Nipissing sills

[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.

[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 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.