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RECOGNIZING ICE-CONTACT TRACHYTE-PHONOLITE LAVAS AT THE MOUNT EDZIZA VOLCANIC COMPLEX, BRITISH COLUMBIA, CANADA

LaMoreaux, Kristen (2008) RECOGNIZING ICE-CONTACT TRACHYTE-PHONOLITE LAVAS AT THE MOUNT EDZIZA VOLCANIC COMPLEX, BRITISH COLUMBIA, CANADA. Master's Thesis, University of Pittsburgh. (Unpublished)

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Abstract

Mount Edziza Volcanic Complex (MEVC) lies within the Northern Cordilleran Volcanic Province (NCVP), in northwest British Columbia, Canada. The eruption products have been emplaced in a variety of subaerial, sub-ice and subaqueous environments from about 8Ma to less than 2000 y.b.p. (Souther, 1992). Ice Peak Formation (IPF) trachyte lava flows of approximately 1Ma age (Souther, 1992) are exposed at Ornostay Bluff (OB) and Koosick Bluff (KB). These flows comprise basal flow breccias overlain by massive conchoidally-fractured lava with large, poorly-developed columns, and local flow banding. Edziza Formation (EF) approximately 1Ma (Souther, 1992) phonolite is exposed at Triangle Dome (TD). TD can broadly be divided into an upper and lower zone. The upper zone comprises poorly-developed columns in addition to prominent jointing. In the lower zone the columns are planar and 75cm-3m-wide in the interior of the complex grading into fan-like and curved subhorizontal columns <75cm-wide in the outer margins of the lower zone. The upper zone is interpreted as an "entablature" where slow cooling was overprinted by joints formed during abrupt cooling due to water ingress. Local areas with well-developed columnar jointing in the upper zone may reflect endogenous growth by late-stage intrusive emplacement, or areas where water ingress was less efficient. The lower zone is interpreted as a "lower colonnade" with slower cooling and less water ingress during cooling. The fan-like columns in the outer margins of the lower zone reflect cooling by direct contact with curved margins of the ice cavity. The estimated minimum thickness of the ice-contact zone is ~60m reflected by the thickness of the lower zone. Identifying ice-contact structures in trachytic-phonolitic lavas is difficult, especially in glacially eroded examples such as OB and KB, where marginal cooling-columns and structures caused by direct contact with ice have been eroded. Trachyte lavas display a wide range of viscosities, flow thicknesses, and aspect ratios therefore caution is required in interpreting "overthick" flows as having formed by confinement by former ice. Studies that focus on comparisons of estimated flow velocities and rates of ice melting are useful, though there are numerous unaccounted for variables in these models.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
LaMoreaux, Kristenkal46@pitt.edukal46@pitt.edu
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairSkilling, Ianskilling@pitt.eduskilling@pitt.edu
Committee MemberRamsey, Michaelramsey@ivis.eps.pitt.eduramsey@ivis.eps.pitt.edu
Committee Member, taco@pitt.edutaco@pitt.edu
Date: 28 September 2008
Date Type: Completion
Defense Date: 17 June 2008
Approval Date: 28 September 2008
Submission Date: 3 August 2008
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Geology and Planetary Science
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Cordilleran Ice Sheet; geochemical; Jeffreys equation
Other ID: http://etd.library.pitt.edu/ETD/available/etd-08032008-221140/, etd-08032008-221140
Date Deposited: 10 Nov 2011 19:56
Last Modified: 11 Jun 2012 14:59
URI: http://d-scholarship.pitt.edu/id/eprint/8863

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