Lothar Ratschbacher, Hans-Gert Linzer, and Franz Moser. Institut f'tir Geologie und Palâ¢iontologie, Universitfit,. Ttibingen, Germany. Robert-Octavian Strusievicz ...
TECTONICS, CRETACEOUS AND
TO MIOCENE
WRENCHING
SOUTH
ALONG
CARPATHIANS
EFFECT OROCLINE
DURING
DUE
VOL. 12, NO. 4, PAGES 855-873, AUGUST 1993 THRUSTING
THE
INTRODUCTION
CENTRAL
TO A CORNER
COLLISION
AND
FORMATION
Lothar Ratschbacher,Hans-Gert Linzer, and Franz Moser
Institutf'tir Geologieund Pal•iontologie, Universitfit, Ttibingen,Germany Robert-Octavian Strusievicz, Horia Bedelean, Nicolae Hat,
and Petru-AdrianMogos Catedrade Geologie- Paleontologie, Universitatea BabesBolyai, Cluj, Romania
The arc of the Carpathianfold and thrustbelt resultedfrom Cretaceous to Miocene convergenceand collision of the Europeanplate with severalsmall continentalblocks,filling a recessin the combinedEuropean-Moesian foreland(Figure 1). The wealth of geologicand geophysicdata in this area led to case studiesin the evolutionof a basin systemformed in the rear of an orogenic arc (the Pannonianbasin, Figure 1) and motivated reconstructionsof paleotectonicsin a region of complex plate geometry [e.g., Royden and Horvfith, 1988]. Thesereconstructions, aiming to or startingfrom a still mainly hypotheticalJurassic-Cretaceous postriftconfiguration(Figure 2a) [e.g.,S•dulescu, 1988], encompass two-dimensional, successiveapproximationstudies(Figure 2b; block models)[e.g., Balla, 1985; Csontoset al., 1992] and three-dimensionalmodels
Abstract.Field studiesin the RomanianSouthCarpathians (longitude 22.5ø to 24.2øE and latitude 45.2ø to 45.6øN) demonstrate (1) Cretaceous top-to-NEshearingparallelto the present strike of the thrust system connectedwith coaxial flatteningwithin the generallynorthwestdippingfoliation,(2) Paleogeneductile-brittledextml wrenching,E-W compression (o•: 87_15ø), and basinformation(Petrosanibasin)alongthe Cema-Jiufault system,(3) large-scale Miocenedextralwrenching alongthe northernmarginof Moesia(oh:143-16ø),and(4) probably Pliocene-earlyPleistoceneN-S compression(o•: 205__.25ø). We discussthe tectonicsof the SouthCarpathians stressingthe comereffectof the Moesianforelandpromontory duringconvergence and formationof the Carpathianorocline. Up to thelate Early Cretaceous subduction of oceaniccrustwas activebetweenEurope-Moesiaon one sideandEastCarpathiaRhodopiaon the otherside.Collisionandintmcontinental deformationoccurredduringthe lateEarly andLate Cretaceous. The pinningof the thrustfront at the westerntip of Moesiaandthe forelandrecessnorthof it causedsuperposition of thrustingand wrenchingduring collisionand lateral translation,tangential stretchingduring orocline formation,and spreadinginto the recess.Further convergenceduringthe early Tertiary resulted in dislocation of the previously welded East CarpathianRhodopianand Moesian fragmentsalong the Cema-Jiufault system and the further northeasttranslationof the western segment.The intramontanePetrosanibasinopenedas a northeasterly propagating,transientpull-apart structurealong the Cema-Jiufault system,which acquireda curved,northwesterly convex, transtensionaltrace due to the shapeof the Moesian promontory. Tightening of the Carpathian orocline and/or rearrangementof the microplategeometryduringthe formation of the Pannonian basin system led to large-scaledextml wrenchingalongthe northernmarginof Moesia.PlioceneN-S compression reflectsfinal shorteningin the Carpathiansystem before ongoingconvergencebetweenEuropeand Africa was transferred
to the Mediterranean.
Rotation
of material
lines
aroundthe Moesian comer is corroborated by paleomagnetic studies.
Copyright1993 by the AmericanGeophysical Union.
(collision-backarc model) [e.g., Roydenand Burchfiel, 1989], (indentation-escape-collapse model)[Ratschbacher et al., 1991a, b]. Currently,a phaseof modelrefinementaimsto improvethe data base on crustal fault zone kinematics, basin subsidence,
deep structure,and stratigraphy[e.g., Mesk6 et al., 1990]. Paleotectonic reconstructionsmay be constrained and deformationundercomplexplate geometrymay by understood by quantitativekinematicanalysisof the major fault zones.In thispaperwe presentfield dataon deformationand kinematics of the centralSouthCarpathiansin Romania,whichoccupythe southerncomer of the Carpathianforelandrecess(Figure 1). Prompted by model predictions (see above), we aim, in particular,to elucidatethe role of transcurrent motionalongthe northwesternmargin of Moesia. Finally, we proposethat the tectonicevolutionof the centralSouthCarpathians reflectsthe comereffectof theMoesianpromontoryduringAlpinecollision and orocline
formation.
THE CENTRAL
SOUTH
CARPATHIANS
The SouthCarpathiansstretchbetweenthe forelandof the Alpine belt, represented by the Moesianplatformin the south, and the Transylvanianbasin and the Mures ophiolitic zone, representinga remnantof the Vardaroceanin thenorth(Figure 1). They comprisea thrustsystem,first recognizedby Murgoci [1905]. His model of a single,the Getic nappe,incorporatedin an independentEast Carpathian-Rhodopian fragment [e.g., Burchfiel, 1980] thrust over Danubian autochthon(EuropeMoesia), was completedby identifyingthe Suprageticnappes, the Severin nappe, which probably includesoceanic crust locatedbetweenEast Carpathia-Rhodopiaand Moesia (Figure 2a), and the nappestructureinsidethe Danubianunit [Gherasi et al., 1968; Sfftnoiu, 1973; Berza et al., 1983, and references
therein](Figure 3a). Major crustalshorteningis attributedto Late Cretaceousand early Tertiary [e.g., S•tndulescu, 1975], overprintinga pre-Alpine tectonicedifice [Balintoniet al., 1989]. Both the Getic-Suprageticand the Danubianrealms comprisebasementwith Proterozoic,early Caledonian,and Variscanmetamorphites and granitoids,Variscanmolasse,and a Mesozoicsequence[e.g., S•dulescu, 1975]. We studiedan area in the central South Carpathians, betweenthe Timis fiver in the westand the Olt fiver in the east (Figure 3a), covetingbasementand Mesozoiccover rocksof the Getic, Severin, and Danubian thrust systems,and the intramontanebasinsof Haleg and Petrosani(Figure 3). To
Paper number 93TC00232.
reveal the Alpine kinematicsof the Alpine-Carpathian-
0278-7407/93/93TC-00232510.00
Pannonianorogenicsystem,we focuson Alpine deformation
856
ii!i L
Ratschbacher etal.:South Carpathian Orocline Formation
?,V I
'..,x ?.
"---..
.....
