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Title: Metamorphic record of collision and collapse in the Ediacaran- Cambrian Araçuaí orogen, SE-Brazil : insights from P–T pseudosections and monazite dating.
Authors: Peixoto, Eliza Inez Nunes
Alkmim, Fernando Flecha de
Soares, Antônio Carlos Pedrosa
Lana, Cristiano de Carvalho
Chaves, Alexandre de Oliveira
Keywords: Barrovian metamorphism
Buchan metamorphism
Extensional collapse
Fold-thrust belt
Issue Date: 2017
Citation: PEIXOTO, E. I. N. et al. Metamorphic record of collision and collapse in the Ediacaran- Cambrian Araçuaí orogen, SE-Brazil : Insights from P–T pseudosections and monazite dating. Journal of Metamorphic Geology, v. 36, p. 147-172, 2018. Disponível em: <>. Acesso em: 08 fev. 2019.
Abstract: The Arac ua ı orogen is the Brazilian counterpart of the Arac ua ı-West Congo orogenic system (AWCO), a component of the Ediacaran-Cambrian orogenic network formed during the amalgamation of West Gondwana. The northwestern portion of the Arac ua ı orogen is dominated by a succession of metasedimentary rocks made up of Meso- to Neoproterozoic rift, passive margin and syn-orogenic sequences, locally intruded by post-collisional granites. These sequences are involved in three distinct tectonic units, which from west to east are: the southern Espinhac o foldthrust system (SE-thrust system), the normal-sense Chapada Acau~a shear zone (CASZ) and the Salinas synclinorium. Three deformation phases were documented in the region. The first two phases (D1 and D2) are characterized by contractional structures and represent the collisional development stage of the orogen. The third phase (D3) is extensional and currently viewed as a manifestation of orogenic collapse of the system. The distribution of the metamorphic mineral assemblages in the region characterizes two metamorphic domains. The MDomain I on the west, encompassing the SE-thrust system and the CASZ, is marked by a syn-collisional (syn-D1) Barrovian-type metamorphism with P–T conditions increasing eastwards and reaching ~8.5 kbar at ~650°C between 575 and 565 Ma. The M-Domain II comprises the Salinas synclinorium in the hangingwall of the CASZ, and besides the greenschist facies syn-collisional metamorphism, records mainly a Buchan-type metamorphic event, which took place under 3–5.5 kbar and up to 640°C at c. 530 Ma. The northwestern Arac ua ı orogen exhibits, thus, a paired metamorphic pattern, in which the Barrovian and Buchan-type metamorphic domains are juxtaposed by a normal-sense shear zone. Lithospheric thinning during the extensional collapse of the orogen promoted ascent of the geotherms and melt generation. A large volume of granites was emplaced in the high grade and anatectic core of the orogen during this stage, and heat advected from these intrusions caused the development of Buchan facies series over a relatively large area. Renewed granite plutonism, hydrothermal activities followed by progressive cooling affected the system between 530 and 490 Ma.
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