67 76 Deep Structure of the Inner Carpathians in the Maramures Tisa Zone East Carpathians

Rom. J. Geophysics, 1993, 16, p. 67- 76

DEEP STRUCTURE OF THE INNER t ARPATHIANS IN THE MARAMUREŞ-TISA ZONE (EAST CARPATHIANS)

Mircea SĂNDULESCU , Marius VISARIO N, Dumitru STĂN ICĂ , Marcela STĂN ICĂ, Ligia ATANASIU

Instit.utul de Geologie ş i GCOfiZ1Că . StI' . Ca.J'anse be~ 1, 78 344 Buc lU'cş ti 32.

Q K e y words: Tectonic un ils. Nappe. Faults. Mohorovicic discontinuity. Models. East Carpathians.

Abstrac t: T he st ructural model elabo ratcd based a n the geological aud geophysical data in Maramurclj and the Subcarpa th ian Ukraine reveals t he ex is lence o f two cO lI s umption paleo pla nes of the prima ry bascmcnts of the flysch aud PiClli llY nappes between which lies the sialic block cor respollding to the Mcdiau Dacides. The relat ive c10seness of the Lwo planes suggests the more rest ri ct.ed ini tial widtlt o f the Medi an Oacid es and t.heir transversal s hortening . From W lo E l he blocks separated are characlerized by different thicknesses of the crust: 25- 26 km , 30- 33 km a ud 50- 52 km . T he tectonic dra[t elaborated reveals t he marked bent of the Pieu.ides in th e terminal zone of the Gutii­Maramureş determin ed by lhe Tertiary overthru st of t he Inner Dacides. The separation of thc B~be§ti-Tiacovo Nappe, consis t iug of Mesozoic form a tions a nd ophiolitic rocks, and the prolongation of the Kricevo N appe in Ro mani a represent new elemen ls.

The Maramureş-O"" area and the Subcarpathian Ukraine, situated south and north , respectively, of t he upper Tisa Valley, correspond to a part of the Inuer

Carpathians realm. It is possible to distinguish a lower tectonic stage (following Wegman's deffini tion), COIl­

sisting of the deformed Cretaceous and Lower Miocene uni ts (Inner, Median and Outer Dacides as weB as the Pienides), and the upper tectonic stage, consist­ing of the Neogene ulOlassic depressions and the Neo­gene calc-alkaline volcanic arc. The ai tn of t his note is to analyse the correlat ion between th. different Creta­ceous and Lower Miocene deformed units and the deep structure of the crust, taking into accoun t the corre­lat ion between the geologic"l, drilling and geophysical data.

T he geological invest igations in Maramure§ have a relat ively long history. The latest information concern­ing t he lithostratigraphy of t he Mesozoic and Paleo­gene formations belongs to Antonesc u et al. ( 1975) , Dicea et a l. (1980), Săndu lescu et al. (1982) , Săndu lescu, Bratu ( 1984), Săn dulescu et al. (1989a, 1991). The general structure of t he area and the cor­relations with the Ukrai nian Carpathians are due to Săndulescu (1975, 1980a, 1984).

Major contributions on the deep structure, partic­ularly of the Neogene volcanics stru cture, have been brought by gravimetric an d magnet.ic surveys accom­plished during several stages (Fotopolos, 1962- 1970;

Cristesc u, Ştefănciuc , 1968) by petrophysical studies effect uated on different. types of rocks and geological formations (Botezat u et al. , 1970) as well as by synthe­sis works based on them (Andrei et al. , 1970 ; Borco~ et a l. , 1979). On small a reas the seism ic surveys car­ried out in the eastern part of the Pannonian Depres­sion, in the Sighet and Văratec Mts- Rodnei Mts ar­eas (Stanchievici et aL, 1983; Ionescu , Popov ici, 1979; Milea, Popescu, 1988) have brought sound evidence on the Neogene formations structures as well as a few disparate data on deeper levels. The resul ts obtained have been taken over and reinterpreted within regional studies based on the integrate analysis of t he geological and geophysical data (Vis.rion et al. , 1979, 1988).

Several studies referred ta the speci fi cation of the position of the Mohorovicic discontinuity (Enesc u et a l. , 1967; Răd ulesc u et al., 1976), the establishing of the horÎzontal nonhomogeneit ies of the electric condu c­tiv ity by the geomagnetic sounding method, t he sim­pli fi ed version represented by Wiese induction vectors (Calotă et al. , 197 1; Soare, 1989), the particul arities of t he regional flux (Veliciu , 1987) , and the seismicity of the northern part of Romani a (Polonic, 1980).

R.esearches effectua ted by the magnetotelluric sounding method in the Medie~u l Aurit-Remetea Oa.~ulu i-Cimpulung la Tisa profile provided new in­formation concern ing the deep structure of t he arca. Their integration in the actual struct ura l model al-

68

lowed sOl1le important specifi cations mostly about the position and mutual relatio lls between the crystalline (crustal) block and the position of the suture zones.

