DETRITAL ZIRCON AND MONAZITE FROM THE HYLAND GROUP (NORTHERN CANADIAN CORDILLERA AND ALASKA): EVIDENCE FOR INTRACORDILLERAN “GRENVILLE” BASEMENT

The Hyland Group comprises a regionally extensive sequence of low grade metasedimentary rocks that occur in the Selwyn Basin of the Yukon and in adjacent parts of Alaska. Although formerly considered correlative with the Windermere Supergroup it is now considered a younger sequence that spans the Cambrian-Precambrian boundary. A distinctive feature of the Hyland Group are coarse pebbly sandstones deposited by turbidites which contain up to 10% coarse feldspar granules. In order to examine the provenance of these sediments we conducted U-Pb ID-TIMS analyses of detrital zircon and monazite from 5 widely scattered but stratigraphically equivalent localities in the Yukon and the Fairbanks district of Alaska. A total of 90 grains were analyzed the results of which are dominated by Archean (2600-2900 Ma) and Paleoproterozoic (1800-2000 Ma) ages. However 26 grains returned Mesoproterozoic ages between 1010-1450 Ma, similar to ages reported from the Grenville Province of eastern North America. On the basis of the range of U-Pb crystallization ages is tempting to suggest that the Hyland Group was derived largely from erosion and recycling of material from sequence B sandstones, locally common in the eastern Selwyn Basin and known to be rich in “Grenville age” detrital grains. However when the patterns of sequence B sandstones are compared with the results from the Hyland there is a clear mismatch in ages. Furthermore, the coarse feldspar in the Hyland could not have been derived from the sequence B sandstones which are largely medium grained quartz arenites. We suggest that late Precambrian rifting in the Selwyn Basin exposed crystalline basement as an outboard high that fed the Hyland dispersal system. If correct, it follows that intraCordilleran basement of broadly “Grenville age” may reside in the northern Cordillera, consistent with the SWEAT reconstruction proposed by Moores in 1991.