Nipissing sills

47°24′N 79°41′W^[1]

Nipissing sills associated with Ungava magmatic event

The Nipissing sills, also called the Nipissing diabase, is a large 2217– to 2210–million year old group of sills in the Superior craton of the Canadian Shield in Ontario, Canada,^[2] which intrude the Huronian Supergroup.^[3] Nipissing sills intrude all the Huronian sediments and older basement rocks in the northern margin of the Sudbury Basin;^{[4]: 25, 67} they were emplaced after the faulting and folding of Huronian rocks, and are hornblende gabbro of tholeiitic basalt composition.^[4]: 25 In the Sudbury–Elliot Lake area the Nipissing diabase is deformed; outcrops are parallel to the fold axes of the Huronian sedimentary rocks.^[3] Nipissing diabase intrusions are east-northeast trending and are no wider than 460 m (1,510 ft).^[5]: 972

The Nipissing sills in the Southern Province of the Superior craton are thought to originate from a radiating dike swarm area 1,300 km (810 mi) to the northeast.^[6]: 3 The mantle source for the Nipissing sills did not come from the mantle beneath the Southern Province that had generated the 2500– to 2450–million year old Matachewan dike swarm.^[6]: 3 The 2217– to 2210–million year old Ungava magmatic event – located under the Labrador Trough – fed the Nipissing sills;^{[6]: 3, 5} evidence shows the sills were laterally fed from a mantle plume center 1,500 km (930 mi) away via the 2216–million year old Senneterre dikes which form part of the radiating dike swarm.^[7]

In 1911, Willett G. Miller named the Nipissing diabase type area at Cobalt, Ontario.^[1][8]

See also

• Volcanism of Eastern Canada