HR: 08:30h
AN: T41C-03    [Abstracts]
TI: Detrital Zircon Record of Colorado River Incision
AU: * Kimbrough, D
EM: dkimbrough@geology.sdsu.edu
AF: San Diego State University, Department of Geological Sciences, San Diego, CA 92182- 1020, United States
AU: Grove, M
EM: marty@ess.ucla.edu
AF: UCLA, Department of Earth and Space Sciences, Los Angeles, CA 90095-1567, United States
AU: Gehrels, G
EM: ggehrels@geo.arizona.edu
AF: University of Arizona, Department of Geosciences, Tucson, AZ 85721, United States
AU: Dorsey, R
EM: rdorsey@uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403, United States
AU: House, K P
EM: khouse@unr.edu
AU: Howard, K
EM: khoward@usgs.gov
AF: U.S. Geological Survey, MS 973, Menlo Park, CA 94025, United States
AU: Pearthree, P A
EM: phil.pearthree@azgs.az.gov
AF: Arizona Geological Survey, 416 W. Congress #100, Tucson, AZ 85701, United States
AU: Spencer, J E
EM: jon.spencer@azgs.az.gov
AF: Arizona Geological Survey, 416 W. Congress #100, Tucson, AZ 85701, United States
AU: Mahoney, B
EM: MAHONEJ@uwec.edu
AF: University of Wisconsin Eau-Claire, Geology Department, Eau-Claire, WI 54702, United States
AB: The Colorado River is a large, youthful, unequilibrated continental drainage system the base-level for which was established rather abruptly between 5 and 6 million years ago in conjunction with Gulf of California rifting and establishment of the modern river course through the western Grand Canyon and lower Colorado river region. New laser ablation ICPMS detrital zircon U-Pb analyses (~3000) from ~40 samples provide insight into details relating to the cause, timing and consequences of river inception. These samples encompass (1) the modern Colorado River delta, (2) major tributaries including the Green, "Grand", San Juan, Little Colorado and Gila rivers (3) late Miocene to Pliocene sediments along the lower Colorado (4) late Miocene to Pleistocene deltaic and fluvial sediments of the Imperial and Palm Spring Groups in the western Salton Trough, and (5) late Miocene- early Pliocene Bidahochi Formation of eastern Arizona. Data from the western Salton Trough and modern delta yield strata yield remarkably homogeneous age distributions that indicate there was little evolution in Colorado River sediment composition since 5.3 Ma. Detrital zircon is dominated by a mix of local southwest US cratonal basement (1.7 and 1.4 Ga) plus reworked supracrustal sequences of the Colorado Plateau that provide Neoproterozoic, 1.1 Ga, and early Paleozoic zircons. A relative paucity of Grenville-age grains in the earliest part of the delta sequence may reflect an early stage of the modern river prior to deep incision through Colorado Plateau erg deposits. The strong homogeneity of the detrital zircon record from late Miocene to the present is consistent with the ‘lake spillover model' for inception and integration of the modern Colorado River drainage. Abrupt integration of the lower Colorado River after 5.6 Ma is clearly recorded by detrital zircon ages from the laucustrine Bouse Formation and Bullhead alluvium aggradational package. Fluvial-laucustrine deposits of the Bidahochi Formation may represent a lake that overtopped the Kaibab upwarp to initiate western Grand Canyon incision.
DE: 8110 Continental tectonics: general (0905)
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: 2007 Joint Assembly