'
........... "• '"*:..(!kl I('"'•"'•'"'"'"'•""":••:•'•••iiii•i •," i'
•
Fig. 1. Tectonicsketchmap showinglocationof the central South Carpathiansin the Alpine-Carpathian-Dinaric orogenic belt.
zones (preferablyincludingMesozoic rocks),Tertiary basins, and brittle fault tectonics. We draw the reader's attention to the
work of S,•tndulescu [1975, 1988], Burchfiel [1976, 1980], and
Balintoniet al. [1989], who reviewedthe geologichistoryof the Romanian South Carpathians.Most of our data are summarizedin Figures3 to 11 andTables1 to 3. Observations are basedon evaluationof structureson the geologicmapsof Romania (1:50000-1:200000) and mapping of meso- and microstructuresalong crosssections. CRETACEOUS-EARLY
TERTIARY
TECTONICS
Methodsof KinematicAnalysis Penetrative,crystal-plasticstructuresand their continuous tracingenableus to analyzethe orientationof strainassociated
with the formationof the thrust system.The Alpine age is inferredfromtheretrograde typeof metamorphism overprinting medium to high-gradeProterozoicand Paleozoicbasement rocks, isotopic dating of synkinematicminerals, and the Mesozoic age of intercalatedsedimentaryrocks.Finite strain was calculatedfrom shapesof deformedpebblesand coarse quartzand feldspargrainsin metasandstones andgneisses. Information on the noncoaxialcomponentof strain was obtainedfrom shearcriteria in the XZ plane of finite strain (X>Y>_Z, principalstrainaxes): S-C and shearband fabrics, asymmetricboudinageandstrainshadows,rotatedremnants of fracturedminerals,and shearedminerals [see Simpsonand Schmid, 1983]. Deformationpath interpretations of quartz texturesare based on comparisonswith texturesfrom other deformation zones where the path was establishedby independent criteria[e.g., Schmidand Casey,1986].Natural calcite textures were compared with those derived from polycrystal-plasficity modelsandexperimental data[e.g.,Wenk et al., 1987]. Displacement dataare basedon two assumptions: (1) strainsare largein thedeformationzonesaccompanying the Alpine thrustsof thepile; (2) simpleshearwasa component of deformationat leastduringthe main periodof rock flow. Structures,Strain,Kinematics,and Timing
A simplifiedtectonicsubdivisionis shownin Figure 3a emphasizingAlpine nappes.The schematicblock diagramof Figure 4 definesthe major structures. A penetrativefoliation (S1) runssubparallel to bedding(in Mesozoicrocks)andthrusts and,in general,dipsnorthwest(Figures4 and5). It is defined by phyllosilicates, films of opaqueminerals,elongatedquartz and calcitegrains,and flattenedpebbles.Anastomosing S patternsare common,and a distinctionbetweenS - andC -
b earliest Cretaceous
.
early
plate motions
" ß
'••'"ß•
East.Ca•athia/
Rhodopta .
..'.......' 20 ."N35 '".•_ 0 :::
.............. Apuli "••...•::'" '"....'... '•i:"•j'••;7• :-"....
':
\
:....v,0
."
'-,'.80. :
:.. .' ,,0,/':'.:• '...'..']. •'.•s '"" ..... •0 . •" "•'&.-•. Moesia
Aust•'oalpine •:!!iiiii:?>t.,•7• '•.
Ma •
0: ""4130
•
Africa 10,c
Apuli '•'"'"'""'•"'•'"'"' '" -'"•2'-"•'-. "::" :•-'-.-'.'•• '"" .':' '""' ßVarda '" r
Apu,,a"!•:•:i:i:i:i:i:i:i:•:?:•::i::i::iii?:i::•ii::•::•iii•i•?' Fig. 2. (a) Palinspastic sketchof the Carpathians duringthe earliestCretaceousbefore onsetof convergence (modifiedafter Siindulescu [1988]), and Late Cretaceous paleodeclinations at two points northand west of the Moesianplatform[from Piltra,scu et al., 1990]. Note increaseof rotationangle aroundthe Moesianpromontoryacquiredduringthe formationof the Carpathianorocline.(b) Twodimensional, successive approximation reconstruction of earlyMiocenepaleotectonics of theCarpathian belt simplifiedafterBalla [1985].(c) Platemotionvectorsfor threepointslocatedon Africa (Tunisia), Apulia(EasternAlps),andEastCarpathia-Rhodopia (SouthCarpathians) compiledafterDercourtet al. [1986].
ß
ß o
o,
c..)
(D
•
ß
. ,
ß
e-
X
x
X
x
•
X
JeA.l.l•.1•1.11
X
X
858
Ratschbacher et al.:SouthCarpathian Orecline Formation orientation
of structures
S1+S2
Cretaceous-early Tertiary displacement
0
n=178 Miocene
dextral shearing
-1•
0.0
+1•
displacement partitioninginto thrustshear,pure shear flattening, and wrench
shear
Fig.4. Schematic block diagram (center) defining themajor structures, orientation diagrams (topright; lower hemisphere, equal area) ofmajor crystal-plastic structures, andstrain (bottom row).S1+S2,firstand second Alpinefoliation; LI+L2,firstandsecond Alpinestretching lineafion (second deformation asfull
symbols); F1,firstAlpine folding. Definition ofes,v ofstrain diagram (bottom righ0seeTable1;circles andarrowshow strain gradient approaching thethrust contact between upper Danubian andSeverin-Getic
nappes. Model forstrain accumulation during crystal-plastic deformation (bottom left): displacement (open arrows) is partitioned intothrust shear, pureshear flattening dueto transpression, tangential stretch, gravitational spreading, andwrench shear, concentrated along theCema4iu faultsystem. Finitestrain is strongly oblate.
surfaces ispossible in moderately deformed rocks. Highstrain shearzonesshowmultiplesetsof shear planes withextensional character;they correspond to shearbands.A subhorizontal
stretching lineation (L1)liesinS1andtrends northeast (Figures 4 and5). It is defined byoriented minerals, elongated and/or pulledapartpebblesand minerals, and the longaxesof asymmetric strainshadows. Opencrackswerefilledwithdebris
andchlorite, calcite, andquartz fibers. Folds(F1)arefightto isoclinal,recumbent,and their axes (B1) have variable orientations. In highstrainzonesB1 parallels L1.
somewhat steeper thanfirstdeformation structures andformed, together withmesoscale dextral strike-slip faults,attheductilebrittletransition. The overallgeometric effectof the second deformation is a stretch alongL1-L2.
Localhigh-strain zones inthebasement arecharacterized by intense retrometamorphism (chloritization, albitization). Structureswereformedat andunderfallingAlpinemetamorphic temperatures,finally crossingthe ductile-brittletransition.
Throughout crystal-plastic deformation (firstands,econd Alpine deformation) strain orientation wasmaintained (e.g.,Figure 5a,
Second deformation isportrayed byoutcropandmap-scale stationRO5in thebasement of thelowerDanubian unit,station
folding(F2), a crenulation cleavage andassociated intersection lineation,anda stretching lineation. Bothlineations andthefold axes are subparallel to L1. In incompetent rocks(e.g., carbonafic phyllites of theSeverin nappe, phyllites of thelower
Danubian unit,station RO33,Figure5b),F2isfighttoisoclinal andverges toward SE.Preferably in Mesozoic sequences south of thePetro•ani basin,we observed a second generation of shear bands (SB2instations RO19,RO27; Figure 5).Theydip
RO19in Liassicblackphyllites of theupperDanubian thrust system);we interpretthe distinctstructures as a resultof a single progressivedeformation.
