Berg, Jonathan H.
M.S. (Master of Science)
Department of Geology
Igneous rocks--Antarctica; Geochemistry--Antarctica
The Cenozoic volcanic rocks of the Transantarctic Mountains (TAM) provide a plethora of xenoliths which allows for a viewing of the lower crust. Ninety lower- crustal xenoliths from the TAM were analyzed for major and trace elements and 20 for rare-earth elements. Typical mineralogy consists of two-pyroxene-plagioclase (dominant) and clinopyroxene-piagioclase (subordinate) xenoliths. The mineralogy and textures exhibited by the xenoliths allow for their classification as granu- 1i tes. Many of the xenoliths exhibit "1iquid-1ike" chemical characteristics that are atypical for the lower crust. Previous studies of other xenolith suites have established a basaltic cumulate composition for the lower crust. Contrary to those findings, the composition of these xenoliths shows the lower crust in the TAM to be comprised of a "1iquid-1ike" basaltic andesite composition, based on a weighted average. Since many of the xenoliths appear "liquid-like" rather than cumulate, it is useful to characterize and classify these inclusions in terms of magmatic affinities. Based on an average major-element composition and using definitions for orogenic andesites, the xenoliths from this study are classified as having a basic, medium-k, calc-alkaline orogenic andesite affinity. The lower-crustal xenoliths from the TAM exhibit continental as well as oceanic-isi and arc signatures. Due to the "liquid-like" characteristics and andesitic composition of the 1ower-crustal xenoliths, a mechanism of emplacement of this material into the lower crust probably involves tectonic underplating rather than the magmatic underplating that is typically associated with a basaltic cumulate 1ower-crustal composition.
Matheney, Jane, "Geochemistry of lower-crustal xenoliths from the Royal Society Range of the Transantarctic Mountains, Antarctica" (1989). Graduate Research Theses & Dissertations. 3271.
viii, 159 pages
Northern Illinois University
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