A Review of the Problems of the Sudbury Irruptive

Abstract

The problems of the Sudbury irruptive are approached here mainly from two points of view: (1) the nature of the zone intermediate to the acid and basic portions and (2) the place of these rocks in the general Keweenawan petrographic province of Ontario. It is considered that the nature of the rocks of this intermediate zone does not support the theory of gravitational separation of the basic member but indicates rather the formation of hybrid types at the contact of two separate magmas-one, the more basic, well crystallized; the other, the more acid, still mostly liquid. From an analysis of the now excellent chemical data and a comparison with the allied bodies elsewhere in the province, it is concluded that the basic member represents the product of fractiona-tion of the liquid of the parent diabase magma of this petrographic province and an early separating olivine-diabase component, probably through some filter-pressing action, and that much of the heterogeneity of the rock is primary in the sense that it was brought about by this process of evolution.