Nipissing sills explained

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,^[1] which intrude the Huronian Supergroup.^[2] Nipissing sills intrude all the Huronian sediments and older basement rocks in the northern margin of the Sudbury Basin;^[3] they were emplaced after the faulting and folding of Huronian rocks, and are hornblende gabbro of tholeiitic basalt composition.^[3] In the Sudbury - Elliot Lake area the Nipissing diabase is deformed; outcrops are parallel to the fold axes of the Huronian sedimentary rocks.^[2] Nipissing diabase intrusions are east-northeast trending and are no wider than 460m (1,510feet).^[4]

The Nipissing sills in the Southern Province of the Superior craton are thought to originate from a radiating dike swarm area 1300km (800miles) to the northeast.^[5] 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.^[5] The 2217– to 2210–million year old Ungava magmatic event  - located under the Labrador Trough  - fed the Nipissing sills;^[5] evidence shows the sills were laterally fed from a mantle plume center 1500km (900miles) away via the 2216–million year old Senneterre dikes which form part of the radiating dike swarm.^[6]

See also

• Volcanism of Eastern Canada

Notes and References

1. http://www.largeigneousprovinces.org/06may.html Ancient LIPS Reconstructed (2.50, 2.45, 2.22 & 2.10 Ga): The Utility Of Precise Magmatic “Barcodes” And “Piercing Points” In Matching Ancient Continental Fragments
2. 10.1139/E06-096. Magnetic Fabric Studies of the Nipissing sill province and Senneterre dykes, Canadian shield, and Implications for Emplacement. Palmer, H. C.. Ernst, R. E.. Buchan, K. L.. Canadian Journal of Earth Sciences. 44. 4. April 1, 2007. 507–528. NRC Research Press. 2007CaJES..44..507P .
3. Differential Uplift of the Archean Basement North of the Sudbury Basin: Petrographic Evidence from tahe Matachewan Dyke Swarm. Siddom, James P.. submitted in conformity with the requirements for the degree of M.Sc. Graduate Department of Geology University of Toronto. 1999. June 12, 2010.
4. "Sudbury Breccia" at Whitefish Falls, Ontario: Evidence for an Impact Origin. Parmenter, Andrew C.. Lee, Christopher B.. Coniglio, Mario. Canadian Journal of Earth Sciences. 39. 6. 971–982. 2002. 10.1139/E02-006. June 12, 2010. 2002CaJES..39..971P .
5. Large Igneous Provinces in Canada Through Time and Their Metallognic Potential. Ernst, Richard E.. June 12, 2010.
6. Mapping Flow Patterns in Nipissing sills of the Southern Province, Canadian shield: a Magnetic Fabric Study. AGU Spring Meeting Abstracts. 2004. GP34A–04. Palmer, H.C.. Ernst, R.E.. Buchan, K.L.. American Geophysical Union, Spring Meeting 2004, abstract #GP34A-04. 2004AGUSMGP34A..04P. 2004.