Strainmeasurements showthatL1 parallels X of finite
strainandthatS1is subparallel to theXY plane(flattening plane).Strainis oblate (Table1, Figures 4 and5), intensity increases, andstrainratiobecomes progressively moreoblate towardthrustboundaries (e.g.,station RO20,we sampled a
Ratschbacher et al.: SouthCarpathian OreclineFormation
859
a
•
••7:•777:i:!:•'•7:.'; .......................
R09
-'•"'•"-"'=•.'.'.••i•i•i•i•"•'•:..'.:•:•:•=_.. •"••.......:•i•i•i•ii•i•i•i•i•i•i•i•i•i•ii``
/•:•//!?:11111iiiii!"'""••-" sta-••••.'.••• '",•" ••
i
'""',-'•'".':':..::• "'""':••
i
.....'....... --,..
......
::•::•i•::•!•?:•;?:•::•?:•i!i•i?':/..:.:•....::•:..%... _,'-•"'7" .....),," qgs.b. "......... '.....................................................
'?i•;•'5:•i•i•:;i•i•::i::. '........ •:i:i:!:::i'i'i! ........... •i:i:i tz •x
strain(XYprojection)
O stallohs "
-'
Jt2•ty and unit spl'•ro
"'l"
foliation trajectory •
stretchin0 trajectory .-., displacement vector
Fig. 5. Orientation, structural, strain,andkinematic dataof deformation in the(a) Ha•eg- Petroõani and (b) Petro•ani - ¾idrabasinareas.Stereonets (lowerhemisphere, equalarea):0, pre-Alpine deformation; 1, 2, Alpinestructures; L, stretching lineafion;S, foliation;SB, shearbands;F: fold axes;TG, tension gashes; beamed,meanorientations. Shearbanddataareplottedas greatcircleswith lineafionas arrows
heading intodirection of displacement of thehanging wall.Abbreviation forshearsense criteriaonmaps: ab,asymmetric boudinage; cc,calcitetexture; qtz,quartztexture; cLsigmaclast;sb,shearband;sf, shear fold; sz, shearzone.Calciteandquartzc- axistextures: all oriented parallelto XZ-principalplane (containing stretching lineationandfoliafionnormal,seeFigure$a bottomleft); line andarrowwithin diagramgiveinterpretation of planeandsense of shearof noncoaxial flowcomponent. Notethat(local) top-to-SW shearis particularly pronounced southof thePetro•ani basin(stations RO20,RO25);analysis of texturesacrossa well-exposed 100 m profileindicates homogeneous flow.
straingradientapproaching thethrustcontact betweentheupper Danubian and Severin-Geticnappes in pebble bearing metaarcose rocks,Figure4 - strainplot - cirlcesand arrow). The straingeometryimpliesthatthethrustsystemwasstretched nearlyradially (Figure4, lower left). Figure5 showsfoliationandstretching trajectories anddisplacementvectorsconstructedbasedon evaluationof field and sampledata. Strike of S1 and thrusts,and trendof L1 are, in general,subparallel.Displacementduringboth the first and
second Alpinedeformation wasgenerally top-to-NE,butcoaxial flow contributedsignificantlyto the overalldeformation.Noncoaxialstrainis demonstrated by shearbandsoccurringin singlesets.Coaxialstrainis indicated by conjugate shearbands, but particularlyby orthorhombic quartztextures,and textures indicatinglocaltop-to-SWshear(Figure5). The latterseemsto be pronounced alongthe southern rim of the Petro•anibasin (stationsRO20, RO25), wherewe sampleda profileacross Mesozoicrocksto studystrainpathvariations (seequartztex-
860
Ratschbacher et al.:SouthCarpathian Orocline Formation
b
ß
'
R •,.'-•ii!i mIoa. t•:::::::::::::::::::::::::::::::::: s/r• ½?:i½i!ii•:.
•
,z-'--./
1
Petro$ani-Vidra
..::........'•'"'•:i:!:!½•:[:!::':'::!:i:!:i:!:!:•:[:•..,,
R030
(RO31Q'I'D
• '" '"?..i!:..!i½"•'.':"':"½::'• ..... • t½$ 2 I ' .............. •:i•?:ii!i!:ii}:ii:iiiili!i?:•:•:::•½•:'•'"i'! -.... .....
R020
(RO14QTZ)
R020
R020
o
R025
R027
R030
•
o
o
o
Fig. 5. (continued) tures in Figure 5). During the seconddeformation,S1 lithons were boudinagedand rotated antitheticallyto the top-to-NE shear.
Very low to low-gradeAlpinemetamorphism is syntectonic with the describedstructures. The youngest rocksinvolvedin thrustingand crystal-plasticdeformationare AptJan(Getic, Danubianand Severinnappes)[Berzaet al., 1988;Iancuet al., 1990].Rupelianto Pannonian rocksof theHalegandPetro•ani basins[BerzaandDrilgAnescu, 1988] lie unconformably upon deformedand metamorphosed rocks.Figure6 summarizes the available isotopic ages concerningthe Alpine tectonometamorphicevent. K/Ar biotite agesfrom rocksof all units clusterbetween90 and 120 Ma. Due to the relativelylow
Alpinemetamorphic conditions in theSouthCarpathian nappe pile, we interprettheseagesasformationages.A thermalpeak at about100 Ma is alsoindicatedby the youngest amphibole agesfrom the basement,and wholerock agesfrom Mesozoic metasediments.Consequently,deformationduring the first AlpineeventmusthavestartedduringEarly Cretaceous times; thethmstsystemrelaxedthermallyduringongoingdeformation (secondAlpinedeformation; likely Late Cretaceous). Metamorphictemperatures may be evaluated by examining resettingof theK/Ar isotopicsystemin differentminerals.PreAlpine muscovitewas not rejuvenatedin the Getic nappe, whereasbiotite was partially to completelyreset,at least in deformedrocks(seerock descriptionof Soroiuet al. [1970],
TABLE 1. Crystal-Plastic Strainin theCentralSouth-Carpathians Station
Specimen
RO20 RO20 RO20 RO27 RO30 RO32
RO14s RO15s RO18s RO25s RO31s RO32s
X' Y'Z 1.39: 1:51: 1.70: 2.14: 1.53: 1.66:
1.28:0.59 1.24:0.53 1.29:0.48 1.58: 0.30 1.46:0.45 1.36:0.44
t.
v
k
0.673 0.791 0.947 1.489 0.972 1.011
0.806 0.623 0.569 0.689 0.942 0.695
0.074 0.163 0.184 0.084 0.021 0.108
2+(•-e;5 2+(•7•;5] 112 X>Y>7.,principal strainaxialratio;Strainintensity, •, • 43/3[(s7-s• , where
ln(l+h) is a prin_cil:•l_ ._.ha_rural_ sU'aincorresponding to 4, its conventional counterpart; Strainratio,(Lode's parameter) v = (•2-•-•)(•,-•)'• andk = (X/Y)(Y/Z)'•.
