Anorthosites mantle source

Seismic evidence for a mantle source for mid-Proterozoic anorthosites and implications for models of crustal growth... 

Whether derived from a mantle or crustal source, the origin of anorthosites must have left a distinct signature in the lower crust. The bulk composition of the lower crust is expected to be of gabbroic composition (metamorphosed in Grenville time) if the anorthosite magma was derived... 

The seismic properties of the Grenville lower crust are inconsistent with pyroxene-rich or high-grade metapelites (Fig. 2). This is crucial in determining which source, mantle or crust, is responsible for generating the mid-Proterozoic meta-anorthosites, as we will discuss below. 

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