POSITIONING PALEOGENE EURASIA PROBLEM: SOLUTION FOR 60-50 MA AND BROADER TECTONIC IMPLICATIONS

Abstract

Recently published paleomagnetic data from the Faroe Islands and SE England have enabled a "hybrid" pole (72.0°N, 177.9°E, A95 = 7.9°) to be calculated for "stable" Eurasia ~ 55 Ma. It is somewhat different to previous proposals, being a further 8-9° from the present-day North Pole. A strong positive test of the new pole is provided by 2002-published paleomagnetic data from basaltic rocks in the Tien Shan range in Kyrgyzstan: the paleolatitude derived from the inclination angle matches the predicted value to within 0.2°. An unfortunate drawback with Kyrgyzstan pole is its large age error: ± 15 m.y. for rocks estimated to have formed ~ 50 Ma. Fortuitously, an alternative test is now available using paleomagnetic data from Paleocene basalts in the Tien Shan range of western China, for which a robust radiometric age-date (59 ± 1 Ma, based on two Ar-Ar results) also exists. Although the locality has experienced a large vertical-axis rotation, the mean declination being 54.5°, the inclination angle appears undisturbed, and the derived paleolatitude matches the value predicted by hybrid pole to within 4.0°. Thus, it is contended, the Faroe-Sheppey pole provides one of the most reliable means of fixing Eurasia's position for the interval 60-50 Ma. It also impacts on various model proposals for the India-Asia collision and subsequent crustal shortening and/or extrusion between southern Tibet and stable Eurasia (north of the Tien Shan). © 2006 Elsevier B.V. All rights reserved.