GEOLOGICA BALCANICA, 31. 3-4, Sofia, Decemb. 2001, p. 3-36 Late Alpine (Palaeogene) superimposed depressions in parts of Southeast Bulgaria Ivan Boyanov, Alexandar Goranov Geologica/Institute, Bulgarian Academy ofSciences, 1113 Sofia (Submitted: 6. 11.1995; accepted.for publication: 3. 04.1996; .final version received: 4. 06.200 I) 11. EoRII06, A. FopaHoa - llo3iJHeOJI&nuucKue (nOJieozeHo- Abstract. The Late Alpine superimposed depressions in the 8ble) naROJICei/Hble iJenpeccuu 6 'lacmu !Ozo-Bocmo•IHOU south-eastern part of the Balkan peninsula are structures of Eoll?apuu. TioJ.uHeanbnHikKHe HaJJO>KeHHbte .uenpeccHH 8 collisional-collapse type. They play a role of neoautochton 10f0-80CTO'IHOH '!aCTH baJJ.KaHCKOfO nonyoCTp08a .ll8nJUOTC.ll which overlays a highly disintegrated Middle and Late Al­ cTpyKT)'paMH KonnHJHOHHO-Konnanco8oro THna. 0HH Hrpa­ pine orogen ofcollage-accretional character. It is represented IOT pOnb HeOaBTOXTOHa, pa3nonmKeHHOfO Ha.ll rny60KO pac­ by the Sredna Gora and Rhodope superunits. The superim­ '!neHeHHblM KOnna>KHO-aKKpeUHOHHblM cpe.UHe-8epXHe­ posed depressions are of Palaeogene-Neogene age and are aJlbOHHCKHM oporeHOM, KOTOpblH npe.UCTaBeH .ll8YM.ll Ha.Ube­ elements of a separate tectonic entity (Maritsa superimposed .llHHHUaMH: Cpe.uHeropcKOH H Po.uoncKOH. BoJpaCT .uenpec­ graben system) within the boundaries of the Balkanides­ CHH - naneoreH-HeoreH08biH. CaMH OHH .ll8n.liiOTC.ll :meMeH­ Anatolian segment of the Alpine mobile belt. The following TaMH MapHUCKOH Hano>KeHHOH rpa6eH080H CHCTeMbl, T.e. three wide depressions on South Bulgarian territory are char­ caMOCTO.liTeJibHOH TeKTOHH'IeCKOH e.UHHHUbl, npHHa.une>Ka­ acterized in this paper: Upper Thrace Depression (UTD), LUeH K baJJKaHH.UHO-AHaTOnHHCKOMY cerMeHT)' AnbnHHCKO­ East Rhodope Depression (ERD) and the East Thrace De­ fO no.u8H>KHoro no.11ca. B pa6oTe npH8e.UeHa xapaKTepHCTH­ pression (ETD). The Tertiary evolution of each depression is Ka Tpex o6wiipHblX .uenpeccHH, paJMeLUeHHbiX 8 IO>KHOH characterised by three up to five destructive stages. The Late EionrapHH : BepxHe<jlpaKHHCKOH .uenpeccHH (UTD), Boc­ Eocene and Oligocene stages are accompanied by an active TO'IHopo.uoncKoro UOHH>KeHH.ll (ERD) H BOCTO'IHO!f>paKHHC­ polycyclic or monophase magmatism mostly represented by KOH .uenpecCHH (ETD). intermediate to acid volcanics. Ca-alkaline, subalkaline and B JBOniOUHH .uenpeccHH 8bi.li8JICHO no HecKOJibKO (c Tpex alkaline magmas are distinguished. Basic volcanics of .uo nliTH) TpeTH'!HbiX .uecTpyKTH8HbiX 3Tano8. BepxHeJoue­ toleiitic, subaikaline to alkaline composition are rare. During HOBbre H OnHfOUeHOBbiC JTanbl conp080)l(.llaJJHCb aKTH8HblM the stages outlined, phenomena of compression or extension nOnHUHKnH'IeCKHM HnH MOHO!f>aJ08biM MarMaTHJMOM. Tipe­ with exhumation are recorded. A number of important faults o6na.uatOT synKaHH'IeCKHe nopo.Ubl - cpe.uHeKHCnbte .uo and fault zones formed during those stages, some of them KHCJlbiX. J.ix xapaKTep H3SeCTK080-lUeJI01iHOH, cy6LUeJIO'I­ being now represented by dike bundles. Essential HOH H LUeno'IHOH. ToneHT08bie, cy6LUeJIO'IHbie H LUeJIO'!Hbie overthrustings took place only along some faults of late