Ratschbacher et al.: SouthCarpathian OreclineFormation
!
!
!
-
.
_
861
......
wholerock
3 r'•amphibolo 2 3
4
upperDanubian
4
lower Danubian
Rb/Sr ages Fig. 6. Histograms(age againstnumberof samples)of isotopicdata (o2>o3,principal stressaxes) and N-S extension (03: 176ñ16ø;Figure7). Relatedlarge-scale structures havenot been identified so far, but mesoscalestructuresare mostly boundto a zone alongthe Petro•anibasinand the fault system borderingit to the east(imbricationzoneof the Getic, Severin, and upper Danubiannappes).Berza and Dfftgilnescu[1988] describedan anastomosing fault zonesouthwest of, and unconformablycoveredby thesediments of thePetro•anibasinasthe Cerna-Jiufault system.They proposed3040 km of dextral displacementfrom Late Cretaceousto Chattiantimesbasedon lithologicand faciescorrelations. In addition to stressorientation,the computationof the reducedstresstensordeterminesthe ratio R, whichexpresses the relationship between the magnitudesof the principal stresses.Extreme valuesof R correspondto stressellipsoids with 02=03 (R=0) or o2=o• (R=I). As Table 2 and Figure 7 (stressratio diagram)show,threestationsare closeto a normal fault solution,three are hybrid solutionsbetweennormaland strike-slipfaulting (o• and o2 permutate),andthreestationsare closeto a strike-slipsolution.The only stationin the sediments of the Petro•anibasinwhere we encounteredset 1 fault striae data is a hybrid strike-slipnormal fault solutionand lies in Chattianconglomerates and sandstones at the northernrim of the basin (station RO23). Set 2 comprisesmostof the data.Relatedstructures, interpreted from maps (Figures3b and 8) and parfly verified by field observation(Figures8 and 9), outline a major Tertiary dextral strike-slipfault zone.The orientationsof structures and stressesalong the zone are summarizedin Figure 10a, and closely resemblethose of large-scaledextral wrench zones
862
Ratschbacher et al.:SouthCarpathian Orocline Formation TABLE 2. CentralSouthCarpathians: Locationof Stations andParameters of theDeviatoricStressTensor
Sites
Method
E longitude
N latitude
Number
o•
o2
•3
R
F
Tertiary Basins RO1-DEX RO10-DEX ROll-DEX RO13-DEX RO17-DEX RO17-SIN RO21-DEX RO23-DEX RO23-EW RO26-DEX
inversion iteration iteration iteration P/T iteration P/T iteration iteration iteration
22048'42" 22050'55" 22059'40" 23059'40" 23023'24" 23023'24" 23005'06" 23005'34" 23005'34" 23ø08'12"
45029'34" 45030'26" 45035'32" 45035'32" 45027'32" 45027'32" 45019'34" 45019'54" 45019'54" 45020'39"
21/21 27/25 15/15 17/13 25/25 13/10 08/08 23/19 11/08 09/08
072 73 135 30 330 10 138 70 310 01 000 20 132 06 320 10 280 60 150 10
167 02 007 47 076 58 337 19 217 66 180 70 020 75 140 80 085 29 273 72
258 17 243 28 234 30 245 06 040 24 270 00 223 14 050 00 179 06 057 15
0.22 0.2 0.7 0.7
14ø 14ø 10ø 14ø
0.3
17ø
0.7 0.6 0.3
12ø 10ø 12ø
CrystallineBasementRocks RO3-DEX iteration RO4-DEX P/T RO6-DEX iteration RO6-SIN iteration RO7-DEX iteration RO7-SIN iteration RO9-DEX iteration RO12-DEX iteration RO12-SIN iteration RO12-EW iteration RO16-OLD-DEX iteration RO16-YOU-DEX iteration RO25-DEX iteration RO25-SIN P/T RO25-EW iteration RO29-DEX iteration RO29-EW iteration RO34-DEX iteration RO34-EW iteration RO37-DEX iteration RO38-DEX P/T RO38-EW P/T
22054'35" 22054' 17" 22044' 14" 22044' 14" 22045' 37" 22045'37" 22ø49'01" 22058'36" 22058'36" 22058'36" 23ø21'11" 23021' 11" 23008'05" 23008'05" 23008'05" 23023'02" 23ø23'02" 23050'34" 23050'34" 24006'02" 24006' 11" 24006' 11"
45028'22" 45025'33" 45020'52" 45020'52" 45023' 16" 45023' 16" 45026'57" 45ø39'15" 45039' 15" 45039' 15" 45026'53" 45026'53" 45ø21'17" 45ø21'17" 45021' 17" 45018'04" 45018'04" 45025'55" 45025'55" 45020'58" 45004' 12" 45004' 12"
16/15 06/06 29/26 17/13
180 30 356 01 307 20 244 20
14ø
0.8 0.3 0.7 0.2 0.1 0.6 0.9 0.7 0.2 0.5 0.1
25ø 07ø 15ø 10ø 09ø 13ø 10ø 15ø 15ø 11ø 19ø
0.2 0.6 0.1 0.2 0.9 0.9
09ø 13ø 14ø 12ø 14ø 21ø
49/47 09/09
120 00 060 00 120 50 332 70 225 30 305 70 318 20 120 10 320 10 197 18 286 20 206 80 240 10 000 50 270 10 130 10 320 16 081 13
090 00 086 07 212 14 149 12 210 18 330 30 224 11 230 04 119 26 203 04 070 47 024 30 050 00 100 20 191 12 071 07 333 17 246 19 006 32 034 30 054 11 174 13
0.6
27/19 17/16 14/13 13/10 13/11 12/12 21/17 21/19 30/24
000 60 259 83 089 65 030 66 030 72 150 60 323 38 139 19 355 48 111 19 212 37 226 58 140 80 326 63 073 66 340 07 122 70 143 34 165 56 236 58 177 70 307 72
23ø13'18" 23ø13'18" 23ø01'51" 23ø01'51" 23ø01'51" 23004'57" 23004'57" 23004'57" 23ø08'21" 23022'58" 23024'35" 23024'35" 23ø27'41" 23ø27'41" 23049' 11" 23049' 11" 23053'30" 23ø53'30" 23054'45" 23054'45"
45ø26'51" 45ø26'51" 45019'28" 45019'28" 45019'28" 45020' 19" 45020' 19" 45020' 19" 45018'49" 45ø21'56" 45028'23" 45028'23" 45024'50" 45024'50" 45025'35" 45025'35" 45026'02" 45026'02" 45025'35" 45025'35"
60/46 15/15 39/32 34/26 12/09 32/23 10/10 26/24 20/20 11/09 37/31 28/27 20/18 05/05 35/33 24/23 43/42 29/26 19/14 05/05
315 30 177 20 330 10 169 30 080 00 138 20 210 26 095 20 307 02 222 70 120 00 200 10 346 08 077 18 150 10 097 18 342 06 222 70 332 70 098 24
135 60 005 70 098 74 349 60 350 55 279 65
225 00 268 02 238 12 079 00 170 35 042 14
0.4
22ø
336 50 318 64 151 88 12602 030 72 082 70
105 28 192 17 037 01 035 20 210 18 293 17
0.3 0.6 0.8 0.3 0.92 0.3
16ø 13ø 20ø 20ø 05ø 25ø
0.6 0.5 0.6
05ø 17ø 11ø
191 81 221 69
076 04 343 12
256 58 305 70 210 81 060 19 152 10 206 35
054 30 190 09 073 06 328 06 062 00 341 45
0.5
16ø
0.5 0.9 0.68
17ø 14ø 07ø
06/06
09/08 56/50 09/07 36/33 11/08 60/50
Permomesozoic Units
ROI5-DEX RO15-SIN RO18-DEX RO18-SIN RO18-EW RO22-DEX RO22-SIN RO22-EW RO27-DEX RO30-DEX RO31-DEX RO31-SIN RO32-DEX RO32-EW RO33-DEX RO33-EW RO35-DEX RO35-EW RO36-DEX RO36-EW
iteration P/T iteration iteration iteration iteration inversion iteration P/T iteration iteration iteration P/T P/T iteration P/T P/T iteration iteration inversion
Sitenumbers locate stations in Figures 5 to 11.Letters afterthesitenumber givesubsets (set1 to 3, seetext)separated froma single faultpopulation: EW:set1, DEX: set2, SIN: set3. Number: first,number of measurements, second, number of measurements usedfor calculation. •-•3: azimuth(firstnumber) andplunge (second number) of theprincipal stress axes.Stress ratioR = (•2-03)(•-•3) 4 (1:uniaxial extension, 0: uniaxial shortening). Fluctuation F givestheaverage angle between the measured striae and the orientation of the calculated theoretical shear stress.
