Date of Award

Spring 2015

Project Type

Thesis

Program or Major

Earth Sciences

Degree Name

Master of Science

First Advisor

Samuel B Mukasa

Second Advisor

Julia G Bryce

Third Advisor

Joseph M Licciardi

Abstract

The presence of volatiles in the local mantle magma source region has been suggested as a contributor to the observed high melt production rates in the volcanic segments of the island of Iceland. However, the source of volatiles beneath this island remains enigmatic. New volatile (CO2, H2O, F, S and Cl) concentration data for 157 olivine-hosted melt inclusions in concert with noble gas data (He and Ne) from the Reykjanes Peninsula, Iceland, allow for the reconstruction of magma degassing and the distribution of volatiles in the mantle beneath Iceland. Water concentrations in olivine-hosted melt inclusions from this study record a maximum H2O concentration of 1.99 ± 0.06 wt. %. The H2O concentrations are not correlated with any of the major oxides, but are in some cases elevated relative to other incompatible elements. Solubility models we have tested show that olivine-hosted melt inclusions from the Reykjanes Peninsula have considerably less CO2 for the observed H2O, which implicates degassing to be a more important volatile-loss process than diffusion. Volatile concentrations are negatively correlated with R/Ra, a relationship that implies lower H2O concentrations in the primitive high-3He mantle component and higher-water concentrations in samples that approach Mid Ocean Ridge Basalt (MORB) R/Ra values. Water concentrations are highest along the atmosphere-MORB mixing line on a three-neon isotopic plot, and primitive samples plotting along the atmosphere-solar mixing line have lower water concentrations. These relationships suggest that a volatile-enriched recycled component with high H2O and low 3He/4He values has mixed with a primitive mantle component that is low in H2O but has high 3He/4He values. These two end-member compositions are consistent with a plume component and a depleted MORB source component – potentially enriched and fluxed by subducted components – mixing in the mantle beneath Iceland, and melting to produce the observed volcanic products. These findings support previous suggestions for a three-component-mixing model to explain the relationship between He and H2O in Reykjanes Ridge lavas.

Download

Share

COinS