nopO.llbl OCH08HOfO COCTa8a 8CTpe'!aiOTCll pe.UKO. _neCTpyK­ Laramian and Savian age. UHOHHbie JTafibl COUpOBO>K.llaJIHCb JKCfYMaUHOHHbiMH, KOM­ npCCCHOHHbiMH H JKCTeHCHOHHbiMH npoueccaMH. HeKoTo­ pbre H08006pa308aHHble pa3JIOMbl H pa3JIOMHbie 30Hbl JHa­ 'IHTeJibHbiX pa3MepOB .liBJl.liiOTC.A H .UaHKOSbiMH ny'IKaMH. DOnee cyLUeCTBeHHble Ha.ll8Hf08ble .llBH>KeHH.A ocyLUeCT8- JieHbl TOJlbKO no HeKOTOpblM U03.UHenapaMHHCKHM H CaBC­ KHM pa3JIOMaM. Boyanov, I., Goranov, A. 2001. Late Alpine (Palaeogene) superimposed depressions in parts of South­ east Bulgaria - Geologica Bale., 31, 3-4; 3-36 Key words: Palaeogene; Late Alpine depressions; collisional orogen 3 Introduction placa. The paroxysm of the okanism is mani­ fested during the Late Eocene and Early Oli­ The Late Alpine superimposed depressions in gocene on the background of tbe specific col­ the eastern part of the Balkan Peninsula are struc­ lapse tectonics, caldera formari - and a partial tures of collision-collapse type. They play a role rift formation. As a result of that acti'ity, a con­ of neoautochthon situated over a highly disinte­ siderable quantity of lavas and pyroclastic mate­ grated Alpine orogen of a collage-accretion char­ rials are deposited in the marine basin. There are acter which is represented by Sredna Gora and epiclastics and tephroid rocks formed as a conse­ Rhodope superunits (with Zagora, Maritsa, Har­ quence of a volcanics resedimentation synchro­ manli-Sakar, East Rhodope and parts of Asenitsa nous to the volcanjsm which shows a rhythmic and Ardino units). These depressions are filled character in some localities. by Palaeogene sediments, sedimentary-volca­ The depressions are of a various configuration, nogenic and magmatic rocks of a thickness of2-3 size, age, type of evolution and origin. There are km in South Bulgaria and reach more than 7000- multiele-interrelated archipelago basins (EoSI­ 8000 m outside our territory (in the area ofETD). HOB, HocH<Poa, 1986) formed in condjtions of a They are considered as elements of a separate marine regime. Isometric blocks built up by tectonic entity of Palaeogene-Neogene age, and highly metamorphic and magmatic rocks of Me­ namely, the so-called }1aritsa superimposed gra­ sozoic, Palaeozoic and mainly of Precambrian ben system (Eo.RHOB, HocH<Poa, 1986). That geo­ age are formed in the boundary areas of the de­ tectonic system has a global character. It includes pressions. enormous areas between both orogen branches of The following topics are considered in the the Alpine-Himalayas mobile belt: from the Alps present study: tectonic position, internal struc­ to the Pamir. ture, lithostratigraphic filling, Palaeogene cover Each separate depression has specific struc­ correlations in the separate block structures as tural features and is characterized by a certain well as the basic stages of the palaeogeographic group of lithostratigraphic units and with or with­ and palaeogedynamic evolution of the Upper out manifestations of synchronous magmatism, Thrace . Depression (UTD), East Rhodope De­ respectively. The depressional structures are lo­ pression (ERD) and East Thrace Depression cated on different crustal blocks characterized