For correla tiolls with the Suhcarpathi.in Ukraine we have iaken into account the geological and tectonic maps (scale 1:200,000) (Krugliov et al. , 1977), the structural map of t he pre-Neogene formatiolls of the Solotvino depression ( Katîlk et al. , 1974), data 0 11

gravity a nd elect. romagnetic indu ction surveys (Mel­nici uc e i a t. , 1974; Burianov eL aL, 1980 ; Adam , \-Vall­ner, 198 1), as well as t,he results of seismic su rveys car­ried out on the intern at ional profiles IP-III and NP-17 (Berâl1ek et a l. , 1972) .

Overlook an the G eological Structul'e

T he correlation of the geological and geophysical data in the Oa~-M aramure§ zone with those in the Ti acovo-Sockyrnitza-Teresva Valley area in the Sub­carpathi an Ukraine made possible the elaboration of a tectonic draTt. (Plate I) which includes several new element.s.

The major str uct.ural group of units presen ted on t his map belongs .to the Inner Oacides, Pienides, Me­dian and OuLer Dacides up to the boundary of t.lw la.'5t. ones with the Moldavides (Fig. 1) .

,...-" ~

Fig. 1 'J'ectonic sketch showlIlg thc pos il.ion of the Main Tethyan Suture (MTS). 1, Pre- Apulian continent.al p late (Inner Dacides ); 2, Main Tet.hyan Sut ure: a, Transylvanides; b , Blbe§tj -Tiacovo Nappe; c, Pienidesi 3, Continent al Median Dacidcs; 4, O uter Dacidian Suture; 5, Moldavides.

The Pienides belong to t he Major Tethyan Sutur., squ eezed between the Inner Dacides and the Med ian Dacides, both contin ental crusts bearing groups of

M . SĂNDULESCU et al.

units. The Pienidian units are cover nappes , whereas the Inner and Median Oacides group toget.her conti­nental basement shearing nappes . In an outer pos ition is respect with t he Med ian Dacid es df've~op tllli ts - the OuLer Dacides - which come rrom a satellite suture generated within an intracontillen tal rirt zone (with Jurassic thinned orJand oceanic- t.ypf' .rust.).

The l11ain deformation periods of the difre rcilt majo r groups of t.ectonic units are differenL in age. T hc old­est - Mid-Cretaceous - defor mation s have strudured the Median Oacides and involved at least a part of the Major Tethyo.n Suture , corresponding to the obduc­tions of Transy lvani an elements known mostly south­east. anei south of the Maramure§ area (Săndulescu ,

1975, 1984) . The Inner Oacides were structured dur­ing the Turonian (Late Turonian?) t ime, while the Ouler Dacides recorded the Mid-Cretaceous deforma­tiol1s a nd al50 the End-Cret.aceous ones (Latc Senon­ian) . T he Pieni des show in t. heir actual shape t he traces of importan t Early M ioccnc deformations, but within seme of thei r unit.s traces of End-Cretaceous deformation s are also preservecl.

The 1 n n e r Da c i d es extend from the Apuseni Mts and nOl'th-west Transylvania up to the w:esternmost Slovakia; they correspond to t he Austro­AlpÎne nappe syste m of the Easlern Alps . In the area prcsented in th is note t he I llller DaciJes are mostly I'cpresell ted by t he Bihor Unit., which is their most ex­te rnaL consequently the deepest zone. T he metamor­phi t formati ons, of Precambria n age (Someş Series), are largely developed in the Bihor Unit , intruded in places by Paleozoic granitic massifs. In the a rea un­deI' disc lJss ion the Somcş Series crops out in the T icB.u aud FfigeL "crystalline isla nds" from under the mo-1a.':iSic Neogene deposit.s of the Panllonian Depression and , practically, represents by itself t he whole Bihor Unit. This situatio ll is determined by a n important pre- PaJeogene (probably pre-Senonian) erosion which removed the Mesozoic envelope of tlle unit, .preserved in iLs southern a l'eas (Apuseni Mts) . In the Pre­lu ca " mass if' metamorphic formatÎons CfOp out, which have been correlated (Rusu et a l. , 1983) with the Baia de Arie~ Series of the Apuseni Mts or with the Rebra Ser ies of the East Carpathians. T his problem , as weB as the correlation of the Pietr iş " massif' siLuaLed north of Preluca, is a more complex question concerning the Paleozoic geotecion ic history, the Tethyan rifting and oceanic spreadi ng and t he actua l posit ion of the Major Tethyan Suture.

The M aj o r T e t h y a n Sut u r e (MTS ) groups together the units which proceed from the oceanic Tethys. Following the age of their main deformations (tectogeneses) t he Transylvanides (Cretaceous defor­mations exclusively) and the Pieni des (Cret.aceous and Early Miocene deformations) have been distinguished

