Late tertiary volcanic episodes in the area of the city of Santiago de Chile: new geochronological and geochemical data

In the area of the city of Santiago de Chile, it is possible to distinguish at least three subvolcanic episodes. The first is late Oligocene (30.9–25.2 Ma), and its products range from basalt to rhyolite. The second episode is early Miocene (22.3–20.3 Ma), and its products are two-pyroxene basalts to basaltic andesites. The third episode, though also early Miocene, is slightly younger than the second (20.3–16.7 Ma) and produces mainly amphibole-bearing dacitic porphyries. s from the three episodes are medium- to low-K calk-alkaline rocks. All are enriched in LILE relative to N-MORB and have La/Nb ratios >1.6 and Ba/La ratios >20. Each episode differs from the others in heavy REE concentrations and La/Yb ratios. Sr-, Nd-, and Pb-isotope ratios for the early Miocene rocks are similar to those of Quaternary volcanic rocks from the central SVZ (37°–41.5°S) of the Andes and unlike those of the Quaternary of the northern SVZ. Three samples reported here have nearly identical isotope ratios, though the La/Yb ratios range from 3 to 35.