PRELIMINARY U–Pb GEOCHRONOLOGICAL DATA FROM THE MEALY MOUNTAINS TERRANE, GRENVILLE PROVINCE, SOUTHERN LABRADOR

Preliminary U–Pb geochronological studies of zircon and titanite collected from samples of gneissic monzodiorite, foli-ated quartz monzodiorite, and an undeformed monzonite that occur in the southwestern part of the Grenvillian Mealy Moun-tains terrane (MMT) give igneous emplacement ages of 1659 ± 5 Ma, 1650 ± 1 Ma and 1643 ± 2 Ma, respectively. Despite the significant textural and structural differences between the samples, the isotopic data suggest that all three of these pyrox-ene-bearing granitoid rocks are components of the Mealy Mountains intrusive suite (MMIS), a mid-Labradorian AMCG suite. In contrast, zircons from a sample of foliated granite from the MMT give a 1514 ± 10 Ma age, interpreted to be the time of igneous emplacement. This data is significant because it demonstrates that the southwestern MMT includes Pinwarian intrusions, and that it has been overprinted by Mesoproterozoic, post-1514 Ma, deformation. Lower-intercept ages from the two deformed MMIS rocks and the Pinwarian granite are loosely constrained between 1050 and 940 Ma, suggesting the tectonothermal event overprinting these rocks is Grenvillian. However, the data do not eliminate the possibility that the region has been affected by overprinting Paleoproterozoic and Mesoproterozoic events. The fact that the ca. 1643 Ma monzonite is undeformed and has apparently escaped deformation is consistent with field observations that the state-of-strain in the area, at all scales, is heterogeneous, although there is a general increase in both the degree of recrystallization and tectonic fabric development toward the southern MMT