Sarah Davis HBSc thesis abstract

Thesis Title: 
Petrology and Geochemistry of the Wolfcamp Lake Basalts

The Wolfcamp Lake Basalts are Midcontinent Rift-related volcanic rocks that have been linked with other MCR volcanic rocks such as the Coubran Lake Basalts and the Osler Volcanic Group along the north shore of Lake Superior. Basalts of the Wolfcamp Lake volcanic unit are exposed in two main areas bisected by the TransCanada highway northwest of Marathon, Ontario. The entire unit is approximately 2 km east-west by 4 km north-south with one large exposure northeast of the highway east of Wolfcamp Lake and a second exposure south of the TransCanada highway cropping out as large cliffs, railway cuts and outcrops on the north shore of Lake Superior near Port Munroe. Flow thicknesses are generally 2-4 m with variations present locally. The main lithology comprises basalt flows which are dominantly ophitic or sub-ophitic. The mineralogy is dominated by feldspars (primarily plagioclase), olivine and pyroxenes. Alteration minerals including hornblende, sericite, chlorite, biotite, opaques (primarily magnetite) are present in all samples at concentrations from 3% up to 40%.

All of the samples of the Wolfcamp Lake basalts show very consistent trace element geochemistry with OIB-like characteristics on primitive mantle normalised plots. They are characterised by negative zirconium, hafnium and titanium anomalies with no negative niobium anomalies observed. The Wolfcamp Lake basalts were compared to the closest volcanic rocks the Coubran Lake basalts, but differences were observed when compared to other volcanic rocks in the area.

When compared to the Coubran Lake unit the Wolfcamp Lake basalts lack the strong negative niobium anomaly displayed by the Coubran Types A and B which have been interpreted to be the result of contamination. The Wolfcamp Lake basalts also show lower Mg numbers, Ni and Cr than the Coubran Lake basalts indicating that the former are more evolved. This suggests that the Wolfcamp basalts are uncontaminated MCR magmas despite their more evolved compositions.