Evidence of Protolith Contamination in the Generation of an Anatectic Complex: Pe?a Negra, Central Spain

摘要

The Pe?a Negra complex, in central Spain, provides a superb opportunity for the study of Variscan partial meltingprocesses. The heat source for the anatexis has been controversial. The presence of mafic rocks in the vicinity hasgiven rise to the suggestion that mafic magmas of mantle origin provided the requisite heat for the generation of theanatectic granites. Experimental petrology can be used to support this concept, but the volumes of mafic magma necessaryfor the anatexis appear improbably large. Geophysical models for Central Iberia do not support the presence of such largebasic complexes at depth. Furthermore radiometric dating of the scarce mafic outcrops indicates that they are too old tohave been involved in the granitic magma genesis. The alternative interpretation is that melting of the protolith was promotedby the radioactive decay of K, U and Th. Anatexis was enhanced by the existence of a fertile protolith and by thepresence of shear structures that permitted volatile fluxing. The situation is believed to have been analogous to that inother European Variscan terrains.