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40 Ar −39 Ar dating of the Beja Gabbro: TIming of the accretion of southern Portugal
Author(s) -
Ruffet Gilles
Publication year - 1990
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl017i012p02121
Subject(s) - gabbro , geology , carboniferous , paleozoic , geochemistry , igneous rock , absolute dating , thermoremanent magnetization , paleontology , quaternary , magnetization , remanence , physics , structural basin , quantum mechanics , magnetic field
The 40 Ar −39 Ar dating of the amphibole from the Beja gabbro (Southern Portugal) yields a plateau age at 336.4 ± 0.8 Ma (2σ 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 335Ma and 315Ma, assuming cooling rates between 10°C/Ma and 100°C/Ma. These results, combined with palaeomagnetic 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 Northern Iberia in Early Carboniferous times and was accreted to Europe during the Late Carboniferous.