Monitoring of geodynamic processes by modern GNSS techniques in the area of Sofia and South-Western Bulgaria has continued for 25 years. To study the modern crustal movements in the area, Global Positioning System (GPS) data acquired between 1996 and 2021 are analyzed to obtain the velocity field for South-Western Bulgaria. For a time period of almost 25 years, the monitoring has covered 28 stations. They have been measured in different years and in a number of campaigns. Despite the difference in the measurements, the obtained results are quite homogeneous in the different localities of the studied area and show clear uniform tendencies. All velocities are in the southern direction. They are in the range of 1.5 mm/year to slightly over 3 mm/year, almost reaching 4 mm/year. The velocities of the stations tend to increase from north (stations around Sofia), passing through an intermediate locality (between Sofia and Kyustendil–Pazardhik), clearly increasing in the southernmost part of the country (around Gotse Delchev). This velocity field motivates N–S expressed extension with increasing rates from North to South. The difference in the velocity rates tends to change along geologically suggested active fault zones. The obtained results generally confirm previously data, but with much better accuracy and details at the local level. This way, both the repeated measurements and extension of the geodynamic network prove to be a powerful tool for a better understanding of present-day geodynamics.
The agardite from the Osenovlak deposit (indications data of Cu-porphyry and epithermal systems) has been found in small amounts among the zone of oxidation of altered and mineralized granodiorites and porphyritic diorites. Together with agardite supergene minerals are observed: malachite, azurite, chrysocolla, smithsonite, jarosite, seladonite, rozenite, cerussite, hemimorphite and romaneshite. Most often agardite associates with hemimorphite and romaneshite. Its color is bright green and forms radial aggregates up to 1-2 mm of rod-like crystals. They represent thin hexagonal prisms, elongated parallel [001]. In the chemical composition Y, Nd, La, Eu, and Sm are present. At least three phases seem to exist: first, without Y, with domination of La and Eu (or Nd); second, with Y and different values of La and Nd; third, with dominating Nd, compared to Y and La. Ca is always present. The value of PbO is high (5.77 to 7.51 wt.%), confirming previously published experimental data dealing with the crystal-chemical peculiarities of the mixite group (OLMI et al. 1991) and the role of Pb together with REE, Bi and Al.
Modern gas migration territorially coincides with discontinuous disturbances in the sedimentary cover and deposits of combustible fossils in previous epochs of sediment accumulation. The geodynamics of the region determined the stages of its formation, accompanied by platform transformations and tectonic-magmatic processes, as well as the formation of sedimentary complexes with shale, coal seams and oil and gas reservoirs. Vertical, relatively disturbed, and lateral, intraplate migration of hydrocarbons were the main factors in the formation of deposits in the region. The presence of discontinuities and stratigraphic unconformities in the deposits of the Pre-Dobrudzh trough and near them is regarded as a key factor in the low conservation of most of the paleo-reservoirs of these deposits. All samples contain an insignificant amount of hydrogen and C6 hydrocarbons, which indicates modern gas migrations to the Earth's surface, mainly in the zones of faults.
The Alpine geodynamics of the eastern Balkan Peninsula is determined by several episodes of extension and compression. After the final closing of the Vardar Ocean during the Late Cretaceous-Early Paleogene the main episode of compression and deformation in the Balkan FTB occurred in Middle Eocene time, creating a well expressed fold-thrust pattern. At this time the belt was overthrusted to the north on the Foreland (Moesian Platform). After this main episode of compression, excepting local thrusting in its easternmost part during the Oligocene, the frontal part of the belt was thought to be inactive. Since Late Eocene extension is the main form of deformation. The extension is spread between the Aegean subduction system to the south and the Moesian Platform (the southern edge of the Balkan Range) to the north. During the Neogene, extension has created numerous extensional continental basins (grabens) to the south of the Balkan Range. They occurred in several well distinguished consecutive stages of extension. Instead, to the north of the range was created the marine (Miocene) to brakish (Pliocene) basin which western part belonged to the Central Parathetys (Fore-Carpathian basin) and the eastern to the Eastern Parathetys (Euxinian) basin.
