page_title: Geological history of the Precordillera terrane
section_title: Late Ordovician unconformity
hierarchical_section_title: Geological history of the Precordillera terrane / Evidence of rifting / Stratigraphic records / Late Ordovician unconformity
caption_attribution_description: English: Evolutionary diagram of Precordillera from Early Cambrian to Mid-Ordovician showing A) Separation of Precordillera from Laurentia. B) Passive margin at the same time Famatina formation from volcanicity. C) Collision of Precordillera towards Gondwana-Famatina mass
context_page_description: The Precordillera terrane of western Argentina is a large mountain range located southeast of the main Andes mountain range. The evolution of the Precordillera is noted for its unique formation history compared to the region nearby. The Cambrian-Ordovian sedimentology in the Precordillera terrane has its source neither from old Andes nor nearby country rock, but shares similar characteristics with the Grenville orogeny of eastern North America. This indicates a rift-drift history of the Precordillera in the early Paleozoic. The Precordillera is a moving micro-continent which started from the southeast part of the ancient continent Laurentia. The separation of the Precordillera started around the early Cambrian. The mass collided with Gondwana around Late Ordovician period. Different models and thinking of rift-drift process and the time of occurrence have been proposed. This page focuses on the evidence of drifting found in the stratigraphical record of the Precordillera, as well as exhibiting models of how the Precordillera drifted to Gondwana.
context_section_description: The sedimentary records no longer continuous on top of the San Juan Formation, and it is marked as an erosional unconformity. On top of the black shale the eastern Precordillera crust received a continental rise, inducing the rapid intensive events shown by the rifting structure on the deposits above the unconformity. The western basin consists of black graptolitic shale with non-constant thickness which contains silicate clasts, believed to be a kind of rifting-related deposit. The unconformity symbolizes the increasing tectonic activity, probably the start of rifting events and the collision between Precordillera and Gondwana.
caption: Evolutionary diagram of Precordillera from Early Cambrian to Mid-Ordovician showing A) Separation of Precordillera from Laurentia B) Passive margin at the same time Famatinian arc existed C) Collision of Precordillera towards Gondwana-Famatina mass
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