A positive fold test from Nipissing diabase

Positive fold tests are reported on two remanence components resolved from the same Nipissing diabase sills. These tests conclusively indicate that the region south of the Sudbury Basin in the Southern Structural Province has been subjected to two distinct deformational episodes subsequent to the intrusion of the Nipissing diabase. One event precedes (1850–2150 Ma) and one event postdates (1250–1850 Ma) intrusion of the Sudbury irruptive. Some evidence also exists for a third event that may be related to the development of the Sudbury structure, around 1850 Ma. Evidence that the Nipissing was intruded into already folded Huronian sediments confirms previous suggestions of four separate orogenic pulses in the period 2300–1250 Ma.