DOI: http://dx.doi.org/10.5027/andgeo%25x

The country rocks of Devonian magmatism in the North Patagonian Massif and Chaitenia

Francisco Hervé, Mauricio Calderon, Mark Fanning, Robert Pankhurst, Carlos Rapela, Paulo Andres Quezada Pozo

Abstract


Previous work has shown that Devonian magmatism in the southern Andes occurred in two contemporaneous belts: one emplaced in the continental crust of the North Patagonian Massif and the other in an oceanic island arc terrane to the west, Chaitenia, which was later accreted to Patagonia. The country rocks of the magmatic arcs consist of metasedimentary complexes which crop out sporadically in the Andes on both sides of the Argentina–Chile border, and additionally of pillow metabasalts for Chaitenia. Detrital zircon SHRIMP U–Pb age determinations in 13 samples of these rocks indicate maximum possible depositional ages from c. 370 to 900 Ma, and the case is argued for mostly Devonian sedimentation as for the fossiliferous Buill slates. Ordovician, Cambrian–late Neoproterozoic and ‘Grenville-age’ provenance is seen throughout, except for the most westerly outcrops where Devonian detrital zircons predominate. Besides a difference in the Precambrian zircon grains, 76% vs 25% respectively, there is no systematic variation in provenance from the Patagonian foreland to Chaitenia, so that the island arc terrane must have been proximal to the continent: its deeper crust is not exposed but several outcrops of ultramafic rocks are known. Devonian metamorphic rims in rocks from the North Patagonian Massif have no counterpart in the low metamorphic grade Chilean rocks. These Paleozoic metasedimentary rocks were also intruded by Pennsylvanian and Jurassic granitoids.

How to cite this article Hervé, F., Calderon, M., Fanning, M., Pankhurst, R., Rapela, C., and Quezada Pozo, P., 2018, The country rocks of Devonian magmatism in the North Patagonian Massif and Chaitenia: Andean Geology, v. 45, no. 3, p. 301-317., doi:http://dx.doi.org/10.5027/andgeo%x