Thermochronology and tectonics of the Merida Andes and the Santander Massif, NW South America

New apatite U-Pb and multiphase 40Ar/39Ar data constrain the high to medium temperature (similar to 500 degrees C-similar to 300 degrees C) thermal histories of igneous and metamorphic rocks exposed in the Merida Andes of Venezuela, and new apatite and zircon fission track data constrain the similar to 500 degrees C-similar to 60 degrees C thermal histories of pre-Jurassic igneous and metamorphic rocks of the adjacent Santander Massif of Colombia. Computed thermal history envelopes using apatite U-Pb dates and grain size information from an Early Palaeozoic granodiorite in the Merida Andes suggest that it cooled from >500 degrees C to <350 degrees C between similar to 266 Ma and similar to 225 Ma. Late Permian to Triassic cooling is also recorded in Early Palaeozoic granitoids and metasedimentary rocks in the Merida Andes by numerous new muscovite and biotite 40Ar/39Ar plateau dates spanning 257.1 +/- 1.0 Ma to 205.1 +/- 0.8 Ma. This episode of cooling is not recognised in the Santander Massif, where 40Ar/39Ar data suggest that some Early Palaeozoic rocks cooled below similar to 320 degrees C in the Early Palaeozoic. However, most data from pre-Jurassic rocks reveal a regional heat pulse at similar to 200 Ma during the intrusion of numerous shallow granitoids, resulting in temperatures in excess of similar to 520 degrees C, obscuring late Palaeozoic histories. The generally accepted timing of amalgamation of Pangaea along the Ouachita-Marathon suture pre-dates Late Permian to Triassic cooling recorded in basement rocks of the Merida Andes by >30 Ma, and its effect on rocks preserved in north-western South America is unknown. We interpret late Permian to Triassic cooling in the Merida Andes to be driven by exhumation. Previous studies have suggested that a short phase of shortening and anatexis is recorded at similar to 253 Ma in the Maya Block, which may have been adjacent to the basement rocks of the Merida Andes in the Late Permian. The coeval onset of exhumation in the Merida Andes may be a result of increased coupling in the magmatic arc, which was located along the western margin of Pangaea. Triassic extension is documented in the Central Cordillera of Colombia and Ecuador between similar to 240 Ma and similar to 215 Ma, although extension at this time has not been clearly identified in the Merida Andes or the Santander Massif. Permian to Triassic cooling is not recorded in the structurally isolated Caparo Block in the southern Merida Andes, suggesting that it may have constituted a distinct fault block in the Triassic. New fission track data from the Santander Massif suggest that it started exhuming at similar to 40 Ma during a period of accelerated convergence between the Nazca/Farallon Plate and the western margin of South America. Exhumation in the Santander Massif occurred diachronously since similar to 18 Ma in distinct fault blocks at rates of 0.5-1 km/Ma, and may have been driven by east-west compression as a result of the indentation of the Panama-Choco terrane to western Colombia. (C) 2016 Elsevier B.V. All rights reserved. New apatite U-Pb and multiphase 40Ar/39Ar data constrain the high to medium temperature (similar to 500 degrees C-similar to 300 degrees C) thermal histories of igneous and metamorphic rocks exposed in the Merida Andes of Venezuela, and new apatite and zircon fission track data constrain the similar to 500 degrees C-similar to 60 degrees C thermal histories of pre-Jurassic igneous and metamorphic rocks of the adjacent Santander Massif of Colombia. Computed thermal history envelopes using apatite U-Pb dates and grain size information from an Early Palaeozoic granodiorite in the Merida Andes suggest that it cooled from >500 degrees C to <350 degrees C between similar to 266 Ma and similar to 225 Ma. Late Permian to Triassic cooling is also recorded in Early Palaeozoic granitoids and metasedimentary rocks in the Merida Andes by numerous new muscovite and biotite 40Ar/39Ar plateau dates spanning 257.1 +/- 1.0 Ma to 205.1 +/- 0.8 Ma. This episode of cooling is not recognised in the Santander Massif, where 40Ar/39Ar data suggest that some Early Palaeozoic rocks cooled below similar to 320 degrees C in the Early Palaeozoic. However, most data from pre-Jurassic rocks reveal a regional heat pulse at similar to 200 Ma during the intrusion of numerous shallow granitoids, resulting in temperatures in excess of similar to 520 degrees C, obscuring late Palaeozoic histories. The generally accepted timing of amalgamation of Pangaea along the Ouachita-Marathon suture pre-dates Late Permian