Petrogenesis of the igneous Mucajai AMG complex, northern Amazonian craton - Geochernical, U-Pb geochronological, and Nd-Hf-O isotopic constraints

The ca. 1525 Ma igneous Mucajai anorthosite-monzonite-granite (AMG) complex in northern Brazil is a rare manifestation of Mesoproterozoic intraplate magmatism in the northern Amazonian Craton. The complex comprises a two-phase rapakivi granite batholith with subordinate quartz-fayalite monzonites and syenites and the closely associated Repartimento anorthosite. Zircon U-Pb (ID-TIMS) geochronology reveals that the anorthosite (1526 +/- 2 Ma), monzonite (1526 +/- 2 Ma), and the main-phase biotite-hornblende granite (1527 +/- 2 Ma) of the complex intruded the Paleoproterozoic (similar to 1.94 Ga) country rocks simultaneously at similar to 1526 Ma and that the more evolved biotite granite is marginally younger at 1519 +/- 2 Ma. Intraplate magmatism in the Mucajai region was relatively short-lived and lasted 12 million years (1529-1517 Ma) at maximum. The Nd (whole-rock, ID-TIMS; epsilon(Nd) from -1.9 to -2.8), Hf (zircon, LAM-ICP-MS; epsilon(HF) from -2.0 to -3.1), and 0 (zircon, SIMS; delta O-18 from 6.1 to 7.0 parts per thousand) isotopic compositions of the studied rocks are fairly uniform but still reveal a small degree of isotopic heterogeneity in the Paleoproterozoic crust enclosing the complex. The small isotopic differences observed in the two types of rapakivi granites (biotite-hornblende granite and biotite granite) may result either from an isotopically heterogeneous lower crustal source or, more likely, from contamination of the granitic magma derived from a lower crustal source during prolonged residence at upper crustal levels. (C) 2011 Elsevier B.V. All rights reserved.