Sedimentary provenance of the inner segments of the Paraguay Belt: Paleogeographic domains from a distal passive margin?

Author(s)

Gabriella Labate Frugis

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Geociências (IG/BT)
• Defense date: 2022-12-12

Examining board members

Mario da Costa Campos Neto; Marly Babinski; Bernardo Tavares Freitas; Joseneusa Brilhante Rodrigues

• Advisor: Mario da Costa Campos Neto

Abstract

The Western Gondwana final agglutination is recorded in diachronic Neoproterozoic-Paleozoic orogenic belts with distinct tectonic settings englobing several continental blocks. The Paraguay Belt, the westernmost orogenic arm of the Tocantins Province, is the result of the interaction between the Amazonian, Paranapanema and São Francisco-Congo cratons. The easternmost segment of the belt comprises metasedimentary and metavolcanic sequences which recorded a rift to passive margin setting during Tonian-Cryogenian times. This work present wholerock elemental and Nd-Sr isotopic geochemistry and zircon U-Pb, Lu-Hf and O on metasedimentary, metavolcanic and metavolcaniclastic rocks as well as on orthogneiss and granitoids from the Eastern Paraguay Belt and westernmost sequence of the Goiás Magmatic Arc from the Brasília Orogen. The geochemical and geochronological approach suggest the Nova Xavantina Metavolcanic-sedimentary Sequence recorded a 715-750 Ma rifting stage at the back-arc setting as response to the Goiás Magmatic Arc rising due to the Goiás-Pharusian Ocean convergent regime. Zircon Hf-O systematics on tuffs suggest ca. 710 Ma juvenile material input at shallow asthenosphere. The presence of evolved older material on the tuff zircon record propose erosion of old basement rift edges. The ca. 750 Ma volcanism recorded by the Bom Jardim de Goiás Metavolcanic-sedimentary Sequence, on the Brasília Orogen side, is likely associated to the evolution of a juvenile magmatic arc accreted to the Goiás Magmatic Arc. The Glaciomarine Unit, a Cuiabá Group-like sequence, registers the Meso to Paleoproterozoic basement erosion and deposition on passive margin environment at the Amazonian cratonic edge. Zircon Hf-O results indicate juvenile accretion on Mesoproterozoic provinces in the craton. The small amount of Cryogenian-Tonian material on the sedimentary record suggest greater distance between the Goiás Magmatic Arc and the passive margin basin. The Foreland Unit metasedimentary rocks document the direct erosion of a 700-800 Ma juvenile source located at the Goiás Magmatic Arc with lesser influence of older material. The obtained results suggest the Eastern Paraguay Belt geological history started in response to the Brasília Orogen evolution, where the rifting in the back-arc setting would separate the Amazonian and the Paranapanema paleoplates at 715- 750 Ma. The rift evolution could have opened the possibility to oceanic crust formation giving space to a proto-oceanic basin. The Glaciomarine Unit passive margin environment would have been stablished on the Amazonian cratonic edge with influence of marine and glacial regimes until ca. 650-630 Ma. The switch from extensional to contractional regimes is recorded by the Foreland Unit at ca. 550-530 Ma, being deposited on the Goiás Magmatic Arc, depicted by 615-630 Ma orthogneiss from the basement, indicating a prolongation of the arc westward beyond the Paraguay-Brasília orogens limits. (AU)

• FAPESP's process: 17/18174-6 - Sedimentary provenance of the Paraguai belt inner segments: distal paleogeographic domains from a passive margin?
• Grantee: Gabriella Labate Frugis
• Support Opportunities: Scholarships in Brazil - Doctorate