DEEP STRUCTURI': TN THE MARAMURES- TTSA ZONE: 69

(Săndulescu, 1984). The Pienides develop north of the North-Transy lvanian Fault only. T he Transyl­vanides represenL t he \Vhole MTS souLII of the North­Transy lvanian Faul t. Nevertheless, nor t.h and north­east of this fau lt Cretaceous obd ucted (a bove the Eu­ropean continental ma rgin represented by the Med ian Dacides) units (t he Transylvanian na ppes) proceedin g [rom the ocean ic Tethys (=MTS) are known ; this fact suggests that. Transylvanidian element.s take part in the build ing of the MTS toget her with the Pienides in parallel positions. In t.his discussion signi fica nt data were suppl ied by the borehole 2805 Băbeşt i . At 2620 m deep bela w 8adenia n deposits, it penetrated a carbon­atic sequence wit ll dolomites and limestones ass igned to the Middle Tri assic (or Upper Jurassic ?). Below this rocks a dark-coloured clayey breccia with elements of eruptive roc ks a nd mafi c cineri tes was dri lled. At about 28;5 m deep, the borehole intercepted basic and ul trabas ic (picri te) erup t ive rocks, which could be observed up to the bottom of t he driJling (2909 m). This last sequence dr iJled in the Băbeşti borehole can be referred to a Mesozoic ophiolitic complex li thos­trat igraphi cally covered by the carbonat ic (Triassic or Jurass ic) sequ cnce; both belollg ta the MTS and must be situated in front of (and below) the Inner Dacides with continenta l crll st (as repr~se lltcd on the tecton ic sketch) . In a relatively c10se vicÎllity wiih the Băbeşti

borehole several boreholes (Tiacovo, Sokyrni tza) are known in the southern Subca l' pathi an Ukraine, which have dr illcd Mesozoic (Tri a'>sic aud Jurassic) forll1a­l iolls cOll s t. itut.~d of clayey-calC'pl'eo ll !) sequences with in t.erca lat ions of blackish si ltic lillll-'stones; basic and al­kalin~ magmatic I'ocks are associatcd (in an imbricated strud urc ?). We- group together the fo rmat iolls occur­ring in t he Băbeşti, Tiacovo and Sokyrnitza boreholes in a Băbeşti-Tiacovo Nappe, the illnermost un it of the MTS situated in front of the Inner Dacides. T he age of the tectogenesis which yielded (.he Băbeşt i -Tiacovo Nappe is, however, difficult to specify; it can be Cre­taceous only or Cretaceolls a nd Early Miocene.

External in respect with t.he O ăbeş t i-Tiacovo Nappe another teeLonic unit devclops, that belongs to ihe Pienides (and consequen tly to the MTS) - the Kri cevo Nappe. First ident ified in the Subcarpath ian Ukraine (Jivko, Pctrashkevici, 1971 ), its prolongation south of the Tisa Ri ver was su pposed (Sănd ulescu , 1980b) be­low t he Neogene molasses and volcan ics. This supw position was confirmed by the borehole 4201 Sarasău (Fig. 2). Thc Kri cevo Series, in tercepted in the Subw

carpathian Ukra ine in boreholes ( 1 and 3 Tereblea, Il Teresova, 2 Irsha va, 4 and 5 Solotv ino), consisls of dark-grey calca reous clays with in terbeds of grey sand­stones, marls and limestones. ILs age extends from Ap­tian to Senonian. The borehole 4201 Sarasău crossed between 2250.m and 2740 m a pelitic seq uence of grey-

blackish colour , perfectly compal'able with those in boreholes 4 and 5 Solotvi no (Fig. 2) . Starting with the Sarasău a rea t he Kricevo Nappe d isplays a major south-west bending.

One of the most specifi c element of the P ien ides is represented by the Piell iny Klippen Zone whi ch in Ro­mania's territory crops out only in the Poiana Botizei­Strâmbu Băiuti area, in the frontal part of the Botiza Nappe (the " frontal scales" which involve Pieniny- type klippen wi th J urassic-Cretaceous formatiolls and an End-Cretaceous tectogenes is). This element was inter­cepted in a borehole at the western peri phery of the Baia Ma re locali ty. North of Rollldllia , the Pieniny I( lippen Zone can be traced, across Ukraine, Slovakia a nd Poland , up to Vienna. In Ukraine, as in the Poiana B6tizeiwStrâmbli Băiuti area, this zone is char­acterized by a very imbri caled tectonic structu re in a rela tively narrow strip . The ' firsl compressions are Meso(?)- and End-Cretaceous , the second one Early Miocene. In some places a gap is known between the Cretaceous and t he Paleogene. The same tectogene­sis seeJllS t.o be recorded in the Kricevo Nappe, too, a Paleogene (Eocene '1) sand y ft ysch overlying the Cre­taceous Kri cevo Series.

The Botiza Nappe, cropp ing out. south of the Bog­dan Vodă Fau lt and carrying in its fronta l part the Poiana Bot izei-Strâmbu Băiuti Pieniny-type klippen, has apparent ly the same tectonic pos ilion as the Kri cevo Nappe, but the li thost ra tig raphic sll ccession is, at least partia lly, diITerent. The most important volume of the Botiza Nappe is repl'esented by an Eocene fl ysch suCceSSiOIl , with var iegated Paleocene shales and Turonian(?)-Senonian red marls, at its base. In front and below the Botiza Nappe deve!ops the Wild fJ ysch Nappe , constituted of Middle and Upper Eocene formations, with alternat ing levels of flysch, olistostromes , massive sandstones, sedimentary beec· cias and polymict ic conglomerates , and of O ligocene salldy f1 ysch. Both the Botiza and th e Wil dfl ysch nappes were recognized (Săndulescu et a l. , 1983, L984) below the Neogene volcanic chain , in boreho les and mine workings, south of t he Bogdan Vodă Fault, west of their oulcropping area.

