Bergerat, F

Csontos, L

English

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REEVALUATION OF THE NEOGENE BRITTLE TECTONICS OF THE MECSEK-VILLÁNY AREA (SWHUNGARY)byL. CSONTOS* and F. BERGBRAT***ELTE TTK Fötdtani Tanszék, t088 BUDAPEST, Múzeum krt. 4/a, Hungary** Université de Paris VE Lab. de Geotectonique, 4 pi. Jussieu,75250, PARIS, France('Æecetverf.* 27;A February, 79&9)AbstractPrevious brittie tectonic measurements made in the Mecsek and Viiiány Mountains (SW Hungary) have enabied us to differentiate 5 paieo-stress-fieids of Neogene and unknown ages. Further anatyse of the data and of detailed maps have precised the proposed stroy of tectonic events in the Neogene.These mapping, fracture and sedimentoiogica) data suggest that the most intense deformations occur in wet) known strips i. e. the Northern Thrust Zone, the Southern Mecsek Lineament, and the thrusts of the Vitlány Mountains. Basins between and around these zones are very probabty reiated to the strike-siip tectonics and they witness the superposition of the different tectonic events.We suppose a NW-SE directed compression in the Lower Miocene, creating right iaterai wrench faults of E-W strike and NNW-SSE oriented ieft tatéra) ones in discrete zones (fig.3.). This stress woutd be fottowed by N-S compression in the Badenian and by NE-SW compression in the Lower Pannonian. The tatter one has created NE-SW trending teft taterat and N-S trending right taterat wrench fautts and thrusts in the previousty existing wrench zones. Because of intense fotding of Pannonian sediments, the first mentioned stress-fietd, the NW-SE compression is very tikety to be rejuvenated in the Upper Pannonian (Pontian).introductionThe present paper deals with the Mesozoic-Tertiary outcrops of the Mecsek and Viiiány Mountains, which are part of the South Pannonian (BALLA, 1984) or Tisia (KOVÁCS, Í982) microcontinent. We have studied the microtectonic features of these mountains by measuring the fauit related features (like slickenslidcs, gauges, etc.) and have deduced 5 different stress-fields (BERGERAT and CSONTOS, 1989). Since this work was completed, we have carried on the study of Neogcne brittle tectonics in the Pannonian basin, and we have analysed a detailed map of the Mecsek Mountains (HETÉNYI et al.. 1982; CHIKÁN ct al., 1984). These works enabled us to reevaluate the importance and timing of the main stress-fields affecting the Mecsek-Villány region in the Neogene and to give some ideas on the main deformation zones, limiting the Mesozoic outcrops.The bigger deformation zones of SE HungaryThe maps of the Mecsek-Villány area (/?#. 77 reveal three important E-W trending fault zones : the Northern Thrust Zone (WEIN, 1963), the Southern Thrust zone (the Mecsek lineament W from Pécs), and the thrusts of the Villány Mountains (LÓCZY, 1912). In all of these places, we have measured dextral and sinistra! strike-slips and oblique thrusts (/Igy. 2, ^7-Although the NNW-SEE and N-S trending strike-slips arc widespread in the Mecsek Mountains, the main location of them seems to be a strike-slip zone between the E- and the W- Mecsek (NEMED!-VARGA, 1983), or elsewhere called the Villány-Szalatnak deep fracture zone (KASSA!, 1973). Both sinistral and dextral movements can be measured on these fault surfaces (yigr. 2,The map analyse shows that two major NE-SW trending deformation zones exist in the area : the S-Mecsek Lineament (NEMED!-VARGA, 1983), and the Kapós Lineament (NÉMED!-VARGA, 1977) (/?#. 