Interpretation of gravity and geoid in the Central Andes between 20 ° and 29 ° S

Most recently the MIGRA group with participants from Chile, Argentina and Germany has surveyed some 3.500 new gravity observations in an Andean Geotraverse covering N-Chile and NW-Argentina between 64 °–71 °W and 20 °–29 °S. MIGRA is an international gravity research group which was established under the umbrella of the “Collaborative Research Center” “Deformation Processes in the Andes” at Freie Universität Berlin (Germany). Oil and mining industry gravity data were reprocessed and included into the MIGRA data base which contains more than 15.000 gravity data at present. Due to big logistical problems (terrain access, no maps, no levelling lines etc.) the overall error of the calculated gravity anomalies results of approximately 4–5 mGal which is about 1% compared with the magnitude of about 450 mGal11mGal is used throughout this paper: 1 mGal = 10−5 m s−1. e Bouguer anomaly. Under the framework of the interdisciplinary research project CINCA (Crustal Investigations Off- and Onshore Nazca/Central Andes) gravity surveys of the MIGRA group has been extended to the Pacific ocean. In summer 1995 MIGRA took part in the “CINCA” offshore experiment SO-104 of the German Research Vessel “Sonne” between the latitudes 20 °S and 24 °S. ta base which includes point data and 10 km ∗ 10 km data grids of free-air-, different types of Bouguer- and isostatic-residual anomalies are presented here in maps of the isostatic residual field along with an interpretation by 3D density modelling. Constraints were mainly taken from results of 2D ray tracing refraction seismics and tectonics. Offset-free modelling is achieved by fitting both gravity field and geoid with one density structure of the lithosphere-system and by modelling relative to a reference density structure derived from the Preliminary Referende Earth Model (PREM, Dziewonski and Anderson, 1981).