A review of the geology of the Argentinian Fuegian Andes

Seven stratigraphic units reflect the tectonic evolution of the Argentinian Fuegian Andes: Basement (Paleozoic-Jurassic); Lemaire Formation (Upper Jur assic); Yahgan-Beauvoir formations (Lower Cretaceous); Cerro Matrero Format ion (Upper Cretaceous); Rio Claro Formation (Paleocene); La Despedida Group (Eocene): and Cabo Pena Formation (uppermost Eocene-Lower Oligocene). Base ment rocks (garnet, quartz-sericite, and chlorite schists; and amphibolites ) are unconformably covered by the Lemaire Formation (rhyolites; basalts; s lates; and acidic volcaniclastic breccias, tuffs, conglomerates, and turbid ites), formed during extensional tectonism. The post-rift Yahgan Formation (deep-marine black mudstones, andesitic volcaniclastic turbidites and tuffs ) interfingers northward with the Beauvoir Formation (slope and platform bl ack mudstones), and covers the Lemaire Formation unconformably. The Yahgan Formation represents an andesitic, volcaniclastic apron, coeval with a Paci fic volcanic-are, filling a marginal basin floored with oceanic crust. The Late Cretaceous: compressional orogeny resulted in tectonic inversion, clos ure of the marginal basin, peak metamorphism and folding, and initial uplif ting of the Fuegian Andes. By the latest Cretaceous-earliest Paleogene, the Andes were exposed to subaerial erosion, and the lowest Danian Rio Claro F ormation bears clear evidence of an Andean elastic provenance. The Rio Clar o Formation represents the first molasse deposits of the foreland stage of evolution of the Fuegian Andes. Earliest Paleogene north-verging thrust pro pagation deformed the Rio Claro Formation and older units, producing northw ard depocenter migration. La Despedida Group rest!; unconformably on the Ri o Claro Formation and is involved in the thrust and fold belt. Important Eo cene compression resulted in thrusting of central Andean basement schists a nd the Lemaire Formation over Lower Cretaceous and continental Paleogene ro cks, respectively. In the Argentinian Fuegian Andes, the compressional orog eny ceased by the Late Eocene and the subhorizontal Cabo Pena Formation unc omfortably overlies folded La Despedida Group strata. Field mapping suggest s a left-lateral offset of 20-30 km of Cretaceous-Eocene rocks along the Ma gallanes-Fagnano Fault System; this is clear evidence that the strike-slip regime has been active since at least the latest Eocene. (C) 2001 Elsevier Science Ltd. All rights reserved.