Correlation of gravity with the Maquereau Group, southern Gaspe Peninsula, Quebec

Gravity observations at 150 locations in the Port-Daniel and Chandler area, southeastern Gaspé, Quebec, delineate an E-W to ENE-WSW trending elliptical positive Bouguer gravity anomaly with an amplitude of 19 mGal and a residual gravity anomaly of circa 22 mGal. This anomaly correlates closely with the Lower Cambrian and/or Hadrynian Maquereau Group, the steep gradients defining it coinciding with the contact between the group and the surrounding Ordovician and Siluro-Devonian sedimentary rocks. On the basis of its similar geological setting, this gravity anomaly may be compared with the positive Bouguer anomalies observed over the Fleur de, Lys zone to the east of the Baie Verte lineament in Newfoundland. Tridimensional modelling of the gravity data is inconsistent with a serpentinite dome as originally proposed and it suggests that the Maquereau Group represents an upthrusted slice of deep-seated volcanosedimentary sequences. These were originally located on the lower segment of the continental slope; they constituted a topographic high during the final process of the mountain building at the Taconic phase (Middle to Upper Ordovician time). The most probable way of emplacement of the Maquereau block is through a tear-fault running E-W to ESE-WNW in the southern Gulf of St. Lawrence west of Cape Breton and resulting from Early Paleozoic continental collision between a Eurafrican continent and a North American continent which had a salient located beneath the site of the modern Gulf. The Maquereau may then have been reactivated with a left-lateral motion accompanied of a rotation about a sub-horizontal axis. The presumed Baie Verte-Brompton line ought to be displaced to the north and the Humber zone is narrowed.