Date of Award

5-23-2010

Document Type

Honors Thesis

Department

Earth Sciences

First Advisor

Benjamin Edwards

Language

English

Abstract

Mantle xenoliths from the Canadian Cordillera are the most direct source available for studying the petrology and structure of the lithospheric mantle. The formation of the Cordillera from the accretion of tectonostratigraphic assemblages and terranes brings into question the homogeneity of the upper mantle. Craven Lake volcanic center is a new study location within the Stikine terrane, offering a variety of xenolith types and textures that can help determine the homogeneity of the upper mantle across the Canadian Cordillera. Studies of other xenolith suites to the north (Harder and Russell, 2005) and south (Peslier et al., 2002) revealed a coarse to protogranular texture with equigranular grains in peridotites. Craven Lake xenoliths, however, exhibit a smaller grain size on average (~2.0 mm or less) and grains are generally seriate in texture. Other textures, such as the presence of amphibole veins could be an indication of metasomatism at some point. Chemical analysis of mineral compositions reveals olivine, orthopyroxene, and clinopyroxene similarities between various sites throughout the Canadian Cordillera. Spinel, however, varies not only between Craven Lake samples, but also between different volcanic centers. The presence of am phi bole, not seen at other volcanic centers, makes the Craven Lake site unique and may have important implications for the formation of nephelinite magmas. Two-pyroxene temperature estimates for the xenolith suite also reveal a wider range of values than other sites (898-1231 °C). The data presented in this study, when compared to other xenolith studies in the Canadian Cordillera, vary enough from previously reported textural, chemical, and mineralogical data to speculate that the lithospheric mantle beneath Craven Lake is not homogeneous with the rest of the Canadian Cordillera upper mantle.

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