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CRYOGENIAN TO ORDOVICIAN DETRITAL-ZIRCON PROVENANCE OF THE RIFTING CORDILLERAN MARGIN, MONTANA, IDAHO AND UTAH


LINK, Paul K., Department of Geosciences, Idaho State University, Pocatello, ID 83209, YONKEE, Adolph, Department of Geosciences, Weber State University, 2507 University Circle, Ogden, UT 84408, DEHLER, Carol M., Department of Geology, Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505, MAHONEY, J. Brian, Department. of Geology, University of Wisconsin Eau Claire, Eau Claire, WI 54702, BALGORD, Elizabeth, Geology, University of Arizona, 242 E 5th St, Tucson, AZ 85705, KEELEY, Joshua A., Department of Geosciences, Idaho State University, 619 N. Arthur, Pocatello, ID 83204 and MAHON, Robert C., Geology and Geophysics, University of Wyoming, Dept. 3006, 1000 E. University Ave, Laramie, WY 82071-2000, linkpaul@isu.edu

Cryogenian to Ordovician siliciclastic rocks in the northern Rockies record distinct stages of rifting and development of the Cordilleran passive margin, coupled with regional changes in detrital-zircon provenance. The first stage (ca. 770-740 Ma; Uinta Mountain Group and related strata) represents deposition in an E-trending tidal, intra-cratonic basin. Provenance was from uplifted Archean Wyoming province to the north and the Proterozoic Grenvillean-Yavapai-Mazatzal provinces to the south and east.

The second stage (ca. 720-660 Ma; Perry Canyon and Pocatello Fms and related strata) marks deposition of diamictites and laterally variable immature siliciclastic rocks in an overall N-S trending rift basin system. Associated mafic and felsic volcanics have rift-like geochemical signatures. Two phases of glaciation are recorded, with the first prior to 710 Ma and the second lasting >10 Ma, based on ~700 Ma and 685 Ma volcanic zircon grains respectively at the bases and tops of diamictites. Provenance includes locally derived 1.6 to 1.8 Ga and 2.45 Ga zircon grains from the Farmington zone, along with reworked Proterozoic zircon grains and 710 to 670 Ma syndepositional volcanic grains.

The third stage (ca. 650-580 Ma; lower Brigham and McCoy Creek groups) includes mature strata deposited in a broadly subsiding basin. Provenance is mix of the distal Proterozoic Grenvillean-Yavapai-Mazatzal provinces. The fourth stage (ca. 580-510 Ma; Prospect Mountain Qzte and related strata) marks an influx of coarse-grained, arkosic debris and minor mafic volcanism at the base, interpreted to record final rifting, followed by deposition of siliciclastic strata during transition to drift, grading upward into carbonate platform strata. Provenance, restricted by the eustatic Sauk transgression, shifts to a sharp peak at about 1.79 Ga with mixed Neoarchean grains (Flathead Ss).

The fifth stage (Late Cambrian; 505-495 Ma) includes the Worm Creek Qzte Member of the St. Charles Formation and contains a nearly syndepositional 500 Ma zircon population likely derived from unroofing of the Beaverhead Pluton along the Lemhi Arch. The sixth stage (Middle Ordovician; 470-460 Ma) includes the Swan Peak Qzte and correlative units marked by an influx of north-derived Paleoproterozoic and older (>1.8 Ga) detrital zircon grains.

Session No. 153

T161. Detrital Zircon Provenance of Neoproterozoic to Lower Paleozoic Strata of Northern and Western Laurentia
Tuesday, 6 November 2012: 8:00 AM-12:00 PM
203B (Charlotte Convention Center)
Geological Society of America Abstracts with Programs. Vol. 44, No. 7, p.378
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