Pinwarian to Grenvillian magmatic evolution in the central Grenville Province: new constraints from ID–TIMS U–Pb ages and coupled Lu–Hf S–MC–ICP–MS data

Abstract

Understanding the magmatic evolution of the rocks once comprising the hinterland of the Grenville Orogen through their Mesoproterozoic formation is a key to understanding the Grenvillian Orogeny as a whole. In this contribution, we present high-precision isotope dilution thermal ionization mass spectrometry (ID–TIMS) U–Pb and coupled solution multicollector inductively coupled plasma mass spectrometry (S–MC–ICP–MS) Lu–Hf zircon data from magmatic rocks occurring in the allochthonous belt of the Grenville Orogen in the central part of the Grenville Province. We document the presence of a large tract of Pinwarian crust represented by a 1497 ± 5 Ma granitic gneiss, as well as large late Geon 14 to early Geon 13 (1434 +7/−11, 1413 ± 12, 1393 ± 8, 1383 ± 1 Ma) magmatic complexes. One Grenvillian plutonic suite of 1015 ± 2 Ma that cross-cuts the host-rock metamorphic fabric has also been dated. This age provides a minimum age of Ottawan metamorphism in the region. The Hf-isotopic data show that the magmatic rocks of Geons 14 and 13 had mixed mantle and crustal sources compatible with intrusion in a supra-subduction setting as is also supported by the whole-rock geochemical data presented. Emplacement of the magmatic rocks occurred in settings varying from a distal margin arc to a contractional and extensional continental arc. Grenvillian-aged magmatism is more ambiguous, but our data indicate that rocks as young as ca. 1015 Ma may have formed in an ensialic setting.