Ion microprobe and ID-TIMS U-Pb dating on zircon grains from leg 173 amphibolites: evidence for Permian magmatism on the West Iberian margin

In this paper, we report evidence for Permian magmatism at the ocean–continent transition zone of the West Iberian margin, by dating magmatic intrusion of amphibolite precursors drilled at site 1067 during ODP leg 173. The P–T conditions recorded by the amphibolites indicate that the latter was emplaced at the bottom of a 25‐km‐thick crust. Subhedral to rounded and colourless zircon grains were obtained from samples at the base of the cored section. ID‐TIMS dating on these zircon grains yielded a lower intercept age of 247 ± 5 Ma and a poorly defined upper intercept around 2 Ga. In situ dating of single zircons by ion‐microprobe (CAMECA IMS 1270) provided an age of 246 ± 5 Ma. This Permian age is interpreted as a minimum estimate for the emplacement of the gabbroic melts at the base of the Hercynian crust during the early stage of rifting between the Iberia–Newfoundland conjugate margins.