An Upper Mesozoic island-arc–back-arc system in the southern Andes and South Georgia

Abstract

SummaryThe Upper Jurassic–Lower Cretaceous strato-tectonic belts of the southern Andes and South Georgia, 2000 km apart, can be correlated and explained as the products of an island-arc–back-arc system. From the Pacific Ocean to the Atlantic, these belts, which exhibit structural and metamorphic differences, are: (1) a pyroclastic belt developed on an ensialic volcanic arc; (2) a back-arc flysch sequence underlain in the southern Andes by a basic complex with oceanic affinities; this was intruded into continental crust as a result of sea-floor spreading which created a marginal basin; (3) a slate sequence deposited on a continental shelf. The pyroclastic and marginal basin belts and the adjacent part of the continental shelf were folded and uplifted during the early Upper Cretaceous, whereas the foreland part of the continental shelf assemblage underwent deformation during the early Tertiary.

Continental underthrusting and obduction during the Cretaceous closure of the Rocas Verdes rift basin, Cordillera Darwin, Patagonian Andes

“…By the Early Cretaceous, the extension had formed the Rocas Verdes basin, a rift basin floored by quasi-oceanic crust [Katz, 1973;Dalziel et al, 1974, Dalziel, 1981Fildani and Hessler, 2005;Calderón et al, 2007]. South of 51°S, deformed remnants of the upper part of the Rocas Verdes basin floor now form the Sarmiento and Tortuga ophiolitic complexes (Figure 1) [Suárez and Pettigrew, 1976;Stern, 1980;Allen, 1982;Wilson, 1983;Alabaster and Storey, 1990;Calderón et al, 2007]. The basin fill includes the shale-dominated Lower Cretaceous Zapata, Yahgan, and La Paciencia formations, which overlie the Tobifera Formation [Wilson, 1991;Dalziel and Elliot, 1971;Alvarez-Marrón et al, 1993;Olivero and Martinioni, 2001;Olivero and Malumián, 2008].…”

The tectonic regime along the Andes: Present‐day and Mesozoic regimes

“…Craton-ward turbiditic and distal platform facies are interbedded with tuffs (Olivero and Martinioni 2001;Olivero et al 2009), while in the inner facies pillow lavas, lava flows and volcanic breccias are indicating the proximity to the magmatic arc (Suárez and Pettigrew 1976;Dalziel 1988). …”

Petrological vestiges of the Late Jurassic-Early Cretaceous transition from rift to back-arc basin in southernmost Chile: New age and geochemical data from the Capitán Aracena, Carlos III, and Tortuga ophiolitic complexes

“…Stratigraphic and sedimentological constraints from the Rocas Verdes basin (Katz, 1964;Watters, 1965;Suárez and Pettigrew, 1976;Winn and Dott, 1978;Suárez et al, 1985;Fildani and Hessler, 2005) indicate that ophiolitic crust was progressively covered by successions of hemipelagic sediments and volcanoclastic turbidites derived from the erosion of a proximal active (or remnant) volcanic arc and pre-Jurassic continental basement rocks having zircon detrital components of Permian, Cambrian, and latest Neoproterozoic ages (cf., Calderón et al, 2007a). The absence of precise geochronological data in the mafic rocks and a precise biostratigraphic record in the sedimentary rocks make it difficult to establish an upper age limit of mafic back-arc magmatism.…”