The Lower Paleozoic Magmatism of Southwestern Gondwana and the Evolution of Famatinian Orogene

RAPELA, C.W.; COIRA, B.; TOSELLI, A.J.; SAAVEDRA, J.

INTERNATIONAL GEOLOGY REVIEW

TAYLOR & FRANCIS INC

Lugar: Londres; Año: 1992 vol. 34 p. 1081 - 1142

0020-6814

This is a version modified and updated for a broader audience, of a paper in Spanish by the same authors: ?El magmatismo del Paleozoico Inferior en el Sudoeste de Gondwana,? published in the symposium volume Paleozoíco Inferior de Ibero América, 1992, J. G.. Gutiérrez Marco, J. Saavedra and I. Rábano (Eds.), Universidad de Extremadura, Badajoz. Spain. Lower Paleozoic magmatism in South America is most clearly recorded in central and northwestern Argentina (Sierras Pampeanas. Famatina System. Puna, Eastern Cordillera) extending into southern Bolivia, northeastern Chile and southwestern Peru. Exposures are much more scattered south of 33° 5, where they appear as the basement rocks of the Patagonian massifs (North Patagonian and Deseado) and are recognized in drill core as far south as the Straits of Magellan. The best exposed terranes are in the Sierras Pampeanas and the Famatina System between 28-33° S, where foreland thrusting associated with Upper Tertiary flat-slab subduction uplifted mountain blocks to as much as 6200 meters above sea level. The geological, geochronological and geochemical characteristics of the Lower Paleozoic magmatism in the various geological provinces are reviewed and compared. The metamorphic and igneous sequences register a complex history extending over some 230 m.y. indicating that they were pan of an orogen?the Famatinian orogen. Early and Middle Cambrian basic alkaline volcanism intercalated in the turbiditic and sedimentary sequences of the Puma and the Eastern Cordillera Oriental suggest an early episode of supercontinent rifting (Pampean Cycle). Upper Cambrian and Lower Ordovician island-arc magmatism suggests convergence near or along the margin of the supercontinent. During this episode, a protracted eastward-dipping subduction regime along the western margin produced a wide belt of calc-alkaline volcanic rocks, metaluminous granitoids and hybrid products of basic and granitic magma (Puna and Famatina System), A coeval inner Cordilleran belt of peraluminous granites was developed in the eastern Sierras Pampeanas, associated with rhyolites in the easternmost sector of this province. The period of convergence ended with a continental collision, probably involving more than one episode, whose timing is stiIl not well established. The age distribution of granites with a significant crustal component (post D2, G2 group) shows conspicuous peaks associated with deformation events in the Upper Ordovician Ocloyic (Taconic) phase and the Upper Devonian Chanic (Acadian) phase. Both the subduction and collision-related magmatic events are known as the Famatinian Cycle; correspondingly, the deformational events that occurred In the Upper Cambrian-Upper Devonian interval are known as the Famatinian orogeny. Paleozoic intrusive activity in the central sector of the orogen culminated with the intrusion of, first, large batholiths of K-eldspar megacryst-bearing-monzogranites that are typical of post-collision uplifts at 35O Ma, and second, small plutons showing geochemical characteristics of withinplategranites at ~320 Ma. The final configuration of southwestern Gondwana was attained during these late episodes of the Famatinian orogeny. In late Paleozoic time the main igneous activity shifted to the west and a new magmatic are was established in the high Andean Cordillera and the Coast Ranges of Chile.