T he Pet rova Nappe is the most. extern al unit of the Pienides; it cor responds westwards to the Măgura

Nappe of the Slovakia n- Po lish Carpathians. The main part of the Petrova Nappe is represented by an Eocene (Middle and Upper) fl ysch. The Petrova Nappe devel­ops only norUl of the Bogdan Vodă Fau lt ; south of the fau lt it possibly corresponds (at least as regards the tecton ic posit ion and with some lithofacia l changings) to t he "Vildfl ysch Nappe (Sănd ulescu in Săndulescu et al. , 1989b).

The M e di a n D ac i d e s belong to the deformed European continental margin and rep-

s

o

3

~~

4

5

6 ~1 ~

ROMANIA

4201 Sara său

. ,.

:,' :.Numm:

....

'1 ,1' 1,

f': ',«,12

UKRAINE

4 So lo fvin

'.: :-:".: .. '. :':: ." : :::::

1, I

r----q3 - - ~4 L.....:-J

rig. 2 - Ccnlogical c r QSs- sect.ÎOH in t.hc Sarasltu-Solo Lvilio arca.

"s So lotv in

o 2km ,

.............. 5 ·••··•· .. Nulll"'. 6 t7

1, Ncogcll c IlIl)lasscs; 2, Bado\' ScrÎcs _. Uppc/' ( '! ) EOCC I1C; 3, I<ricc"Q Sc rics (Aptil\ II-SCn o ni /ul) ; 4 , Eocene sandy flysch; 5, O\'cl'thms t. ; 0, NlIlIllllulitic-bcaring levels; 7, .Dri ILing:s.

N

.... O

.S:

I~ ,-~

DEEP STRUCTURE IN T HE MARAM URES- T ISA 7,QNE 71

resent t he proximal group of units of t his margin , in respect with t he Maj or Tethyan Sut ure. The Median Dacides group together basemenl shear ing nappes (with precambrian and /or PaleozoÎc metamor­phic formations a nd Triassic-Lower Creiaceous sedi­mentary fo rmations) overihrust each other during the Meso-Crelaceous tectogenesis. The Post-Tect.ogene tic Cover of t he Median Dacides, which la rgely devel­aps in Maramurc§ a rea , shows 1wo mai n sedimen­tary cyeles: Ccnomanian-Senonian and Eoccnc- Lower Miocenc .. The' fa rmec slaris with conglomerates , [01-

lowed by a mad y sequence (Turonian-Senonia n) . . The IaUer s ta rts a l50 witll cong lomcrates, followed by det ri­tai sequenccs, carbonal,es a lid marls (Pri aboni an) a nd thick O ligocene forma LÎoJl s (pelitic, a lternating with massive sa ndy sequellces). In some distal parts of the sed imentary basin of t he Post-Tectogenetic Cover of the Med ian Dacides a cOJlI.inuous sedimentation devel­ops rrom t he Ceno manian up to the Oligocene, with a condensed pclagic succession during the Turollia ll ­Pri aboni an timei tiie Oligocent' formations are sim­ilar t '; the ma rginal fac ies ment.ioned a.bovc. 'fIle ' youn ges t. leve ls of the Post-Tectogenetic Cover ( Bo rşa

Sandstone) may be Ea rLY Miocene in agc. The Post­Tectogcll e ti c Cover of the Median Dacides is tec to n­ically overthrus t by the Pienid ian un its dur illg t he Lower iVliocene ( Intra- Burdigalia ll) . T he formations of the cover were de ro rme~1 du r'ing the sa me time (folds and scales partI" de tar.hcd rrom their s ubstra tum).

T he O LI t e r O ac i ci e sare represcnted by a group of nappes with Cretaceous (Meso-Cretaceous and Enu-Crcta.cco us) !.ectogeneses. 'fhey proceed from an intraconti nenta l rift, situated withi n the European cont. inenta l ma rgin (Să lldule8cu , 1980b, l f)R3) ~ where thi nn ed and/ol' oceani c Lype crust dev(' lol)ed . This crust (a nd lithosp herc) was cons umed (by subd uc­tioll) belo \V t lJ e"contincllta l !Vlcdian Dacides, gener­a.t ing a "sate llitc sut tlre" il ~ respect wit ll the MTS. In Maramu reş anei the Subca rpat.hi a n Ukra.in e th e Outer Dacide5 incl ude t he Black flysch Nappe (=t he Ka meny Po tok Unit=Civcin Unit) and the Cehlă u Nappe (= Rahov a nd I3nrku t IIll its). They are bui lt up mostl)' of fl ysch forlllat iolls (Jurass ic- Lower Creta­ceous or o nly Cretaccous ) \".., lrich , in SOIll E-' a rcas, prc­served at thei r bot to m maflc complexes.

Outside the O uter Dac ides develop the M o i d a _ v id i a Il Na p p e s with a M iocclle t.('cl.ogencs is.

