A 534 ± 10 Ma age has been obtained on zircons from Jbel Boho volcano by the U–Pb method; previous assumptions of older ages for the Anti-Atlas Infracambrien (Morocco) cannot be maintained. This formation belongs to the lower Paleozoic. A slight thermal event has affected the volcanic rocks during Variscan (or Hercynian) times and induced opening of the K–Ar and Rb–Sr systems; but the U–Pb system of the zircons has not been affected. These U–Pb data are further reasons to raise the Precambrian – Cambrian boundary to an age of 550–560 Ma.

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