Сравнительная петрлого-геохимическая характеристика домезозойских гранитоидов Средногорской зоны

pp. 35-74

St. Boyadjiev. Comparative petrologic-geochemical eharacterization of the Pre-Mesozoic granitoids of the Sredna Gora zone. Pre-Hercynian (Late Proterozoic!) and Hercynian (South Bulgarian) types of granitoids are described. Grounds are given for their palingenetic origin and crustal level of magma generation.
   On the basis of the analysis performed, the South Bulgarian granitoids are determined as a bimodal superformation, respectively presented by: a) Formation of basic and ultrabasic rocks of a probable Precambrian age- mainly embedded in single layers among the Precambrian crystalline complex; regarding them as a single gabbro-granite formation is not grounded. b) Formation of the batholitic granitoid complex which is distinguished for its polyphase-polyfacies structure. It is presented by three temporarily and laterally defined granitoid phases (impulses): first - marginal facies built by contaminated (a result of assimilation of basic and ultrabasic rocks) rocks which are gradually and centripetally transformed into granitoids up to granites; second – predominantly medium- up to coarse-grained, porphyroid biotite to two-mica granites, partially to granodiorite; third – medium-grained, predominantly biotite to two-mica granites, rarely granodiorites. On the basis of the relationships presented and on the basis of geochemical criteria as well, the development of a fourth granitoid phase - aplite-pegmatoid biotite to two-mica subalkaline granites to leucogranites of not elucidated, probably Alpine age - is grounded.
   The granitoids are referred·to the K-Na series. They are characterized by a very high aluminity, weak ferreous and magnesium properties, which determine the low content of mafites and the strongly expressed leuco-rate frequency of rocks.
   Ba, B. Pb, Th have contents below the clarke, while the other elements studied have contents about or under the clarke; the granitoids of fourth phase are enriched in So, W, Mo, Ag which determines their metallogenic specialization. They are characterized by a deficiency of REE, Eu and a negative europium anomaly; in the fourth granitoid phase REE is two times higher.
   A complete petrologic and phase-facies analogy is established between the pre-Mezozoic granitoids from the Sredna Gora zone and from the Rhodope Massif.