Anatomy and global context of the Andes : Main geologic features and the Andean orogenic cycle

Abstract

The Andes is the largest orogenic system developed by subduction of oceanic crustalong a continental margin. Subduction began soon after the Rodinia break-up in LateProterozoic times, and since that time has been intermittently active up to the present.The evolution of the Pacific margin of South America during the Paleozoic occurred inthe following stages. (1) An initial Proterozoic rifting followed by subduction and finalre-amalgamation of the margin in Early Cambrian times, as depicted by the Puncoviscanaand Tucavaca basins and related granitoids in southern Bolivia and northern Argentina.(2) A later phase of rifting in the Middle Cambrian with subsequent collisions in MiddleOrdovician times of para-autochthonous terranes derived from Gondwana such asParacas, Arequipa, and Antofalla, and exotic terranes originated in Laurentia such asCuyania, Chilenia and Chibcha. (3) Final Permian collision between South America andNorth America to form Pangea during the Alleghanides orogeny; this collision left behindrifted pieces of Laurentia as the Tahami and Tahuin terranes in the Northern Andes andother poorly known orthogneisses in the Cordillera Real of Ecuador in the Late Permian-Early Triasic. (4) The amalgamation of the Mejillonia and Patagonia terranes in EarlyPermian times were the last convergence episodes recorded in the margin during theGondwanides orogeny. This set of rifting episodes and subsequent collisions along thecontinental margin were the result of changes of the absolute motion of Gondwana related to global plate reorganizations during Proterozoic to Paleozoic times. Ageneralized rifting during Pangea break-up in Triassic times concentrated extension in thehanging-wall of the sutures that amalgamated the Paleozoic terranes. The opening of theIndian Ocean in Early Jurassic times was associated with a new phase of subductionalong the continental margin. The north-eastward absolute motion of western Gondwanaproduced a negative trench roll-back velocity that controlled subduction under anextensional regime until late Early Cretaceous times. The Northern Andes of Venezuela,Colombia and Ecuador recorded a series of collisions of island arcs and oceanic plateausfrom the Early Cretaceous to the Middle Miocene as a result of the interaction with theCaribbean plate. The remaining Central and Southern Andes recorded periods oforogenesis and mountain building alternating with periods of quiescence and nodeformation as recorded in parts of the Oligocene. Based on the generalized occurrenceof flat slab subduction episodes through time, as recorded in most of the Andeansegments in Cenozoic and older times, a conceptual orogenic cycle is proposed toaccount for the sequence of quiescence, minor arc magmatism, expansion and migrationof the volcanic fronts, deformation, subsequent lithospheric and crustal delamination, with final foreland fold and thrust development. These episodes are related to shallowingand steepening of the subduction zones through time. This conceptual cycle, similar tothe Laramide orogeny in North America, may be recognized wherever a subductionsystem is or was active in a continental margin.