(Figure10b).The dextralmasterfaultsstrike95-110ø (Figure 8, fault strike diagram,and Figure 10a), the averagecompressiondirectiontrends143øñ16 ø (Figure8, stressorientation diagram).Dextralwrenchingis distributed throughout a broad deformationzone,typicalof deformationin continentalcrust. Wider distributionof set 2 faultingas indicatedby the current stateof mapping(Figures3b and 8) is evidentfrom stations
sampledoutsidethe main fault zone(e.g., RO6, RO7, RO9, RO29). Basedon our mesoscale data,we attemptedto determinethe
relativeimportanceof reverse,strike-slip,and normalfaulting on a regionalscale.03 axesplungecloseto horizontalin all sites, showing that the strike-slipand normal-sliptectonic regime dominated.The relative importanceof strike-slip,
Ratschbacher et al.:SouthCarpathian Orocline Formation
863
TABLE 3. AdditionalK/Ar and Rb/Sr Data From the SouthCarpathians Station
Size, gm
Mineral
Sample
RO8
RO8s
RO20 RO27
RO14s RO23s
amphibolea muscovite• muscovitec
Station
Sample
Mineral
>125 > 125 •2->•3, principalstresses) calculatedfrom all stations;stress
ratiodiagram plotscalculated stress ratiosR=(G2-G3)(GFG3) 4 (R=I, uniaxialextension; R=0, uniaxial compression; modifiedfrom Oncken[1988])versusplungeof (• for thereverse,normal,and strike-slip faulting tectonicregimes.
864
Ratschbacher et al.: SouthCarpathian Orocline Formation
Tertiary basin sediments
stress ratio fault strike-•._, stress orientation.•
RO23-EW
i 0ø ßß • '" 3•! ø 3
..................................................................................................................
eTertiary basin sediments ß Permomesozoic
Permomesozoic RO18-EW
rocks
rocks
e Crystalline basementrocks
-
-
3 -
...................................................................................................................................................................
Crystalline basement rocks RO35-EW
RO36-EW
RO
RO12-EW
RO25-EW
;
..................................
Fig. 7. (continued) normal, and minor reversefaulting,however,changesspatially, outliningtranstensional andtranspressional segments. Strike-slip plays a dominantrole close to the ESE trendingmap-scale fatfits(e.g., stationsRO10, RO32, RO33, RO35, RO37; Figure 8). Dextral-obliquereversefaultingandfoldingdominates along E to NE trending segments.Accordingly,we interpretthe northwesternmarginof the Petro•anibasinas a major dextraloblique reverse fault zone (e.g., station RO25, Figure 8; compareto Berza and Draganescu,[1988]). Its northeastern part is probably part of a major triangularpop-up structure
(e.g., stationsRO15, RO16, RO31), markingan interruption of the master fault zone (Figures 3b and 8). Transtensional segmentstrend NW and, for example,delineatethe southern part of the Hateg basin(e.g., stationsRO10, Figure9, which providesa recordof fatfiringand f-acturingin poorly sorted, Paleogeneconglomerateswith red argillaceousmatrix, and RO3, ROll, RO12, RO13, Figure8).
Fault striae data also provide evidence for local block rotation.StationsRO15 andRO16 (Figure8) showtwo groups of predominantlydextralstrike-slipfaults,separated in strikeby 300-40ø. The two groupsmay representthe samestressstate, but may have rotateddifferentiallyduringprogressivedextral wrenching (raw data were not separatedinto subsetsfor calculationin RO15, but wereseparated in RO16: RO16-OLD, RO16-YOU). StationRO34 (Figure8) may representa smallscale block, rotated and tilted along the major dextral strand (represented by stationsRO33 and RO35). The stressratio R (Table 2; Figure8, stressratio diagram) varies and indicatesthat pure strike-slipand pure normal-slip rarely occurred.The calculatedratios imply that both vertical and horizontal compressivestress interacted (local {J•-lJ2 permutation).A comparisonof resultsof the quantitativefault striaeanalysisand of qualitativestraingauges(tensiongashes, boudinage and fold axes) points to a simple stress-strain
Ratschbacher etal.' South Carpathian Orocline Formation
865
Tertiarytectonics:dextralstrike-slipfaulting
Ha•eg basin.,. .... ..:..,..::• ..-"!:iiiiii.,.,....:..•iiiiiiii!!iiiililil ! :"•:i;:i:• "'"' •::r
o
:::.. ..........
n=31 •o. 3
::::::::::::::::::::: ß13'" ' ß
1 5 km
Petro,•ani basin
3 km
Vidra basin
/ Brezoi
.....
-
5 km
compression direction (0' 1) • extension direction (0.3) • extension direction (e 3) Fig. 8. Large-scaleMiocenedextralstrike-slipfaultingalongthenorthernmarginof theMoesianforeland. SeeFigure7 for explanation of symbolsanddiagrams.
analogy.Bothe3 (minimumcontraction) and03, ande] (maximum contraction)and o] axescorrespond (Figures8 and 9). No quantificationof the amountof displacement is possible at this stage of structuralanalysis(further tracinginto the easternand westernSouthCarpathians is required).Due to the
distributednatureof faulting,we speculatethat the totaloffset is not very large, but probably>t0 km. Set 3 fault striaedatacompriseonly a smallportionof the total data and recordmainly sinistralstrike-slipfaultingwith NNE trending01 (01: 205_+25ø; Figurett). Relatedlarge-scale
866
Ratschbacher et al.: SouthCarpathian Orocline Formation
Tertiary basin sediments
RO 17-DEX
R
2'
-
............................................................................................................................................................................................
