The territory of Bulgaria covers part of the active continental margin of the Eurasian plate. Several first-order tectonic units may be distmguished: Moesian platform, paraautochthonous margin of the platform, zone of Mid-Mesozoic collage units, Late Cretaceous island-arc system and a system of Cenozoic collisional and post-collisional grabens. The Alpine magmatism is genetically related to the evolution of the Eurasian margin and the Tethyan ocean south of it.
The earliest Alpine magmatic activity is represented by Triassic, basic and intermediate, strongly altered volcanics (NW Bulgaria, in boreholes). They are related to initial, embryonal rifting of the Moesian platform.
The Triassic and Jurassic-Lower Cretaceous small bodies of basic volcamcs in the SE collage units are interpreted as ensimatic.
During the Upper Cretaceous an ensialic island-arc system originated. The related intensive magmatism formed the Srednogoric volcano-intrusive zone (SVIZ). The magmatic rocks are products of complex differentiation processes. Their formation was accompanied by deep-water sedimentation. All magmatic groups, according to SiO2 content, occur. By the K2O/SiO2 ratio they belong to the TH, CA, HKCA, SH, HKTR (high-K transitional) and BG (bulgaritic) series. Longitudinal and transversal zonahties may be traced. In a global aspect SVIZ is one of the most ancient segments of the Alpine-Himalayan volcano-intrusive belt. The bulgaritic petrochemical trend is related to the earliest generation of K-cnriched magmas in the Mediterranean region.
The products of the collisional magmatism are exposed in the Macedonian-Rhodope-North Aegean volcanic zone (MRNAVZ) located south of the Late Cretaceous island arc. It originated during the Eocene-Oligocene (37-25 Ma) as a result of the collision between Eurasia and the Apulian promontory of Africa.
The magmatic rocks belong dominantly to the intermediate and acid groups and to the CA, HKCA and SH series. The distribution of intermediate and acid rocks in this zone is controlled by the thickness of the crust. In the Eastern and Central Rhodopes the K-content increases from south to north. The volcanic activity in the zone occurred in conditions of intensive block orogeny and was accompanied by terrigenous molasse sedimentation.
During the Neogene a zone of transversal faulting developed in the collisional orogen (remainding of Himalayan-type orogen) and parts of the Moesian platform. This zone is marked by small bodies of basic and ultrabasic, Na-alkalinc and subalkalinc rocks. The K-content increases in southward direction, toward the collisional front.
No abstract is available for this article.
The Albian Stage in Northwest Bulgaria is of more restricted occurrence compared to the other Lower Cretaceous Stages. It consists of marls interbedded by clayey limestones and by less common sandstones (Sumer Formation) and glauconitic sandstones, siltstones and marls (Malo Peštene Formation). The Albian sediments are of considerable thickness without any hiatuses and condensations in the sections. The deposits contain diverse macrofaunas dominated by ammonites. This paper describes the ammonite and lithological successions in 15 Albian sections. The Albian is considered here to include the L. (L.) tardefurcata Zone from its base up to the S. dispar Zone. The three Albian substages are characterized and new evidence is reported on the Albian ammonite successions in Northwest Bulgaria. It has made it possible to supplement and to further subdivide the zonations proposed by previous authors. Part of the zones where possible, have been subdivided into subzones. The following biostratigraphic units are characterized in ascending order: L. (L.) tardefurcata Zone with L. (L.) tenuicostata Subzone and L. (N.) regularis Subzone; D. mammillatum Zone with P. (I.) steinmanni Subzone; H. dentatus Zone with L. lyelli Subzone and H. spathi Subzone; E. loricatus Zone with A. intermedius Subzone; E. lautus Zone; M. (M.) inflatum Zone with H. orbignyi Subzone, H. varicosum Subzone and C. auritus Subzone; S . dispar Zone. An attempt is made to correlate them with units already established in other parts of the Mediterranean Region.
As a result of the biostratigraphic analyses on conodont sequences eight conodont zones of Lower Devonian were subdivided: two zones in Lochkovian – Icriodus wosclzmidti Range-zone and Icriodus postwoschmidti Range-zone; one zone in Pragian - Icriodus huddlei curvicauda - Polygnathus dehiscens Interval-zone. and 5 zones in Emsian- Polygnathus dehiscens dehiscens Range-zone; Polygnathus gronbergi Range-zone, Polygnathus laticostatus Range-zone, Polygnathus serotinus - Polygnathus costatus patulus Interval- zone and Polygnathus costatus - Polygnathus costatus partitus Interval-zone. In Lochkovian and especially in Pragian the individual zones are important for the local biostratigraphic subdivision of the studied area and the correlations with remote regions are approximate and not adequately comparable like the zones of Emsian.
D. Kozhoukharov. Konstantinovo Metaconglomerate Formation in Sakar Mountain and Marica Zone between Simeonovgrad and Dimitrovgrad, Haskovo District. Konstantinovo Metaconglomerate Formation is introduced for the first time in the Bulgarian lithostratigraphic nomenclature. It is represented by fine to medium in pebble size conglomerates with gne1ss-schist to gneissic ground mass and irregularly ditsributed pieces of pegmatites and aplites, less commonly of quartz-epidote-muscovite schists, microgranites and monomineral grains of quartz and feld spars. The pieces are rounded, lens-shaped or flattened, with ellipsoidal crosssection and dominant dimensions 2 × 3 to 5-7 × 3 × 5 cm, rarely to 15 cm in diameter. The ground mass is formed of coarse-grained mica, quartz and plagioclase. The metamorphic evolution of the rocks of Konstantinovo Formation reflects changes of progressive by regressive stages of metamorphism which define the polymetamorphic evolution of the Precambrian basement. The first regional metamorphism was in amphibolite facies (E 1) and culminated in regional migmatization. It is of general occurrence and defines the general features of the Precambrian rocks from the southern slopes of Sakar Mountain and Marica Zone.
No abstract is available for this article.
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