Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 69. (Budapest 1977)
Embey-Isztin, A.: The Szigliget amphibolitelherzolite compound xenolith as an evidence for diapiric uprise in the mantle below Hungary
morphic and no evidence for or against a cumulus origin could be found. While large domains seem tectonically undisturbed, other domains show abundant signs of cataclysis such as tiny crystals due to recrystallization or distorted twin lamellae. However, it is evident that this texture has nothing in common with that of the lherzolite: the amphibolite must have intruded into the lherzolite long after this last one had metamorphosed. Besides large amphibole crystals, the amphibolite contains n i.ior euhedral opaque inclusions, probably ilmenite, and very subordinate grains of spinel. This spinel diffeis from the lherzolite spinel in its greenish colour. (The lherzolite spinel is chest-nut brown.) In addition to the primary mineral association, a secondary one has also to be mentioned. This secondary association is apparently due to a partial melting of small degree. It is composed of newly formed amphibole, jolagioclase crystals and a vitrous matrix. In contrast to large primary amphiboles, the small secondary ones have perfect crystal faces and show optical zoning. Electron microprobe analyses have been carried out on minerals of amphibolite and lherzolites by the aid of a MS-46 type microanalyzer in the B. R. G. M., Orléans, La Source, (France) (EMBEY-ISZTIN 1976bj. Lherzolite silicates are high in Mg and low in Fe, therefore they characterize an environment depleted in basaltic constituents (KUNO & AOKI 1970, CARTER 1970). The composition of olivine is: Mg 90.20-90.29 Fe 9 . 80-9 71, that of the orthopyroxene: Mg 891 Fe 9 2 Ca 17 and that of the clinopyroxene Mg 49 .o Fe 5 . 7 Ca 45 3 . The spinel with a composition of Mg 78 Fe|J as well as Al|J Fef + Cr^+ (the ¥e 2 + ( Fe 3+ has been calculated from structural formula), falls into the field of magnesio-picotite, near the field of magnesio-chrom-picotite in SOKOLOV'S classification. —• The carbonate which replaces olivine is a very pure calcite. The amphibolite is in sharp contrast to the lherzolite because its minerals are rich in basaltic constituents. As its accessories are quite subordinate, the chemical composition of the whole amphibolite is well represented by the primary amphiboles. The primary amphibole is a pargasite rich in Ti, the number of Ti being slightly smaller than 0.5 per half unit cell. Mg/27Fe = 2.62; 100 Mg/Mg + TFe = 72.39. No evidence could be detected in favour of chemical zoning traversing primary amphiboles by electron beam. Fig. 1. Microprobe scans for Fe and Ti accros a secondary amphibole.— Fig. 2. P —T diagram of Hungarian and French nodules (in prep.). Closed circles Hungarian, crosses French nodules. A, B, C fields of plagioelase, spinel and garnet-lherzoiite. Ps: dry peridotite solidus, Go: oceanic geoterm, Gc: shield geotberm. Chemical Mineralogy 2
