SUBDUCTION TO RIFT-RELATED EVOLUTION OF TRIASSIC AND JURASSIC ROCKS IN THE NORTHERN ANDES

Triassic and Jurassic rocks of the northern Andes are grouped into two belts. The western belt includes the Putumayo-Central Cordillera- San Lucas Range-Santa Marta massif and adjacent Magdalena-Cesar and Rancheria basins. This belt comprises large intrusive Jurassic bodies to the west and a belt of tuffs, lavas and volcaniclastic rocks that overlies uppermost Triassic-lowermost Jurassic marine strata and underlie unconformably mid-Cretaceous marine rocks. U-Pb geochronological data constrain the middle-late Jurassic age of plutonic rocks, geochemical analysis in volcanic rocks indicate a calc-alkaline composition, and MORB diagrams show the typical signature of magmatic arcs; the high content of K, Rb, Ba and Pb indicate the involvement of crustal material in the magma source.

The eastern belt include inverted orogens, like the Eastern Cordillera (EC), Santander Massif (SM), Merida Andes (MA), Perija Range (PR), Cosinas Range (CR), and buried Jurassic graben structures. This belt consists mainly of thick continental siliciclastics successions in the southern ranges (EC, SM), interbeds of continental siliciclastic, volcanoclastic and volcanic beds in the PR and MA, and farther north in the CR dominate again continental siliciclastic succession that passes laterally to marine succession. Large granitc bodies of middle Jurassic age associated to subduction processes have been documented in SM, and minor bodies in PR and CR. Most of the thick Jurassic siliciclastic successions are bounded by normal faults and they are overlain by lowermost Cretaceous succession that accumulated in extensional settings.

Paleomagnetic data indicate that rocks from the western belt and basement of the EC-SM originated in southern latitudes (northern Peru), whereas the paleolatitudinal location of northern ranges like the MA, PR and CR indicate that siliciclastic strata accumulated more likely in northern paleolatitudes. Lower-middle Jurassic magmatic arc related to subduction had a linear trend, whereas in middle Jurassic to early Cretaceous time both the northern ranges and translated southern blocks were affected by extensional activity related to the break up of Pangea.