HR: 16:15h
AN: GP44A-02    [Abstracts]
TI: Geochronology and Tectonic Significance of Mafic and Ultramafic Rocks From Yakutia, Russia
AU: * Layer, P W
EM: player@gi.alaska.edu
AF: Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775
AB: Mafic and ultramafic (ophilite) rocks from the western edge of the Kolyma-Omolon Superterrane (KOS) in central Yakutia record a Paleozoic to Mesozoic history of formation, accretion and post accretion deformation. Previous geochronologic and geochemical work focused on the Uyandina and Munilkan ophiolites, from the northern Chersky Range. Amphibole ages from these gabbros and amphibolites are 370 to 430 Ma reflecting the age of ocean crust, while micas record obduction and amalgamation of the KOS at 170 to 174 Ma. New data from the Ucha (Indigirka), Debin, Garbyn'ya ophiolite fragments and gabbros from the Tommot massif in the central and southern Chersky Range indicate that these units have different ages and thus record different aspects of the tectonic history of the region. For example, mafic rocks from the Ucha ophiolite have ages of 150 to 160 Ma, reflecting either younger oceanic crust or resetting at the time of arc volcanism. The Debin mafic-ultramafic fragment has an age of 144 Ma, reflecting the time of collision of the KOS. Ages from the highly sheared Garbyn'ya ophiolite reflect an even later resetting event at 90 Ma and may reflect the time of reactivation of strike-slip fault movement parallel to the Chersky Range. This age is also seen in samples from altered granitic rocks in the central Chersky range, again reflecting later faulting. Less well understood are similar ages from the Alazaya uplift in the central KOS and their relation to contemporaneous events in the South Anyui Suture zone or to Okhotsk Chukotka volcanism. The Tommot massif has late Devonian to Carboniferous ages, perhaps recording mid-paleozoic rifting. New 40Ar/39Ar geochronology from arc-related volcanic rocks from the Uyandina-Yasachnaya volcanic arc of the Chersky Range, confirms the late Jurassic age of subduction. These ages are consistent with previously published ages from subduction- and collision-related plutonic rocks recording the accretion of the KOS to Eurasia.
DE: 9320 Asia
DE: 8157 Plate motions--past (3040)
DE: 3640 Igneous petrology
DE: 1035 Geochronology
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting