New perspectives on the tectonic evolution of the eastern Paraguay Belt revealed through zircon U-Pb-Hf-O systematics of the inner units

Abstract

The Paraguay Belt and Brasília Orogen, the western and eastern segments of the Tocantins Province, respectively, recorded the interactions among the Amazonian, São Francisco-Congo Craton, and Paranapanema Block during the amalgamation of Western Gondwana. The Paraguay Belt joins the Brasília Orogen in the Transbrasiliano Lineament, which separates metasedimentary rocks to the west from metavolcano-sedimentary rocks to the east. This study focuses on four geological units cropping out in Brazil, between the Mato Grosso State southeastern region and the Goiás State western region: the Nova Xavantina Metavolcano-sedimentary Sequence (NXS), the Cuiabá Group (CG), the Barra do Garças-Coxim Unit (BGCU), a newly identified register of foreland sedimentation, and the Bom Jardim de Goiás Metavolcano-sedimentary Sequence (BJGS). Whole-rock elemental geochemistry and Nd-Sr isotopes, along with zircon U-Pb-Hf-O systematics, provide insights into the evolution of this domain.

Metavolcanic rocks from the NXS suggest that it represents a back-arc extensional tectonic environment with oceanic spreading (zircon age of ca. 710 Ma with δ¹⁸O of 4.8 ‰ and chondritic εHf_(t) formed along the southeastern edge of the Amazonian Craton. Metarenites preserve bimodal sources of ca. 0.85 Ga and ca. 1.90 Ga, while lithic metarenites exhibit Mesoproterozoic zircon grains suggesting sources from both the Amazonian Craton and the Paranapanema Block. The maximum depositional age of the lithic metarenites is ca. 715 Ma, coinciding with the age of the volcanic peak. The CG is interpreted as passive margin deposits through the erosion of depleted Mesoproterozoic (1.50–1.45 Ga and 1.23–1.17 Ga) and more evolved Paleoproterozoic (1.97–1.77 Ga) rocks from the Amazonian Craton.

Metasedimentary rocks from the BGCU present age peaks of 800–600 Ma, recording the input of juvenile material into the basin as revealed by zircon grains of ca. 716 Ma and ca. 810 Ma with δ¹⁸O of 4.7–4.8 ‰ and εHf_(t) of + 7. These findings indicate Goiás Magmatic Arc juvenile sources and disclose the evolution of the unit towards a continental arc, as suggested by more evolved zircon grains younger than ca. 700 Ma. Gneisses of ca. 690–655 Ma occur as basement rocks of the BGCU and suggest prolongation of the Goiás Magmatic Arc westward within the Transbrasiliano corridor.