FLARE-UP AND CESSATION OF THE FAMATINA ARC LINKED TO CHANGES IN OBLIQUE CONVERGENCE AND TRANSLATION ON THE GONDWANA MARGIN

The Famatina orogen preserves a long-lived and regionally extensive arc system whose magmatic, structural, and metamorphic history provides unique insight into tectonic effects on Cordilleran arc processes. Magmatism within the Famatina arc in northwest Argentina is interpreted to record the transition from a Cambrian convergent margin to an Ordovician collisional orogen with the accretion of the allochthonous Precordillera terrane. Magmatic flare-up and shut down of the arc, however, occurred along a much greater extent of the margin than the occurrence of the Precordillera terrane. Therefore wide-spread changes in the plate margin conditions likely drove magmatic processes within the arc.

The Famatina arc initiated as a continental arc on Middle Proterozoic basement following the onset of regional convergence and east-dipping subduction beneath the Gondwana margin by 515-495 Ma. Voluminous arc magmatism in the central portion of the Famatina arc occurred from 486-463 Ma with a distinct magmatic flare-up between 472-468 Ma. Arc magmatism dropped off significantly after 465 Ma and ceased by 440 Ma.

The main phase of magmatism and arc flare-up was driven by oblique convergence and underthrusting of forearc sediments beneath the arc. This time period coincided with drowning of the Precordillera carbonate platform, deep burial of the Famatina forearc along oblique thrusts, regional granulite facies metamorphism, and development of shear zones in the retroarc. Abrupt shutdown of the arc at 440-435 Ma coincided with Late Silurian – Early Devonian translation on ductile shear zones in the retro- and forearc regions, suggesting that a change from shortening to strike-slip dominated plate motion lead to the demise of the Famatina arc. Thus, the Famatina arc evolved in a regime far from static and variation in oblique convergence dominated the evolution of the arc – forearc evolution, similar to many aspects of Mesozoic arcs of the North American Cordillera.