Origin of Early Carboniferous pseudo-adakites in northern Brittany (France) through massive amphibole fractionation from hydrous basalt

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State: Public
Version: Final published version
Serval ID
serval:BIB_1C54E0486D54
Type
Article: article from journal or magazin.
Collection
Publications
Institution
Title
Origin of Early Carboniferous pseudo-adakites in northern Brittany (France) through massive amphibole fractionation from hydrous basalt
Journal
Terra Nova
Author(s)
Barboni M., Bussy F., Chiaradia M.
ISSN-L
0954-4879
Publication state
Published
Issued date
2011
Peer-reviewed
Oui
Volume
23
Pages
1-10
Language
english
Abstract
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.
Create date
01/10/2012 19:07
Last modification date
20/08/2019 12:52
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