Patrick Belshaw's Honours Thesis Abstract

Thesis Title: 
A Textural and Geochemical Study of a Granophyric Sill in the Jarvis Area, Thunder Bay

The occurrence of red granite and quartz diabase along the Jarvis Bay Road, in the Jarvis District of Thunder Bay, Ontario was found to be a tholeiitic Logan intrusion, formed primarily by the processes of fractional crystallization and associated assimilation. This is observed in the identification of fractionated plagioclase clusters, possessing a relative Sr, and Eu enrichment, as well as plagioclase compositions  and other mafic phases in disequilibrium  relative to the surrounding rock  (more An-rich, allowing greater substitution of Sr2+ for Ca2+).  Assimilation of upper crustal rocks in conjunction with fractionation processes can be shown on a primitive mantle normalized multi element diagram, where a relative Nb trough, and a consistent enrichment in LREE is found in all samples of the red granite and quartz diabase.

The mechanism that produced the granophyric intergrowths is observed to involve the interaction of a late stage volatile phase. This is shown through the pervasive iron oxide alteration, forming irregular patches, staining feldspar phenocrysts (in the red granite most notably), as well as replacing and rimming anhydrous mafic phases. The presence of abundant volatile phases such as hornblende, and biotite in all samples collected also support this interpretation.