Chemismus und Texturen von Chromiten in ultramafischen Gesteinen des Chalkidiki Komplexes, Nordost-Griechenland

Abstract

The lower ultramafic part of the Chalkidiki Ophiolite Complex consists of a successive alternation of chromitite, dunite, and harzburgite, which is repeated periodically in a cyclic manner. This cyclic pattern is consistent with an origin as magmatic cumulates. However, the tectonic fabric superimposed on the cumulate texture of this sequence suggest a solid-state deformation at considerable depth. In the present study, the textural and chemical features of chromite are discussed. The interrelationships between the compositions of chromite, its mode of occurrence as well as the associated silicates are emphasized. It is found that the investigated chromites have properties in common with both podiforn and stratiform chromites. From a geometrical and structural point of view, they are of podiform type. On the other hand, their appreciably high iron content, the strong interdependence between the composition of chromite and the coexisting silicates together with the cryptic layering exhibited by the two mineral groups contrast markedly with podiform chromites. An alternative hypothesis is proposed involving fractional crystallization of an ultrabasic melt introduced to the magma chamber as periodic inflows of essentially the same composition. An upwelling upper-mantle that is subjected to stepwise partial fusion may fulfill these conditions.