ERUPTIVE STYLES OF THE PALEOGENE COLLISIO N VOLCANISM OF THE EASTERN RHODOPES, BULGARIA

Collision volcanism of the Eastern Rhodopes (37-25.5 Ma) display calc- alkaline and shoshonitic affinities, with (A) intermediate to basic an d (B) acid compositions. (A) Intermediate volcanism has produced mostl y latites and andesites, also shoshonites and basaltic andesites, as d ifferent eruptive styles: lava flows (often autobrecciated), domes, as h and scarce pumice falls. Moreover, lahars are frequent. (B) Acid vol canism (rhyolites, trachyrhyolites and trachydacites) is well represen ted Several eruptive types are distinguished: pyroclastic flows (weakl y and strongly welded ignimbrite deposits), ash and lapilli falls, dom es and lava flows with often autobrecciated perlitic outer zone. The l arge (30 x 10 km) Borovitza caldera is the result of a paroxysmic expl osive phase. Intense hydrothermal episodes, contemporaneous with and f ollowing the volcanic activity, has converted large amounts of explosi ve products into bentonite and zeolites deposits, In some volcanoes, l arge ore deposits (Pb, Zn, Ag, Au) are exposed.