The 40Ar-39Ar dating of the amphibole from the Beja gabbro (southern Portugal) yields a plateau age at 336.4¿0.8 Ma (2&sgr; level). The corresponding calculated isotopic closure temperature is around 800 ¿C. The comparison of this temperature with the magnetic blocking temperature (~570 ¿C) allows an estimation of a probable thermoremanent acquisition age for the characteristic magnetization component of the Beja gabbro between 335 MA and 315 Ma, assuming cooling rates between 10 ¿C/Ma and 100 ¿C/Ma. These results, combined with paleomagnetic results from the Beja gabbro and Late Paleozoic rocks from Southern Portugal [Perroud et al., 1985>, suggest that the southermost part of Spain and Portugal was separated from North Iberia in Early carboniferous times and was accreted to Europe during the Late carboniferous. ¿ American Geophysical Union 1990