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| Titel |
Origin of Lava-Hyaloclastite Sequences in South Iceland as Revealed by Volatile Contents in Magmatic Glasses |
| VerfasserIn |
Tenley Banik, Ármann Höskuldsson, Calvin Miller, David Furbish, Paul Wallace, Charles Bacon |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083861
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| Zusammenfassung |
| In the Síða District of south Iceland, Pleistocene basaltic lava forms flame-like apophyses,
dikes, and disaggregation structures (cf. Bergh and Sigvaldason, 1991; Smellie, 2008) that
invade overlying hyaloclastite. These features are exposed in valley walls composed of at
least 14 (Bergh and Sigvaldason, 1991) paired basalt-hyaloclastite +/- diamictite depositional
units. These units are dominated by hyaloclastite deposits that reach over 100 m in thickness,
with underlying lava up to 50 m thick. Apophyses as well as underlying lavas show cube
jointing, indicating rapid cooling due to formation in a wet environment and suggesting that
hyaloclastite and lava were emplaced almost concurrently, while hyaloclastite was wet and
weak.
Dissolved volatile concentrations in glass give an indication of ambient pressure on
quenching and cessation of degassing. FTIR analysis of basaltic glasses from chilled lava
margins and hyaloclastite glasses indicate total H2O from below detection to 0.49 wt% with
only one sample above 0.15 wt%; CO32- is below detection in all samples. These
concentrations suggest extensive degassing at or near atmospheric conditions. S and Cl
contents in both glass types were also below or near their respective detection limits by
electron microprobe (70%. These data support an eruption that occurred under
significantly lower-pressure conditions than previously proposed (Smellie, 2008).
The presence of a large volume of hyaloclastite suggests the presence of ice or
external water, which is consistent with results of prior studies (Smellie, 2008). Based
on the volatile data presented here, the Síða deposits were likely erupted under
near-atmospheric pressure and in the presence of significant water. In order to account for the
required environmental conditions and volatile data, one possible scenario is that a
subglacial eruption near the edge of a glacier may have produced hyaloclastite that was
incorporated into a meltwater lake-draining jökulhlaup. Ensuing subaerial lava
from the ongoing eruption or from a distal portion of the vent may have interacted
with the hyaloclastite, resulting in the formation of the observed field relations. |
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