HR: 08:30h
AN: T51D-03 INVITED     [Abstracts]
TI: Detrital Record of Phanerozoic Tectonics in Iran: Evidence From U-Pb Zircon Geochronology
AU: * Horton, B K
EM: horton@ess.ucla.edu
AF: University of California, Dept. of Earth and Space Sciences, Los Angeles, CA 90095-1567 United States
AU: Gillis, R J
EM: bgillis@ess.ucla.edu
AF: University of California, Dept. of Earth and Space Sciences, Los Angeles, CA 90095-1567 United States
AU: Stockli, D F
EM: stockli@ku.edu
AF: University of Kansas, Dept. of Geology, Lawrence, KS 66045-7613 United States
AU: Hassanzadeh, J
EM: jamshidh@khayam.ut.ac.ir
AF: University of Tehran, Dept. of Geology, Tehran, 14155-6466 Iran (Islamic Republic of)
AU: Axen, G J
EM: gaxen@ess.ucla.edu
AF: University of California, Dept. of Earth and Space Sciences, Los Angeles, CA 90095-1567 United States
AU: Grove, M
EM: marty@oro.ess.ucla.edu
AF: University of California, Dept. of Earth and Space Sciences, Los Angeles, CA 90095-1567 United States
AB: Ion-microprobe U-Pb ages of 91 detrital zircon grains supplement ongoing investigations of the tectonic history of Iran, a critical region bridging the gap between the Alpine and Himalayan orogenic belts. These data improve understanding of the distribution of continental blocks during a complex history of Late Proterozoic (Pan-African) crustal growth, Paleozoic passive-margin sedimentation, early Mesozoic collision with Eurasia, and Cenozoic collision with Arabia. U-Pb analyses of detrital zircon grains from four sandstone samples (two Lower Cambrian, one uppermost Triassic-Lower Jurassic, one Neogene) collected from the Alborz mountains of northern Iran reveal a spectrum of ages ranging from 50 to 2900 Ma. Most analyses yield concordant to moderately discordant ages. The Lower Cambrian Lalun and Barut sandstones yield age distribution peaks at approximately 550-650, 1000, and 2500 Ma, consistent with a Gondwanan source area presently to the south and west in parts of Iran and the Arabian-Nubian shield (Saudi Arabia and northwestern Africa). The uppermost Triassic-Lower Jurassic Shemshak Formation exhibits a broad range of U-Pb ages, including peaks of approximately 200-260, 330, 430, 600, and 1900 Ma, requiring a Eurasian source area presently to the north and east in the Turan plate (Turkmenistan and southwestern Asia). Neogene strata display both the youngest and oldest ages (approximately 50 and 2900 Ma) of any samples, a result of substantial sedimentary recycling of older Phanerozoic cover rocks. Because the youngest zircon ages for three of the four samples are indistinguishable from their stratigraphic (depositional) ages, these data suggest rapid exhumation and help constrain the termination age of Late Proterozoic-Early Cambrian (Pan-African) orogenesis and the timing of the Iran-Eurasia collision.
DE: 9320 Asia
DE: 8102 Continental contractional orogenic belts
DE: 8105 Continental margins and sedimentary basins
DE: 8110 Continental tectonics--general (0905)
DE: 8149 Planetary tectonics (5475)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting