Agradecimentos: We are grateful to Marcial and Rosendo Pérez and families, Juan Arancibia and Ramón Urriche for all their kindness, aid and assistance during our field work in sierras de Umango, Maz and surroundings. Our several field works within the Western Sierras Pampeanas, Precordillera, San Rafael and Las Matras blocks were possible thanks to the financial support of the grants UNLP 11/N435 and 11/N447, CONICET PIP-5855 and PIP-112-200801-00119 (Argentina), and FAPESP 05/58688-1 (Brazil). The satellite images were provided by CONAE (Comisión Nacional de Investigaciones Espaciales of Argentina). We are most grateful with the observations and suggestions of J.E. Otamendi and an anonymous reviewer, which greatly improved the manuscript Ver menos

Abstract: A comprehensive review of the geological, geochronological, and isotopic features of the Mesoproterozoic Grenvillian terranes attached to the southwest of the Río de la Plata craton in Early Paleozoic times is presented in this paper. They are grouped into the northern (sierras de Umango, Maz and del Espinal and surroundings), central (Sierra de Pie de Palo, southern Precordillera and Frontal Cordillera), and southern (San Rafael and Las Matras Blocks) segments. The Mesoproterozoic basement consists mainly of arc related, intermediate to acidic and mafic–ultramafic rocks of 1,244–1,027 Ma, with juvenile, Laurentian affinity. Exception to it is the Maz Group, with a protracted history and reworked character. They are affected by 846–570 Ma, extensional magmatism in the northern and central segments, which represents the Neoproterozoic breakup of the Rodinia supercontinent. Successive passive margin sedimentation is registered in Late Neoproterozoic (~640–580 Ma) and Cambro-Ordovician (~550–470 Ma) times. The southern segment is noted for the younger sedimentation alone, and for showing the exclusive primary unconformable relationship between the Mesoproterozoic basement and Early Ordovician cover. The effects of Early Paleozoic Famatinian orogeny, associated with the collisions of Cuyania and Chilenia terranes, are recorded as main phase (480–450 Ma), late phase (440–420 Ma), and Chanic phase (400–360 Ma). Among them, the tectonothermal climax is the Ordovician main phase, to which klippe and nappe structures typical of collisional orogens are related in the northern and central segments. Preliminary data allow us to suggest a set of paired metamorphic belts, with an outboard high-P/T belt, and an inboard Barrowian P/T belt Ver menos