by (ETD). The last one is represented on the Bulgar­ a variable crust thickness (35-40 km) to the East ian territory only by its most south-western part. and up to 40-45 km to the West in the West Structures of second and third order are de­ Rhodope Mountains as well as a lithosphere fined in the areas of the three basic depression thickness of about 90-100 km. The crustal thick­ structures in correspondence with the worked out ness in the uplifted blocks bounding the depres­ map of the block structure (Plate I, Fig. I) as fol­ sions exceeds 40 km. A recently made seismic E­ low: in the Upper Thrace Depression (UTD) - W profile between Ivaylovgrad and Ardino (A. Pazardzhik Depression with Plovdiv step (PD), Velev, Y. Yanev, I. Boyanov, Crustal structure of Asenovgrad-Peshtera zone (APZ), Plovdiv De­ the East Rhodope Mts after data from the seismic pression with Maritsa Depression (MrD) and profile Ardino-Ivaylovgrad, unpublished report, Momino-Orizovo Depression (MOD), Popovit­ 1996) shows a 2-3 km thick sedimentary-vol­ sa-Stryarna Horst (PSH), Chirpan threshold, canogenic cover located over a complex overth­ Zagora Depression with West Maritsa Basin rust plate of a four-layered structure. Its total (WMB) and East Maritsa Basin (EMB), Elhovo crustal thickness is 38-40 km and it shows an Basin (EB); in the East Rhodopes Depression WNW vergency. The Moho boundary is ERD - Topolovo Wedge (TW), Northeast Rho­ fragmentarily represented with a tendency of up­ dope Zone (NERZ), Borovitsa Caldera (BC), lifting to the East, and the upper part of the crust Tatarevo Caldera (TC), Lozen-lbredzhek Zone in the ERD area between depths of I Oth and 30th (LIZ) with Lozen and Mezek Calderas, Dzhebel km is broken by Palaeogene magmatic columns Depression (DD), Dobromirtsi-Chorbadzhiysko and chambers. The mantle material nearing to the zone (DCZ), Zvezdel-Krumovgrad volcano-tec­ upper crust layers determines the intensity and tonic structure (ZKVS) with Zvezdel and Kru­ the type of the magmatism which has a calc-alka­ movgrad domain structures, Madzharevo Depre­ line and potassium-subalkaline character. The ssion (MD), Bryagovo Depression (BrD); in the volcanism started in Late Eocene time following East Thrace Depression (ETD)- South Sakar De­ a long amagmatic period of a specific continental pression (SSD), Mandritsa Depression (MdD) and marine coarse-terrigenous sedimentation with Bela-reka graben (BIG). which is accompanied by a considerable olisto­ The enumerated structures are situated on dif­ strome formation and presence of huge olisto- ferent fragments of the Sredna Gora and Rhodope 4 II TI ~~Ito rz::3 t7 ~ L_U11 [[[Jt8 CJ6 ~13 II:Si}a ~21 ~==::;..a, rrmh o,4 ~2, e 24 Fig. I. Tectonic sketch ofthe block structure of the UTD, ERD and ETD 1a - Pazardzhik Depression with the Plovdiv step (PD); 1b- Asenovgrad-Peshtera Zone (APZ); 2- Plovdiv Depression with the Maritsa Depression (MrD) and Momino-Orizovo Depression (MOD); 3 - Popovo-Stryama Horst (PSH); 4 - Chirpan threshold (CT); Zagora Depression: 5- West Maritsa Basin (WMB); 6- East Maritsa Basin (EMB); 7- Elhovo Basin (ED); East Rhodope Depression: 8- Topolovo Wedge (TW); 9-Northeast Rhodope Zone (NERZ);