GEOLOGICA CARPATHICA, 49, 5, BRATISLAVA, OCTOBER 1998
POST-OROGENIC UPLIFT-INDUCED EXTENSION:
A KINEMATIC MODEL FOR THE PLIOCENE TO RECENT
TECTONIC EVOLUTION OF THE EASTERN CARPATHIANS
, WOLFGANG FRISCH and HANS-GERT LINZER
Institut für Geologie, Universität Tübingen, Sigwartstr. 10, D-72076 Tübingen, Germany
(Manuscript received January 12, 1998; accepted in revised form September 1, 1998)
Abstract: We propose a new tectonic model for the Pliocene to Recent tectonic evolution of the Eastern Carpathians,
especially for the formation of the Braºov-Gheorghieni basin system in the hinterland and for the shortening in the
foreland during the Valachian Phase of deformation. Kinematic analysis of fault-slip data indicates the formation of
the Braºov-Gheorghieni basins due to NW-SE oriented extension, but with joints displaying varying orientations
suggesting regional uplift as the source of extension. The trend of regional folds in the foreland indicates NW-SE
oriented shortening. The sedimentation rate of coarse material in the foreland basin reflects a high post-Miocene rate
of uplift, very accelerated during PlioceneQuaternary time. The seismological data show active offset along two
strike-slip faults (the Trotuº and Intramoesian faults), which border both the region of extension in the hinterland and
the area of shortening in the foreland. A third strike-slip fault (the Sinaia Fault) is constrained south of the Braºov-
Gheorghieni basins by kinematic and seismological data. All these observations have been combined in the following
new tectonic model: succeeding the continental collision in Miocene, a very high rate of uplift occurred in the Eastern
Carpathians during PlioceneQuaternary time. The uplift induced gravitational mass transfer from the uplifted area,
which had a high potential energy, towards the surrounding areas with low potential energy. The mass transfer took
place through the southeastward motion of a crustal block between the Trotuº sinistral and the Sinaia dextral strike-
slip faults above an older, reactivated detachment horizon of the Eastern Carpathians fold-and-thrust belt. The motion
of this crustal block resulted in extension in the hinterland and the formation of the Braºov-Gheorghieni basin system;
the extension was accommodated by shortening in the foreland.
Key words: Pliocene, Recent, Eastern Carpathians, Braºov-Gheorghieni basins, post-orogenic uplift, extension,
This paper regards the last stage of tectonic evolution of the
Eastern Carpathians from Pliocene to Recent, addressing
mainly the problem of the formation of the Braºov-
Gheorghieni basin system (Fig. 1a). This system consists of a
series of intramontaneous basins with up to 1000 m
subsidence (Bandrabur & Codarcea 1974), superimposed on
older Cretaceous-Tertiary structures. The basins were formed
in the Eastern Carpathians hinterland in a post-orogenic
stage, after the oceanic crust was consumed and continental
collision occurred in Miocene time (Csontos 1995). Another
important characteristic feature of this last stage of tectonic
evolution is the folding of Plio-Pleistocene formations in the
Eastern Carpathians foreland during the Valachian Phase of
deformation, described and characterized by Dumitrescu &
Sãndulescu (1968) and Sãndulescu (1984). Also, in Pliocene
Quaternary time up to 10 km of sediment accumulation is re-
corded in the Eastern Carpathians foreland (Paraschiv 1979),
while in the hinterland alkaline basaltic and calc-alkaline
andesitic volcanism occurred in the Perºani and Harghita Mts.
(Peltz et al. 1971; Pécskay et al. 1995). The Vrancea Zone
must also be mentioned here as the place of strong seismicity
with both crustal and intermediate-depth earthquakes. The ac-
tive tectonics is reflected mainly by vertical movements and
All the mentioned Pliocene-Quaternary features are locat-
ed in the southern Eastern Carpathians, between the Trotuº
and the Intramoesian strike-slip faults (Fig. 1a). The aim of
this paper is to interpret the formation of the hinterland
Braºov-Gheorghieni basin system in terms of its kinematics
and relation with the folded foreland. Our study is mainly
based on kinematic analysis of fault-slip and joint data, as
well as on reinterpretation of published profiles and seismo-
logical data. The fault-slip and joint data were collected from
Pliocene-Quaternary sedimentary and volcanic rocks from
the Braºov-Gheorghieni basins and Perºani Mountains, but
also from older rocks. In this latter case we used only the
youngest data sets which were separated on overprinting cri-
teria observed in outcrops.
