Abstract

Natural remanence inclinations and paleointensities have been obtained from six drill cores of oceanic tholeiite pillow basalt taken from within a 4 km by 3 km area of the median valley of the Mid-Atlantic Ridge near 45 °N. Only two of the remanence inclinations agree with the predicted value for the area of +64°. Two others are of normal polarity but at +37 °and +47 °are significantly shallower than the predicted inclination. The remaining two cores have reverse inclinations of −14 °and −47°. Bottom photographs suggest that at least the +37 °and −47 °drill cores were obtained from in situ material.The paleointensities are uniformly high, ranging from 0.63 Oe to 1.17 Oe.The combined remanence inclination and paleointensity results are consistent with the presence on the floor of the median valley of basalts erupted during the Laschamps event, a conclusion in line with the fission-track ages for the basalts.It is suggested that the general lack of agreement between measured and predicted remanence inclinations, a feature that may be widespread in North Atlantic submarine basalts, is a side effect of the tectonic process responsible for the transport of new crust from the floor of the Median Valley to the adjacent crestal mountains.

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