P>The first Variscan pseudo-adakites were identified in close
association with the Saint-Jean-du-Doigt (SJDD) mafic intrusion
(Brittany, France) in a geodynamic context unrelated to subduction.
These rocks are trondhjemites emplaced 347 +/- 4 Ma ago as 2-3 km2
bodies and dykes. Trace-element concentrations and Sr-Nd-Pb isotope
ratios indicate that the SJDD pseudo-adakites probably resulted from
extreme differentiation of an SJDD-type hydrous basaltic magma in a
lower continental crust of normal thickness (0.8 GPa). Modelling shows
that garnet is not a required phase, which was commonly believed to be
the case for continental arc-derived adakite-like rocks. A massive
fractionation of amphibole fits the data much better and does not
require high pressures, in agreement with the inferred extensional
tectonic regime at the time of pluton emplacement. Alternatively, the
SJDD pseudo-adakites could have resulted from the melting of newly
underplated SJDD mafic precursors, but thermal considerations lead us to
believe that this was not the case.