High-pressure eclogite facies metamorphism and decompression melting recorded in paleoproterozoic accretionary wedge adjacent to probable ophiolite from Itaguara (southern São Francisco Craton - Brazil)

• Published in: Journal of South American earth sciences Vol. 94; p. 102226
• Main Authors: de Oliveira Chaves, Alexandre, Alexandre Goulart, Luiz Emanoel, Coelho, Raphael Martins, Miranda, Daniel Andrade, de Oliveira Aranda, Ramon, Lima de Moraes Ramos, Sérgio Luís
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2019
• Subjects: Accretionary wedge; Decompression melting; HP eclogite facies metamorphism; Ophiolite; São francisco craton; Thermobarometry; U-Th-Pb geochronology; HP eclogite facies metamorphism; São francisco craton; Thermobarometry; U-Th-Pb geochronology; Decompression melting; Ophiolite; Accretionary wedge
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2019.102226

Thermobarometry and monazite U-Th-Pb geochronology of the phengite + chloritoid + biotite + garnet + kyanite bearing mica-quartz schist and of the nearby phengite + garnet bearing Córrego do Peixoto granite from Itaguara Sequence (IS) of the southern São Francisco Craton (SFC) have revealed that, at 2.05±0.05 Ga, metamorphic peak achieved ∼18.5 kbar and ∼626 °C. These pressure-temperature (P-T) conditions correspond to amphibole eclogite facies metamorphism that occurred around 60 km depth, consistent with geothermal gradient of about 10 °C/km, typical of subduction zones in continental collision settings. The continental collision-related tectonic exhumation would have triggered a decompression process of the high-pressure (HP) mica-quartz schist, which was partially melted to generate the Córrego do Peixoto granite at 2.05 Ga in P-T conditions inserted in the wet granite solidus field. The younger 1.93±0.02 Ga monazite age found in both mica-quartz schist and granite could be related to the orogenic collapse-related decompression late stage with amphibolite facies overprint. The mica-quartz schist has been modified by this late stage metamorphism, which partially overprinted primary mineral assemblages. Taking into account that ophiolites, represented in the IS by metamafic-ultramafic rocks, are typically associated to an accretionary wedge in continental collision settings, it is here suggested that mica-quartz schist is part of a probable Paleoproterozoic accretionary wedge formed above a paleo-subduction zone. It would represent a unique case of a very old accretion prism linked to a continental collision. •Rocks from Itaguara Sequence have revealed that, at 2.05 ± 0.05 Ga, metamorphic peak achieved ∼18.5 kbar and ∼626 °C.•Continental collision-related tectonic exhumation triggered decompression process of the high-pressure mica-quartz schist.•High-pressure mica-quartz schist was partially melted to generate the Córrego do Peixoto granite at 2.05 Ga.•Mica-quartz schist is part of a probable Paleoproterozoic accretionary wedge formed above a paleo-subduction zone.