Temporal and geochemical characterization of the Negros de Aras (northern Chile) monogenetic volcanic field.

Negros de Aras is a monogenetic volcanic field located in the Central Volcanic Zone of the Andes in northern Chile, 26 km towards the north from active Socompa volcano, at a zone dominated by N-S trending faults. It is formed by lava flows and subordinate scoria cone, dated between < 1.5 and 0.6 ± 0.4 Ma, referable to six formations. Geochemically, lava flows display a range from 54.28 to 64.47 wt.% SiO2, respectively and show a compatible trending of major elements as Fe2O3, TiO2, MgO, whereas K2O and Na2O present an incompatible trending. Trace elements display elevated Sr/Y and La/Yb ratios, high Sr values, depleted Y and HREE values, absence of an Eu anomaly, Nb and Ti negative anomalies, and relative enrichment LILE and LREE. The geochemical features suggest that the magma has fractionated garnet ± amphibole in its origin, with a low degree of contamination during its ascents to the surface. Besides, considering the small-volume magma batches, it is possible to suggest that the magmas did not have any prolonged stopping on the ascent to the surface. The content of volatiles dissolved, and the ascent rate of these magmas played an essential role in the definition and the change of dominant eruptive styles.