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Vitorello, Icaro, der Voo, Rob Van (1977) Late Hadrynian and Helikian pole positions from the Spokane Formation, Montana. Canadian Journal of Earth Sciences, 14 (1) 67-73 doi:10.1139/e77-007

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Reference TypeJournal (article/letter/editorial)
TitleLate Hadrynian and Helikian pole positions from the Spokane Formation, Montana
JournalCanadian Journal of Earth Sciences
AuthorsVitorello, IcaroAuthor
der Voo, Rob VanAuthor
Year1977 (January 1)Volume14
Issue1
PublisherCanadian Science Publishing
DOIdoi:10.1139/e77-007Search in ResearchGate
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Mindat Ref. ID475038Long-form Identifiermindat:1:5:475038:7
GUID0
Full ReferenceVitorello, Icaro, der Voo, Rob Van (1977) Late Hadrynian and Helikian pole positions from the Spokane Formation, Montana. Canadian Journal of Earth Sciences, 14 (1) 67-73 doi:10.1139/e77-007
Plain TextVitorello, Icaro, der Voo, Rob Van (1977) Late Hadrynian and Helikian pole positions from the Spokane Formation, Montana. Canadian Journal of Earth Sciences, 14 (1) 67-73 doi:10.1139/e77-007
In(1977, January) Canadian Journal of Earth Sciences Vol. 14 (1) Canadian Science Publishing
Abstract/Notes The natural remanent magnetizations of Beltian argillites from the Spokane Formation (formerly Grinnell Formation) have been analyzed with alternating field and thermal demagnetization techniques. Two groups of magnetic directions have been observed. One is assumed to be the primary magnetization, representative of the Helikian (approx. 1300 Ma) geomagnetic field: D = 201.5°; I = +40°; k = 61; and α95 = 5.1° for N = 14 sites (51 samples), yielding a pole position at 15.5 °S. 134.5 °W, dp = 3.7°, dm = 6.2°. Comparisons with contemporaneous pole positions reveal good agreement. The other direction of magnetization corresponds to a Late Hadrynian age (approx. 600 to 750 Ma) and resulted from low-grade metamorphism. It is speculated that this thermal event resulted from enhanced heat flow during continental breakup in the Late Hadrynian. This direction (D = 267.5°; I = +17; k = 10; α95 = 9.1° for N = 28 specimens) yields a pole position at 5°N, 163.5°E, with dp = 4.9°, dm = 9.4°. Both groups of directions of magnetization are pre-folding, which occurred during the Laramide orogeny. Laramide deformation was only moderate, however, and the eastward thrusting of the Beltian sediments over the Lewis thrust was probably not accompanied by significant structural rotation.


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