Paleomagnetism of the Jacobsville Formation and the apparent polar path for the interval −1100 to −670 m.y. for North America

Chemical, thermal, and alternating field (af) treatments performed on 257 specimens (37 sites) of the Jacobsville Formation show that the magnetization was acquired gradually over a very long period of time. Three phases of magnetization can be recognized and sequentially separated chemically. Thermal (up to 675°C) and af (up to 290 mT) treatments are unable to distinguish and separate the first two phases. The results are consistent with a three-phase magnetization model previously proposed and again demonstrate the necessity of performing chemical leaching experiments in red bed studies. The early phase remanence isolated chemically indicates that the Jacobsville is of upper Keweenawan age (≃− 1100 m.y.). Poles obtained from three areas, Sault Ste. Marie (SSM) (175°E, 12°N), Marquette (182°E, 03°S), and the Keweenaw Peninsula (KP) (184°E, 10°S), indicate that the sediments of SSM are older than those of KP. A detailed study (nine sites: mean pole at 190°E, 16°S) of a 5.3-m stratigraphic section at Jacobsville shows significant apparent polar motion and the occurrence of at least one field reversal. The trend of the pole movement relative to North America was then southward. Vector analyses show that during the acquisition of the intermediate and late phase remanences the apparent pole started to move northward; by the end of the magnetization process it had reached high latitude (307°E, 72°N). Explanation of the Jacobsville results and other high-latitude poles requires a major revision of the apparent polar path during the Hadrynian. The proposed path executes a loop into the southern hemisphere (−1100 to −950 m.y.) and then roughly follows a great circle path (Hadrynian Track) from 160°E near the equator up to the present north geographic pole and down to the equator at 340°E (−670 m.y.). The controversial Grenville poles could easily be incorporated into that loop, supporting the hypothesis that the Grenville Province has always been an integral part of Laurentia. The Hadrynian Track, with its large pole displacement (180° in 300 m.y.), is an extremely useful stratigraphic tool that can be used to great advantage for global correlations of late Precambrian rock units.