Abstract

The area studied lies southeast of Lake Temagami in Northern Ontario and comprises 30 miles of the contact between the Temiskaming and Grenville sub-provinces, two divisions of the Canadian Shield. The age relationship between these sub-provinces has long been a problem, and the present work was undertaken to obtain further information toward a solution. The Grenville sub-province, in the southeast part of the area, is underlain by gneisses invaded by granite. In the area studied, the Temiskaming sub-province consists of granitic rocks overlain by sedimentary rocks of the Cobalt series which are cut by sills and dikes of diabase. The work has shown that the two sub-provinces are in fault contact along a zone of northeast-striking, east-dipping faults, with displacement of the Grenville, or southeast side, upward. The amount of displacement at these faults ranks them with the major tectonic features of the earth's crust. Movement has taken place many times, the latest in late Precambrian. This movement produced a lineation in all rocks of the area and especially in the Grenville sub-province. A second set of faults strikes northwest parallel both to the movement on the earlier northeast-striking faults and to a prominent set of vertical joints. Throughout the area, northeast-striking schistosity and foliation dip southeast, and the dip flattens progressively south-eastward. Metamorphism increases in grade in the same direction. In granitic rocks of the Temiskaming sub-province the biotite isograd and zones of increasing metamorphism parallel the contact between the sub-provinces. The gneisses in the Grenville sub-province immediately east of the contact are similar in chemical composition to the granites of the Temiskaming sub-province and are considered their metamorphosed equivalent. These gneisses are cut by younger granitic rocks that are high in potash that probably originated, in part at least, by granitization. Both these granites are pre-Cobalt and probably post-Temiskaming.

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