Medium-sized continental block in Uruguay, eastern Argentina and southern Brazil
The Rio de la Plata Craton (RPC) is a medium-sized continental block found in
Uruguay, eastern
Argentina and southern
Brazil. During its complex and protracted history it interacted with a series other blocks and is therefore considered important for the understanding of the amalgamation of West Gondwana. Two orogenic cycles have been identified in the RPC: a 2000 Ma-old western domain representing the old craton and a 700–500 Ma-old eastern domain assigned to the
Brasiliano Cycle.[1] It is one of the five
cratons (ancient nuclei) of the
South American continent. The other four cratons are:
Amazonia,
São Francisco,
Río Apa and
Arequipa–Antofalla.
Along the Uruguayan east coast (reaching into Brazil) is the Cuchilla Dionisio Terrane, an
allochthonous African block juxtaposed to the RPC along the
Sierra Ballena Shear Zone (SBSZ).[1]
West of Cuchilla Dionisio, the Nico Pérez Terrane is delimited by two longitudinal shear zones: the SBSZ and the Late Mesoporterozoic
Sarandí del Yí Shear Zone (SYSZ). In the Nico Pérez Terrane
Archean-
Paleoproterozoic-aged
metamorphic and
granitoid rocks as well as Neoproterzoic
sedimentary successions crop out.[1][2] The Neoproterzoic sedimentary successions probably deposited on an Atlantic-style
continental shelf.[1] The terrane hosts a
swarm of NEE-SSW oriented dykes that date to the Neoproterozoic.[3] It has however not been established to which degree Nico Pérez Terrane belongs to –or has affinity with– the Río de la Plata Craton.[2]
East of the SYSZ, the latitudinal
Colonia Shear Zone (CSZ) separates the Palaeoproterozoic (2000±100 Ma) Piedra Alta Terrane to the north from the Tandilia Terrane to the south.[1] A period of
extensional tectonics in the Late Paleoproterozoic coincided with the formation and
intrusion of the
Piedra Alta mafic dike swarm and the
rapakivi granites of
Illescas Batholith.[4] The 1790±5 Ma-old Late Palaeoproterozoic Piedra Alta mafic dike swarm was subsequently affected by the 8 km (5.0 mi)-wide Mesoproterozoic SYSZ and its eastern end bends along the dextral megashear zone.[1][5]
Tectonic evolution
Today, the Río de la Plata Craton
crops out in southern
Uruguay and parts of
Buenos Aires Province,
Argentina.
Crystalline rocks of the Río de la Plata Craton are dated between 2200 and 1700 million years ago, such as rocks in Uruguay which are dated at 1790 ±5
Ma.[6]Dikes trending east-northeast in the same area are dated by
argon-argon dating at 1727 ±10 Ma.[7] The craton has a size of about 20,000 square kilometres (7,700 sq mi).
West Gondwana was assembled along the
Transbrasiliano lineament in the Mid-Cambrian as, on one side, Amazonia, Río Apa, and some minor blocks collided with, on the other side, São Francisco/Congo, Río de la Plata, and some minor blocks. South of this lineament, along the western margin of the Río de la Plata Craton, the 535-520 Ma-old
Pampean orogeny is partly
made of an exotic terrane that was accreted to Gondwana's proto-Pacific margin (i.e. before the Andes had formed.)[8]
The
Adamastor Ocean, a "proto-Atlantic" ocean that opened with the break-up of the
Rodinia supercontinent 780-750 Ma, separated the Río de la Plata Craton from the Congo Craton. The inversion of the Adamastor Ocean began 640 Ma with the development of a large
back-arc basin along the western margin of the
Kalahari Craton and the ocean closed when Río de la Plata collided with Kalahari about 545 Ma along the sinistral
Sierra Ballena Shear Zone.[9]
The São Francisco and Río de la Plata cratons amalgamated 630–620 Ma, closing the Adamastor Ocean on the South American side and forming the
Mantiqueira Mountains around 600 Ma.[10]
^Rivalanti, G.; Mazzucchelli, M.; Molesini, M.; Petrini, R.; Girardi, V.A.V.; Bossi, J.; Campal, N. (1995). "Petrology of late proterozoic mafic dikes in the Nico Perez region, central Uruguay". Mineralogy and Petrology. 55 (4): 239–263.
Bibcode:
1995MinPe..55..239R.
doi:
10.1007/BF01165120.
S2CID127280699.
^Teixeira, Wilson; D'Agrella-Filho, Manoel S.; Hamilton, Mike A.; Ernst, Richard E.; Girardi, Vicente A.V.; Mazzucchelli, Maurizio; Bettencourt, Jorge S. (2013). "U–Pb (ID-TIMS) baddeleyite ages and paleomagnetism of 1.79 and 1.59 Ga tholeiitic dyke swarms, and position of the Rio de la Plata Craton within the Columbia supercontinent". Lithos. 174: 157–174.
Bibcode:
2013Litho.174..157T.
doi:
10.1016/j.lithos.2012.09.006.
^Mazzucchelli, Maurizio; Rivalenti, Giorgio; Piccirillo, Enzo Michele; Vitorio Girardi, Vicente Antonio; Civetta, Lucia; Petrini, Riccardo (1995). "Petrology of the Proterozoic mafic dyke swarms of Uruguay and constraints on their mantle source composition". Precambrian Research. 74 (3): 177–194.
Bibcode:
1995PreR...74..177M.
doi:
10.1016/0301-9268(95)00014-v.
Teixeira, W.; Renne, P.R.; Bossi, J.; Campal, N.; D'Agrella Filho, M.S. (1999). "40Ar-39Ar and Rb-Sr geochronology of the Uruguayan dike swarm, Río de la Plata Craton and implications for Proterozoic intraplate activity in Western Gondwana". Precambrian Research. 93 (2–3): 153–180.
Bibcode:
1999PreR...93..153T.
doi:
10.1016/S0301-9268(98)00087-4.