4 /  They are probably main strike-slip surfaces, functioning at various times, for example in the Pannonian and may be even in the Pleistocene (op. cit.). The microtectonic data (/Ig. 27 reveal intensive sinistral movements on similarly oriented surfaces.All of the above zones arc subject to polyphase deformation. Several generations of slicken-slides, often in opposed directions can be observed in these zones (BERGERAT and CSONTOS, 1989). Naturally, these observations point to longer strike-slip zones functioning at several episodes. The nature of the movement on these surfaces is often changing in time : we can frequently find or deduce dextral or sinistral wrenching followed by oblique reverse faults, resulting in the complexity of these zones.!n the following, we trz to give the main events generating, or rejuvenating the deformation yones, and we will not deal with allt he 5 episodes, differentiated4__________________L. CSONTOS and F. BEROERAT___________________REEVALUATION OF THE NEOGENE BRITTLE TECTONICS _5Fig. t. The main deformation zones of the Mecsek-ViM&ny area, i . Hercynian granitoids; 2. Permian; 3. Triassic; 4. Jurassic; 3. Cretaceous; 6. Miocene without Power Pannonian; 7. Lower Pannonian to Quaternary; 8. Main brittie tectonic surfaces and zones (most)y strike-stips);9. Smaiier fauits; iO. Thrusts; ]]. Sycniines, t2. Anticiines;]3. Site of microtectonic investigations6 L. CSONTOS and F. BERGERATSr С О<2 э'§ Е '-2 >К О с" 2 'çО о '§ .3 Е. 5 ^ 3g -о "*П  ^*ё ^С  ̂ ^1 * 5 0- ^ .§ 5о -  ? "" 'зь .&Ï.3. Сs ë ^ S<  2 *5 м т)-*3;,оЗ-  *5. д  = ..2 c g-  Е s S.м ^м й*" ё -  (У 5 & " °" ° ё о<9^3:.. т з ё З -g о — об с oofS = 5 "* с с ^s 3 â g§ § S ¿Я V 5E = " Sо V ^ ^0 b о §^  Ь с> 2 !С,J'2<3V)Z S' § -° g ^  =S^Ts'Sв S f= о и*=.Ы - 2  ̂ -о -о J= ^ с" п :й 21  с ё S.LE Е Е о*REEVALUATION OF THE NEOGENE BRITTLE TECTONICS _7CQopë3T3sFeoaa.Soo-5*osr̂nobm8 L. CSONTOS and F. BERGERATFig. 4. Basin subsidence directions reiated to the deformation zones of SW Hungary. AfterFOl.OP et a)., 1987, modified.1. Main deformation zones; 2. State boundary; 3. Depth of Neogene basins, isodepth lines are at 500 m intervals. + means relative rise, -  means basin. 4. Axis of E-W directed, and of NNW-SSE directed subsidence. 5. Axis of NE-SW directed subsidence.by eartier work (BERGERAT and CSONTOS. 1989). but we will select the 2 most important of them.Chronological controlOne of the main results of the compilation of data on Tertiary brittle tectonics (BERGERAT et al.. 1989) was that we have found very similar tectonic events in the whole Pannonian basin. This, and a space problem in BALLA's model (1984) suggests that there is probably no major microcontinent rotation of the Tisia during Neogene. That doesn't exclude larger scale horizontal movement of microcontinents, but this conclusion enables us to use -  with sufficient reserve -  the chronological constraints of stress-fields gained elsewhere in the Pannonian basin.The timing constraints of tectonic events in SW Hungary come from different sources. We have observed most of the brittle tectonic events in the Lower Miocene volcanites (BERGERAT and CSONTOS. 1989). Two important events have remained however undated : the NW-SE compression and the NE-SW compression.Further analyse of our data has shown that the latter has affected the Lower Miocene strata, hence its age is younger. Geological evidence in the Mecsek (S. Mecsek Lineament and N. Thrust Zone) shows that an ENE-WSW directed large scale strike slip separates the mesozoic from the Pannonian sediments (WE1N, 1963; NÉMED1-VARGA, 1989) 2 /  In the abovementioned zones and in the Villány Mountains (NAGY and NAGY, 1976), even Pannonian sediments arc implied in the polyphase thrusting on E-W directed, steeply dipping surfaces. Striae on these faults indicate an inverse oblique slip, pointing to a NE-SW compressiona! regime (/ig. 29- In the Mecsek. NW-SE directed folds affect even Sarmatian and Lower Pannonian sediments (HÁMOR, 1966) 0%. 