Abstract

At Kakagi Lake, a sequence of basaltic rocks is overlain by about 2000 m of pyroclastic rocks. These rocks lack mesoscopic layering, and are very poorly sorted. Most fragments are accessory in nature. Analysis of variation of maximum fragment size, matrix percent, and sorting imply vent areas to the west and south of the Kakagi Lake area.The rocks are calc-alkaline rather than tholeiitic in lineage, poor in K2O, particularly the most silicic. Fragments are more salic and depleted in FeO and MgO relative to their matrix.Thickness and lack of layering, coupled with poor sorting, suggest several ash flows. Chemical differences between accessory fragments and matrix suggest differentiation of magma between eruptions, such that the upper portion of the magma chamber became more salic than the lower portion; hence the products of each eruption vary in composition.

You do not currently have access to this article.