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

A. P. Heinonen*, L. M. Fraga, O. T. Rämö, R. Dall'Agnol, I. Mänttäri, T. Andersen

*Corresponding author for this work

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

The ca. 1525Ma igneous Mucajaí 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±2Ma), monzonite (1526±2Ma), and the main-phase biotite-hornblende granite (1527±2Ma) of the complex intruded the Paleoproterozoic (~1.94Ga) country rocks simultaneously at ~1526Ma and that the more evolved biotite granite is marginally younger at 1519±2Ma. Intraplate magmatism in the Mucajaí region was relatively short-lived and lasted 12million years (1529-1517Ma) at maximum. The Nd (whole-rock, ID-TIMS; ε Nd from -1.9 to -2.8), Hf (zircon, LAM-ICP-MS; ε Hf from -2.0 to -3.1), and O (zircon, SIMS; δ 18O from 6.1 to 7.0) 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.

Original languageEnglish
Pages (from-to)17-34
Number of pages18
JournalLithos
Volume151
DOIs
Publication statusPublished - 15 Oct 2012

Keywords

  • Anorthosites
  • Brazil
  • Geochemistry
  • Isotope geology
  • Petrogenesis
  • Rapakivi granites

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