PETROGRAPHIC AND GEOCHEMICAL ANALYSIS OF QUARTZOFELDSPATHIC BODIES IN THE SLEEPING GIANT INTRUSION, HARTFORD BASIN, CT

The Sleeping Giant diabase intrusion located in the Triassic-Jurassic Hartford Basin has been interpreted to be a laccolith connected to the West Rock Sill and comagmatic with the Fairhaven-Higganum dike complex and Talcott Basalt. This laccolith locally preserves quartzofeldspathic dikelets and pods in an otherwise wholly mafic environment. Small, fine to medium grained dikelets (most < 4 cm wide) with high SiO₂ (68-79%), K₂O (1.5-6%), Na₂O (1-6%) and low Fe₂O₃^T (1.5-3.5%) extend throughout the intrusive body. Petrographic and field observations indicate their origin to be a result of partial melting and injection of arkosic country rock into the partially crystallized mafic intrusion. These dikelets contrast with coarser grained meter scale quartzofeldspathic pods and sheets that occur in the inferred upper central portion of the original intrusion and that are high in Fe₂O₃^T (17%) and TiO₂ (2.7%) and lower in SiO₂=52% and alkalis. These pods are attributed to extensive magmatic differentiation and segregation of the original basaltic magma.