, ACCRETION, ANATEXIS AND RELAXATION OF A CONTINENTAL TERRANE IN THE PROTO-ANDES IN THE WAKE OF PANGEA

Recent geochronological studies performed in the northern Andes have revealed the presence of a major Permian-Triassic magmatic/metamorphic belt running along the cordilleran backbone, from the Illescas massif in northwestern Peru to the Guajira peninsula in northernmost Colombia. U-Pb dating of zircons and geochemical analyses imply different stages for the evolution of this belt, represented as an early suite of I-type subduction-related granitoids intruded between ca. 290 to 255 Ma, shortly followed by a more volumetric series of peraluminous S-type granites intruded within the age range from ca. 247 to 239 Ma. This last granitic event is coeval with mid- to high-grade metamorphism and anatexis recorded in para- and orthogneissic units, and is presumably related to the accretion of this terrane to the paleopacific proto-Andean margin. A minimum age for significant shearing and deformation is defined by the intrusion of undeformed granodioritic plutons at ~230 Ma, which crosscut the metamorphic foliation, generate localized metamorphic imprints, and reset regional muscovite Ar-Ar ages. This domain strongly differs from other Andean segments south of the Huancabamba deflection where both I- and A-type magmatism dominates. Therefore, we suggest that this oroclinal bend represents a major tectonic boundary that marks the transition between peri-Pangean accretionary orogens and internal Alleghanian-Ouachitan collisional belts.