Dear Marcello!
There is a study of Williams et al. 1995, where mainly tonalites are
produced by partial melting of basic rocks at ~10 kbar. The data of
Barboza & Bergantz are mainly tonalites or trondhejmitic melts in the
Ivrea zone (but also granitic leucosomes exist).
However, the often observed more tonalitic composition in anatexites
are produced by "in situ" fractionation during the sergeation and
crystallization process see Sawyer 1986. These is a common phenomena
in outcrop or even larger scale. In some cases you will find the
K-feldspar rich leucosomes at another locations. Together there are
perfect melts expected by partial melting in pelitic rocks.
Best Regards
Alfons
Literature
Williams ML, Hanmer S, Kopf C, Darrach M (1995) Syntectonic
generation and segregation of tonalitic melts from amphibolite dikes
in the lower crust, Striding- Athabasca mylonite zone, northern
Saskachawan. J. Geophys. Res., 100: 15717-15734
Barboza SA, Bergantz GW (2000) Metamorphism and anatexis in the mafic
complex contact aureole, Ivrea Zone Northern italy. J. Petrol., 41:
1307-1327
Sawyer EW (1986) The role of partial melting and fractional
crystallization in determining discordant migmatite leucosome
composition. J. Petrol., 28: 445-473
see also
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