科研之友
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摘要
A paleomagnetic investigation of the Alno carbonatite complex dikes was undertaken in an attempt to refine the apparent polar wander path for Baltica. The currently available paleomagnetic database for the Ediacaran-Cambrian segments of the Baltica APWP is marked by disparate (and often supposedly) coeval poles. This has led to remarkable conclusions about rapid rates of drift or true polar wander. Our study shows that the Alno Complex (584 +/- 7 Ma) is coeval with the Fen Carbonatite Complex (583 +/- 15 Ma) via Ar-40/Ar-39 dating of biotite and K-feldspar. We identify three components of remanent magnetization in the Alno Complex. The first is a low unblocking/coercivity component with a mean declination of 51.2 degrees and inclination of +70.2 degrees (k = 22, a95 = 8.3 degrees). A paleopole calculated from this direction falls at 62.7 degrees N, 101 degrees E. The high coercivity and unblocking components show a large spread in both declination and inclination. A somewhat artificial grouping of shallow-intermediate vectors (inclinations less than 60 degrees) yields a mean direction with a declination of 108.1 degrees and an inclination of 10.5 degrees (k = 5.3, a95 = 32.1 degrees). This direction is statistically indistinguishable from that obtained by Piper [Piper, J.D.A., 1981. Magnetic properties of the Alnon complex. Geol. Foren. Stock. Forhandlingar, 103, 9-15 (Part 1)] and yields a paleomagnetic pole at 3.5 degrees N, 269 degrees E. Conversely, the remaining high unblocking/coercivity components (inclinations > 60 degrees) yields a second grouping with a mean declination of 28 degrees and inclination of 76.8 degrees (k = 24; a95 = 16.1 degrees; Fig. 5E). This direction is indistinguishable from the present Earth's field at the site. We conclude that the Alno Complex poles (and indeed many of the Ediacaran poles for Baltica) should be viewed with scepticism when used for paleogeographic/geodynamic models.
- 出版日期2007-4-15
