Emplacement of the Monteregian Hills of Quebec; Geophysical evidence

Constraints are placed on the shape of intrusions of the Monteregian Hills and a model of their emplacement is proposed. Integrated geophysical data (magnetic, gravimetric and seismic reflection) and drainage pattern information indicate that the Monteregian Hills are shallow intrusives having the form of saucers nourished by thin planar feeders. These feeders are apparently tectonically controlled by steeply dipping normal faults in the crystalline basement and intermediate to low-angle thrust faults in the overlying Lower Paleozoic sequence. Field geological evidence, geochemical and geophysical data indicate a slow ascending motion of the cooling magma and a sub-vertical rather than sub-horizontal injection mode. In view of the relatively cold state of the intruded magma and paleomagnetic data, partial and progressive melting of an olivine basalt magma is a more acceptable origin for the Monteregian Hills than a continental hot spot theory.