The 1800-1770 Ma Colider silicic large igneous province in the Amazonian craton: crustal evolution using zircon in situ REE compositions, U-Pb ages and Hf isotope analyses

Abstract

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.