Masters Theses

Keywords and Phrases

Geochemistry; Mantle Evolution; Olivine; Petrography; Petrology; Trace Element


"This article presents the crystallization age of, and composition of olivine phenocrysts within an alnoite of, the Avon Alkaline Igneous Province (AAIP) of Ste. Genevieve County, Missouri. The AAIP is an ultramafic igneous province consisting of approx. 80 known intrusives of diverse lithology and texture. 40Ar/39 Ar geochronology indicates an emplacement age of 386 +/- 1 Ma, which establishes the AAIP as the only known Devonian-age ultramafic igneous body in the Midwestern U.S. Study of the AAIP provides a unique opportunity to characterize the Devonian-age subcontinental mantle and the processes that generated the suite of ultramafic rocks present in the province. The compositions of 52 olivine crystals are characterized using electron microprobe analysis. Olivine major element compositions are homogeneous, Mg-rich (Fo86.9-Fo89.9), and exhibit variation in trace element (e.g., Ni, Cr, Co, Ti, P) abundances consistent with fractional crystallization. These results indicate that AAIP olivines are phenocrysts rather than mantle xenocrysts. Olivine geothermometry indicates derivation at temperatures of approx. 1500-1750⁰C at pressures of 1.6 to 5.4 GPa. Olivine trace element discrimination diagrams indicate AAIP magmas were derived from mantle sources with a compositional alkalic affinity, similar to other continental alkaline rocks and kimberlite. A mantle origin via partial melting of peridotite mantle is suggested due to the high Mg content, results of geothermometric modeling, and high Ca and Ti abundance within olivine phenocrysts. Disequilibrium textures observed in alnöite olivine are consistent with resorption of magmatic olivine as a result of decompression and fractional crystallization"--Abstract, page iv.


Hogan, John Patrick

Committee Member(s)

Bridges, David L.
Yang, Wan


Geosciences and Geological and Petroleum Engineering

Degree Name

M.S. in Geology and Geophysics


Geological Society of America
Missouri Department of Natural Resources
Missouri Geological Survey


Missouri University of Science and Technology

Publication Date

Summer 2016

Journal article titles appearing in thesis/dissertation

  • Avon Alkaline Igneous Province: 40Ar/39 Ar geochronology, characterization of subcontinental mantle source and magmatic evolution via trace element analysis of olivine


xi, 103 pages

Note about bibliography

Includes bibliographical references.

Geographic Coverage

Sainte Genevieve County, Missouri

Time Period



© 2016 Zachary William Freeman, All rights reserved.

Document Type

Thesis - Open Access

File Type




Thesis Number

T 11342

Electronic OCLC #