MORPHOTECTONIC EVOLUTION OF THE MEJILLONES PENINSULA, NORTHERN CHILE: A NEW CHARACTERIZATION OF THE NEOGENE COASTAL TERRACE SEQUENCE USING DIFFERENTIAL GPS AND ESR DATING

The Mejillones Peninsula of northern Chile is a salient of the Pacific margin of South America that extends westward towards the active subduction zone. Ongoing work to determine the tectonic and climatic evolution of the forearc of northern Chile is being performed on the late-Neogene coastal-terrace sequence of this region. Data collection includes remotely sensed imagery, elevation ground points measured with dual-frequency GPS and Electro Spin Resonance (ESR) dating of mollusk shells. The collected data is being used to construct a three-dimensional model of post-Pliocene tectonic deformation and morphological development of Mejillones Peninsula.

Extremely arid conditions have preserved at least seven continuous terrace levels along the northwest margin of this area; four of them can also be identified in its southeast tip. Five samples of late-Pleistocene articulated mollusk shells were collected for ESR analysis from three different levels exposed in these two localities, and one sample from a higher level offset by the Mejillones Fault, east of Morro Mejillones.

Due to the rough topography in certain zones of Mejillones Peninsula, a preliminary orthomosaic has been generated and a DEM automatically extracted from the 70,000 scale aerial photographs to assess problematic areas in the accurate representation of the surface. GPS ground elevation data are being used to construct a new orthomosaic from the 30,000-scale aerial photographs. The extraction of a new high-resolution DEM will allow documenting the Pleistocene fault slip history of structures affecting the coastal terrace sequence.