DRASTIC PROVENANCE CHANGE BETWEEN NEOPROTEROZOIC STRATA IN NORTHERN AND CENTRAL WASATCH RANGE, UTAH: CONSTRAINING PALEOGEOGRAPHY OF NEWLY FORMED RIFT BASINS

We report new SHRIMP and LA ICPMS U-Pb dating of detrital zircon populations from the Neoproterozoic (Cryogenian-Ediacaran) lower Huntsville sequence of northern Utah, schist of Stevens Spring in the Raft River Range near Dove Creek, Utah and the Mineral Fork Tillite in the central Wasatch Range, Utah. Populations include 1) 2.4 to 2.8 Ga (Wyoming Province and unknown Paleoproterozoic Farmington Zone source), 2) 1.8-1.6 Ga Paleoproterozoic and 3) Grenville-age 1.2-1.0 Ga. The data show a local Archean and Paleoproterozoic source terrane for the northern Wasatch Range near Willard, Utah and a distal Grenville-aged provenance for strata in the central Wasatch Range (Mineral Fork Tillite) and Raft River Range.

Northern Wasatch samples from allochthonous units that directly overlie the Willard Thrust include the diamictite-bearing, formation of Perry Canyon (75% grains >2.34 Ga) and overlying feldspathic Maple Canyon Fm (all grains >2.34 Ga). The Perry Canyon has minor Paleoproterozoic and Grenville-aged populations. This is consistent with a local source during deposition prior to integration of drainages along the rifting margin.

In contrast, the autochthonous Mineral Fork Tillite in the central Wasatch Range shows a dominant Grenville-age population (70% of grains are 1.0 to 1.25 Ga) with 20% Archean grains (2.6 to 2.9 Ga) and minor influx of Mesoproterozoic and Paleoproterozoic grains. K-S statistics reveal that the Mineral Fork, the Caddy Canyon of the Brigham Group in SE Idaho, and the Stevens Spring schist of the Raft River Range have identical provenance. All show the same dominant Grenville-age population. This may represent a large river system that flowed along the southern margin of the Wyoming Province delivering 1.2-1.0 Ga grains from the Grenville highlands of eastern and south-central Laurentia during Cryogenian glaciation and rifting or 2) northward transport from the Grenville Province in Texas across subsided intervening Paleoproterozoic provinces, or 3) a mystery western terrane that produced 1.2 to 1.0 magmatic zircons.