Abstract
Supracrustal rocks of the Araí Group, together with coeval A-type granites represent a ca. 1.77-1.58 Ga old continental rift in Brazil. Two granite families are identified: the older (1.77 Ga) group forms small undeformed plutons, and the younger granites (ca. 1.58 Ga) constitute larger, deformed plutons. Sr-Nd isotopic data for these rocks indicate that the magmatism is mostly product of re-melting of Paleoproterozoic sialic crust. Initial Sr ratios for both granite families are ca 0.726 and 0.720. Most TDM model ages are between 2.58 and 1.80 Ga. epsilonND(T) values are between +3.6 and -11.9. Araí volcanics are bimodal, with basalts and dacites/rhyolites interlayered with continental sediments. The felsic volcanics show Nd isotopic characteristics which are very similar to the granites, and are also interpreted as reworking of Paleoproterozoic crust. Detrital sediments of the Araí Group revealed T DM model ages between 2.4 and 2.16 Ga, indicating that they are the product of erosion of Paleoproterozoic crust. The data indicate that the Araí rift system was established on crust that had just become stable after the Paleoproterozoic orogeny.
Highlights
The Araí Group sediments and volcanics represent a well preserved Paleo- to Mesoproterozoic continental rift association in the central-eastern part of the Tocantins Province, central Brazil (Figure 1)
The Brasília Belt supracrustals occupy the eastern part of the Tocantins Province and constitute a ca. 1000 km long N-S fold-and-thrust belt formed along the western margin of the São Francisco plate
Initial 87Sr/86Sr ratios, poorly defined, are high, indicating that the original magmas are melts derived from older sialic crust; 3
Summary
The Araí Group sediments and volcanics represent a well preserved Paleo- to Mesoproterozoic continental rift association in the central-eastern part of the Tocantins Province, central Brazil (Figure 1). In this study we present new Sr and Nd isotopic data for the granitic and volcanic rocks, as well as for detrital sediments of the Araí Group, and discuss Sr and Nd isotopic data for the granite rocks and Araí volcanics and sediments are listed on Tables I and II.
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