LE3 .A278 2006

2006

Van Wagoner, Nancy

Acadia University

Bachelor of Science

Honours

Geology

Earth & Environmental Sciences

This thesis interprets the geology and lithogeochemistry of part of the Silurian Letete Formation in southwestern, New Brunswick, based on detailed mapping of a 910- m thick section, petrographic analysis of 52 thin sections, and major and REE geochemistry of 11 samples. The mapped Letete section generally represents a shoaling upward sequence. The section is subdivided into three parts. The lowest contains an upward shoaling sequence of subaqueously emplaced mafic pillow flows, pillow breccias, and sheet flows, overlain by subaerially emplaced sheet flows that are interbedded with Surtseyan-style phreatomagmatic tuffs. The middle section contains black and grey siltstones interbedded with felsic volcaniclastic rocks indicating pulses of volcanism separated by periods of relative quiescence. The shallowest water depths occur at the upper 50 m of the section represented by a mafic tuff interpreted to be the result of a shallow water Surtseyan-style eruption. The upper section contains black siltstones interbedded with increasing volumes of felsic volcaniclastic rocks and overlain by massive grey siltstones that are interpreted to record a shoaling upwards deltaic sequence with increasing felsic volcanism. At the top of this section a 360-m thick section of massive and bedded felsic tuff is interpreted to represent steady plinian and waning pulses of subplinian volcanism. Processes of fractionation and crustal contamination account for the decreasing Mg#, increasing ratio of LILE/MORB, and decreasing HFSE/MORB upward in the section. The rocks are bimodal, and the mafic rocks have a within-plate geochemical affinity consistent with the interpretation that volcanism occurred during extension continental rift. This rift may have been the back-arc to the Kingston arc.

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https://scholar.acadiau.ca/islandora/object/theses:488