U-PB DETRITAL ZIRCON GEOCHRONOLOGY RESULTS OF THE OLDEST ROCKS OF THE MESOZOIC SCOTIAN BASIN AND UNDERLYING BASEMENT IN OFFSHORE NOVA SCOTIA, CANADA

Rocks of offshore Nova Scotia consist of Paleozoic and/or older crystalline basement rocks, overlain by Mesozoic sedimentary rocks that were deposited during the breakup of Pangea. The latter were deposited in multiple partially interconnected and fault-bounded sedimentary basins that can be interpreted using seismic data. We performed U-Pb LA-ICP-MS zircon analysis of more than 20 rock cuttings and core samples collected from the Scotian Basin, offshore southeastern Nova Scotia, to investigate the source of its oldest Mesozoic strata, the Eurydice Formation, and to investigate the origin of the metamorphic basement. Preliminary results are presented here.

Since the present geometry of the sedimentary basins interpreted from seismic data does not reflect their initial geometries, we used U-Pb detrital zircon analysis to further constrain sediment paths during the deposition of the Eurydice Formation, at the onset of the breakup of Pangea. Sandstone samples of the late Triassic Eurydice formation show a large ~700-500 Ma population and smaller ~800 Ma and ~2.2-2.0 Ga populations, and rare or no Mesoproterozoic and Archean grains. A ~380 Ma population is present in three samples from offshore Cape Breton Island, but absent in two samples farther south, suggesting a possible local source.

While Gondwanan terrane boundaries in eastern North America are well constrained on land, offshore, they are interpreted from geophysical data, such as aeromagnetic and gravity surveys. We used U-Pb LA-ICP-MS zircon analysis to investigate these rocks further. U-Pb zircon data from a metasedimentary rock south of Halifax shows major ~2.2-2.0 Ga and ~800-500 Ma populations, and minor Archean and Mesoproterozoic grains (n=92). The youngest zircon population is from the late Ediacaran. Another metasedimentary rock from offshore Cape Breton Island shows a predominant ~650-500 Ma population, a smaller ~800 Ma population and a few Archean and Paleoproterozoic grains (n=128). The youngest zircon population is from the early Cambrian. These detrital signatures suggest an important contribution of Northwest African sources, which is consistent with rocks of the Meguma terrane onshore Nova Scotia. Alternatively, they may be other northwest African crustal fragments as recently discovered throughout the northern Appalachians.