Permomesozoic RO15-DEX
rocks 1 -
2 -
3-
3-
3-
• certain ss..pole tobedding RO35-DEX O36-DE•••-• • reliableTG..pole totension gashes
'FG
1unreliable BA..boudinage F..fold axes axes Jvery poor (•) ol r•J02 slipsense •:>o3 Fig. 8. (continued) structures have not been identified so far. Mesoscale structures
indicatesinistralreactivationof dextral-oblique reversefaults along the northernmarginof the Petroõanibasin.Spectacular overprinting structuresoccur at station RO31, where dextral
faults,showingmajordisplacements (e.g.thickfaultgauge),are reactivatedor overprintedduringsinistral,generallysmall-scale displacement(fibrous calcite behind fault steps). At other stationsno convincingoverprintingrelationship hasbeenfound. Set 1 faultingaffectedthe (Chattian)basalsediments of the Petro•anibasin;it probablyrepresents a stagein theprolonged
deformationhistoryof the Cema-Jiufault system[Berzaand Drilganescu,1988]. Deformationof Paleogene-early Miocene stratain the Petro•aniandHaleg basinsby set2 fracturingand faulting(Petro•anibasin:overthrusting alongthenorthwestern margin,rightsteppingoffsetof thebasement-basin contact,and sigmoidalbendingof beddingstrike, stationsRO17, RO21, RO23, RO26; Haleg basin:stationROll, Figure8) dates dextralmotionasMioceneor younger.A seriesof poorlydated, Miocene basinsare lined up along the major dextralfault zone (Figure 3b; Haleg, Dealu Babii, Vidra, Titeõti-Brezoibasins)
Ratschbacher etal.:South Carpathian Orocline Formation
867
Crystalline basement rocks
R
-
16
R01-
•RO34-DE./•••
3 -
'%0o
..'2'0
stress orientation
lo•iorg Bosin so•imonIs Permom•ozoic
rocks
90 ø
Crystalline basement rocks
fault strike
stressorientation
Fig. 8. (continued) [Pop, 1963; Marinescuand Popescu,1978; Moisescu,1980; Nichiforescuet al., 1984]. Two-stagesubsidence characterizes both the Petro•aniand the Haleg basins:late Oligocene-early Miocene and late Miocene. Unfortunately,litfie is published about the history of these basins. Age constraintsare not availablefor set 3 faulting. DISCUSSION
Deformation in the central South Carpathiansshowsthe following characteristics: (1) Late Early and Late Cretaceous
tOlYto-NE shearingparallel to the presentstrike of the belt (average054ø) as indicatedby highvaluesof principalstretch, the average059ø trendof the regionalstretching lineation,and noncoaxialflow criteria(firstAlpinedeformation; Figures4 and 5); (2) coaxialflatteningwithin thenorthwest(unlessrefolded) dipping foliation implied by consistentlyoblate finite strain (Figure4); (3) progressivedeformationand exhumationof the thrust system during the Late Cretaceousand Paleogene. Ductile-brittleobliquethrustingand wrenching(secondAlpine deformation)is followedby brittledextralwrenchingwith E-W compression and N-S extension,mostlyconfinedto the Cema-
868
Ratschbacher etal.:South Carpathian Orocline Formation R010
cleavage s:168/81
•
.._,. m. ain fault
tg:246/76•
•
tension gashes
tg:251/71
P-shear
10cm
f: 238/60 normal
R010
f:208/85 faults
Fig. 9. Fieldsketches andorientation of deformation structures in Paleogene conglomerates of the southwestern Halegbasin(northof therailwaytracksnearBucova). SeeFigure7 for explanation of diagrams.
a
a progressive deformation model(stages1-5 below)at thescale of the southernpart of the orogenicbend (Figure 12). 1. Up to the late Early Cretaceous, intraoceanic subduction with probablysouthwestward directedunderthrusting wasactive between Europe-Moesiaon one side and East CarpathiaRhodopia(Gefic fragment)on the other side (stage1, Figure
natural pattern
o'1
_3 R'
14••}-/' 4
ø'3
2
Y
1: poleto beddinginTertiarysediments 2: strikeof majorthrusts 3: contraction from folds
4: strikeof majornormalfaults
b theoretical pattern /
•3 •
'¾'•d•/ In•rmal •R • faults c i: incremental stress axes
Fig. 10. (a) Illustrationof the relationship betweenstructural elementsand strainm•d stressorientationmeasuredalong the
Miocenedextralstrike-slipzone(set2 fault striaedata)along the northernmarginof Moesia.(b) Theoretical orientation of principaland secondary shearfractures, fold axestrend,and strike of normal and thrust faults in a dextral wrench zone with 100 ø strike.
Jiu faultsystem(Figure5 andset1 faultstriaedata,Figure7) [cf. Berza and Dr/iganescu,1988]; (4) large-scale Miocene dextralwrenching alongthenorthern marginof Moesia(Figures 3b, 8, and9); (5) late-stage N-S compression (Figure11). The studyareaconstitutes a partof thesouthern branchof the Alpine-Carpathian orogenicbend.In the following,the presented data(structures, strain,kinematics, stress) areintegratedandobservations andinterpretations areusedtoconstrain
12) [cf. S/lndulescu,1988; Dercourt et al., 1986; Burchfiel, 1980]. 2. After obducfionof oceanic crust (ophiolific rocks of Severinnappe)ontoMoesia(Danubiannappes),thedeformation became intracontinental,and intensedeformationtook place
along the collisionzone. The existenceof a recessin the forelandimpliesthedevelopment of a comerat thewestern tip of Moesia(stage2, Figure12).Progressive deformation caused a superposition of deformation components duringformation of the SouthCarpathian orocline[Marshak,1988].For example, site1 (stage2, Figure12)mayhaveexperienced thefollowing deformation sequence: (1) Thrusting duringfrontalcollision; (2) transpression, with dextral wrench shearing,horizontal shortening, andverticallengthening actingtogether continuously
duringcollision withandlateraltranslation alongMoesia;(3) tangential stretching (orocline formation) andspreading intothe recessnortheastof Moesia. Even in a simple homogeneous deformation model, the deformation matrix involves thrust
simpleshear,wrenchsimpleshear,andpureshearcomponents, havingoperatedduringtranspression, tangentialstretching, spreading, and,possibly, volumeloss.Ourobservational data baseprecludes anyattempt of factorization of finitedeformation into thesecomponents (i.e., a quantitativediscussion of the observed finite strain in terms of superposedincremental
deformation). A significant pureshearcomponent, however, had to be presentto explaintheoblatestrainandthecoaxialflow component (Figures4 and5). Our deformation model stressesthe comer function of the
Moesianplatform.Due to thepinningof the collisionfrontat the westerntip of Moesia,the thrustsystemshows(1) an increase in thedipapproaching thecomer(i.e.,thrusts dipmore shallow where the collisionis frontal than where it is highly
oblique;stage2, Figure12),and(2) a progressive curvature of the cartographic traceof the thrusts.The changein dip and
Ratschbacher et al.: SouthCarpathianOroclineFormation
869
Late Tertiarytectonics
Petrosani basin $.- --m-
I
m
,
'•.....,.•'....
::"'
...
