REMAGNETIZATIONS AND POSTFOLDING OROCLINAL ROTATIONS IN THE CANTABRIAN ASTURIAN ARC, NORTHERN SPAIN

Devonian carbonates in the Cantabrian Are reveal characteristic magnet izations with coherent, shallow, upward inclinations. nle magnetizatio ns appear to be carried by magnetite. Within-site directions are very well grouped, but site-mean declinations range from easterly to south- southwesterly in in situ as well as tilt-corrected coordinates, as has also been observed in previous studies of other formations in the are . The widely varying declinations of all studies roughly correlate wit h tile overall structural trends of the are and suggest that the sites underwent rotations in a process that involved folding about vertical axes and tightening of are. Upon tilt correction the inclinations of our study, on the other hand, become scattered, and it is concluded th at the magnetizations were acquired after Late Carboniferous folding a bout horizontal axes. The oroclinal rotations therefore also must have occurred after the Late Carboniferous folding phase. The previous pal eomagnetic results had been interpreted mostly as primary magnetizatio ns residing in hematite. However, inclination only fold-tilt tests app lied to these results suggest that many, if not all, of the directions were acquired during the earlier stages of the Late Carboniferous fol ding. Thus all paleomagnetic results from the Cantabrian Are appear to be remagnetizations, but the ages of the remagnetizations vary from p re- to synfolding for the mostly hematitic formations to postfolding f or the Devonian carbonates. The reversed-polarity inclinations of the hematite-bearing formations have mean values ranging from +25 degrees to +5 degrees, whereas the carbonates have a mean inclination of -8 de grees. On the basis of inclinations predicted for the area from result s from stable Europe, the Pyrenees, and the Iberian Meseta, the ages o f these remagnetizations can be inferred to range from about 320 Ma to 260 Ma. Because all the remagnetizations reveal rotated declination p atterns, the oroclinal rotations occurred well after the main phase of Hercynian deformation (320-280 Ma). While the timing of the rotations is unconstrained at the younger end, they must have occurred during o r after the Permian (best estimate is less than 260 Ma), which is much later than anticipated from other geological considerations.