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

Abstract : The Central Atlantic Magmatic Province (CAMP) is the world's largest known continental igneous province and is 15 contemporaneous with the Triassic–Jurassic (T–J) boundary that marks one of the five largest biological extinctions in the last 16 600 Ma. Although constraints on the duration of the CAMP volcanism remain yet poorly defined, the assumption that the CAMP 17 may have had a causal relationship with the climatic and biotic crisis was suggested [Marzoli, A., Bertrand, H., Knight, K., Cirilli, 18 S., Buratti, N, Verati, C., Nomade, S., Renne, P.R., Youbi, N., Martini, R., Allenbach, K., Neuwerth, R., Rapaille, C., Zaninetti, L., 19 Bellieni, G., 2004. Synchrony of the Central Atlantic magmatic province and the Triassic–Jurassic boundary climatic and biotic 20 crisis. Geology 32, 973–976.]. In this paper, we present new 40Ar/39Ar ages on basaltic flows from Moroccan (central High Atlas, 21 Oujda and Argana) and Portuguese (Algarve and Santiago do Cacém) basins where CAMP lava flows are interlayered with T–J 22 sedimentary sequences. 23 In the Moroccan basins, where the basalts were erupted across the T–J boundary, well defined 40Ar/39Ar plateau ages (n=12) 24 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 25 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 26 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 27 end-Triassic mass extinction: First on land, then in the sea? Geology 28, 39–42.]. The topmost lava flows (recurrent unit) yield a 28 significantly younger mean age of 196.6±0.6 Ma, highlighting late episodic eruption of CAMP magmas. These late basalts 29 represent a small magma volume (b10% of the total), which was erupted most likely due to asthenospheric upwelling and 30 lithospheric extension within the T–J central High Atlas basins. 31 In the Portuguese basins, stratigraphical and palynological studies of the associated continental sedimentary sequence 32 underlying the volcanic units suggest an age close to the T–J boundary for the CAMP basaltic flows. This is confirmed by new 33 40Ar/39Ar data for the Portuguese basalts, which provide the first accurate radio-isotopic ages for lava flows in the European 34 CAMP, with two plateau ages yielding a mean value of 198.1±0.4 Ma. These plateau ages (plus three concordant mini-plateau 35 ages) suggest synchronous rifting and volcanism both in south-western Europe and Morocco (central High Atlas and Oujda basins).In summary, the eruptive history of the CAMP, with an early extremely widespread and intense peak at 199.1 Ma and a tail of 37 episodic eruption events until 196.6 Ma is consistent with the biotic turnover at the T–J boundary, which was likely caused by 38 devastating effects of extensive volcanic eruptions.
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Submitted on : Monday, September 18, 2006 - 1:52:53 PM
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Chrystèle Verati*, Cédric Rapaille, Gilbert Féraud, Andrea Marzoli, Hervé Bertrand, et al.. 40Ar/39Ar ages and duration of the Central Atlantic Magmatic Province volcanism in Morocco and Portugal and its relation to the Triassic-Jurassic boundary. Palaeogeography, Palaeoclimatology, Palaeoecology, Elsevier, 2006, in press, in press. ⟨10.1016/j.palaeo.2006.06.033⟩. ⟨hal-00095804⟩



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