.M o l as 5 ieD e p r e 5 s i o n s devclo p si ll ce the Middl e Mioccne abo\'c t lle dcfo rmed Illlw r ( :arpathi ­ans. In the s t udy a rea there is the no rth-('rl.ill. corner of the Pa llllonian Depression and the Transca rpathi an Depressio ll (d ifferen t from t.!te T ransca rpat.h ia ll Fly­sch Zone wh ich groups the olltcroppillg Picnides and the Median Oacides post- tectogenet ic cover) whi ch is a sort o f gul f of the former o ne. Part ly contempora-

Ileous and partly a bove these depressions develops a Vo i c a n i c eh ai n generated in con necLion with subduction processes.

Ma.in Deep Fault SystcnlS

T he most expressive fract ures are t hose which were active dur ing t !Je Neogene time; so me of them can be oldcr but \Vere reactivated .

On e of t he most im portant deep fracture, reaching the Moho, is the No r t h - T r a Il s y I v a 1\ i a Il

F a u i t (NTF) (Să ndulesc u , Visa rio n , 1978). It ex­. tends a long about 800 .km fro m eastern Trallsylvania up to south Hungary and crops out 0 11 t he Ilorthern border of the Preluca " massif' (Plate 1), where i( is kllown as Prelu ca Fa ul t. T he tra nscrus ta l character of t he North-Transy lvanian Fa ul!. was ass ign ed by deep seismi c soundings (Ră.dulesc u c t a L, 1976); t. he dis­placemenL a t t"h€" Moho le vei is of aboHt 5 krn . This character is stressed o ut a lso by t lle seismic act ivity in the '1'g. Lă pu§-Copaln i c-Cr i sci o r ~rca, charac teri zed by earthqu a kes o f low magnitude (Po lonic, 1980) and by t he high content ofth e endogellc heli ulll in the Coa§, Copa ll1i c- Măn ă~tur anei 8rabeni a reas (Vcli ciu el a l. , 1982). The displacements a lo ng thc fradure show a composite ami long act ivi ty. T ire signifi ca nt role of t he North-Transy lvani an Fa ult is stressed o ut , a lllo ng other fact.s , by the diffe rent tectollic evolu t ioll of t ire struc tural uni ts situa-ted on either part of the fract llfc. North of the rault. ti I(' C retaceolls tectogencses were followcd in Uit' Pi l'Jlidi<l1l !'calm by thc Ea rly Miocene oneS 1 whereas .'iO trt.J1 of it only C reta.ceous defofm at ions are rccorded ( S ă nd ulesc u . 1975, 1984; Sănd ulescu , Vis­al' ion , 1978). The act ua l ~hape of the N'l'F is t haL of a normal fa ul t wit h dO\\' ll ward northern block . In fact, s tri ke-slip compo llcnts wcre act ive duri ng the C reta­ccous and tlie Early M iocene.

No rth and generally para llel to NT F develops a ll ­

other im portant rracture: the B o g d a Il V o ci ă l' au i t (BVr) (Săndu lescu , 1975). This is a l50 a t ra nscrllstal fault , s t ill seism ica lly act ive, with compos­ite displacelllents - left- Iate ra l st rike-s li p fault in the Ea rly Miocene a nJ norma l fault wi t h downward sout h­e ,." block durin g tlte Middle and' Upper Miocene BVI' ca n be t raced il! oULcropS east of the volcanic chain ; it continues below the Neogene volcan ics where it was t raced using t he drilling a nd mining data (Săndulescu et aL, 1983, 1984 ) as well as salellil,e images and g rav­iLy a noma ly ( Vâjdea e t al. , 1983) . Hs trend is ma rked a lso by epicenters of crusta l ea rthqu akes in t he Rac!ia, Li vad'a , Ora!iul Nou a nd Nisipeni a reas.

Bet ll'ee ll NTF and BVF develops tlte Neogelle Satu 'Mare G raben sharply s ubsequenl. in respect with UIt' deforllled uni ts of t ire Inner Dacides and Pien ides. T he graben is divided by NE- SW and ENE- WSW Lransversal fa ul ts inLo severa l blocks . The Făge t Fau lt

72

is oile of the m08t important one, extcnding la rgely north and south of the graben b0undary. West of t he Făget Fau lt the Andrusat-Url11eni~ Block is the maÎn sunk one, with important Sarmatian-Pan nonÎan sub­sidence . Another young subsided clongated a rea", with a transversal position in respect with t he Salu Mare Graben , is the Baia Sprie (transversal) Graben gener­aled betwecn the Ma ra a nd Săsar faults, within wh ich t he pre-Badenian basement was dri lled at depths of more than 2500 m (Săn dulesc u et a l. , 1983).

North of BVF and west of the Făget Fault the post­tectogenetic (Neogene) block-fau lted style is largely developed (Plate 1). O ne of the relat ively most elevated blocks is the Ora~u l Nou-Negre§ti Block where meta­morphic formations of t he Io ner Dacides were drilled at 675 m (Ora§ul Nou boreho le) and which is c1early outl ined by a major gravity maximum with a n east­west trending. The gravity maximum closes abrupt ly in the Livada area, on the Halmeu F'aull. This rradure is relatively young, with right-Iatera l strike-slip trans­lations and ma rked actually by epicent res of crustal earthquakes (Oraşu l Nou, Li vada and Halmeu).

