Variability of quaternary marine terraces and uplift rates in the Andean coastal zone at 23°S

Abstract

During the Quaternary most of the coastal areas along the Andes were uplifted due to subduction related processes. At 23°S, along the Mejillones Peninsula and the shoreline of the Coastal Cordillera, there is an abundance of Quaternary marine terraces, coastal cliffs, eroded dikes, alluvial fans, and fault scarps which preserve evidence of this uplift. The hyper-arid conditions have minimised subaerial erosion to the extent that the Quaternary marine terraces (QMT) can be carefully studied to understand the amount of permanent deformation in the forearc and the variability of uplift rates along the coast. A morpho-metric analysis using remotely sensed imagery from ALOS-PALSAR, drone survey and local differential GPS data allowed us to define the best-preserved QMT sequences and the elevation at which they were found with respect to the modern mean sea level. We propose a correlation between the individual paleo-shorelines of each marine terrace with a Quaternary Marine Isotope Stage (MIS). We determined two representative areas with well-preserved marine terraces: Morro Mejillones, in the western zone of the Mejillones Peninsula (∼12 × 10 km2) and the combined Hornitos – Punta Chacaya zone (∼16 × 7 km2), in the northern part of the Mejillones Bay. Within these areas we identified 12 QMT's in Morro Mejillones with estimated uplift rates between 0.31 and 0.76 m/ka over the last 600 ka, 3 QMT's In Hornitos with uplift rates between 0.28 and 0.4 m/ka over the last 220 ka, and 4 QMT's in Punta Chacaya with uplift rates between 0.25 and 0.39 m/ka over the last 330 ka. We link differences in uplift rates as related primarily to the distance from the coastal zone to the subduction trench and, locally, to their variable location with respect to faults active during the Quaternary.