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
such araphibole-mantled spinel grains in a peridotite nodule from Marais de Limagne.) The amphibole is thought to be a product unrelated to the original crystallization of the peridotite. All the amphiboles from different localities treated above are chemically more or less similar. They represent highly undersaturated olivine nephelinitic to olivine melilite nephelinitic compositions. Contrary to expectation, the compositions of the amphibole from the Szigliget xenolith is nearer to that of the typeLZB from Lherz. The type-LZA has markedly higher 100 Mg/Mg+2Te (82.99) than the type-LZB (70.25) or Szigliget (72.39). However, the Szigliget amphibole differs from both in having a higher K content; K 2 0/Na 2 0 = 0.86 (Szigliget), 0.27 (LZA, Lherz), 0.50 (LZB, Lherz). Unfortunately, the comparison with the amphibole of Kakanui composite xenolith could not be executed, because of lack of chemical analysis. However, judging from optical determinations DICKEY 1968) this amphibole must also be a titaniferous pargasite or a kaersutite with a composition not much different from those mentioned above. Besides the amphibole of type-LZB Lherz, that of the Grand Canyon amphibolite is also very similar to the Szigliget amphibole, though it is also lower in K (K 2 0/Na 2 0 = 0.57) and slightly bigher in Al (100 Mg +ZFe = 73.92). The amphibole of lherzolite of Siberia Crater, California (No. 2 inWILSHIRE & TRASK 1971) is more ferrous and less magnesian similarly to the secondary amphibole of Szigliget (100 Mg/Mg + XFe = 63.90 Siberia Crater; 62.64 secondary amphibole Szigliget). To reconstruct the probable physical conditions that existed at the time of formation of the Szigliget amphibolite vein is not an easy task. The understanding of stability relations of amphiboles is still incomplete. For example, kaersutites of the same composition have been crystallized experimentally from nepheline mugearite in the presence of 2 to 5 percent water at pressures ranging from 2.2 to 22.5 kbar (MERILL & WYLLIB 1975). VARNE describes a hornblende lherzolite where the amphibole, a Ti-poor Naand Cr-rich pargasite, is thought to be stable within a hydrous mantle to a depth of 100 km or more (VARNE 1970). The amphibole is thought to be a primary phase here in the lherzolite, in contrast to all occurrences that have been mentioned so far. The amphibole-bearing material that intrudes lherzolite at Lherz, Kakanui, Szigliget or elsewhere may be regarded as high pressure heteromorphs of nephelinitic-basanitic lavas (BEST 1970, MASON 1968, VARNE 1968). However, certain features of their chemistry may be due to processes such as subsolidus and wall-rock reactions (BEST 1973). On the basis of the surprising similarity between the amphibolite of Lherz and that of the Szigliget xenolith, it may be concluded that their histories might have been also similar to some extent. To the formation of highly undersaturated nephelinitic liquids entrapped at depth, represented by the chemistry of amphibolites, large scale differentation processes must be admitted. Rock-types originated from differentiating hydrous liquids are excellently represented —• with possibility to evaluate chronological order —-in the symmetric complex vein systems of theul trabasic massif of Lherz. CONQUÉRÉ, using data of experimental work (KORNPROBST 1970, BOYD 1959, GREEN & RINGWOOD 1967, KTJSHIRO 1968, YODER & TILLEY 1962, O'HARA 1967), has concluded that in the hydrous adiabatic rising diapir {a term of GREEN and RINGWOOD) an important partial melting took place at about a pressure of 27 kbar, which had resulted in 20% liquid, probably an olivinericfi tholeiite. With falling temperature and pressure, the anhydrous rock-rypes crystallized (about 27-16 kbar), followed by amphibole-bearing rocks (about
