PAN-CONTINENTAL RIVER SYSTEM DRAINING GRENVILLE OROGEN RECORDED BY U-PB AND SM-ND GEOCHRONOLOGY OF NEOPROTEROZOIC QUARTZARENITES AND MUDROCKS, NORTHWESTERN CANADA
Rh. Rainbird et al., PAN-CONTINENTAL RIVER SYSTEM DRAINING GRENVILLE OROGEN RECORDED BY U-PB AND SM-ND GEOCHRONOLOGY OF NEOPROTEROZOIC QUARTZARENITES AND MUDROCKS, NORTHWESTERN CANADA, The Journal of geology, 105(1), 1997, pp. 1-17
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.