The central Andes in South America is an ideal location to investigate the interaction between a subducting slab and the surrounding mantle to the base of the mantle transition zone. We used finite-frequency teleseismic P-wave tomography to image velocity anomalies in the mantle from 100 to 700 km depth between 18°S and 28°S in the central Andes by combining data from 11 separate networks deployed in the region between 1994 and 2009. Deformation of the subducting Nazca slab is observed in the mantle transition zone, with regions of both thinning and thickening of the slab that we suggest are related to a temporary stagnation of the slab in the mantle transition zone. Our study also images a strong low-velocity anomaly beneath the Nazca slab in the mantle transition zone, which is consistent with either a local thermal anomaly or a region of hydrated material. The shallow mantle (<165 km) under the Eastern Cordillera is generally fast, consistent with proposed underthrusting of the Brazilian cratonic lithosphere or a string of localized lithospheric foundering. Several discontinuous low-velocity anomalies are observed beneath parts of the Altiplano and Puna Plateau, including two strong low-velocity anomalies in the upper mantle under the Los Frailes volcanic field and the southern Puna Plateau, consistent with proposed asthenospheric influx following lithospheric delamination.

Abstract Basin classification rests on a plate tectonic foundation, highlighting lithospheric substrate, proximity to plate margin and relative motion of the nearest plate boundary. Major mechanisms for regional subsidence and uplift are subdivided into isostatic, flexural and dynamic groups. Basin-forming mechanisms and basin types do not exhibit simple cause-and-effect relationships, but rather reflect a matrix-type relationship. Different basin types have different spans of existence, with generally shorter life spans related to more tectonically active settings. Many ‘polyhistory’ basins, composed of two or more megasequences, reflect a long evolution dominated by different basin-forming and basin-modifying mechanisms. The supercontinent cycle is marked by distinct sets of basin types, developed during successive phases of the cycle. Major classification schemes are reviewed briefly, before surveying the range of basin types represented in the Proterozoic of several key cratonic areas. Basins examined encompass almost the entire Neoarchaean–Neoproterozoic period. All of these basins have a relatively long history of preservation, which can be tied to the essentially continental character of their basement rocks and concomitant enhanced ‘survivability’. Their preservation thus underlines the longevity and inherent stability of the continental lithosphere. The distinction between basin occurrence over geological time and preferential preservation is important when viewing the geological record.

Abstract This work integrates the available geological information and geochronology data for the Cretaceous–Recent magmatism in the South Atlantic, represented by onshore and offshore magmatic events, including the oceanic islands along the transform faults and near the mid-ocean ridge. The analysis of the igneous rocks and their tectonic settings allows new insights into the evolution of the African and Brazilian continental margins during the South Atlantic opening. Following the abundant volcanism in the Early Cretaceous, the magmatic quiescence during the Aptian–Albian times is a common characteristic of almost all Brazilian and West African marginal basins. However, rocks ascribed to the Cabo Granite (104 Ma) are observed in NE Brazil. In West Africa, sparse Aptian–Albian ages are observed in a few coastal igneous centres. In the SE Brazilian margin, an east–west alkaline magmatic trend is observed from Poços de Caldas to Cabo Frio, comprising igneous intrusions dated from 87 to 64 Ma. Mafic dyke swarms trending NW also occur in the region extending from the Cabo Frio Province towards the Central Brazilian Craton. On the West African side, Early Cretaceous–Recent volcanism is observed in the Walvis Ridge (139 Ma), the St Helena Ridge (81 Ma) and the Cameroon Volcanic Line (Early Tertiary–Recent). Volcanic islands such as Ascencion (1.0–0.65 Ma), Tristão da Cunha (2.5–0.13 Ma) and the St Helena islands (12 Ma) most probably correspond to mantle plumes or hot spots presently located near the mid-Atlantic spreading centre. Within the South America platform and deep oceanic regions, the following volcanic islands are observed: the Rio Grande Rise (88–86 Ma), Abrolhos (54–44 Ma), the Vitória–Trindade Chain (no age), Trindade (2.8–1.2 Ma) and Fernando de Noronha (12–1.5 Ma). There are several volcanic features along the NW–SE-trending Cruzeiro do Sul Lineament from Cabo Frio to the Rio Grande Rise, but they have not been dated. The only known occurrence of serpentinized mantle rocks in the South Atlantic margin is associated with the Saint Peter and Saint Paul Rocks located along the São Paulo Fracture Zone. The Cameroon Volcanic Line in NW Africa is related to the magmatism that started in the Late Cretaceous and shows local manifestations up to the Present. The compilation of all available magmatic ages suggests an asymmetrical evolution between the African and South America platforms with more pre-break-up and post-break-up magmatism observed in the Brazilian margin. This is most likely to have resulted from the different geological processes operating during the South Atlantic Ocean opening, shifts in the spreading centre, and, possibly, the rising and waning of mantle plumes. Supplementary material: A complete table with radiometric dates that have been obtained by universities, government agencies and research groups is available at: www.geolsoc.org.uk/SUP18596

The southern Brazilian Shield comprises a number of tectonostratigraphic blocks representing two terranes. The São Gabriel block consists of relics of two Brasiliano juvenile magmatic arcs; the Porongos belt located on the Encantadas block formed in a passive margin setting. Plate tectonic evolution started with opening of an oceanic basin to the east of the Rio de la Plata craton since at least 0.9–1.0 Ga. An intra-oceanic island arc formed due to eastward subduction and was subsequently accreted to the eastern margin of the Rio de la Plata craton. Westward subduction beneath the newly formed active continental margin occurred between ca. 850 and 700 Ma. At the same time, the Porongos basin formed on stretched continental crust of the Encantadas passive margin. Collision of the two terranes took place at ca. 700–660 Ma followed by left-lateral ductile shear along the Dorsal de Canguçu Shear Zone between 670 and 620 Ma and 630- to 610-Ma sinistral shearing in the Dom Feliciano belt farther east. The episodic character of orogenic evolution can be observed throughout Brazil. The Brasiliano belts cannot be directly linked with pan-African belts in southwestern Africa because main deformation in the latter occurred 50–70 Ma later. The assembly of Gondwana comprises a series of collisions of cratons and microcontinents over a time span of nearly 400 Ma; however, a number of orogenic episodes can be discriminated. Their synchroneity suggests that temporally equivalent episodes are coupled with the global plate tectonic framework, which, however, is far from resolved.

