Constraints on the origin of the coolest rocks of Flin Flon Field School: Boundary Intrusion breccias

Please join us for a graduate student seminar this Friday October 18 at 3:30 pm in rm 155 Geology presented by Nancy Normore, MSc candidate:

“Constraints on the origin of the coolest rocks of Flin Flon Field School: Boundary Intrusion breccias”

The Boundary Intrusions are a suite of felsic to ultramafic dykes and sills, which intrude the Flin Flon Arc assemblage in the Flin Flon-Creighton (MB and SK) area. The intrusions were emplaced during the waning stages of volcanism associated with island arc accretion (ca. 1842 Ma) prior to metamorphism and deformation during the Trans-Hudson Orogeny. Breccias have been observed in all the Boundary Intrusion types, having a matrix of either felsic, mafic or ultramafic composition and containing fragments of volcanic or possibly earlier crystallized phases of Boundary Intrusion. No study has been conducted to date which examines the relationships between the brecciated units within the study area, or the relationships of the components within the breccia units themselves. This study aims to expand on the current knowledge of the Boundary Intrusions by using field observations, petrography, and geochemical data from the intrusions at Green Street (Creighton) and Louis Lake (Flin Flon) to surmise their petrogenesis and the origin of their brecciated units. Breccias of the Boundary Intrusions include polymictic matrix and clast-supported breccias with mosaic and chaotic textures, with some fragments possibly representing earlier crystallized Boundary Intrusions. Fragments are typically less than 30 cm in diameter, but fragments up to 2 meters in diameter give insight to maximum possible ascent rates during emplacement ranging from <1km/hr to 30 km/hr. Geochemical data suggests calc-alkaline rocks of volcanic arc setting and that gabbroic fragments may be cogenetic to the intrusions.