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Magnetic measurements have been made on some lavas found at 60ºN and 90ºW. The inclination angle is 37º. If the horizontal direction of magnetism of these lavas is due west, calculate the position of earth's magnetic pole when these lavas errupted.

I found the magnetic latitude using $\arctan(\frac{1}{2}\tan(37^{\circ})) = 20.6^{\circ}$, but I'm not sure how to get the pole location since we are not given declination angle. I think you use this formula:

$\cos\theta_p = \cos\theta_s \cos\theta_m + \sin\theta_s \sin\theta_m \cos D$

but not sure how without declination angle D.

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You say you're "not given the declination angle", but you also say "the horizontal direction of magnetism of these lavas is due west". That's your declination angle, right there! Since I assume (from the very round-numbered location) that this is a homework exercise or similar, I won't work through the rest of the calculation here. However, if you need more guidance on VGP calculation, I can recommend Chapter 7 of Robert F. Butler's freely available book.

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