First alkaline magmatism during Iberia–Newfoundland rifting

• Published in: Terra Nova
• Main Authors: Grange, Marion, Schärer, Urs, Cornen, Guy, Girardeau, Jacques
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2008
• Subjects: Newfoundland
• Online Access: http://dx.doi.org/10.1111/j.1365-3121.2008.00847.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-3121.2008.00847.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3121.2008.00847.x

Abstract The age and origin of alkaline rocks emplaced into the sediments of the rift‐related continental Lusitanian basin were investigated to constrain earliest magmatic activity occurring prior to oceanic plate formation between Iberia and Newfoundland. The U–Pb titanite ages are 146.5 ± 1.6 (2σSTERR), 145.3 ± 1.4 and 142.3 ± 1.0 Ma, and initial Pb isotopic ratios of feldspars lie at 18.418–18.978 for 206 Pb/ 204 Pb, at 15.594–15.925 for 207 Pb/ 204 Pb and at 37.105–39.216 for 208 Pb/ 204 Pb. Initial 87 Sr/ 86 Sr ratios measured in the same feldspar fractions lie at 0.705409–0.706462. This episode of magmatic activity lasting for at least 4.2 ± 2.6 Myr most likely marks a phase of maximum lithospheric thinning during which zones of weakness were created to allow deep magmas to reach the surface. Such zones are preferentially re‐activated Palaeozoic faults of the Iberian plate. The isotope data suggest that the dominant volume of alkaline magmas was generated by partial melting of the metasomatized subcontinental Iberian mantle.