Paleomagnetism of the Sainte-Cécile and Saint-Sebastien granitic intrusive

Abstract

A middle to Upper Devonian acidic intrusive from southern Quebec yields paleornagnetic directions unlike those determined for the stable North American platform or the Avalon Zone. Thirty one (31) sites from the three different types of granites give mean residual magnetizations of 045°, -14°, α₉₅= 11° y 102°, 48°. The corresponding paleopole positions are 164°E, 31°N (antipole: 016°W, 31°S) and 170°E, 13°S (antipole: 010°W, 13°N). This granite appears to be unaffected by the mid-Devonian Acadian orogeny and by local rotation. Geological evidences indicate that granitic intrusions like the one of Ste-Cecile and St-Sebastien represent the very last phase of the Acadian orogeny. Considering the quantity of data available, it is still premature to make clear subdivision between the poles corresponding to the Avalon microcontinent and the ones from the central Mobile Belt at Middle to Late Devonian times. Because an important disparity of the cleaned NRM orientations is observed for different phases of intrusion which occurred in a relatively short span of time, a rapid APW is presumed to have taken place during this time interval. No definite statement can be made on the possibility of the presence of a shear zone parallel to some of the tectonostratigraphic zones.