THE ECLOGITES IN THE MONOTONOUS SERIES OF THE MOLDANUBIAN ZONE AND THE THEORY OF THERMAL PULSES - A DISCUSSION

O'Brien and Vrana (1995) recently interpreted textural and paragenetic relations as well as garnet zoning occurring in the rare eclogites of the Monotonous Series as evidence of (a) prograde evolution from lowe r pressures, (b) eclogite facies overprint and (c) granulite facies ov erprint caused by a thermal pulse of less than 1-Ma duration. The ther mal pulse was interpreted as the result of the convergence of the ther mal patterns of a hot-rock association over the cooler Monotonous Seri es metabasites. Re-evaluation of the data presented shows that the pos tulated prograde evolution is not supported. Similarly, the Fe-Mg-part itioning relations at garnet rims and associated orthopyroxene in thes e rocks point to cooling rather than heating. The age of less than 1 M a dates a certain stage during cooling of the rocks, rather than the d uration of a thermal pulse. The rare metabasites of the Monotonous Ser ies are re-interpreted as tectonically incorporated bodies derived fro m the higher Moldanubian units during the intra-Moldanubian nappe stac king.