TOWARDS A MORE QUANTITATIVE APPROACH TO PALINSPASTIC RECONSTRUCTIONS: THE NORTHERN ANDEAN-PANAMA ARC OROGEN (Invited Presentation)

Paleogeographic reconstructions —palinspastic or not— attempt to recreate ancient geographic configurations based on limited geologic datasets. Datasets usually include sea-floor magnetic anomalies that impose rigid-body translations and rotations to lithospheric entities. Infrequently, they include paleomagnetic declination data, and even more infrequently, piercing points from different fields like paleontology, petrology, provenance and molecular biology. We show a reconstruction that explicitly incorporates shortening estimates from structural cross-sections, paleomagnetic declination data, and different kinds of displaced piercing points. Two arc-continent collisions dominate the evolution of this margin: first, a discontinuous upper Cretaceous arc system progressively collided with an irregular continental margin imposing oblique convergence in reactivating tectonic blocks. Pieces of the arc and its basement were accreted to the continental margin in latest Cretaceous to Paleocene time, and are now rotated and sheared, obscuring the original cross-cutting relationships. Syntectonic clastic wedges separated by intraplate uplifts record the inboard response of the margin. A short-lived, Paleocene early Eocene magmatic arc developed on the margin, which shut off by choking of the subduction zone as thicker lithosphere arrived in late Eocene times, causing cooling and renewed deformation and molasse accumulation. As the arc system swept the margin, the rigid Maracaibo block was detached, and started to rotate around vertical axes, simultaneously opening the lower Magdalena valley basin, and inverting the northeast-trending Perija range, and then the Merida Andes. A second arc-continent collision took place as the Panama arc arrived to the South American margin by middle Miocene times, and Nazca plate subduction was established under northwestern South America. This quantitative paleogeographic template should help researchers in different fields to better frame questions about the timing and mode of isolation of the Caribbean Sea, the formation and emergence of the Central American Arc, the rise of the Andes, or the evolution of Andean-Amazonic drainages and biotas, all of them with unquestionable tectonic and paleo-biogeographic significance.