29. From widespread observation in the other parts of the Pannonian basin (c. g.: CSONTOS. 1988) this NE-SW compression has acted in the Upper Pannonian (Pontian).All these features point to a young, at least Pannonian NE-SW compressional event which could have originated in the Upper Badcnian (Middle Miocene).The NW-SE compression hasn't been recorded by the Ottnangian rocks but this can be due to lack of observation.The Mioccne-Pliocene rocks record an extensive folding with generally NE-SW or locally E-W directed axis (HÁMOR. 1966. CH1KÁN et a.. 1984, HETÉNY1 et al.. 1982. NÉMED1-VARGA. 1983) (/tg. 2;. In the vicinity of Komló the axis of some folds are even slightly distorted in a left lateral way, along a main NNW-SSE fracture zone. These folds arc fitting perfectly in aREEVALUATION OF THE NEOGENE BRITTLE TECTONICS 9NW-SE compressional strike-slip type stress-field. That aiso means that this compression has to be young, i. e. younger than Upper Pannonian.There is however a timing probicm : the same event is catibratcd as Karpatian (Lower Middle Miocene) in the Vienna basin (FODOR et a!.. 1989). The main surfaces of this event arc E-W trending wrench faults, which create subsidence of basins of similar strike (pig. 49 in the nearby Zala basin at the same age (KOROSSY, 1988).An early creation of E-W strike dcxtral faults and NNW-SSE strike sinistral faults in supported by the fact that all the "thrust sheets" in the Mecsek-Villany area arc acting as paleogcographic boundaries in the early Ncogene. Moreover, they bear oblique sinistral striae on their steeply dipping surfaces (9%. 29- In a NE-SW compression (former paragraph) the E-W directed surfaces are not ideally oriented, they are certainly not created but only rejuvenated as oblique left lateral faults. That is why these zones or at least their root zones must have been created by a former stress-field, not by the NE-SW compression.Although it is difficult to prove, we suppose, on the base of analogies, that a NW-SE compression has acted first in the Karpatian then in the Upper Pannonian.There is a further, seemingly much less important strike-slip type stress-field with N-S compression directions. This N-S compression affects the Lower Miocene voleanites, thus its age is younger. We have encountered this type of compression in the Lowermost Miocene and in the Badenian (Middle Miocene) in the Pannonian basin. The one found in the Mecsek is evidently the younger than the Badenian one.Proposed history of Miocene brittle tectonic events in SW HungaryAssessing the given data we have compressiona! stress-regimes of strike-slip type in the Mecsek-Villany area during Miocene-Pliocene with main directions o] and 02 changing in time. The of direction (maxima! compression) is seemingly pointing towards the NW-SE in the Lower Miocene. It changes to N-S in the Middle Miocene and to NE-SW in the Upper Miocene. Most probably the NW-SE compression appears once more after the Upper Pannonian (Pontian). We understand quite poorly the rcappcarencc of this latter stress-field. For a detailed analyse we should know the present day stress-field, the basic data of which arc being collected by others.We haven't deal with the various extensions measured in SW Hungary (BERCERAT and CSONTOS, 1989) but we are persuaded that these phenomena, although very important, are only accompanying the basic strike-slip tectonics. Multitude of seismic data (e. g. RUMPLER and HORVATH, 1988) acquiredIP_________________L. CSONTOS and F. BERCERAT__________________in