Abstract
Orogenic peridotites typically contain abundant mafic layers or lenses of basaltic to picritic compositions. A popular hypothesis for the origin of such mafic layers is that they represent crystal precipitates from mafic magmas flowing in the upper mantle in various depths (Suen and Frey, 1987). Some mafic rocks have been suggested to be of gabbroic origin from their geochemical and mineralogical signature such as positive Eu anomaly and the presence of corundum (e.g., Kornprobst at al, 1990) By examining the whole rock compositions of these rocks and associated rocks, the author proposes a new criterion of identifying mafic layers of gabbroic. According to the new criterion, mafic layers of gabbroic origin appear to be more pervasive than previously thought in mantle derived peridotites.
