DETRITAL ZIRCONS IN THE FLUVIAL KAYENTA FORMATION (LOWER JURASSIC) ON THE COLORADO PLATEAU

Detrital zircon grains (n=100 per sample) of the Kayenta Formation (Lower Jurassic) were collected from southern outcrops at Moenkopi Wash just outside Tuba City in northern Arizona where paleocurrent indicators record flow from the southeast, from eastern outcrops near the Dolores River in western Colorado where paleocurrent indicators record flow from the northeast, and at North Wash in southern Utah. Detrital zircon grains were analyzed individually by LA-ICPMS using a beam diameter of 50 microns. Four grains from Moenkopi Wash, ten from Dolores River, and seven from North Wash were removed from consideration due to >20% discordance or poor precision, leaving 96, 90, and 93 reliable analyses respectively. Varied detrital zircon age populations in all three samples include prominent clusters of Permian-Triassic grains (4%-7% with frequency peaks at 240-260Ma), Paleozoic and Neoprotrozoic grains (16%-23% in the range of 340-680 Ma), and Grenville-derived grains (38%-58% in the range of 880-1340 Ma). Subordinate clusters include middle Proterozoic (5%-8% at 1360-1480 Ma), early Proterozoic (6%-12% at 1580-1920 Ma), and Archaean (2%-4% at 2700-2900 Ma) grains. Distant transport or recycling is indicated for most of the grain populations, with Paleozoic-Grenville grains probably derived from the Appalachian-Ouachita orogen, and Permian-Triassic grains possibly derived from the East Mexico arc. Only 10%-20% of the detrital zircon grains could have been derived from the nearby Yavapai-Mazatzal basement belt of southwest Laurentia.