Abstract
In Sm-Nd studies aimed at constraining crustal growth history, Sm-Nd systematics are normally considered to be undisturbed at the whole rock scale during intracrustal processes such as alteration, metamorphism or even partial melting. However, if Sm-Nd systematics are disturbed during intracrustal processes, this could put wide ranging conclusions from Sm-Nd crustal studies into question. Migmatites are ideal rocks to study the chemical and isotopic fractionation which may occur during high grade metamorphic events. From this perspective, we carried out Sm-Nd, U-Pb work associated with major and trace element analyses on three outcrops of migmatites generated during the 2.0 Ga orogeny in the Central Zone of the Limpopo Belt (Botswana and South Africa). The Central Zone which is mainly composed of orthogneisses and paragneisses underwent granulite facies metamorphism followed by decompression metamorphic conditions (clockwise P T loop) at 2.0 Ga. Partial melting following the Bt breakdown reaction in high temperature, low pressure rocks did lead to different behaviour of Sm-Nd systematics for metagreywacke and metapelite. In the first case, chemical equilibrium and full Nd isotope exchange were not reached due to the effect of accessory minerals (monazite and apatite) on the compositions of the partial melt. Monazite entered the melt in preference to apatite,
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