DOI

10.17077/etd.7zqdp7ln

Document Type

Thesis

Date of Degree

Spring 2018

Degree Name

MS (Master of Science)

Degree In

Geoscience

First Advisor

Peate, David

First Committee Member

Ukstins, Ingrid

Second Committee Member

Foster, C. Tom

Abstract

Magmatism on Iceland is dominated by the eruption of tholeiitic lavas along two NE-SW trending rift zones that represent the loci of new crustal formation. Small volumes of transitional to alkaline magmas erupted along the ~120 km long Snæfellsnes Peninsula in western Iceland. The Snæfellsnes Peninsula is broken into three distinct volcanic systems; Ljósufjöll, Lýsuskard, and Snæfellsjökull. This study examines the geochemical compositions and depths of crystallization of alkaline basaltic glass to see if these features vary spatially along the peninsula. Glass MgO values range from 3.4 to 9.0 wt %, TiO2 ranges from 0.9 – 4.8 wt. % increasing westward along the peninsula. Estimations of crystallization pressures, based on the pressure dependence of ol±plag±cpx, average 4.6 ± 2.8 kbar, translating to depth a depth of 16.1 ± 10 km generally increasing with distance from the main rift zones. In some cases, cox-melt barometry was also used as a check on the glass cotectic pressures. Crustal thickness beneath Snæfellsnes has been estimated to be ~25 km, suggesting mid to lower crustal magma storage depths. Calculated depths in Snæfellsjökull and Lýsuskard are consistent and deep (22 ± 2.4 km) whereas the Ljósufjöll system is more varied. The Ljósufjöll system displays two groupings of depths, split lengthwise. The northern group exhibits depth between 15-26 km, like the rest of the peninsula, while the southern group has no discernable pattern. Previous data on post-glacial lavas reveals broad spatial trends in REEs across the peninsula. Basaltic glasses exhibit a wide range of La/Sm (1 – 5.6) suggesting a variation in melting percentage over a small area. Samples west of 22.33⁰W have higher Dy/Yb (>2.1) indicating a deeper melting depth due to residual garnet as well as a higher La/Sm (>10) indicative of a smaller degree of melting and/or an enriched source. These data have shown that melt storage occurs at near Moho depths along the peninsula but is highly variable in the eastern Ljósufjöll.

Keywords

Geobarometry, Geochemistry, Glass, Iceland

Pages

xii, 116 pages

Bibliography

Includes bibliographical references (pages 77-82).

Copyright

Copyright © 2018 Alex Maruszczak

Included in

Geology Commons

Share

COinS