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Federman, A.N., 1985

Correlation and petrological interpretation of abyssal and terrestrial tephra layers

Bibliographic Reference

Federman, A.N., 1985, Correlation and petrological interpretation of abyssal and terrestrial tephra layers: Corvallis, Oregon, Oregon State University, Ph.D. dissertation, 241 p.


Chemical analyses of distal tephra components from the 1912 eruption of Novarupta, Alaska, indicate both glass and mineral compositional heterogeneity. A combination of a 150 degrees C range in temperature deduced from iron-titanium oxide geothermometry, and non-linear major element correlation plots of glass compositions indicate that a chamber of compositionally zoned magma existed prior to the eruption. Results for these distal tephras are comparable to those from a recently completed study at the source. Eruptions from chambers of zoned magma may account for many of the heterogeneous tephra layers in the Gulf of Alaska. Studies of the geochemistry of distal volcanoes are based on the assumption that no chemical exchange has taken place between the glass and adjacent pore water. This assumption has been questioned by some workers. Study of newly erupted tephra glass reveal low water contents of 0.3 to 1.0 wt.%. Analysis of tephra glass from piston and Deep Sea Drilling Project Cores reveal that water uptake is initially rapid, increasing to 4 wt.% in 100,000 yrs. Any additional water uptake takes place very slowly over the next several million years. Traverses across shards do not show any indication of chemical exchange. Study of 116 samples of both primary air-fall and alluvially reworked tephra layers on the Columbia River Plateau of south-central Washington state have revealed 16 groups of compositionally distinct layers. Some of these groups are correlated with the eruptions of Mount Mazama (Crater Lake), Glacier Peak, Mount St. Helens 'S', 'M', 'C', and 'Wn.' Some layers are mixtures of two or more of the groups previously mentioned. Several of the groups have unique compositions and are dissimilar from anything previously reported in the literature.

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