Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 14. 1989. (Budapest, 1989)
most efficient. To check clustering, the non-linear mapping is an excellent technique. Revealing the inter-sample and inter-group relationships we can take conclusions on the differentiation trends as well. Principal Component Analysis can be applied to the study of the processes affecting the chemistry of the volcanics: differentiation, subsequent alteration. Step-wise PCA indicates the phases controlling the changes in composition. Such a complex study can lead to a working-hypothesis for the following investigations. The mathematical-geochemical study of Mecsek volcanics resulted in the separation of the main rock-types within the suite: various basalts, tephrites, transitional basaltic-andesitic rocks, trachyandesites, phonolites and trachytes. Regional petrochemical differences were revealed among phonolites and trachytes. Although various groups of altered samples were separated,the effects of subsequent alterations (oxidation, submarine alteration, CaCC>3enrichmentl did not disturbed entirely the original compositional features of the rocks. Two different trends were recognized within the suite, ending with phonolites and trachytes respectively. The curvature of the basalt-trachyandesite-phonolite trend indicated alkali differentiation, while the Si0 2-K 2 0 enrichment led to the formation of trachytes. ACKNOWLEDGEMENT I would like to thank L. O. KOVÁCS for the computer time and discussions on multivariate statistical methods. REFERENCES BERTRAND, H. and COFFRANT, D. (1977) : Geochemistry of tholeiites from North-East American Margin; Correlation wit h Morocco. - Contrib. Mineral. Petrol., 63: 65-74. BUTLER, J. C, (1979I : Trends in ternary petrologic variation diagrams - fact or fantasy? Amer. Miner., 64: 1115-1121. CHAYES, F. and VELDE, D. (1965): On distinguishing basaltic lavas of circumoceanic and ocean-island type by means of discriminant functions. - Amer. J. Sei., 2 63 : 206-222. COOLEY, W.W. and LOHNES, P. R. (1971): Multivariate data analysis. - J. Wiley and Sons, New York, 364 pp. DAVIS, J.C. (1973): Statistics and data analysis in geology. - J. Wiley and Sons, New York, 550 pp. EVERITT, B. (1981): Cluster analysis. - Halsted Press, 136 pp. EWART, A. and LE MAITRE, R.W. (19801: Some regional compositional differences within Tertiary-Recent orogenic magmas. - Chem. Geol., 30: 257-283. GARRETT, R.G. (19731: Regional geochemical study of Cretaceous acidic rocks in the northern Canadian Cordillera as a tool for broad mineral exploration. - in: JONES, M. J. fed. ): Geochemical Exploration 1972. - Inst. Mining Metall., London: 208-219. HARANGI, Sz. (1988): Major element chemistry of Lower Cretaceous igneous rocks of the Mecsek Mountains (Southern Hungaryl, I. - Annls. hist.-nat. Mus. natn. hung., 80: 1 1-24. HOWARTH, R.J. (19731: Preliminary assessment of a nonlinear napping algorithm in a geological context. - J. Int. Assoc. Math. Geol., 5(1): 39- 57. HOWARTH, R.J. (ed.) (1983): Statistics and data analysis in geochemical prospecting. Handbook of Exploration Geochemistry Vol. 2., Elsevier, New York, 437 pp. HOWARTH, R.J., CRONAN, D.S. and GLASBY, G. P. (19 77) : Non-linear mapping of regional geochemical variability of manganese nodules in the Pacific Ocean. - Inst. Min. Metall., Trans., Sect. B. 86: 4-8. LE MAITRE, R.W. (1968): Chemical variation within and between volcanic rock series a statistical approach. - J. Petrol., 9 (2) : 220-252. LE MAITRE, R.W. (1982): Numerical Petrology. - Elsevier. Amsterdam. 281 pp. MARRIOTT, F.H.C. (1971): Practical Problems in a method of cluster analysis . - Biometrics, 27: 501-514.