-
3 km
Fig. 11.Late-stage(probablyPliocene-early Pleistocene) NNE-SSWcompression connected with sinistral strike-slipfaultingwhichreactivates formerthrustsin the Hal;egandPetro•anibasinsarea(set 3 faultstriaedata). SeeFigure 7 for explanationof symbolsand diagrams. strike of the thrustzone reflectsthe changefrom the thrustdominated to the wrench-dominatedregime. Stacking and wrenchingis late Early to Late Cretaceousas indicatedby synchronismof deformationwith Alpine metamorphismand coolingof the thrustsystem. 3. Subructionof continentalcrust terminatedalong the (south)westernmargin of Moesia due to buoyancyreasons. Furtherconvergence duringtheearlyTertiarycauseddislocation of the previously welded East Carpathian-Rhodopian and
Moesianfragments alongtheCerna-Jiufaultsystem(seeabove) and the further northeasttranslationof the westernsegment. Due to the shapeof the Moesian promontory,the Cerna-Jiu fault systemacquireda northwesterly convextraceat thepoint where the foreland recess allowed advance of material toward
east (Figure 13a). One may comparethe basin location to regionsof meanstressreductionalongcurvingstrike-slip faults. Schultzand Aydin [1990] demonstrated that mean stressis reducedalong the convex side of a fault bend and increased
along the concaveside,leadingto subsidence alongthe convex and uplift alongthe concaveside.Figure 13b showsthe mean stress distribution derived from a model calculation with a low
frictioncoefficientto induceslip alongthe entirestretchof the fault [afterSchultzand Aydin, 1990]. Another possibilityis that the Petro•anibasin developed during orogenicbending.This hypothesispredictsdeep, Vshaped,outwardswideningbasinsat the insideof fault apices (Figure 13c). Such a basin is inconsistent with the shallow depthand the shape(longfault paralleloutcroppattern)of the Petro•anibasin.Additionally,theoroclinalbendingwouldhave producedoppositeslip alongthe strandslocatedon bothsides of the apex of the bend, which is not observed. We interpret the Petro•ani basin as a northeasterly progradingpull-apartstructureformingsuccessively alongthe curvingtraceof the Cerna-Jiufault system(Figure13d). Set 1 fault striae data portray the state of stressduring the dextral strike-slipand N-S openingof half grabens,reportedfrom the
870
Ratschbacher et al.:SouthCarpathian Orocline Formation
Tertiary basin sediments
7....•
-o.,• R01 ,,,•..• •
fault strike•-•--• ..... 0ø •lr.•.ss.
! •
Permomesozoic RO 15-SI
øø"•
stress ratio
or,entat, on •-'""..x. •,10•1 o
rocks 1 -
_
-
Crystalline basement rocks RO6-SIN
-
-
-
Fig.11 (continued) Petroõanibasin[BerzaandDr•tg/tnescu, 1988].Note thatthere is a spatialrelation of set 1 structuresto the Cema-Jiufault system(Figure7), andit is, at leastin a few stations,indicated that set 1 reprsentsthe pre- to syn-Petro•ani basinformation
stress.Both the Jiul de Est - Sadulineament(Figure3b) [cf. Berzaand Dr,'tg/tnescu, 1988] andthe imbricationzoneeastof thePetro•anibasinmaycomprise continuations of theCema-Jiu fault system. Sedimentationin the Petro•anibasin dates wrenching alongtheCema-Jiufaultsystem asPaleogene-early Neogene. 4. A reorientation of the stress field from a W-E to a NW-
SE compression occurred duringtheMiocenealongtheSouth Carpathians (stage3, Figure 12) due to a tighteningof the oroclineand/ora rearrangement of microplategeometry(e.g., subduction roll-backin theEastCarpathians) [Doglioni,1992]. It led to the development of the large-scaledextralwrench zone. We tentativelysuggestthat the fault zone was active coevallywith the formationof the Pannonianbasinsystem. Note, however,thatthefault zonedoesnot compensate for the differential displacement between the South and East Carpathians imposedby extensionin the Transylvanian basin. The latteris, unliketherestof thePannonian basins,principally a thermal sag basin and showslittle lithosphereextension [RoydenandD6v6nyi,1988].We propose thatthrusting in the southernEastCarpathians (Figure12, stage3 upperfight) was
principally driven by extensionin the central and eastern Pannonian basinsandtheblockconsisting of theTransylvanian basinandtheApusenimountains wastranslated relativelyrigid southeastward. Dextral-obliqueconvergence acrossthe South Carpathians seemedtherebyto be decoupled intoa component of convergencenormal and a shearcomponentalong to the plateboundaryas commonlyobservedin accretionary wedges whereplateconvergence is oblique[e.g.,McCaffrey,1992]. In the case of the South Carpathiansthe normal componentis takenup by the slightlytmnspressional thrustbelt of the Getic depressionand the strike-slip componentby the studied transcurrent fault zone (Figure 12, stage3 lower right) and a similarzone, which we suspectto the northof the studyarea. Cretaceous thrustingandwrenching, Paleogene wrenching, and Miocene
transcurrent
motion
are all associated with
clockwiserotationof materialaroundverticalaxesaspredicted for true oroclines[e.g., Eldredgeet al., 1985;Marshak,1988]. The rotationsdemonstrated by paleomagnetic results(Figure2a) [P,'ttra•cuet al., 1990] are larger (circa 80ø) north of the Moesian platform than at its western tip (circa 45ø) in accordance with the orocline model.
Our recognition of two stages of first-order motion(late EarlytoLateCretaceous ductile-brittle thrusting andwrenching andMiocene wrenching) is corroborated byindependent plate motionstudies. Figure2c,derived fromDercourt et al. [1986],
Ratschbacher et al.: SouthCarpathian OreclineFormation
stage 1
871
stage 2
Early Cretaceous
late Earlyto Late Cretaceous
a)
'::ß •
ß
:::::::::::::::::::::::
"i _•i:i:
•
_ry• -•' •
1:: .••
'•[
.•!:!:!:i:i:!:i:i:
:::::::::::::::::::::::::::
•
::::::::::::::::::::::::::::
,.......................... •,...:.:.:.:.:.:.:.:.:.:.:.:.:.
.••
•:.:.:.:.:.:.:.:.:.:.:.:. .•.:.:.:.:.:.:.:.:.:.:.:.:.:
::::::::::::::::::::::::::::::::::::
, ßßß, ß.*....:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:
ø'i";'i':'i':'•:'•"g"i"i":•':i':•':':':':':':':':':':':':':
...........
"%; 'Ooa.. '•
o
-•'•
South
• •--• oceanicsubduction
Carpathians
orecline formation
•
intra-continentalthrusting-wrenching Apuseni
mountains
stage 3 Miocene
Transylvanian
,.:::::::::::::::::
"•:•:•:•:•:•:•:•:•
-.::::::::::::::::: •:::::::::::::::::
basin
Vienna
...........................................
o-1
ß=====================================================================
basinisopaches
Hateg
••
50 km
GeticdepressionPloiesti
Fig.12.Progressive deformation model at thescale of thesouthern partof theCarpathian orecline. Palcomagnetic datafromFgttra,scu et al. [1990]anddisplacement pathtrajectory modelfororoclines modified fromMarshak [1988].Stage1:subduction. Stage 2: collision-transpression-dextral wrenching. Numbers indicate depth (inkilometers) of a mainthrust plane. Tectonic history of site1 isdiscussed in
text.Stage 3:subduction roll-back intheEastCarpathians andsoutheastward translation oftheApuseni mountains - Transylvanian basin blockdriven byextension inthecentral andeastern Pannonian basins. Oblique convergence across theSouth Carpathians isdecoupled intotranspressional thrusting andfolding along theGetic depression andwrench shear along thenorthern margin ofMoesia. Notethattheorogenic arcdeveloped during stage 1 to3 isasymmetric duetodischronous ending ofconvergence around it.See text for discussion.
showsmotion vectorsfor localitieson the African, Apulian
lithospheric plates(Africa- Europe),butmicroplate disinte-
("Eastern Alps"),and East Carpathian-Rhodopian ("South Carpathian") plates: convergence islargest during Middleand
grationduringcollision.
