THE SANTORINI VOLCANIC COMPLEX AND ITS RELATION TO THE STRATIGRAPHY AND STRUCTURE OF THE AEGEAN ARC, GREECE

The Santorini complex is the most active volcano of the southern Aegea n volcanic are. Its relationship to the surrounding area was examined by using a dense set of seismic reflection profiles. Three seismic uni ts were recognized in the surrounding area. Unit A consists of general ly strong subparallel continuous reflectors, into which two subunits A 1 and A2 were distinguished, that are unconformable in the upper slope s and the shelves and conformable at lower sectors. The age of unit A, which consists mainly of volcaniclastic sediments, is considered Quat ernary. Unit B consists of faulted and slightly folded strong continuo us reflectors that pinch out at lower basin margin sectors than unit A . Its age is mainly Pliocene, its sediments are probably terrigenous, and it was deposited in the basins at the early and middle stages of t heir formation. Finally unit C represents the acoustic (mainly metamor phic) basement. The dominant tectonic structure in the area is the NE- SW trending normal faults, superimposed on earlier E-W normal faults. The Santorini complex includes one caldera at Santorini and one crater at Columbus about 7 km to the northeast. The caldera of Santorini con sists of four deep basins (depth from 290 to 390 m). The Columbus volc ano has a well defined crater with a single basin (depth similar to 50 0 m) and was formed in 1650 A.D. by an underwater explosion. The start of volcanic activity of Santorini, which initiated in the Early Pleis tocene and continues up until today, may be related to the change in t he normal fault orientation from E-W to NE-SW, and to the unconformity between units A and B.