ABSTRACT
This paper presents zircon U-Pb, REE and Hf data for Paleoproterozoic felsic volcanic rocks from the Colíder Group with outcrops in the southwestern Amazonian Craton. It is estimated that these rocks cover an area of 85,000 km2 with a volume of 2.7 × 106 km3. The Colíder volcanics are comprised of basalts, andesites and a variety of felsic rocks. The felsic rocks are characterized by rhyolite, andesite and dacite lavas with frequent intercalated pyroclastic and epiclastic deposits. Effusive and pyroclastic rocks are intruded in places by hypabyssal porphyritic rocks. The U-Pb ages obtained for the northeastern domain (1782–1776 Ma) are younger than the ages obtained for the southern domain (1800–1787 Ma). The NE volcanic facies show Hf TDM ages between 2.3 and 2.5 Ga (εHf from +1 to −3) and greater fractionation (Ce/Yb – 0.03–0.06) than the younger facies that has TDM from 2.4 to 2.7 Ga (εHf from −3 to −6) with Ce/Yb values of 0.025–0.030. The Hf isotope compositions, REE contents and U-Pb analyses suggest geographic (north-south) variations in composition, crystallization ages, and TDM age zonation during the generation of the Colíder large igneous province.
Acknowledgments
This work received financial support from FAPERJ (grant number 100.713/2014) and the CAPES sandwich (grant number 99999.006532/2015-02). We would also like to thank the University of Geneva and the University of Lausanne for supporting this research.
Disclosure statement
No potential conflict of interest was reported by the author(s).
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