Neoarchean and Rhyacian TTG-Sanukitoid suites in the southern S~ao
Francisco Paleocontinent, Brazil: Evidence for diachronous change towards
modern tectonics
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Henrique Bruno,
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Vitalino Elizeu,
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Monica Heilbron,
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Claudio de Morisson Valeriano,
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Rob Strachan,
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Mike Fowler,
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Samuel Bersan,
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Hugo Moreira,
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Ivo Dussin,
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Luiz Guilherme do Eirado Silva,
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Miguel Tupinamb a,
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Julio Almeida,
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Carla Neto,
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Craig Storey
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Abstract
The southern portion of the S~ao Francisco Palaeocontinent in Brazil is denoted by Archean nuclei and Paleoproterozoic
magmatic arcs that were amalgamated during Siderian to Orosirian orogenic processes (ca. 2.4–2.1
Ga). New isotopic U–Pb in zircon and Sm–Nd whole rock combined with major and trace element composition
analyses constrain the crystallization history of the Neoarchean Piedade block (at ca. 2.6 Ga) and the Paleoproterozoic
Mantiqueira Complex (ca. 2.1–1.9 Ga). These therefore display quite different magmatic histories
prior to their amalgamation at ca. 2.05 Ga. Sm–Nd and Rb–Sr isotopes imply a mixed mantle-crustal origin for the
samples in both units. A complete Palaeoproterozoic orogenic cycle, from subduction to collision and collapse, is
recorded in the Piedade Block and the Mantiqueira Complex. Rhyacian to Orosirian subduction processes (ca.
2.2–2.1 Ga) led to the generation of coeval (ca. 2.16 Ga) TTG suites and sanukitoids, followed by late (2.10–2.02
Ga) high-K granitoids that mark the collisional stage. The collisional accretion of the Mantiqueira Complex against
the Piedade Block at 2.08–2.04 Ga is also recorded by granulite facies metamorphism in the latter terrane, along
the Ponte Nova suture zone. The collisional stage was closely followed by the emplacement of within-plate
tholeiites at ca. 2.04 Ga and by alkaline rocks (syenites and enriched basic rocks) at ca. 1.98 Ga, marking the
transition to an extensional tectonic regime. The discovery of two episodes of TTG and sanukitoid magmatism,
one during the Neoarchean in the Piedade Complex and another during the Rhyacian in the Mantiqueira Complex,
indicates that the onset of subduction-related melting of metasomatized mantle was not restricted to Neoarchean
times, as generally believed, but persisted much later into the Paleoproterozoic.
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