Hungary shows, that the Neogene tectonics arc controiied by iargc wrench faults.The present day configuration of the major fracture zones and the basins of SW Hungary is in our opinion due to severai tectonic events and processes (/Ig. 4 The eariy fauit zones and basins have been probabiy formed during the Lower Miocene. These structures generaHy have an E-W strike. New basin directions of NE-SW direction are overprinted on the older ones probably in the Middle Miocene. The subsidence in these basins is continuing during the Pannonian, when the older structures are rejuvenated. At the end of the Pannonian (Pontian) we experience a drastic change in the compression directions, creating folds even in Lower Pannonian strata, and once more rejuvenating the old E-W directed deformation zones. This polyphase evolution is the probable reason of the curious crescent shape basins and rises and of the complex "thrust zones" of SE Hungary (/ig. 4 /REFERENCESBALLA Z. (t984): The Carpathian toop and the Pannonian basin: a kinematic anatysis. - Geophys. Transactions, voi. 30. no 4, 3)3-353 BERGERAT F„ CSONTOS L. ()989): Brittle tectonics and paleostress fields in the Mecsek and Villány Mts. (Hungary): correlation with the opening mechanism of the Pannonian Basin. - Acta Geol. Hung, (in press) BERGERAT F.. CSONTOS L.. FODOR L., TAR) G. ()989): Stress-fields in the Carpathian-Pannonian region during the Neogene. - Terra Cognita (in press) CH)KÁN G., CH!KÁN G-NÉ.. RÓKA) A. (!984): A nyugati Mecsek földtani térképe. L25000. - MÁF), Budapest.CSONTOS L. (!988): Étude géologique d'une portion des Carpathes internes: le massif du Bükk (NE de la Hongrie). - Thése, Lilte.FODOR L., NEMCOK M., MARKO F. ()989). Evolution des paléo-champs de contraintes du Bassin de Vienne. - Geodyn. Acta (in press)FÜLÖP L, DANK V. (ed.) ()987): Magyarország földtani képződményei aKainozoikum elhagyásával. ):500 000. - MÁF1. Budapest.HÁMOR G. ()966): Újabb adatok a Mecsek hegység szerkezetföldtani ismeretéhez.- Ann. Rep. Hung. Geol. !nst. )964, Í93-208.HETÉNY) R., HÁMOR G., FÖLD) M., NAGY E., B)L)K ). ()982): A Keteti Mecsek földtani térképe. ):25 000. - MÁF), Budapest.HORVÁTH F.. RUMPLER G.. POGÁCSÁS GY.. TAR) G. ()987): Transtensiona) origin of the Pannonian Basin: new evidence and interpretation. - Terra Cognita, 7. 20!.KASSA! M. (!973): A villányi-szalatnaki pleozoos mélytörés. - MTA X. oszt. Köz). 6 ()^t) 35!-354.REEVALUATION OF THE NEOGENE BRITTLE TECTONICS 11KOVÁCS S. (]982): Problems of the Pannonian "Median Massif" and the piate tectonic concept. Contributions based on the distribution of Late Paieozoic- Eariy Mesozoic isopic zones. - Geo). Rundschau, B. 71. H. 2. 617-639. KÖRÖSSY L. (1988): A zalai medencei kőolaj-és földgázkutatás földtani eredményei.- Ált. Föld. Szemle. 23. 3-162.LÓCZY L. jr. (1912): A Villányi és Báni hegység geológiai viszonyai. - Bull. Soc. Geol. Hung. XLII. 672-693.NAGY E-, NAGY 1. (1976): A Villányi hegység triász képződményei. Geol. Hung., Ser. Geol. T. 17. 111-220.NÉMED1-VARGA Z. (1977): A Kapós vonal. Bull. Soc. Geol. Hung. 107; 313-328. NÉMEDIVARGA Z. (1983): Tectonics of the Mecsek Mts int the Alpine orogenic cycle (Hung). - Ann. Rep. Hung. Geol. Inst., 1981, 467^184.WE1N GY. (1965): Geology of the "Northern Thrust Sheet" of the Mecsek Mts.- Ann. Rep. Hung. Geol. Inst., 1963. 35-50.!2_________________L. CSONTOS and F. BERGERAT___________________

Reevaluation of the Neogene brittle tectonics of the Mecsek-Villány area (SW Hungary)

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Reevaluation of the Neogene brittle tectonics of the Mecsek-Villány area (SW Hungary)

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