SEQUENTIAL NESTING OF MAGMAS IN MARBLE, SOUTHWESTERN GRENVILLE PROVINCE, QUEBEC - FROM FRACTURE PROPAGATION TO DIAPIRISM

In the southwestern Grenville Province (Quebec), 1090-1070 My old K-ri ch alkaline equidimensional plutons, such as the Kensington pluton, oc cur in marble-rich country rock, but coeval dykes bearing lower-crusta l xenoliths are found only in a quartzofeldspathic gneiss complex. The sequential nesting of magmas, the various episodes of skam formation and the progressively more mafic character of the intruding magmas of the Kensington pluton are interpreted in terms of magma ascent through a series of propagating fractures, cessation of upward fracturing and pooling of magma in marble-rich ductile crust, diapirism, radial shor tening of wall rock, and in-situ pluton expansion. This suite provides evidence that at deep crustal levels, the country-rock theology influ ences the mode of magma ascent and emplacement and that diapirism is a possible mechanism of magma transport through rocks behaving theologi cally by a power-law model.