Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 76. (Budapest 1984)

Embey-Isztin, A.: Texture types and their relative frequencies in ultramafic and mafic xenoliths from Hungarian alkali basaltic rocks

relatively undepleted however in diopside and spinel and they are the only ones that may contain amphibole. A similar relation was noted by BROWN et al. (1980) in the case of the Auvergne xenoliths with the exception that there the amphibole appears in porphyroclastic inclusions. Nevertheless, the statistical investigations of texture types of both volcanic provinces indicate that the "early" stages of tectonization processes in the upper mantle may be connected with depletion in basaltic constituents, while on the countrary, in the "later" and more intense stages of the tectonic cycle metasomatic enrichment in incompatible elements of the type described by FREY & GREEN (1974) may be operating. Most of the Hungarian spinel lherzolite and harzburgite nodules are only moderately stressed indicating steady state flow in the mantle, however a few highly strained inclusions may be indicative of earlier movements in mantle shear zones. Fig. 5. Profile of double diapiric intrusion beneath Transdanubia. The line of Moho has been drawn on the basis of seismic data (POSGAY, 1975). Solid triangles show the location of basaltic volcanoes, solid circles represent mantle regions where protogranular, dotted lines where porphyroclastic and equigranular textures should prevail according to the model of COISY & NICOLAS (1978). Remark : the Gérce xenoliths are indeed the only ones to have really porphyroclastic textures!