Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 80. (Budapest 1988)
Harangi, Sz.: Major element chemistry of Lower Cretaceous igneous rock of Mecsek Mountains (Southern Hungary), I.
CaO (x = 6.6, SD = 3.46) : CaO contents of phonolites and trachytes are conspicuously separated from those of the other groups (0-2 vs. 2.5-3.5%). Higher than 8% values were observed in more basic samples. Na 2 0 and K 2 0 (x = 4.11, SD = 2.52 (Na 2 0) and x = 2.53, SD = 1.82 (K 2 Q)): Besides the especially high alkali contents of phonolites, potassium content of the trachytes (3.7-9.6%) is considerable. On the K 2 0/Na 2 0 histogram we can see identical values for phonolites and for other groups, instead of the conspicuous separation observed on the histograms of all other oxides. It may indicate genetic relationships. Only the K-rich trachyte is separated. P 2 0 5 (x = 0.58, SD = 0,84): it displays an approximately monotonous decreasing log-normadistribution. Rock groups do not have characteristic P 2 0 5 contents, the values having a very high standard deviation. Tectonic position Open marine, carbonate sediments were deposited in the Late Jurassic Mecsek sea, topographical highs and lows were formed in the basin due to tectonic movements preceding magmatism. The volcanic activity may have begun during Late Jurassic time, paroxysm was reached during Valanginian and Hauterivian only. According to published observations the melt ascended to the surface through more or less parallel fractures in the continental crust. The volcanic rocks display alkaline character (BILIK 1983, EMBEY-ISZTIN 1981). Usually two methods are applied to distinguish between the alkaline and the subalkaline (tholeiitic) characters of the volcanic rocks. A swift and frequently applied process is plotting the data on Si0 2 — alkali diagram. The analytical data of the Mecsek volcanics are equally distributed between the alkaline and the tholeiitic field (discrimination curve after MACDONALD & KATSURA 1964) (Fig. 4). Conspicuously, the basaltic andésites display mostly tholeiitic, while the basaltic trachyandesites alkaline character. Half of the basalts FeO t MgO Ai 2 0 3 Fig. 8. (MgO- FeO tot- A1 2 0 3 discriminating diagram (after PEARCE et al. 1977) for basaltic-andesitic rocks (Si0 2 : 51-56%) of Mecsek Mts. OI = Ocean Island, CO = Continental, SCI = Spreading Center Island, OR = Orogenic, ORF = Ocean Ridge and Floor.