LateCretaceous andMiocenein theSouthCarpathians. Clearly,
5. Near the end of the Miocene, all oceanic crust was
subducted, andcollisionwascompleted alongthe Carpathian
convergence between AfricaandEurope motionalongdifferentsegments of the Alpine-Carpathian--loop.Continuing to the Mediterranean [e.g., Dinaricplateboundary doesnotreflectmotion of large-scale (Figure2c) was transferred
872
Ratschbacher et al.: SouthCarpathian Orecline Formation
"::::: curved fault trace due to corner
......
SouthandEastCarpathians to quantifytheamountandtiming of theinvolveddisplacements, andnumericalandexperimental
ßß t•/_t
basin formation
investigationsto understandthe mechanicsof the Moesian comerin the Alpine-Carpathian evolution.
'.5:::
•' • •
,..':i•:?•"[T• oroclinal bending . ==============================
REDUCED
Petro•ani basin •_..*•.-. - '"
model •ii!:i•etro•ani basin ß':':':':':':':':-:':':':':':':':':':':':':':':':':':':':':':':':':':':': v3
.. . .:4
.....•:::..
':,'
APPENDIX:
FAULT ANALYSIS
AND CALCULATION
OF
STRESS TENSOR
Faultsizeandattitude,striaeorientation, senseof slip,and polyphase slip and its chronologywere measuredand determinedin the field. Fault size is classifiedqualitatively based on an estimationof the displacementand the lateral extent of the fault. The aim was to discriminate first-order
..•
mean stress distribution around curved fault
faults and to enable a comparisonof faults measuredin outcropswith those inferred from maps. Fault offset and superposition of fibersgrownbehindfault steps,aschronology indicators,enable us to discriminatebetweensuperposed paleostress states.Riedel shears,stepson the fault surface,and fibers grown behind steps were used for sense of slip determination.
Fig. 13. (a) Model for the Cema-Jiufault systemas a curved strike-slipfault dueto theMoesiancomer.The bendbeginsat
We usedthreemethodsto deriveprincipalstress orientations and ratios from fault-striae data. (1) The "direct inversion
the point where the forelandrecessallowedadvanceof material toward east. (b) Mean stressdistributionaround a curved fault
method"[Angelier,1979]. (2) The "gridsearchmethod"[Hard-
trace[fromSchultzandAydin,1990].Contours of 10%change in mean stresslabeledD (down,potentialsubsidence) and U (uplift). Model calculationwith g = 0.4 (frictioncoefficien0 alongthefault.(c) Sketchshowing basins produced by oroclinal bending.Note that this mechanismrequiresoppositedirected slip locatedon both sidesof the apexof thebend,whichis not observedin the SouthCarpathians. (d) Developmentof the
Coulombyield criterion(x > C + [tOn)testare C = 0, because we assumepreexistingweaknesses (faults,fractures,bedding planes),and g = 0.2 to 0.4 (dependingon the rock type analyzedand the presenceof fault gouge),which is closeto naturalobservation [Zobacket al., 1987]. (3) The "pressuretension(P-T) axesmethod"[e.g., Allmendingeret al., 1989]. Conditionedleast squaresfitting is used to derive orthogonalizedloci of o• to 03 [Caputoand Caputo,1988]. The quality and the quantityof field data determined the
Petro•anibasin as a northeastward propagating pull-apart structurealongthe curvingtraceof theCema-Jiufault system.
Burchfiel,1980].We relatelate-stage N-S compression (set3 fault-striae data,Figure11)toPliocene-early Pleistocene folding alongthe northernmarginof Moesia. We concludethatthecomereffectof theMoesianplatform duringAlpine convergence explainsthe main geometricand kinematicfeaturesof the centralSouthCarpathians. It induced an associationof deformationcomponents, e.g., plate motion driven thrust and wrench shear, pure shear stretchdue to oroclinebending,andpureshearflatteningduringtranspression and gravity drivenradial flow of materialinto the recessnorth of Moesia. The study also demonstrates a successive stress reorientationduringprogressive deformationaroundthe comer. Our preliminaryresultsshouldprovokemorefield work in the
castle and Hills, 1990]. Parameters chosen for the Mohr-
selection of the method used for calculation. The P-T axes method was used with scarce data and where insufficient time
wasavailablein the field for carefulanalysisof faultandstriae characteristics.A comparisonof methods is given by Ratschbacheret al. [1993]. The data base for our calulationsis available from the first author.
Acknowledgments. Field work was funded by the Universities of Tdbingen (through the German Foreign ExchangeService)andCluj. IstvanGy6rfi sharedhisfield data. Frank Horv,'ith drew the attention of the German authors to the
Alpine-Carpathian connection and helpedlogistically.L•s16 Csontosand Carlo Doglioni providedexcellentreviews,and WolfgangFrischfundedthe radiometricwork.
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South Carpathains,Annu. Inst. Geol. Geofiz. Bucharest, 60, 31-37, 1983.
Amer.ShortCourse,68 pp.,Geol.Soc.America, Balla, Z., The Carpathianloopandthe Pannonian Berza, T., A. Seghedi,and I. Stlnoiu, Unitl[.ile
Boulder,1989 Angelier,J., Determinationof the meanprincipal
basin:A kinematic analysis, Geophys. Trans.,30, 313-353,1985.
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Bucharest, 72-73/5, 5-22, 1988, directions of stresses fora givenfaultpopulation,Berza,T., andA. Ddg•nescu, TheCerna-Jiu fault Tectonophysics, 56,T17-T26,1979. system(SouthCarpatians, Romania), a major Burchfiel,B. C., Geologyof Romania,Spec.Pap. Angelier,J.,Tectonic analysis of faultslipdatasets, Tertiary transcurrent lineament,Dari Seama Geol. Soc.Am. 158, 1-82, 1976. J. Geophys. Res.,89, 5835-5848, 1984. Sedintelor Inst.Geol.Geofiz. Bucharest, 72-73/5, Burchfiel,B. C., EasternEuropean alpinesystemand
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43-57, 1988.
the Carpathianoroclineas an exampleof eollision tectonics,Tectonophysics, 63, 31-61, 1980. structurein the Danubianwindowof the central Caputo,M., andR. Caputo,Structural analysis: New
Kr•iutner, andG. Uduba•a, Precambrian Metamor- Berza,T., H.-G. Kr'fiutner, andR. Dimitrescu, Nappe phics in the South Carpathians, Guide to
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