Geotectollic Model

The geoledoni c model of t he study a rea, showillg the deep structure of the crust, is based on the data supplied by the ll1agnetotelluri c surveys OII t hc l'vle­dieşul Aurit-Ti." Valley profile correlated witll tlle seismic inforll1ation o btained on the internat iona l pro­file III , the Ukrainian profile NP- 17 ( Ile ra llek et a l. , 1972), the local seismic sOll ndillgs carricd out in the nor th of Romania (Enesc u et a l. , 1067) as well as with the geomagnetic, g rav ity and geot hermal data in the Baia Mare-Sighet anei Solotvino-Sockyrnitza in the Subca rpathian Ukraine. An attempt of geological in­terpretation of a profile which bcgills at Oradea in the Inner Dacieles area anei reachcs t he fl ysch zone of the Ukraini an Carpathians has a lso been taken int.o con­siderat ion ( Rădulescu et a l. , 1976).

T he geotectoll ic model e1aborated (Plate II ) empha­sizes two gaps of t he Mohorovicic surface: one situated under the development area of t he Pielli des anei the other in the frontal part of t.he lnlle l' Dacides. From NE to SW, in t he three cOll1partments separa t. p.d , I.he average t hicknesses of t he crust a re, as follows: !10- 52 krn , 30- 32 km a nei 26- 27 km. T he Illost conclusivp data have becn obtained from t hc south-western area, corresponding to the Pannonian realm wi th thi nned crust, where the e lement.s slI pplied by the in terpreta­tion of the magnetotell uric soundings are grouped sat­isfactor ily anei t hey coin cide with those obtained to the west .and north by seismic surveys. T hc strong t. hicken­ing of the crust toward NE is suggest.ed by the regional decrease of the grav ity values on this trend and it is

M . SĂ NDULESCU el. al.

confirmed hy the gravity mod elling carried out in cor­relat ioll wil.h t he seismic data in the Subcarpathian Ukrai ne (Meln iciuc et a l. , 1974 ).

The fracture situ aled at t. he Moho level be low the ex tern a l part o f t he Pienides (the eastern deep frac­ture OII Pl ate H) has been considered as represent ing the suture of the O uter Dacides! corresponding to an olel plane of crustal consumptioll o f t he pri mary base­ments of the fl ysch nappes. From this point of view it is <comparable with that en.1phasized o n severa l geologi­cal profil es in the East Carpathialls (Săndulescu , 1975, 1980, 1984; Răd ulesc u et a l. , 1976, 1983; Stăni căet a l. , 1986; Visari on et al. , 1988) un der t.he frontal part of the Central East Car path ian Nappes. T h is interpre­talion was also confirmeel by the dist ribu t io n of the Wiese vedors , r.ompu ted for 20- 30 minutes magnetic field variations in the Carpathian a rea (Calotă et al., 1971 ; Iloki t ians ki, 1975; Adam , Wa llner , 198 1). T he resu lts obt.a ined made possible the accurate outlining of an nlignment which marks t he di rect ion change of thc indu ct ion vectors, materi a lizi ng the existence of I.lle cOlldu ct. ing zone in the crust ( Fig. 3). The cal­culatio ns effectuated by bidimensional moelelling in­dicated depths of l6- 25 km for the conducting zone. Although there were difTerent opinions verslls a cer­tain point of view (Visario n e t a l. , 1988) , we consider that thc mClltio llcd a lig nment , located in the study a rea below thc fronta l part of the Pienides, corre­sponds to t.he (,() 11 SIHll ption paleoplane of the primary basel1lent of I.ile fl ysch nappes. This interpretation is a lso bascd 0 11 t.he hypothes is formul ated by Rokitianski (1975), with tI, c specification th at t he depth where the condudive-zonc is sit uated may be explained only by subd ucL ion processes. T his solu t ian is a-lso accepted in ather st.udies on the Carpatho- Pan nonian area (Adam , Wallncr, 198 1). It was also ill ustrated the develop­Illent I,oward depth of the O uter Dacides, represented by th" Illack I'lysch Nappc , equiva lent with t he C ivcin­Kameny Potok Nappe in the 'Subcarpa thian Ukraine, and by t he Ceahlău Nappe, corresponeling to the Ra­hov ami Porcule ~ nappes, as well as o f t he Moldavides repr('!o<c lIl.ed by t he sectioll t.hrough t he Dukla Nappe. Oelo", t.h esC' nappcs, at 9- 10 km deep , is situated the basf~ I II(, ll t of I,he underth rust pla tfor ms overl ain by a relat ivdy thin sed imentary cover and a lso possibly a p<1l'l . . :'l f t l1l' con tinenta l cordi ll eras of the flysch basi ns.

