Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 72. (Budapest 1980)

Embey-Isztin, A.: Major element patterns in Hungarian basaltic rocks: an approach to determine their tectonic settings

Fig. 1. Volcanic regions ofH ungary. 1 = young basalts, 2 = Lower Cretaceous basalts, 3 = Miocene andésites, 4 = Mesozoic diabases teristics in the Pannonian Basin are as follows: the presence of a continental-type crust, though thinner than normally, block tectonism that results in a highly variable degree of sinking in different parts of the basin. Alkali basalt-trachybasalt-trachyandesite-phonolite series Members of this rock series were described in details by MAURITZ (1913) as a "trachydoleritephonolite" association. They were erupted in the Mecsek Mountains (Fig. 1) where they form numerous dykes, stocks sills and probably lakkoliths. The age of the beginning of eruptions can be defined unambiguously, as the igneous bodies cut the Upper Jurassic sediments and synchronous volcanic activity can be deciphered in the Berriasian (~ 136 m.y.) at the base of the Cretaceous (Pantó 1961). Apparently differentiation processes must have been operating on a large scale, since limburggite-like cumulative rocks and complementary trachybasalts, trachyandesites and phonolites are well represented in this area. It is obvious that the parent magma must have had a marked alkalic affinity to be able to yield such highly undersaturated differentiated products. Rocks of this igneous series are by no means so fresh than those of the preceding section: zeolithization is very intense, especially in the case of the more acid members, other alteration products such as calcite, sericite and chlorite are not rare. Diabase-gabbro-oreperidotite association This rock association is situated in the western part of the Bükk Mountains (Fig. 1) and it is composed mainly of a NE-SW striking diabase body about 10 km in length and 2-4 km in width. Smaller bodies of gabbro and peridotite with an unusually high content of magnetite and ilmenite were formed at lower levels, very probably due to gravitative differentiation. Very subordinate acid differentiation products, nests of gabbro pegmatite, nests and veins of albite granite occur in the gabbro itself. The whole series was intruded in a slightly metamorphosed shale of Triassic age. The age of the intrusion itself could not be determined exactly, it may be Triassic or Cretaceous as well. The petrography of the rock association was described at a considerable length by SZENTPÉTERY (1953). There are some localities where the rocks are quite fresh, the mineralogy and chemistry of which enables us to conclude that the parent magma must have been tholeiitic in character.