THE APPARENT POLAR WANDER PATH OF THE EUROPEAN PLATE IN UPPER TRIASSIC LOWER JURASSIC TIMES AND THE LIASSIC INTRAPLATE FRACTURING OF PANGAEA - NEW PALEOMAGNETIC CONSTRAINTS FROM NW FRANCE AND SW GERMANY

In order to constrain the European plate motions during Triassic-Lower Jurassic times, new palaeomagnetic data were acquired from various Tr iassic-Liassic sediments of northeastern France and southwestern Germa ny. A Carnian palaeopole 49 degrees N/131 degrees E, K = 193, A(95) = 7 degrees, N = 4 was obtained for Keuper marls with consistent directi ons of normal and reversed polarities. Rhaetian sandstones, also with both polarities, and Carnian dolomites with a magnetization of probabl e secondary origin, provide a mean pole 51 degrees N/112 degrees E, K = 109, A(95) = 6 degrees, N = 6, more westerly than that given above. The Lower Hettangian, sampled in limestones of the Xeuilley quarry nea r Nancy shows a N-R-N polarity sequence with well-defined anti-paralle l directions. The mean Hettangian pole is 55 degrees N/100 degrees E, K = 123, A(95) = 11 degrees, N = 3. Induan sandstones from the norther n Vosges show two distinct overprints, one consistent with the Ladinia n-Carnian magnetizations already observed in the same region, the seco nd consistent with the recalculated mean Lower Jurassic pole of Europe . Five other sites with different rock types also exhibit late overpri nts with Lower Jurassic directions. The mean pole calculated from thes e overprints is 74 degrees N/124 degrees E, K = 125, A(95) = 6 degrees , N = 6. The revised apparent polar wander path (APWP) presented here shows that for the mid-Permian to the earliest Jurassic the palaeopole s of Europe stayed around 50 degrees latitude, while the longitudes dr ifted from 185 degrees E to 100 degrees E. The previously established Upper Triassic-Lower Jurassic loop of the APWP is shifted westwards by about 25 degrees. The revised APWP involves the following plate motio ns. After the late Alleghanian tectonic phase, which marked the end of the Variscan orogeny, central western Europe rotated counterclockwise during about 70 Myr, up to the earliest Jurassic. The south-north dri ft in latitude by 35 degrees (nearly 4000 km) remained regular from 32 0 to 205 Ma, with a constant rate of 3.4 cm yr(-1). Around 205 Ma, thi s motion ceased, probably because of a collision somewhere in the nort h of Eurasia. Then, in the Lower Liassic, the plate underwent a rapid counterclockwise rotation with a Eulerian pole located in northeastern Asia, synchronous with fracturing in the Atlantic and the Neotethys a reas. It is proposed that the intraplate fracturing of Pangaea was ini tiated by the rapid change of the megacontinent motion at the end of t he Trias.