Paper No. 3
Presentation Time: 9:20 AM
PROVENANCE STUDIES IN THE MEGUMA TERRANE, SOUTHERN NOVA SCOTIA, CANADA
The Meguma terrane of southern Nova Scotia includes clastic sedimentary rocks of the mainly Cambrian to early Ordovician Meguma Group, more than 10 km in thickness, overlain by sedimentary and aerially restricted volcanic rocks of the mainly Silurian-Devonian White Rock and Torbrook formations. The provenance of these sedimentary rocks remains uncertain, although such knowledge is pivotal in paleo-continental reconstructions of components of the Appalachian orogen. The large volume of sediment and its quartz-dominated composition indicate a large continental source region, traditionally assumed to be Africa. This interpretation was supported initially by a limited data base of U-Pb ages from detrital zircon and titanite and 40Ar/39Ar ages from detrital muscovite in the Meguma Group and White Rock Formation. We are undertaking a more detailed study, focused on metasandstone in the Meguma Group and using these same techniques in combination with petrographic and whole-rock geochemical data. Sample locations are well constrained by new mapping and stratigraphic work. The protoliths of the metasandstone units were mainly feldspathic to quartz wacke with subordinate feldspathic to quartz arenite. Quartz is dominantly monocrystalline; locally well rounded, high sphericity grains are possibly second-cycle, derived from eolian sandstone. Quartzite clasts are rare, and the feldspar fraction is mainly plagioclase, with little K-feldspar. Detrital muscovite in the Goldenville Formation is more phengitic in composition compared to that from the Halifax and White Rock formations. Petrographic and chemical data suggest that the source area included calc-alkalic tonalitic and granodioritic rocks; the derived sediment experienced little transport and was poorly sorted during rapid deposition in an active continental margin environment. Previously reported detrital zircon ages cluster at 700-550 Ma and 2150-2000 Ma, compatible with African or Amazonian sources. Available epsilon Nd data are highly negative, and more compatible with an Amazonian source. The source of detrital muscovite is not yet resolved but preliminary data indicate ages of 600-560 Ma. Similarities in age and isotopic compositions suggest some links between sediment provenance in the Meguma terrane and now-adjacent Avalonia.