Abstract The well-known Cenozoic Aegean extensional regime, initiated at c. 25 Ma, thinned the crust so that most of it now lies submerged. North of the western continuation of the North Anatolian Fault the Aegean extensional regime is present in central and southern Bulgaria, northern Greece, Former Yugoslavian Republic (FYR) of Macedonia and eastern Albania. Here the system is exposed on land and offers an opportunity to reconstruct the extensional evolution of the system. The southern Balkan peninsula forms the northern part of the Aegean extensional system; deformation is not as great as in the Aegean, but reconstruction of this part of the extensional regime will provide important constraints on its dynamics. Following a period of arc-normal extension associated with Late Eocene-Late Oligocene magmatism, major lithospheric extension appears have begun between 26 and 21 Ma in northern Greece, involving east-northeast-west-southwest extension east of Mount Olympos, on the Island of Thasos and near Kavala. This period of extension may have been accompanied by a short period of coeval compression north of the arc during Early Miocene time or perhaps a little earlier in the Thrace Basin of northwestern Turkey. Northeast-southwest directed Middle-Late Miocene extension appears to have developed obliquely to the older magmatic arc and migrated northward into southwestern Bulgaria in the Sandanski Graben (and perhaps also into the Mesta and Padesh Grabens) by 16.3–13.6 Ma, and in the Blagoevgrad and Djerman Grabens by c. 9 Ma. Extension in south-western Bulgaria was reorganized by c. 5 Ma and in northern Greece extension on the Strymon Valley detachment fault ended by c. 3.5 Ma, but extension continued on new fault systems. From limited structural and stratigraphic data, it is speculated here that related extension may have also occurred during this time in FYR Macedonia and eastern Albania. This northeast-southwest extension is interpreted to be related to trench roll-back along the northern part of the subduction boundary in the western Hellenides. North-south extension along east-west striking faults in central Bulgaria began only after extension was well underway in northern Greece and the Sandanski Graben of south-western Bulgaria. Within the Sofia Graben, the Sub-Balkan grabens, and grabens to their east, north-south extension began at c. 9 Ma, and may have begun about the same time in the Plovdiv, Zagore and Tundja Grabens of the northern Thracian Basin: north-south extension has continued to the present in these grabens. The cause of the north-south extension is unclear and may be related to trench roll-back along the central part of the subduction zone in the Hellenides, or more local causes of clockwise and counterclockwise rotation of the western Hellenides and western Turkey, respectively. By Late Pliocene time a major erosion surface, the sub-Quaternary surface, was developed over a large area of central Bulgaria creating a major unconformity that marks the beginning of Quaternary deposition in the basinal areas. Many large and small graben-bounding faults in west-central Bulgaria displace this erosion surface and demonstrate the widespread extent of Quaternary north-south extension. North-south extension extended westward, with probably decreasing magnitude, across the older northwest trending graben of southwest Bulgaria (the Simitli and Djerman Grabens) and into eastern FYR Macedonia. During latest Pliocene(?) and Quaternary time, northern Greece developed a complex pattern of northeast-southwest extension associated with northeast to east-west striking right-lateral faults forming transfer faults between more local extensional areas. This system of faults overprinted the older northwest trending extensional faults, such as the Strymon Detachment, and may be related to the propagation of the right-lateral North Anatolian Fault into the north Aegean Sea and formation of parallel faults to its north. These two different tectonic regimes extend into FYR Macedonia, where a third regime of east-west extension in western FYR Macedonia and eastern Albania is present, and where extension may represent the continuation of the east-west extensional regime initiated in Middle-Late Miocene time. Active deformation determined from seismicity and Global Positioning System studies suggest northern Greece, and perhaps southwest Bulgaria and FYR Macedonia, is dominated by north-south extension. This pattern of deformation must have developed as recently as perhaps Late Quaternary time. Except for mountains near the Adriatic Sea all of the mountainous topography in the southern Balkan region may be the result of Miocene-Recent extension.
