Geodynamic Evolution of the Early Palaeozoic Continental Margin of Gondwana in the Southern Central Andes of Northwestern Argentina and Northern Chile

Abstract

The oldest non-metamorphic rocks of the southern Central Andes (NW Argentina and N Chile) are represented by the quartz-sandstone succession of the late Cambrian Meson Group exposed in the Eastern Cordillera. The Meson Group formed on a shallow marine platform deepening towards the NW. This platform developed presumably as an extensional structure on Pampean basement. Above an erosional unconformity of late Cambrian age, the shallow marine sandstones and shales of the Santa Victoria group (latest Cambrian-early Llanvirn) were deposited in a shelf basin located in the Eastern Cordillera. Farther west in the Puna volcanosedimentary successions (VS, c. 3500 m thick) derived from a magmatic arc located in northern Chile, are connected to eastward subduction and active volcanism during the middle and late Arenig. During the middle Ordovician, the Puna Basin deepened significantly leading to the deposition of the Puna turbidite complex (PTC, c. 3500 m thick). High subsidence and sedimentation rates were caused by the onset of collision of the para-autochthonous Arequipa Massif terrane (AMT), transforming the Arenig ensialic backarc basin into a middle Ordovician marine foreland basin. In response to thrusting in the west, a flexural bulge formed in the east, resulting in the emergence of the Eastern Cordillera shelf (Guandacol event). During the Ashgill, the basin fill was folded in the Ocloyic orogeny, resulting in the formation of the positive area of the Arco Puneno, which since suffered only marginal transgressions in the Llandovery and the late Palaeozoic. The folded Ordovician sedimentary rocks were post-tectonically intruded by the presumably Silurian, partly sheared granitoids of the “Faja Eruptiva de la Puna Oriental” (FE). The shear zones in the FE granitoids document sinistral strike-slip movements of possible Silurian age. Magmatism and the strike-slip system were connected to the probably oblique, SE directed collision of the AMT.