PRECAMBRIAN GRANULITES AND ANOROGENIC GRANITES - ARE THEY RELATED

Anorogenic granites, which are emplaced > 100 Ma following orogenic events, are not limited to the Proterozoic but are also widespread in the Late Archean. Archean anorogenic granites are depleted in heavy REE, Y and Sc (and to a lesser extent in Nb and Ta), compared to Proterozoic anorogenic granites, a feature that appears to reflect differences in crustal source composition. Archean and Proterozoic felsic granulites show similar differences. Most analyzed Precambrian granulites and xenoliths cannot represent either sources or restites of Precambrian anorogenic granites. The rarity in exposed granulite terranes of rocks suitable as sources or restites for anorogenic granites, may be related to removal by uplift and erosion following orogeny or/and the fact that anorogenic granites are formed > 100 Ma after orogeny, and thus are not brought to the surface by isostatic uplift. The presence of a positive Eu anomaly in restites is dependent upon not only residual feldspar but also the amount of zircon and apatite left in the residue, and in many or perhaps most cases, restites should have no Eu anomalies or negative Eu anomalies.