Identifier

etd-07092007-173548

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

Over a dozen komatiitic flows in the 3.2-3.5 Ga Barberton Greenstone Belt are topped with unique green silica- and carbonate-rich rocks, which likely formed from interaction of the cooling lava flow with seawater shortly after deposition. This study focuses on an alteration zone in the Mendon Formation. Two styles of alteration are observed in this alteration zone: silicification and carbonation. The goal of this study is to characterize the carbonates in the alteration zone, constrain the timing of alteration, test whether the alteration zones are due to interaction with seawater after deposition, and estimate the elemental fluxes between the rock and the altering fluid. If the zones of silica and carbonate rich rocks are alteration zones due to near-surface interaction with seawater, then studying them will provide constraints on Archean near-surface environments. Cross-cutting relations indicate that after eruption of the komatiitic lava, serpentinization then wholesale replacement of the komatiite by quartz, carbonate, and Cr-muscovite took place before quartz and carbonate veins formed. After vein formation, a sedimentary chert cap was deposited and vertical black chert dikes were emplaced. Carbonates in the alteration zone are compositionally and isotopically homogeneous in veins and the host rock. They are ferroan dolomites, Ca1.0Mg0.7Fe0.3(CO3)2 with d18O ~20‰ and d13C ~2‰. The chemical and isotopic homogeneity of the carbonates suggests that they formed in equilibrium with a large aqueous reservoir, probably seawater. Using the isotopic composition of the carbonates within the samples, a seawater of ~86°C is calculated.

Date

2007

Document Availability at the Time of Submission

Secure the entire work for patent and/or proprietary purposes for a period of one year. Student has submitted appropriate documentation which states: During this period the copyright owner also agrees not to exercise her/his ownership rights, including public use in works, without prior authorization from LSU. At the end of the one year period, either we or LSU may request an automatic extension for one additional year. At the end of the one year secure period (or its extension, if such is requested), the work will be released for access worldwide.

Committee Chair

Gary R. Byerly

DOI

10.31390/gradschool_theses.2984

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