HR: 1340h
AN: V13D-0575    [Abstracts]
TI: An overview of long-lived, peralkaline glacivolcanism within the northern Cordilleran volcanic province
AU: * Edwards, B R
EM: edwardsb@dickinson.edu
AF: Department of Geology Dickinson College, P.O. Box 1773, Carlisle, PA 17013 United States
AB: The Neogene-to-Recent northern Cordilleran volcanic province (NCVP) comprises >50 separate volcanic occurences whose morphologies and deposits record interaction between volcanism and ice. NCVP glacivolcanism includes a broad range of alkaline rock types, from basanite to phonolite, and several different glacial setting (alpine, local ice sheets, regional ice sheets). Although many of the smaller volcanoes erupted beneath the Cordilleran ice sheet, the larger and longer-lived volcanic complexes are high enough in elevation to be associated with local ice caps in addition to valley glaciers. Of the three largest volcanic centers in the NCVP, Mount Edziza#1 and Hoodoo Mountain show a variety of peralkaline glacivolcanic deposits; predominantly trachytic to phonolitic at Hoodoo, but covering a broader compositional spectrum from trachyte to peralkaline rhyolite at Edziza. The third, Level Mountain#2, is probably older and is more heavily dissected than the other two, but also contains trachytic deposits that appear to be glacivolcanic in origin. Taken together these three complexes form a distinct peralkaline magmatic subprovince within the NCVP, referred to as the ``Stikine subprovince'', whose glacivolcanic deposits appear to be unique in the North American Cordillera. Massive and fragmental glacivolcanic deposits at these centers have a variety of distinctive characteristics. Massive deposits include domical shaped lava bodies covered by pervasive, small-diameter cooling joints, and lava flows up to 200m in thickness that have been interpreted as ice-dammed. Fragmental deposits interpreted as having formed beneath thicker ice tend to be non-vesicular, whereas those interpreted as having formed under thinner ice locally have glassy, pumiceous clasts in highly altered, ash-rich matrices. Other distinctive deposits show lobate lava bodies totally enclosed by volcanic breccias with aphanitic clasts. None of the peralkaline deposits described to date contain pillow-like structures. Given the peralkaline characteristics of the Stikine subprovince, it is ideal for geochronology studies aimed at refining the Pleistocene record of glacivolcanism in the North American Cordillera. Hoodoo preserves a detailed chronology of glacivolcanic interaction associated with the ebb and flow of at least local ice over the last 80 k.y., whereas at Edziza and Level Mountain have the potential documenting local and Cordilleran-wide glacivolcanism. Efforts are currently underway to try and provide a more detailed record of glacivolcanism from Edziza. #1Souther, J.G. 1992. The Late Cenozoic Mount Edziza Volcanic Complex, British Columbia, GSC Memoir 420, 320 p. #2Hamilton, T.S. 1981. Late Cenezoic Alkaline Volcanics of the Level Mountain Range, Northwestern British Columbia: Geology, Petrology, and Paleomagnetism [Ph.D. Dissert.], Edmonton, University of Alberta, p. 490.
DE: 1621 Cryospheric change (0776)
DE: 8408 Volcano/climate interactions (1605, 3309)
DE: 8425 Effusive volcanism
DE: 8428 Explosive volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005