Chaîne varisque
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Fig. 13


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Geochemistry of magmatic rocks of the French Massif Central. a) Two mantle sources in the Massif Central (calculated at 315 Ma, an average between the c. 335 Ma lavas and the ca 305 Ma lamprophyres and vaugnerites): note the clear difference between the pre-335 mafic magmas (lavas from the Brévenne Unit (Pin and Paquette, 1997) and diverse lavas from NE Massif Central (Pin and Paquette, 2002)), and the post-335 Ma lavas (lamprophyres: (Agranier 2001); enclaves in granites (Pin, 1990) and vaugnerites (Williamson et al., 1992); underplated mafic magmas (or cumulates) found as enclave in the Cenozoic Bournac volcano (Downes et al., 1990)). b) Change in the nature of the lavas, in Shand (1943) A/CNK vs. A/NK and Peccerillo and Taylor (1976) SiO2–K2O diagrams. Pre-335 Ma lavas are mafic and metaluminous, whereas post-335 Ma lavas are felsic, high-K and peraluminous, essentially similar to MPG granites forming at the same age.

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