The genetic relationship between mafic dike swarms and plutonic reservoirs in the mesozoic of central chile (30°–33°45′S): insights from AMS and geochemistry

Abstract

Five mafic dike swarms between 30° and 33°45′S were studied for their geochemical signature and kinematics of magma flow directions by means of AMS data. In the Coastal Range of central Chile (33°−33°45′S), Middle Jurassic dike swarms (Concon and Cartagena dike swarms, CMDS and CrMDS, respectively) and an Early Cretaceous dike swarm (El Tabo Dike Swarm, ETDS) display the presence of dikes of geochemically enriched (high-Ti) and depleted (low-Ti) basaltic composition. These dikes show geochemical patterns that are different from the composition of mafic enclaves of the Middle Jurassic Papudo-Quintero Complex, and this suggests that the dikes were injected from reservoirs not related to the plutonic complex. The mantle source appears to be a depleted mantle for Jurassic dikes and a heterogeneous-enriched lithospheric mantle for Cretaceous dikes. In the ETDS, vertical and gently plunging magma flow vectors were estimated for enriched and depleted dikes, respectively, which suggest, together with variations in dike thickness, that reservoirs were located at different depths for each dike family. In the Elqui Dike Swarm (EDS) and Limari Mafic Dike Swarm (LMDS), geochemical patterns are similar to those of the mafic enclaves of the Middle Jurassic plutons. In the LMDS, east to west magma flow vectors are coherent with injection from neighbouring pluton located to the east. In the EDS, some dikes show geochemical and magma flow patterns supporting the same hypothesis. Accordingly, dikes do not necessarily come from deep reservoir; they may propagate in the upper crust from coeval shallow pluton chamber.