Positioning Paleogene Eurasia problem: Solution for 60–50 Ma and broader tectonic implications

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 Eurasiaʹs 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).