to Triassic cooling recorded in basement rocks of the Merida Andes by >30 Ma, and its effect on rocks preserved in north-western South America is unknown. We interpret late Permian to Triassic cooling in the Merida Andes to be driven by exhumation. Previous studies have suggested that a short phase of shortening and anatexis is recorded at similar to 253 Ma in the Maya Block, which may have been adjacent to the basement rocks of the Merida Andes in the Late Permian. The coeval onset of exhumation in the Merida Andes may be a result of increased coupling in the magmatic arc, which was located along the western margin of Pangaea. Triassic extension is documented in the Central Cordillera of Colombia and Ecuador between similar to 240 Ma and similar to 215 Ma, although extension at this time has not been clearly identified in the Merida Andes or the Santander Massif. Permian to Triassic cooling is not recorded in the structurally isolated Caparo Block in the southern Merida Andes, suggesting that it may have constituted a distinct fault block in the Triassic. New fission track data from the Santander Massif suggest that it started exhuming at similar to 40 Ma during a period of accelerated convergence between the Nazca/Farallon Plate and the western margin of South America. Exhumation in the Santander Massif occurred diachronously since similar to 18 Ma in distinct fault blocks at rates of 0.5-1 km/Ma, and may have been driven by east-west compression as a result of the indentation of the Panama-Choco terrane to western Colombia. (C) 2016 Elsevier B.V. All rights reserved. New apatite U-Pb and multiphase 40Ar/39Ar data constrain the high to medium temperature (similar to 500 degrees C-similar to 300 degrees C) thermal histories of igneous and metamorphic rocks exposed in the Merida Andes of Venezuela, and new apatite and zircon fission track data constrain the similar to 500 degrees C-similar to 60 degrees C thermal histories of pre-Jurassic igneous and metamorphic rocks of the adjacent Santander Massif of Colombia. Computed thermal history envelopes using apatite U-Pb dates and grain size information from an Early Palaeozoic granodiorite in the Merida Andes suggest that it cooled from >500 degrees C to <350 degrees C between similar to 266 Ma and similar to 225 Ma. Late Permian to Triassic cooling is also recorded in Early Palaeozoic granitoids and metasedimentary rocks in the Merida Andes by numerous new muscovite and biotite 40Ar/39Ar plateau dates spanning 257.1 +/- 1.0 Ma to 205.1 +/- 0.8 Ma. This episode of cooling is not recognised in the Santander Massif, where 40Ar/39Ar data suggest that some Early Palaeozoic rocks cooled below similar to 320 degrees C in the Early Palaeozoic. However, most data from pre-Jurassic rocks reveal a regional heat pulse at similar to 200 Ma during the intrusion of numerous shallow granitoids, resulting in temperatures in excess of similar to 520 degrees C, obscuring late Palaeozoic histories. The generally accepted timing of amalgamation of Pangaea along the Ouachita-Marathon suture pre-dates Late Permian to Triassic cooling recorded in basement rocks of the Merida Andes by >30 Ma, and its effect on rocks preserved in north-western South America is unknown. We interpret late Permian to Triassic cooling in the Merida Andes to be driven by exhumation. Previous studies have suggested that a short phase of shortening and anatexis is recorded at similar to 253 Ma in the Maya Block, which may have been adjacent to the basement rocks of the Merida Andes in the Late Permian. The coeval onset of exhumation in the Merida Andes may be a result of increased coupling in the magmatic arc, which was located along the western margin of Pangaea. Triassic extension is documented in the Central Cordillera of Colombia and Ecuador between similar to 240 Ma and similar to 215 Ma, although extension at this time has not been clearly identified in the Merida Andes or the Santander Massif. Permian to Triassic cooling is not recorded in the structurally isolated Caparo Block in the southern Merida Andes, suggesting that it may have constituted a distinct fault block in the Triassic. New fission track data from the Santander Massif suggest that it started exhuming at similar to 40 Ma during a period of accelerated convergence between the Nazca/Farallon Plate and the western margin of South America. Exhumation in the Santander Massif occurred diachronously since similar to 18 Ma in distinct fault blocks at rates of 0.5-1 km/Ma, and may have been driven by east-west compression as a result of the indentation of the Panama-Choco terrane to western Colombia. (C) 2016 Elsevier B.V. All rights reserved.