Type of Document	Master's Thesis
Author	Cooper, Marc Romain
Author's Email Address	mcoope3@lsu.edu,marc@yocoop.com
URN	etd-06192008-092427
Title	Komatiitic Flows of the 3.3Ga Weltevreden Formation, Barberton Greenstone Belt, South Africa: Stratigraphy, Petrology, and Geochemistry
Degree	Master of Science (M.S.)
Department	Geology & Geophysics
Advisory Committee	Advisor Name Title Gary R. Byerly Committee Chair Darrell J. Henry Committee Member Huiming Bao Committee Member
Keywords	Archean partition coefficients volcanology
Date of Defense	2008-05-08
Availability	restricted
Abstract The 3.29 Ga Pioneer Ultramafic Complex (WPC) is a 1 km thick east-northeast trending tilted (90° dip) section of layered ultramafic rock in the Weltevreden Formation in the west-northwest region of the Barberton Greenstone Belt (BGB). It was originally interpreted as an intrusive complex with slaty zones that have a linear horizontal fabric produced by shear. However, a recent study identifies these slaty zones as komatiitic tuffs and attributes their horizontal fabric to plane and cross bedding. The present study suggests the non-slaty zones are extrusive komatiitic flows with abundant pyroxene spinifex tops, normal volcanic textures and crystal sizes, and no indication of intrusive cross cutting. A geologic map is presented for WPC komatiites along with a stratigraphic section. The stratigraphic section includes 9 flows or flow sets (numbered WP 1 – 9). WP 1, WP 4, and the lower WP 7 are relatively undifferentiated massive olivine cumulate flows with minor interstitial pyroxenes. WP 2 and 3 are layered komatiitic flows with dunitic to peridotitic bases and increasing pyroxene content and changing pyroxene morphology toward pyroxene spinifex flow tops. Pyroxene spinifex komatiitic basalts are dominant in WP 6 – 8. Each flow type has substantially differing rock and mineral chemistry. Layered komatiitic flows are likely to represent more ponded lavas. WPC komatiites are mineralogically well preserved for Archean komatiites with abundant fresh olivine, orthopyroxene, pigeonite, augite, and chromite. The WPC komatiites are of the Al-undepleted geochemical type with rock and mineral Al2O3/TiO2 very similar to other units of the Weltevreden Formation. This geochemical signature is commonly attributed to the depth of partial melting in plumes, with Al-undepleted komatiites representing shallower partial melting (<450km), and also indicates that WPC komatiites may have a magmatic source related to that of the previously studied Weltevreden Formation komatiites. However, WPC komatiites differ from previously studied Weltevreden Formation komatiites in that they are somewhat less magnesian (maximum olivine Mg# 92.9 vs. 95.6), indicating a lower eruption temperature, but have much more complex and variable lithologic layering.
Files	Filename       Size       Approximate Download Time (Hours:Minutes:Seconds)     28.8 Modem   56K Modem   ISDN (64 Kb)   ISDN (128 Kb)   Higher-speed Access  Cooper_thesis.pdf 7.62 Mb 00:35:17 00:18:09 00:15:52 00:07:56 00:00:40 indicates that a file or directory is accessible from the LSU campus network only.

If you have questions or technical problems, please Contact LSU-ETD Support.