Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 12. 1985. (Budapest, 1985)

Additional remarks to the Transylvanian basalts The CIPW norms, D.I., S.I. and mg-values were also calculated for the average composition of the alkali basalts of Transylvania and Bánát. The average composition of the Bánát basalts (Pleistocene ?) corresponds to that of an olivine basanite poor in nepheline (6.2 %) and moderately rich in olivine (14 %). The mg-value (59.8), D.I. (38.9) and S.I. (34.6) show that the Bánát basalts represent differentiated liquids. The mean composition of the basalts of Poiana Rusca (Pleistocene ?) is more undersaturated: it is an olivine basanite, rich in nepheline (18.1 %). This rock is less differentiated than the preceding one (S.I, and mg-value are 37.1 and 61.1, respectively) and D.I. is only 27.2. Probably the most primitive basaltic rocks in Transylvania are those of the Persani Mts near Racosul de Jos (Rákos) (1.35Í0.85 m.y., BALOGH unpublished) because the average mg-value is as high as 65.6 and S.I. 39.4; however D.I. is relatively too high (35.4). The norm corresponds to a nepheline-poor (6.2 %) olivine basanite (olivine 13 %). CONCLUDING REMARKS The young basaltic eruptions in the Carpathian Basin yielded lavas that strongly differ from each other in respect of their under saturation in silica and the grade of differentiation. In general, highly undersaturated basalts (olivine melilite nephelinite, olivine nephelinite and nepheline-rich basanites) may have been originated by a very restricted amount of partial melting of the parental garnet peridotite in considerable depths at high pressures. The partial pressure of CO,, and other volatiles were also important, a condition that approches highly alkalic basalts to kimberlites and carbonatites. The opposite extremity of the compositional spectrum is represented by the least undersaturated hypersthene-rich olivine tholeiites. These latter rocks are considered to have originated by a relatively important amount of partial melting at shallower levels and at smaller pressures in the upper mantle. However, most of the young basaltic rocks in the Carpathian regions occupy intermediate positions between the two extreme cases mentioned above, attesting that they were derived probably by medium but differing amounts of partial melting. Nevertheless, the genetic picture is a complex one, because following the partial melting the basaltic magma suffered crystal/liquid fractionation. None of the examined basalts is primitive (a probable exception may be the basalt of Bondoróhegy), on the contrary some basalts are highly differentiated. Considering the present state of our knowledge about the chemistry of the young basalts of the Carpathian Basin, some generalizations may be appropriate. Thus, the only region where extremely ' undersaturated basalts occur is that of the Graz Basin, however the proximity to the Alpine Mountain Range cannot be regarded as a genetically important factor because the basalts of Burgenland - that are also situated at the border zone of the basin - are partly tholeiitic in character, thus resembling the basalts of the neighbouring Kisalföld (Little Hungarian Plain). The basalts of the Tátika-Group are again on the whole slightly more undersaturated and those of Balatonfelvidék even more so. However, the large basalt flows of Kabhegy and Agártető (Southern Bakony) are composed of rocks that proved to be the least undersaturated among the young basalts. Basalts in the Nógrád region are highly undersaturated and show the maximum grade of differentiation. We are aware of the fact that only a complex evaluation of all kinds of data (major and minor elements, mineralogical records, isotope geochemistry, REE-geochemistry e.g. PANTO 1981, etc.) can lead to a comprehensive understanding of the genesis of basaltic rocks. One of the aims of this paper is to initiate such works concerning the area of the Carpathian Basin. An intensive study of basalts of Transdanubia and the Nógrád region has already been started and will soon be published (EMBEY-ISZTIN & SCHARBERT, in prep.) REFERENCES BALOGH, K. (1984): A K/Ar földtani kormeghatározási módszer hazai bevezetése és alkalmazásának eredményei. (Introduction of the K/Ar dating and some results of its application.) - C. Sc. Thesis (Manuscript), Debrecen, 104 pp.