Petrogenesis of the Purcell Sill Glacier National Park Montana
Mejstrick PF. 1975. Petrogenesis of the Purcell Sill Glacier National Park Montana. University of Montana
The Purcell Sill of Glacier National Park is a Precambrian alkaline olivine diabase that outcrops along the Continental Divide from the southern boundary of the park northward into Canada. The sill is marked by the assimilation and subsequent contamination by quartzite and dolomite xenoliths. Quartzite xenoliths added SiO2 to the diabase and dolomite xenoliths added MgO and CO2, and withdrew Al2O3 and SiO2. Xenoliths rose in the sill in accordance with their densities to collect in a 'granophyric' hybrid zone. Chemical and petrographic data suggest that approximately 4 cubic meters of xenoliths were infused per 28 cubic meters of diabase.