Abstract

Although tuyas in the Western Volcanic Zone (WVZ) of Iceland have been studied in detail, little work has been done on the numerous smaller tindars there. This study compares Bræðravirki Ridge, a 3-km long tindar on the southeastern flank of Ok shield volcano in the WVZ, to regional tuyas and creates a model for ridge formation based on combined mapping and geochemical analyses. Bræðravirki is dominated by palagonitized lapilli tuff with scattered intrusions, rare exposures of intact pillow lavas, and multiple tuff/lapilli tuff units. Whole rock samples were measured for major and trace elements by XRF and ICP-MS. Mineral and glass compositions were measured by SEM-EDS. Major elements show that Bræðravirki is relatively enriched in SiO2 and depleted in CaO, FeO*, and MgO compared to regional data. Comparison of whole-rock fragmental samples with fresh volcanic glasses shows that Al2O3, K2O, and Na2O have been affected to some degree by palagonitization. Rhyolite-MELTS (v. 1.0.1) models are consistent with the two compositional groups being genetically related by 3 kb fractional crystallization of a common parent magma. The MELTS models generate plagioclase (An61 to An70) and two pyroxene (low- and high-Ca) compositions that are observed in the SEM-EDS mineral data. Incompatible trace elements show limited variation between the two compositional groups (Nb/Y 0.27-0.41), suggesting stable melting conditions. Rare Earth Elements indicate a change in melting conditions and construction based on a single batch of magma. I propose a two-stage eruptive model that begins with an explosive phase, followed by a second explosive-effusive phase that forms intrusions and pillows. The second phase is hypothesized to be initiated by a recharge event, emplacing the higher-MgO units. Comparison of Bræðravirki ridges chemistry to that of the regional tuyas indicated a difference between the two. Due to this I hypothesize that Bræðravirki was emplaced during the end of the glacial period. This study demonstrates that small tindars can be constructed through multiple eruptive events that shift in eruptive style and that glaciovolcanic edifices in the same region can have significant compositional differences, possibly providing insights into the understanding of their timing, magmatic history, and paleo-ice conditions.

Advisor

Pollock, Meagen

Department

Geology

Disciplines

Geochemistry | Volcanology

Keywords

Tindar, Iceland, Wester Volcanic Zone, Tuya, Glaciovolcanics, Glaciovolcanism

Publication Date

2020

Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis

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© Copyright 2020 Hannah Grachen