The Bolivian Andes remained in a retroarc position along most of the Phanerozoic. Its evolution can be divided in two major stages; in the first one, restricted to the early Paleozoic, a voluminous transfer of sedimentary mass in the upper crust occurred. In the second stage, reciclyng of the crustal mass predominated. In the early Paleozoic, an epicratonic marine basin formed among the Amazonia, Arequipa-Antofalla, and Pampean cratons. This basin changed from a retroarc-type to a foreland-type before it filled in the late Paleozoic. Along this interval, three deformation stages came to pass: the areally restricted Ocloyic phase (Ordovician-Silurian boundary), the Eohercinian phase (Devonian-Carboniferous boundary), and the Hercinian phase (Late Carboniferous) which was also areally restricted. In the Mesozoic, brief marine incursions ocurred before a protocordillera began to build in the Eocene. The general uplift of the central Andes started in the Late Oligocene involving the present Altiplano and Eastern Cordillera. Three stages of uplift, separated by regional erosion surfaces of 18 and 10 Ma, can be recognized. The western side of the Eastern Cordillera, named the Huarina belt, played an important role in the evolution of the central Andean region. In this belt ocurred most of the retroarc magmatism; also, the major subsidence of the Paleozoic basin was restricted to this belt. Along the Mesozoic, rifting processes and lithospheric thinning took place preferentially within the Huarina belt. In the Paleogene, this belt was the first to be uplifted separating the Altiplano basin from the rest of the continent, and, in the Late Oligocene, the belt became the backthrust zone of the orogen. Deformation in the Altiplano and Eastern Cordillera ended some 10 Ma ago, when the San Juan del Oro surface formed and the folding in the Subandean region began. The retroarc magmatic activity in the Huarina belt was almost continuous from Paleozoic to Quaternary. On the contrary, the volcanic arc arrived to the Bolivian-Chilean border only in the Lower Miocene, some 23-22 Ma. The retroarc volcanic activity reached the climax in the Late Miocene. The chemical characteristics of the magmas and the huge simultaneous eruptions ocurred in the Huarina belt are suggesting that only one deep process triggered this voluminous magmatism: lithospheric delamination of the the mantle which originated the rising of the asthenosphere up to the base of the crust driving the melting at different levels.
|Translated title of the contribution||Tectonomagmatic evolution of the Bolivian Andes|
|Number of pages||32|
|Journal||Revista de la Asociacion Geologica Argentina|
|State||Published - 2009|