VOLUME 19 (4)/August 1989

S . Boyadjiev. The Middle Alpine intrusive magmatism in Srednogorie- zone (Bulgaria). During the Late Cretaceous the Srednogorie zone developed as an intracontinental rift with island-arc type magmatism. It was situated in the back of the frontal arc of the Macedono-Rhodope Massif. In Late Alpine time a new, symmetric and analogous in magmatic and metallogenic respect arc (Oravitza-Ridan-Krepolin-Chalcidic) developed in front of the older arc. This lead to a synchronous activisation and as a "reflected wave"- to analogous plutonism within the Massif (Pirin granitoids, Yugovo, Narecen, Laki, etc.).
   The neointrusive activity in Srednogorie zone shows the following features: homodromous magmatic differentiation, bimodal and contrasting rock series, polyphase temporal and lateral pattern of plutonic bodies. In petrochemical respect the rocks are tholeiitic (the gabbroide impulse); of relatively high general and K-alkalinity (the most abundant Ca-alkaline series) and K-subalkaline character (the monzoinite-syenite series). This defines the Srednogorie neointrusive zone as a model of ''mixed" petrochemical province.
   Four main stages are divided in the temporal and lateral formation of the polyphase plutons: first, basic (pyroxenites, gabbroids); second - intermediate to acid derivatives of the Ca-alkaline (diorites to granites) and K-subalkaline petrochemical series; third - vein granitoids, analogous to the preceding rock varieties; fourth - poor aplite-pegmatite phase. The finish of the intrusive activity is marked by a polyfacial dyke formation which commonly is spacially related and analogous in facies to definite plutonic bodies.
   The producing magmas were formed at a crustal-mantle level and are of hybride origin. It is assumed that the K-alkaline magma is a product of a relatively later and higher stage of abyssal intrachamber alkalization of the primary Ca-alkaline magmatic source. The spatial co-existence and the contrasting end (gabbro-granites) members are related to common petrolineaments.
   Different mineralizations are related to the Srednogorie neointrusive magmatism: orthomagmatic (in the gabbroids), skarn-magnetite with superimposed and in parts sheelite, and Cu-Mo porphyry mineralizations.
   Typomorphic elements of the intrusive magmatism are: Fe, Cu, Mo; second-order - Pb, Zn, Au; trace elements - Ti, V, Bi, Co, Se, Te, etc.