The petrogenesis of the Porter Lake dome, Porter-Blackstone Lakes area, northern Saskatchewan

Abstract

The area is a monotonous granitic comlex with only minor amounts of meta-sediments. Petrographic studies indicate that the granitic rocks may be classified mineralogically as well as chemically into two groups: those hight in potash (usually red), and those low in potash (usually cream or light grey). Genetically three types are represented - granitized sediments, magmatic rocks and palingenetic ones.

Three dome structures dominate the area. The largest one, the Porter Lake dome, represents a dome-like cupola of granitized sediments; the two smaller ones, developed in its margin, consist of a mantle of granitized sediments surrounding granitic cores. The core rocks of one of the smaller domes is shown to be magmatic with its heterogeniety accounted for by metasomatism; the core rocks of the other one are palingenetic.

Magmatism, granitization and palingenesis are shown to have operated contemporaneously during doming. Updoming is attributed to a rising granitic magma. The elevating power of the magma is regarded as due to the differnce in specific gravity between the magma and the intruded rocks aided by major tectonic forces.