A

where At = cmax/cmin and is the degree of anisotropy of TRM. The TRM will be deflected through the angle (9 - <j>), which will have its maximum value when 0 = tan"W^t so that

At-1

For multidomain magnetite and other strongly magnetic minerals A, « An2 from both theory (Dunlop and Özdemir, 1997) and experiment (Cogné, 1987) so that, from (2.3.42)

7 2Av

where Ax = (xmax - Xmi„) and xav = (Xmax + Xmin)/2-anisotropy of TRM is approximately twice the susceptibility. Also, from (2.3.45)

Therefore, the percentage percentage anisotropy of

For an anisotropy of susceptibility of 5%, An = 1.05 and the maximum TRM deflection is 2.7°, for 10% it is 5.2° and for 20% it is 10.0°. Thus 10% anisotropy can be tolerated without seriously deflecting the TRM. The rocks most commonly used in paleomagnetism, such as basic igneous rocks, redbeds and unmetamorphosed sediments, rarely have anisotropies exceeding a few percent, so the effect is only likely to be significant in some metamorphic or strongly foliated rocks.

This Page Intentionally Left Blank

Chapter Three

Methods and Techniques

Was this article helpful?

0 0

Post a comment