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

Melanie Barboni, François Bussy, Massimo Chiaradia

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)1-10
Number of pages10
JournalTerra Nova
Volume23
Issue number1
DOIs
StatePublished - Feb 1 2011
Externally publishedYes

Fingerprint

amphibole
fractionation
basalt
adakite
continental arc
trondhjemite
extensional tectonics
Hercynian orogeny
rock
lower crust
geodynamics
continental crust
pluton
garnet
emplacement
subduction
melting
magma
trace element
isotope

ASJC Scopus subject areas

  • Geology

Cite this

Origin of Early Carboniferous pseudo-adakites in northern Brittany (France) through massive amphibole fractionation from hydrous basalt. / Barboni, Melanie; Bussy, François; Chiaradia, Massimo.

In: Terra Nova, Vol. 23, No. 1, 01.02.2011, p. 1-10.

Research output: Contribution to journalArticle

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