首页|Magmatic origins and storage conditions for the historic eruption of Tseax Volcano, British Columbia, Canada
Magmatic origins and storage conditions for the historic eruption of Tseax Volcano, British Columbia, Canada
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NSTL
Elsevier
The Northern Cordilleran Volcanic Province (NCVP) is the most active volcanic belt in Canada, yet there are few detailed petrologic studies of the individual volcanoes. Tseax volcano is the southernmost volcanic centre of the NCVP, the second youngest (similar to 1700 CE) eruption in Canada, and led to one of Canada's worst natural disasters killing up to similar to 2000 Nisga' a First Nation people. We present a conceptual model for the origins, evolution and pre-eruptive storage of the Tseax magma which erupted in similar to 0.5 km(3) of volcanic material, mainly in the form of valley-filling lava flows. All Tseax products are alkali Fe- Ti- rich basanite-to-tephrite having trace element distributions similar to the other mafic NCVP lavas. Phenocrysts consist of plagioclase, olivine and titanomagnetite, often forming glomemcrysts suggesting co-crystallisation of these 3 mineral phases. Clinopymxene is never observed as a phenocryst phase. The lavas have low Mg-#' s implying they are fractionated relative to a mantle-derived 'parent' magma. Trace elements indicate the magma derives from melting of a fertile mantle source (i.e., (Nb/K)(n) - 1), most likely the upper asthenosphere. There is no evidence in the Tseax volcanic rocks for magma mixing or lithospheric contamination during ascent. The phenocryst assemblage suggests rapid ascent of a low viscosity magma to <5.5 km where titanomagnetite becomes the first phase on the liquidus (similar to 1133 degrees C). There the magma stalled for a very short period of time under PT conditions where clinopymxene did not reach saturation. Based on the size of the plagioclase phenocrysts, the magma stalled for less than a year and cooled down to 1094-1087 degrees C prior to eruption.
NSTL
Elsevier
