Staff directory
Jean-Paul Liégeois
Earth Sciences
Geodynamics and mineral resources
Geodynamics and mineral resources
Publication details
Berger, J, Caby, R, Liégeois, J.P., Mercier, J.C.C & Demaiffe, D. 2009. ‘Dehydration, melting and related garnet growth in the deep root of the Amalaoulaou Neoproterozoic magmatic arc (Gourma, NE Mali)’. Geological Magazine 146: 173-186. DOI: 10.1017/S0016756808005499. I.F. 1.853.
Article in a scientific Journal / Article in a Journal
TheAmalaoulaouNeoproterozoic island-arcmassif belongs to theGourmabelt in Mali. The
metagabbros and pyroxenites forming the main body of this arc root show the pervasive development
of garnet. In the pyroxenites, the latter has grown by reaction between pyroxene and spinel during
isobaric cooling. By contrast, in the metagabbros, garnet textures and relations to felsic veins exclude
an origin through solid-state reactions only. It is proposed that garnet has grown following dehydration
and localized melting of amphibole-bearing gabbros at the base of the arc. The plagioclase-saturated
melts represented by anorthositic veins in the metagabbros and by trondhjemites in the upper part of
the massif provide evidence for melting in the deep arc crust, which locally generated high-density
garnet-clinopyroxene-rutile residues. Garnet growth and melting began around 850 ◦C at 10 kbar and
the tonalitic melts were most probably generated around 1050 ◦C at P = 10 kbar. This HT granulitic
imprint can be related to arc maturation, leading to a P-T increase in the deep arc root and dehydration
and/or dehydration-melting of amphibole-bearing gabbros. Observation of such features in the root of
this Neoproterozoic island arc has important consequences, as it provides a link to models concerning
the early generation of continental crust.