40Ar/39Ar ages and duration across the Triassic-Jurassic boundary of the Central Atlantic Magmatic Province volcanism in Morocco and Portugal.

The Central Atlantic Magmatic Province (CAMP) is the world's largest known continental igneous province and is contemporaneous with the Triassic–Jurassic (T–J) boundary that marks one of the five largest biological extinctions in the last 600 Ma. Although constraints on the duration of the CAMP volcanism remain yet poorly defined, the assumption that the CAMP may have had a causal relationship with the climatic and biotic crisis was suggested [Marzoli, A., Bertrand, H., Knight, K., Cirilli, S., Buratti, N, Verati, C., Nomade, S., Renne, P.R., Youbi, N., Martini, R., Allenbach, K., Neuwerth, R., Rapaille, C., Zaninetti, L., Bellieni, G., 2004. Synchrony of the Central Atlantic magmatic province and the Triassic–Jurassic boundary climatic and biotic crisis. Geology 32, 973–976.]. In this paper, we present new 40Ar/39Ar ages on basaltic flows from Moroccan (central High Atlas, Oujda and Argana) and Portuguese (Algarve and Santiago do Cacém) basins where CAMP lava flows are interlayered with T–J sedimentary sequences. In the Moroccan basins, where the basalts were erupted across the T–J boundary, well defined 40Ar/39Ar plateau ages (n=12) for more than 90% of the total erupted volume of CAMP basalts range from 197.8±0.7 Ma to 201.7±2.4 Ma and display a main restricted peak at 199.1±1 Ma providing a precise estimate of the 40Ar/39Ar age of the T–J boundary, concordant with the current U–Pb age [199.6±0.3 Ma; Pálfy, J., Mortensen, J.K, Carter, E.S., Smith, P.L., Friedman, R.M., Tipper, H.W., 2000. Timing the end-Triassic mass extinction: First on land, then in the sea? Geology 28, 39–42.]. The topmost lava flows (recurrent unit) yield a significantly younger mean age of 196.6±0.6 Ma, highlighting late episodic eruption of CAMP magmas. These late basalts represent a small magma volume (b10% of the total), which was erupted most likely due to asthenospheric upwelling and lithospheric extension within the T–J central High Atlas basins. In the Portuguese basins, stratigraphical and palynological studies of the associated continental sedimentary sequence underlying the volcanic units suggest an age close to the T–J boundary for the CAMP basaltic flows. This is confirmed by new 40Ar/39Ar data for the Portuguese basalts, which provide the first accurate radio-isotopic ages for lava flows in the European CAMP, with two plateau ages yielding a mean value of 198.1±0.4 Ma. These plateau ages (plus three concordant mini-plateau ages) suggest synchronous rifting and volcanism both in south-western Europe and Morocco (central High Atlas and Oujda basins).