Tl1e s('('o ll d fr acl.ure rendered ev ident by the mag­l1ctoll,llllri (' 511rveys is lorated below the frontal pa rt of t iI(' 1111l f' r Dacid es . It nlllst correspond to the MTS and ("' " SP (pwlltly 1.0 t.lw subductioll anei consuption palcoplan,· of the occa ni r- type p rima ry basement of t ile I' i('ni,fia n cover-t.y pl' nappes. T he c-ollision along t.Jlis wd('oplan e occurs between th e deformed continen­t.a.l nusl. of t he Med ian Dacides (E1Iro pean conti nen­ta l IlHlrg in ) and that of' thc lu ner Oa.cides (P reapulian

DEEP STIWCTURR rN TIrE MAIlAi1IUIII';S Tl S.\ 7,ONI: 73

18'

\

, , f/

20'

\

"

22' 24 '

,

26'

~\ i

28 '

., / ~\ PANNONIAN BASIN

1; APUSENI

.... ~ RANSYlVANIAN==

~~'>, ~ ,

\ MTS --- -

Pig. 3 - \Vicse inductioll vectors on a tectonic mai> of the hmer Cal'pathiw16- Pannunian regiml (ace. to Adam, .WaJlner, 1981 and Soare, 1989 ). Legend: 1, Easl European Platform: 2, F'orcdccp; 3, Flysch n appes; 4, Pien iny KlipPcll Belt; 5, Neogene cal k-aJkali ne yolcanic rocks; 6, Turn of direction of the Wi ese veclors.

continen tai margi Il) . The cont inental crust segment.s , corr('spondi ng le

the Median Dacides and Iyillg be twecll t he two CO I1 -sumption paleopla nes, are situated ai. 7 km deep , in the elaborated model, and ,a re successively overl ain by their post-tectoni c cover, the Pienidian nappes and thc Neogene mola.'5se .

The area sit.uated S\V of thc MTS is charadN­ized by a thin Pa.nnon ian-ty pe crust . The cont inen­tal crust of th is area correspollds ta t he Inller Oacides group of ull its. T heir prescnL posit ioll is the resu lt of some Miocene translat.iolls di rected by the Nor tll ­Transy lvanian Fau lt .

A simil ar situation was observed on the Deregovo­Dolhin a segment (Fig. 4) of the- in ternat iona l pro fi le III (Beranek et a l. , 1972) for which a seismo-tcctonic sect ioll was elaborat-ed. T he NE exte lls ioll of the pro­fil e. emphasized the sl.rong t hicken ing zone of the crust Ilot iced belo\V the Aysch nappes a nei 1I1t~ foredeep of t./lf' East Carpathians. It is worth mC/ltionin g the exist.ellc(, of a t,ransit ion layer (ahout 10 km thick) at the lowN part of the crusi, charac!.erized by propagatio ll spcl'ds of7 .2- 7.3 km/s, which eXLell ds an a width of about. 100 krn. Consi dering the westwa rd prolongat.lon of t- h(' U Il ­

derthrust, platform elements up Lo tlie Omer Oacides

SIl t-ure, it. is possible tha!. the Tornquis t.-Teissey re Zone, in its actual acceptallce, mig ht be situated between the crusta l fract ures whi ch dclimi t t his transitia n layer.

In the actual acccptance the Tornquist-Teisseyre Zone (TTZ) rcpresents a transcontinental zone (from the llaltic Sea 1.0 ti", Black Sea) . al. this scale rel­a t.ivcly narra\\' ZOlle, elcli mited toward narth-east by the Tornquist-Tcissey re raul t anei grauping tagether horst and grabcn st ru ctllres, parallel anei close to this fanlt. T he fly sch !lappes of the East Carpath ians covcr, by overthrust, a pproximately the whole TTZ (in tllf' Ukrainian East. Crt rpat,hians a nei t.he northern Ro­manian East Ca rpathians). COllseq ueJltly the south­western border o f !'he TTZ has in this sector a very c10se posit-ion in rf'spect \Vit,h I he su bcl uction zone of thc primary baseil lent-s of tll e f1ysch napres (the satel­lit.e suture).

'1'11 (' direct comparisolJ of t.he res ul ts present.ed , with t , ll os ~ ' oh taill cd nil t, h(> international profi le XI , shows t. lt at. t.hf' crustal h l ock~ implicitly the lithosphere o ne, whic h separates thc two consumpiion zones, is twice lIarrowcr Ilort.hwa rds t. hall southwards (central part of 1,l1c Ea:st C:upijtli ialls) . T his situation mighl, be ex­plained following several hYPoI.heses:

- primary width (prpvio lls 1.0 I, IH' (·fll.<.;l,al shor t,ening

74

detcrmined by t he overthrust processes) of the Median Dacides was smaller northwarcls t han southwards;

- the overthrust processes were "absorbed" in depth leading to t he thickening of the crust in t he north­wcstcrn area.

.11 ' .\.\/J Uf, ESCU et al.

recorded on t he ex terna l subd ucl.iOIi plane. T he crust between the 1.wo subduction plan es is of abou t 30- 35 km thick , whereas south-west o f the MTS it decreases ai 25 km (Panno nian-type crust) . A comparable s itu­alion is recorded a l50 south of the shidy a rea on the Eas t Carpathian-Transylvanian cross-section.

