EXTRAPOLATION OF TECTONIC BOUNDARIES ACROSS THE LABRADOR SHELF - U-PBGEOCHRONOLOGY OF WELL SAMPLES

Near Saglek Fiord, a northerly trending boundary between the early Arc hean Saglek block and the middle Archean Hopedale block extends betwee n drill sires which, respectively, sampled Uivak amphibolite gneiss wi th U-Pb zircon intercept ages of 3742 +/- 12 and 2752 +/- 42 Ma, and m igmatitic Lister gneiss with concordant ages of 3213(-4)(+21) Ma for r estite and 2552(-21)(+4) Ma for leucosome. Titanite ages of ca. 2508 M a are common to both rocks. A nearby metapsammitic gneiss has detrital zircon and monazite ages of 2681 +/- 5, 2700 +/- 4, ca. 2730, and 275 0 +/- 2 Ma representing high-grade metamorphism related to the Hopedal e-Saglek collision and metamorphic monazite of ca. 2560 Ma age represe nting metamorphism of the sediment during reactivation of the Saglek-H opedale suture. Two hundred kilometres southeast, a gneissic granite r ecords a protolith age of 3170 Ma and Late Proterozoic Pb loss. Near t he Nain-Makkovik boundary, 1269 +/- 4 Ma zircons indicate a significan t extension of the Nain Plutonic Suite. South of the Makkovik boundary , a foliated granite yielded an upper intercept age defining intrusion at 1895 +/- 8 Ma and concordant 1872 +/- 5 Ma titanite ages that date subsequent metamorphism, Discordant U-Pb ages from an alkali-feldspar granite also constrain crystallization to ca. 1890 Ma and together wi th the gneiss represent the previously defined Iggiuk event in the Kai pokok domain. Wells near the southerly end of the transect record 1801 +/- 5, 1813 +/- 3, and 1806 +/- 8 Ma ages, respectively, that are typ ical of the synorogenic granitoid suite representing the Cape Harrison domain of southern Makkovik Province.