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 Sequen ce B on the northwest margin of Laurentia includes a 0.5-2 km-thick, l aterally continuous, quartzarenite marker of mainly fluvial origin. Co ncordant U-Pb ages of 54 single detrital zircons from five regionally dispersed samples cluster in the Archean (2.8-2.6 Ga), Paleoproterozoi c (2.0-1.9 Ga), and Mesoproterozoic (1.6-1.0 Ga). The vast majority (8 5%) of the zircons are of Mesoproterozoic age, with a high proportion clustering between 1.25-1.0 Ga, closely matching the age of synorogeni c intrusions in the Grenville Province of North America. A 100 3 +/- 4 Ma zircon from the Pinguicula group in the eastern Ogilvie Mountains provides a maximum age for the quartzarenite marker. Sm-Nd isotopic da ta from intercalated mudrocks indicate a major contribution from sourc es with relatively juvenile model ages (T-DM = 1.54-1.74 Ga), consiste nt with the provenance indicated by the detrital zircons. The isotopic data support both regional lithostratigraphic correlations and the ex istence of a braided river system of pan-continental proportions that may have emanated from sources along the entire 5000 + km length of th e Grenville orogenic front. Proximal parts of this river system may be preserved in a foreland basin setting in the subsurface of the midcon tinental USA and perhaps in a thick molassic sequence in central-easte rn Greenland.