Provincias magneticas de Chile central

Abstract

RESUMEN. La interpretacion cuantitativa del mapa magnetico del pais, entre los 31° y 35°S, ha permitido definir las siguientes provincias magneticas: Costa Central, Valparaiso-San Antonio, Costa Centro Norte, Cordillera de la Costa y cordillera Principal. En cada una de ellas existe una correlacion entre la susceptibilidad magnetica medida en rocas, el mapa magnetico y la geologia regional. Las anomalias de mayor intensidad conforman la provincia de la Cordillera de la Costa, en directa asociacion con afloramientos de granitoides cretacicos, altamente magneticos. Las provincias magneticas de la franja costera (Costa Central, Val paraiso-San Antonio, Costa Centro Norte) estan asociadas a rocas de baja a mediana susceptibilidad, intrusivos precretacicos, rocas sedimentarias y/o volcanicas, triasicas y jurasicas, y sedimentos neogenos. La Cordillera de los Andes presenta anomalias de alta frecuencia y mediana intensidad, relacionadas con intrusivos terciarios, y rocas volcanicas cretacico-terciarias, que presentan susceptibilidades moderadas. Los lineamientos magneticos se asocian, en general, a fallas de rumbo y/o normales. En algunos casos, estos lineamientos definen zonas de debilidad, que parecen haber controlado el emplazamiento de los intrusivos cretacicos. ABSTRACT. Aeromagnetic studies carried out recently in Central Chile (31-35°S) allow grouping the regional magnetic patterns into five magnetic provinces: Central Coast, Valparaiso-San Antonio, Central-North Coast, Coastal Range and Main Andean Range. Within each province there is a close correlation between rock magnetic susceptibility, map magnetic anomalies and regional geology. The most intense anomalies are in the Coastal Cordillera Province where they are closely related to the outcrops of highly magnetic Cretaceous granitoid plutons. The coastal magnetic provinces (Central Coast, Valparaiso-San Antonio, Central-North Coast) show low-intensity magnetic anomalies due to the widely distributed exposures of rocks with low magnetic susceptibility (Paleozoic basement, pre-Cretaceous granitoids, Triassic and Jurassic sedimentary and volcanic sequences and Neogene sediments). The Main Andean Range shows medium intensity, high-frequency, anomalies which correlate with Tertiary intrusives and Cretaceous-Tertiary volcanics, with moderate susceptibility. Magnetic lineaments are generally associated to strike-slip and normal faults. In the Coastal Range Province, some of these appear to coincide with zones 01 deep crustal weakness, along which the Cretaceous magmas could have been carried towards the upper crust.