Vicki McNicoll

Pan-Continental River System Draining Grenville Orogen Recorded by U-Pb and Sm-Nd Geochronology of Neoproterozoic Quartzarenites and Mudrocks, Northwestern Canada

Regional lithostratigraphic correlation of early Neoproterozoic Sequence B on the northwest margin of Laurentia includes a 0.5-2 km-thick, laterally continuous, quartzarenite marker of mainly fluvial origin. Concordant U-Pb ages of 54 single detrital zircons from five regionally dispersed samples cluster in the Archean (2.8-2.6 Ga), Paleoproterozoic (2.0-1.9 Ga), and Mesoproterozoic (1.6-1.0 Ga). The vast majority (85%) of the zircons are of Mesoproterozoic age, with a high proportion clustering between 1.25-1.0 Ga, closely matching the age of synorogenic intrusions in the Grenville Province of North America. A

Lower to Middle Ordovician evolution of peri-Laurentian arc and backarc complexes in Iapetus: Constraints from the Annieopsquotch accretionary tract, central Newfoundland

100 3 \pm 4 Ma

Upper cambrian to upper ordovician peri-gondwanan island ARC activity in the victoria lake supergroup, central newfoundland : Tectonic development of the Northern Ganderian Margin

zircon from the Pinguicula group in the eastern Ogilvie Mountains provides a maximum age for the quartzarenite marker. Sm-Nd isotopic data from intercalated mudrocks indicate a major contribution from sources with relatively juvenile model ages (

Mid–Late Ordovician magmatism and metamorphism along the Gander margin in central Newfoundland

T_{DM} = 1.54-1.74 Ga

The Middle Ordovician to Early Silurian voyage of the Dashwoods microcontinent, West Newfoundland; based on new U/Pb and 40Ar/39Ar geochronological, and kinematic constraints

), consistent with the provenance indicated by the detrital zircons. The isotopic data support both regional lithostratigraphic correlations and the existence of a braided river system of pan-continental proportions that may have emanated from sources along the entire 5000 + km length of the Grenville orogenic front. Proximal parts of this river system may be preserved in a foreland basin setting in the subsurface of the midcontinental USA and perhaps in a thick molassic sequence in central-eastern Greenland.

Basaltic to andesitic volcaniclastic rocks in the Blake River Group, Abitibi Greenstone Belt: 2. Origin, geochemistry, and geochronology

The magnitude of late Mesozoic terrane translation along the western North American continental margin is controversial. Paleomagnetic data suggest more than 3000 km of dextral displacement of the Insular superterrane and associated assemblages between ca. 74 and 50 Ma. Conversely, geologic evidence is more compatible with less than 500 km of offset during this time. Precambrian cratonic rocks older than 2.5 Ga are restricted to northern latitudes (above 40°N) in North America, and the presence or absence of Archean zircons within easterly derived Cretaceous strata has been proposed as a “crucial test” of the major translation hypothesis. There is no plausible source of Archean and Early Proterozoic zircons found in the Queen Charlotte, Nanaimo, and Methow basins other than the Canadian Shield or closely associated Proterozoic strata. The coexistence of Archean–Early Proterozoic, Middle Proterozoic (1.5–1.6 Ga) and Mississippian detrital zircon in these basins indicates deposition in northern latitudes, incompatible with the Baja B.C. hypothesis.