Continental growth through protracted subduction and accretionary processes along Western Gondwana: The case of the Ocloyic Orogeny in southern South America

ASTINI, R.A.; COLLO, G.; MARTINA, F.

Niza, Francia

Simposio; VII International Symposium on Andean Geodynamics (ISAG); 2008

Since the Middle Cambrian and after the consolidation of Gondwana through mayor collisional orogens, the Proto-Andean region of South America faced an open ocean, resulting in quasi-permanent subduction and development of a protracted exterior-orogen during the Paleozoic (the Terra Australis orogen). Within such expanded time interval (~300 m.y.) discrete orogenic features imply development of recurrent processes related to a variety of transient coupling mechanisms. However, Cenozoic structural complexities and spatial superposition of different age mountain-building processes along the Andean margin has prevented finding a simple and universal model to explain the architectural and continuity relationships between temporally constrained orogenies within the Central Andes. Recent stratigraphically and regionally constrained geochronological work has allowed great improvement in our understanding and discrimination of distinct orogenic episodes. Nevertheless, understanding of the across and along-strike variations of any particular orogeny is still unclear. Focussing within the more well-known southern segment of the Central Andes in Argentina during the Ordovician may help understanding the complexities within an orogenic cycle. Probably the most compelling and distinct tectonothermal event including metamorphism, deformation, magmatism and basins development within the Terra Australis orogen occurred during the Ordovician and is known as the Ocloyic Orogeny. This is a composite orogenic episode that in South America can now be traced from Patagonia into Perú (>4000 km) and that has been defined, half a way, in northwestern Argentina, on the basis of stratigraphic relationships. In the Central Andean basin (Northewest Agentina, Bolivia and Perú), the erosive effects of the Late Ordovician glaciation amalgamate with the tectonic effects in the Ocloyic unconformity, implying ~50 m.y. of Proto-Andean history (approximately ranging from 490 to 440 Ma). Various names have been used to embrace the crustal processes occurring within this interval, probably the more commonly being that of Famatinian Orogeny. However, in the light of the more recent geochronological research this term is very loosely defined and has lost its meaning. In the past, the Ocloyic Orogeny has also been correlated with the Taconic Orogeny, but it is now clear that they are independent, being their only similarity that both occurred largely during the Ordovician, although to opposite sides of the Iapetus.