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Volatiles in basaltic glasses from a subglacial volcano in northern British Columbia (Canada): Implications for ice sheet thickness and mantle volatiles

Geological Society Special Publication

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Abstract

Dissolved H2O, CO2, S and Cl concentrations were measured in glasses from Tanzilla Mountain, a 500 m-high, exposed subglacial volcano from the Tuya-Teslin region, north central British Columbia, Canada. The absence of a flat-topped subaerial lava cap and the dominance of pillows and pillow breccias imply that the Tanzilla Mountain volcanic edifice did not reach a subaerial eruptive phase. Lavas are dominantly tholeiitic basalt with minor amounts of alkalic basalt erupted at the summit and near the base. Tholeiites have roughly constant H2O (c.0.56 ?? 0.07 wt%), CO2 (<30 ppm), S (980 ?? 30 ppm) and Cl (200 ?? 20 ppm) concentrations. Alkalic basalts have higher and more variable volatile concentrations that decrease with increasing elevation (0.62-0.92 wt% H2O, <30 ppm CO2, 870-1110 ppm S and 280-410 ppm Cl) consistent with eruptive degassing. Calculated vapour saturation pressures for the alkalic basalts are 36 to 81 bars corresponding to ice thicknesses of 400 to 900 m. Maximum calculated ice thickness (c. 1 km) is at the lower end of the range of predicted maximum Fraser glaciation (c. 1-2 km), and may indicate initiation of volcanism during the waning stages of glaciation. Temporal evolution from tholeiitic to alkalic compositions may reflect compositional gradients within a melting column, instead of convective processes within a stratified magma chamber. The mantle source region for the subglacial volcanoes is enriched in incompatible elements similar to that for enriched mid-oceanic ridge basalt (e.g. Endeavour Ridge) and does not contain residual amphibole. Thus, metasomatic enrichment most likely reflects small degree partial melts rather than hydrous fluids.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Volatiles in basaltic glasses from a subglacial volcano in northern British Columbia (Canada): Implications for ice sheet thickness and mantle volatiles
Series title:
Geological Society Special Publication
Issue:
202
Year Published:
2002
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geological Society Special Publication
First page:
255
Last page:
271
Number of Pages:
17