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The relationship between crustal magmatic underplating and granite genesis: an example from the Velay granite complex, Massif Central, France

By
B. J. Williamson
B. J. Williamson
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H. Downes
H. Downes
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M. F. Thirlwall
M. F. Thirlwall
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Published:
January 01, 1992

The Velay granite pluton (Massif Central, France) is the youngest (304 ± 5 Ma) and largest (∼6,900 km2) of the major Massif Central monzogranites/granodiorites and was formed nearly 50 Ma after the cessation of Hercynian continental collision (Pin & Duthou 1990). It is a highly heterogeneous pluton consisting of I-type, high-Sr granites (Sr= 500–900 ppm) with low εSr(304) (+35 to +41) and high εNd(304) (−3 to −5), at its centre, grading into S-type and mixed I–S-type heterogeneous granites of more normal Sr content (100–420 ppm) and higher εSr(304) (+40 to +210) and lower εNd(304) (−3·8 to −7.3) at its margins.

The metasedimentary lower crust of the Massif Central was underplated/intruded by mafic mantle-derived magmas between 360 Ma and 300 Ma. From 300–280 Ma (Downes et al. 1991) underplating led to partial melting and granulite facies metamorphism of the material (represented by felsic and mafic meta-igneous lower crustal xenoliths, εSr(304) = −11 to + 112, εNd(304) = +2·2 to 8·2, Downes et al 1990). The partial melts assimilated mainly schist but also felsic gneiss and older granite country rock material (εSr(304) = +100 to +300, εNd(304) = −5 to −9) to produce the heterogeneous granites. Plagioclase and biotite were accumulated at the base of the intrusion which was intruded to high levels to form the high-Sr granites.

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GSA Special Papers

The Second Hutton Symposium on the Origin of Granites and Related Rocks

P. E. Brown
P. E. Brown
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B. W. Chappell
B. W. Chappell
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Geological Society of America
Volume
272
ISBN print:
9780813722726
Publication date:
January 01, 1992

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