Metamorphism on Ios and the geological history of the Southern Cyclades, Greece

Abstract

The geology and petrology of the island of los, Greece are outlined in chapter I. The geology is determined by a mantled gneiss dome which forms the basement, on top of which a marble-schist series is emplaced. The various rocks of the island are described petrologically and their mineral contents are listed. The P-T conditions of a decreasing, polyphase regional metamorphism are inferred on the basis of relevant mineral assemblages. The emplacement of the series upon the basement predates the Alpine metamorphism. The petrology of the adjacent island of Sikinos is concisely treated in chapter II. The geological constitution is similar with that of los, although the windows of the basement are relatively small. The rocktypes and their contents are also comparable with those of los. In chapter III the metamorphic phases on los are better distinguished and also the pre-Alpine event in the basement are discussed. Additionally preliminary isotope dating of the Alpine metamorphic phases is sunnnarized and it reveals 43 Ma and 25 Ma respectively. The metamorpic conditions are refined, and a review is given of the distribution of the metamorphic and magmatic events in the Cycladic area. A wider occurrence of basement, for example on Naxos is suggested. A model for the Alpine metamorphic evolution in the southern Cyclades is developed in chapter IV. It is based on petrological data of mineral textures and mineral zonations in rocks from Pholegandros, Sikinos, los, Iraklia and SE Naxos and on chemical microprobe data of minerals mainly from los. The model is consistent with a rapid uplift of deep continental crust, which is supported by geophysical seismic and gravimetric data. The geological map of Greece, sheet of the island of los is presented in a preliminary shape with an extended legend.