~~::'::. :)<i':::; .".:z .. ,~ + +~ + + +

+ + + + + + + +

+ ~ t .. ; + + L' + + :'r'" + + ~

o

'0

o

'0 - ..... + + + + + ' + + + '"*'" ~+ ++ ++++ + + + + + • + + + ~ + +~. • • + • + + + +

vv +'"""+++ + + + + + + + + • f... M v r Iv v v v v v v v v v • + + + 1'" """""""" '1mmf M v v II II V V "'" V + .. ( ""'" V v. ' V

B.' ............ v v v v v v v v V v V + .... V V V V V

20

30

20

30

f :,. ~ ~Mo vvv ..... V V V V V V V

73--- .----: V V V V V V V V V

I • V • V • V-.V . ~ V ~ 40 V V "M - 40

/ V V V V V 7.2 V Mo V V V :;:;

I 1 V V V ~ V V V V

-5 50 o ~ M .",,;,,: V V V

V V V

60 60 v M V

~ ...-

1,~"""ll Ls .. ; ,,1 2 0 3 + + ~, ITiIJs . v • cms D7 Ds C} .. . DIO [][]11

Fig. 4 - C r\l :;: tru geoJogical sectioll Bcrcgovo--Dolina a lollg Ilie profilr or IP- 1I1 (Si' Îs mic data a.x. 1,(1 Bcni ne k el. al " 1912, pos itioll a nd interp re taL ia n of t he op hiolidc su t u res ace . 10 Ihe iUi t hol's). Lcge nd : 1, Mo ho disco ntinu.ÎtYi 2. Conrad di scolll.inuÎ I·Y; C n lstal layers: 3, Upper layer ; 4 , Lower layer ; 5, Crust­mantie tram; it.i OIl layer j (3, Ophi oli tic suturcs; 7, P iclliny Klippen Bclt.; 8, f lysch Nappcs ; 9, FO l'ccl cc P i 10 , Pos t-nappe a nd platfo l'ln CQVCI'S j 11 , Crustal rault.

On Lhe bas is o f t.he ava il ab le data a s tructura l sketch-m ap was ela bo rated a l. t. he level of tho Mo­horovicic disconti nuity ( Fig. 5) for the nort,hern part. of Romania and Suhcar pathi an Ukraine. It was elabo­rated on t he hasis of t he regional gravity anoma ly, cal­cul ated fo r a squa re net lVil.h 20 km each side. T hc po­sition of t he Moho rovicic d iscont inuity was est.abli shed , based 0 11 a fo rmu la elaboratcd by the a ut,ho rs taking into accoun t t. he seismi c soundi llgs and deep ll1agne­totellur ic da. t.a. This map shows the positio lls of the two consum pt.io ll paleop lanes, t hc deep crustal frac­tures as well as t he dist r ibut ion of t hc crustal earth­quake epi cen trcs. By a genera l ana lys is of th is map it, is c1ea rl y possiblf' to s tress out the d iITerent t hickllesses of thc crus l. in t he Car pathia n arca. Outside the ex­tern a l subd uctio ll pa l l~op l a ne CI I hi c:k crusl. of about 60 km develops in a norI h-\\·ps l.e rn bloc k ami 45- 50 klll in a south-easte rn O I]!' . ! II t · rwo blocks be ing separated by a deep transve rsal Ludt . An important displace­ment ( 15- 20 klll ) o f th l' !'vl ohorov icic discontinui ty is

ConclllsiollS

This study br ings new elelne ll ts for a betle r knowl­edge ofthe str ll cLure oft.h e In ner Carpathians by corre­lat ing geologica l and geophysical d a ta from Romanian a lld t he Subca rpa thi an Ukraine . A special s ignificance in s tr uctural respect. shows the spectacular ben!. o f the Pi eniny Klippen Zone in t he Maramureş-C u t.îi areal t he sepa ration o f th e Băbeşt i-T iaco\'o Nappe inclllded in t he units of the Il'l aj or Tct.hyan su t. lIre a nd t he con­LÎnuat ion of the Kri cevo Nappe in t he Roman ian ter­ritory.

In t.his paper s trcss \Vas la. iel 0 1'1 t. he specification of t,lH' deep-sea.t.ed fracture systcms a nei 0 1'1 t he role played by it in the fini shin g off of t he s trllctural edifice. T he d ifferent tectonic evolut.io n of t lH~ ~ t.rllctllra l lIni ts sep­a rated by the North-T ra nsylvan ian f[' .. d ure Îs a lso re­vcaled.

DEEP STRUCT URE IN TfIE MARAMURES TI'i.~ ZONE 75

FiII. .. ." - t\'lohu s t,l1.lCt.ura l lUa p in N" .. !.h l{ul11 ani i1 alld Su l.· I.:arpathian Ukraine a rcas. Lcgc lld : 1, 1\10ho dcpth (in km ); 2, O phio lit. ic S llLII I'C; 3, C rusta l f"ult.; 4, Ma<.: rosc ismÎc e pi ccllt.re; 5, OOS J)l'OflI e; a, MTS pro fil e.

COllsiderin g a li the data knowll 80 fa r a represcJl ­t at. ive geotectoni c nlOdcl has been ela boratcd , which revr:a ls the small ho rÎ zontal dist.ance be t.wecn t he COI1-

sumption paleoplanes of t he primary bascmcnts of t he fl ysch and of the P ienides, as \Ve ll as the probab le ex is­tence of the Tornq uist-Teissey re ZOIlc!, as it. i ~ defined In the present. inte rn at ional research progra lnrnes.

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76

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Received: 5 Decembe,', 199 1

Accepted: 7 Decembe,' 1991

.\1 . S:1. ND ULESCU et al.

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