Tectono-Sedimentary Evolution of the Cretaceous-Early Tertiary and Metallogenic Scheme of Northern Chile, Between 20° S and 26° S

Abstract

A review of the Cretaceous geology and metallogenesis of the Chilean slope of the Southern Andes, between 20° and 26° south latitude (Antofagasta Region) is presented. An attempt is also made to interpret the geologic phenomena which occurred during the Late Jurassic-Early Tertiary time span.The stratified rocks deposited during the period mentioned can be divided into three groups: 1) Sediments, mainly continental, resting on rocks from a fluvio- deltaic environment, which represent the final phase of infill of the Jurassic back-arc marine basin (Kimmeridgian-Barremian- Aptian?). 2) Andesitic-dacitic volcanic continental rocks, with sedimentary-volcanic intercalations (Albian-Cenomanian-Turonian?). 3) Sedimentary-volcanic continental rocks, with alluvial-fan development at the base, and volcanoclastic and volcanic rocks in the middle and upper part (latest Cretaceous- Late Eocene). The intrusive rocks can also be divided into three groups, which are distributed in belts whose longitudinal axes migrate chronologically eastward. These groups are interpreted as being the result of the development of three magmatic arcs: I) Late Jurassic-Early Cretaceous plutonic rocks; which correspond to the end of the Jurassic magmatic event. II) Late Cretaceous intrusive rocks; end phase of the “Mid- Cretaceous” magmatic event III) Early Tertiary plutonic and sub-volcanic rocks; final phases of the latest Cretaceous- Eocene magmatism. The end of the activity of each of these arcs is marked by the development of strike-slip fault systems (Atacama, San Cristóbal and West Fissure-Cordillera de Domeyko), and by folding, which can be considered an effect of the “Araucanian” (Kimmeridgian), “Peruvian” (Campanian) and “Incaic” (during the Eocene-Oligocene transition) tectonic phases.In connection with these succesive periods of magmatic and tectonic activity a series of important metallogenic processes developed, both linked to volcanic and post-plutonic hydrothermal phases, which gave rise to the following metalliferous belts: 1) Coastal Cordillera Copper Belt (Late Jurassic-Early Cretaceous). 2) Central Depression Copper, Gold and Silver Belt (Late Cretaceous-Early Tertiary). 3) Pre-Andean Cordillera Porphyry-Copper Belt (Early Tertiary).