Physics
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmgp21a..05k&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #GP21A-05
Physics
1525 Paleomagnetism Applied To Tectonics (Regional, Global), 8120 Dynamics Of Lithosphere And Mantle: General, 8121 Dynamics, Convection Currents And Mantle Plumes
Scientific paper
The 80 km-diameter Sept-Îles intrusive suite and associated regional dikes are interpreted as the eroded remnant of a plume that was emplaced beneath NE North America in mid-Ediacaran time(1,2). We report here new paleomagnetic, zircon U/Pb, apatite (U-Th-Sm)/He, and conodont alteration results from rocks associated with the Sept-Îles intrusive suite which help constrain the Laurentian apparent polar wander path (APWP) during the newly-defined Ediacaran Period. Our paleomagnetic results are in general agreement with those of an earlier study by Tanczyk et al.(3), which identified a two-polarity, low-latitude component (A), here dated as young as ~562 Ma, overprinted by a more steeply-inclined two polarity magnetization (B), here constrained to be not older than ~561 Ma by U-Pb crystallisation ages on samples that contain only the B component and cross-cut those with the A component. Low conodont alteration index in an early Whiterockian (early Middle Ordovician) fauna extracted from flat, overlying limestone, and early Cretaceous helium closure ages in igneous apatites from the middle part of the intrusion, indicate that neither component of magnetization may be attributable to post-Cambrian thermal remagnetization. Older, robust Ediacaran paleomagnetic studies imply that Laurentia occupied high paleolatitudes for most of the early part of Geon 5. Thus, our results suggest that the emplacement of the Sept-Îles plume was coincident with rapid movement of Laurentia. Perhaps the intrusion triggered a pair of rapid TPW bursts, first moving the site towards the equator and then with subsequent thermal relaxation moving it back to higher latitude. If the Earth's principal and intermediate moments of inertia were of similar magnitude, relatively small perturbations in the Earth's mass distribution could have initiated inertial interchange TPW events. This is consistent with the hypothesis of Evans(4) that multiple bursts of true polar wander dominate the APWP signals for all continents during Ediacaran and Early Cambrian time. 1.M. D. Higgins, Lithos (in press). 2. M. D. Higgins, O. van Breemen, Journal of Geology 106, 421 (1998). 3. E. I. Tanczyk, P. Lapointe, W. A. Morris, P. W. Schmidt, Can. J. Earth Sci. 24, 1431 (1987). 4. D. A. Evans, Earth and Planetary Science Letters 157, 1 (1998).
Bowring Samuel A.
Condon Daniel J.
Evans Daniel A.
Farley Ken A.
Higgins Michael Denis
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