Evolution of an englacial volcanic ridge: Pillow Ridge tindar, Mount Edziza volcanic complex, NCVP, British Columbia, Canada

Benjamin R. Edwards*, Ian Skilling, Barry I. Cameron, Courtney Haynes, Alex Lloyd, Jefferson H. D. Hungerford

*Awdur cyfatebol y gwaith hwn

Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

Crynodeb

Glaciovolcanic deposits are critical for documenting the presence and thickness of terrestrial ice-sheets, and for testing hypotheses about inferred terrestrial ice volumes based on the marine record. Deposits formed by the coincidence of volcanism and ice at the Mount Edziza volcanic complex (MEVC) in northern British Columbia, Canada, preserve an important record for documenting local and possibly regional ice dynamics. Pillow Ridge, located at the northwestern end of the MEVC, formed by ice-confined, fissure-fed eruptions. It comprises predominantly pillow lavas and volcanic breccias of alkaline basalt composition, with subordinate finer-grained volcaniclastic deposits and dykes. The ridge is presently similar to 4 km long, similar to 1000 m in maximum width, and similar to 600 m high. Fifteen syn- and post-eruptive lithofacies are recognized in excellent exposures along the glacially dissected western side of the ridge. We recognize five lithofacies associations: (1) poorly sorted tuff breccia and dykes, (2) proximal pillow lava, dykes and tuff breccia, (3) distal pillow lava, poorly sorted conglomerate and well-sorted volcanic sandstone, (4) interbedded tuff, lapilli tuff, and tuff breccia units, and (5) heterolithic volcanogenic conglomerate and sandstone. Given the abundance of pillow lavas and the lack of surrounding topographic barriers capable of impounding water, we agree with Souther [Souther, J.G., 1992. The late Cenozoic Mount Edziza volcanic complex. Geol. Soc. Can. Mem., vol. 420.320 pp] that the bulk of the edifice formed while confined by ice, but have found evidence for a more complex and variable eruption history than that which he proposed. Preliminary estimates of water-ice depths derived from FTIR analyses of H2O give ranges of 300 to 680 m assuming 0 PPM CO2, and 857 to 1297 m assuming 25 PPM CO2. Variations in depth estimates among samples may indicate that water/ice depths changed during the evolution of the ridge, which is consistent with our interpretations for the origins of different lithofacies associations. Given that the age of the units are likely to be ca. 0.9 Ma [Souther, J.G., 1992. The late Cenozoic Mount Edziza volcanic complex. Geol. Soc. Can. Mem., vol. 420. 320 pp]. Pillow Ridge may be the best documentation of a regional high stand of the Cordilleran Ice Sheet (CIS) in the middle Pleistocene, and an excellent example of the lithofacies and stratigraphic complexities produced by variations in water levels during a prolonged glaciovolcanic eruption. 

Iaith wreiddiolSaesneg
Tudalennau (o-i)251-275
Nifer y tudalennau25
CyfnodolynJournal of Volcanology and Geothermal Research
Cyfrol185
Rhif cyhoeddi4
Dynodwyr Gwrthrych Digidol (DOIs)
StatwsCyhoeddwyd - 10 Medi 2009
Cyhoeddwyd yn allanolIe

Ôl bys

Gweld gwybodaeth am bynciau ymchwil 'Evolution of an englacial volcanic ridge: Pillow Ridge tindar, Mount Edziza volcanic complex, NCVP, British Columbia, Canada'. Gyda’i gilydd, maen nhw’n ffurfio ôl bys unigryw.

Dyfynnu hyn