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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);