Ages of batholithic intrusions of northern and central Chile

Their stratigraphic setting demonstrates that three batholithic intrusions in northern and central Chile are respectively pre-Jurassic, Jurassic, and Cretaceous. Radiometric age determinations, by the lead-alpha (Larsen) method, indicate ages of 265 ± 30, 120 ± 15 to 125 ± 15, and 95 ± 10 to 130 ± 15 million years respectively for samples from the batholiths whose stratigraphic setting has been established or is inferred. With one exception, the radiometric ages are consistent with the stratigraphy. The exceptional determination of 130 ± 15 million years was for a sample of granite that intrudes Cretaceous rocks. Three other samples of Cretaceous granitic rocks were within the range of 95 ± 10 to 105 ± 10 million years. Angular unconformities whose ages are correlative with the intrusions suggest that the three batholiths can be related respectively to Hercynian, Late Jurassic, and middle Cretaceous orogenies.