Detailed mapping and facies analysis of a thick succession of diamictites of the Upper Ordovician Cancañiri Formation in southern Bolivia has revealed a glacioterrestrial origin for these sediments. The Cancañiri diamictites were deposited during three advances of a temperate, grounded ice sheet. They contain subglacial, englacial, and proglacial outwash sediments that increase in abundance from southeast to northwest. Clast fabrics and deformation features indicate SSE to NNW motion of the ice masses. Components of the diamictites usually display abrasion features such as facets and glacial striae. Provenance studies indicate that the pebbles comprise ∼35% of siliciclastic sediments, mainly from the underlying shallow marine Ordovician rocks, 27% of slightly metamorphosed sediments that in part can be attributed to the Precambrian–Cambrian Puncoviscana Formation of northwestern Argentina, and a crystalline basement suite of metamorphic rocks (18%) and magmatic (mainly plutonic) rocks (20%). Due to the absence of typical lithologies, the Brazilian Shield, the Paraguay belt, and the southern Arequipa-Antofalla block could be excluded as possible source areas. The crystalline and metasedimentary clasts display strong affinities with the Pampean basement in central Argentina. All data consistently suggest that the Cancañiri tillites of southern Bolivia were deposited by a regional, low-latitude ice sheet that was independent of the main inland ice mass of Gondwana and centered SSE of the study area, in a Neoproterozoic to Cambrian orogenic belt in the area of the present Argentinean Chaco.

Within the Amazonian Craton, Archean crust is restricted to the Carajás granite-greenstone terrain. The younger Maroni-Itacaiunas province, including supra-crustal sequences and associated calc-alkaline granitoids, is linked with the Birimian system in West Africa, making up a large Paleoproterozoic cratonic nucleus. Beginning at ca. 2.0 Ga, accretionary belts formed along the southwestern margin of this nucleus, giving rise to the Ventuari-Tapajós (2000–1800 Ma), Rio Negro–Juruena (1780–1550 Ma), and Rondonian–San Ignacio (1500–1300 Ma) tectonic provinces. Continued soft-collision/accretion processes driven by subduction produced a very large “basement” in which granitoid rocks predominate, many of them with juvenile-like Nd isotopic signatures. Felsic volcanics are also widespread; however, there is no evidence of Archean basement inliers, and regions with high-grade metamorphics are restricted. The Sunsas-Aguapeí (1250–1000 Ma) orogenic belt, at the southwestern end of the craton, was originated in an extensional environment, later deformed during the Grenvillian collision between Amazonia and Laurentia. Over the cratonic area, a widespread anorogenic granitic magmatism (1000–970 Ma) is a reflection of this orogeny over the stable foreland. After the termination of the Sunsas orogeny, continental fragmentation affected the eastern margin of the Amazonian Craton. The intra-oceanic Goiás magmatic arc, closely associated with the Transbrasiliano megasuture, is the evidence of a large oceanic domain that started its consumption between 900 and 800 Ma, giving rise to juvenile material represented by calc-alkaline orthogneisses. Later, these units were deformed during the Brasiliano orogeny (700–500 Ma), in the process of amalgamation of Gondwana.

An overview of the tectonic and magmatic evolution of the Peruvian Andes since late Oligocene time is presented. From 30 to 26 Ma, the weak deformation and the nearly total quiescence of magmatic activity correlates with a very low convergence rate between the Farallon and the South American plates. From 26 Ma to the Present, the tectonic regime outside the sub-Andean retroarc foreland has been unstable, characterized by long periods of tectonic quiescence separated by five short-lived generalized compressional events dated approximately at 26, 17, 10, 7, and 2 Ma, respectively. During the quiescent tectonic periods, Andean shortening was minor and occurred mainly in the sub-Andean foreland, whereas extensional tectonics prevailed within the High Andes and the fore-arc. Conversely, most of the late Cenozoic Andean shortening, even in the sub-Andean foreland, occurred during the generalized compressional events. The following model can be invoked to interpret this unstable tectonic regime: during the tectonically “quiet” periods, most of the westward drift of the South American plate is accommodated by an absolute westward overriding of the continental plate over a retreating Nazca slab. In this steady-state regime, the compressional events may be considered as instabilities of the dynamic equilibrium between lithospheric motion and Andean deformation. During the compressional events, virtually all the westward drift of South America is accommodated by the tectonic shortening of the Andes, i.e., there is no slab retreat. The calc-alkaline arc remained stable from 26 Ma to the Present in southern Peru and from 26 Ma to 4 Ma in central Peru after which the slab shallowed. Calc-alkaline magmatism is the normal product of a subduction beneath an asthenospheric mantle wedge and is quite independent of the Andean state of stress. In central Peru, back-arc alkaline magmatism appeared when the convergence rate was the highest, i.e., during the Miocene, while in southern Peru, Miocene to Present shoshonitic volcanism was controlled by deep-seated faults. Peraluminous felsic magmatism of the Cordillera Oriental of southeastern Peru was controlled by the underthrusting of the Brazilian shield under the Andes.