The Eastern Carpathians are part of the Carpathian chain,
which extends over more than 1700 km between the Eastern
*Present address: Rock Fracture Project, Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115; email@example.com
**Present address: Rohöl - Aufsuchungs A.G., Schwarzenbergplatz 16, A-1015 Wien, Austria
316 GÎRBACEA, FRISCH and LINZER
Alps and the Balkans. The present tectonic setting of the Car-
pathians is the result of convergence and continental collision
of two continental fragments (the Tisia-Dacia and Alcapa mi-
crocontinents, Fig. 1b) with the European Plate, following re-
treating subduction (Royden 1993) and closure of a basin
floored by oceanic or thinned continental crust (Csontos
1995; Linzer 1996). The first stage of continental collision
between the Tisia-Dacia and the European plates is indicated
in the Eastern Carpathians by the change from flysch-type to
molasse-type sedimentation in Early Miocene (Burdigalian)
time (Csontos et al. 1992).
The Trotuº Fault (Fig. 1a) is an important structure in the
Eastern Carpathians, since the orogen displays different char-
acteristics north and south of it. In the northern Eastern Car-
pathians the crust attains up to 56 km thickness (Starostenko
& Kharitonov 1996). The isostatic response exhumed large
metamorphic complexes (the Median Dacides after Sãndules-
cu 1984), with the present surface reaching up to 2500 m alti-
Fig. 1. a) Location of the study area in the southern Eastern Carpathians and tectonic map showing the Pliocene-Quaternary features be-
tween the Trotuº and the Intramoesian strike-slip faults (after Bandrabur et al. 1971; Sãndulescu et al. 1978; Sãndulescu 1984). The posi-
tion of the dextral Sinaia Fault is inferred from fault-slip data from the southern Braºov Basin (site 107-95 in Fig. 2) and seismological
data (see Table 2). b) Tectonic blocks (Alcapa and Tisia-Dacia) whose convergence and continental collision with the European and Moe-
sian plates resulted in the formation of the Carpathian arc during Tertiary times (after Csontos 1995).
POST-OROGENIC UPLIFT-INDUCED EXTENSION: A KINEMATIC MODEL 317
tude. Apatite cooling ages indicate an exhumation pulse around
10 Ma (Sanders & Andriessen 1996). Post-collisional shorten-
ing at the frontal wedge of the northern Eastern Carpathians oc-
curred until 11 Ma (i.e. Sarmatian) after Roure et al. (1993), in-
ferred from the age of the youngest sediments deposited on the
European Plate which were overthrust by the orogenic front.
The foreland basin contains only Sarmatian formations, in
which no deformation has been recorded (Sãndulescu et al. 1981).
South of the Trotuº Fault the Pliocene-Quaternary features
which are the subject of this work, are exposed: the Braºov-
Gheorghieni basin system and the folded foreland formations
(Fig. 1a). The foreland displays a high rate of subsidence, with
up to 10,000 m of molasse-type sedimentary rocks deposited
during SarmatianQuaternary time (Sãndulescu et al. 1995). In
the Vrancea Zone focal mechanism solutions of intermediate-
depth earthquakes indicate a vertical dense slab in the lithos-
phere (Fuchs et al. 1979; Oncescu 1984). The crustal thickness
in the southern Eastern Carpathians does not exceed 45 km
(Rãdulescu et al. 1976), with maximum surface elevation
around 1800 m.
Fig. 2. Directions of extension recorded in Pliocene-Quaternary rocks or separated as the youngest recorded deformation in pre-Pliocene
rocks from the Braºov Basin. The kinematic analysis is based on fault-slip and joint data (see Table 1 and Fig. 13 for results and graphical
presentation of data sets). The rose diagram shows the orientation of all measured joint planes, indicating that most of them formed due to
NW-SE oriented extension.
318 GÎRBACEA, FRISCH and LINZER
The present rate of uplift, measured by geodetic methods,
has a maximum value of 1.52 mm/a in the Eastern Car-
pathians, south of the Trotuº Fault (Cornea et al. 1979). Seis-
mologic data provided by M. C. Oncescu from Karlsruhe
Geophysical Institute (pers. comm.) indicate the present ac-
tivity of the Intramoesian and Trotuº sinistral strike-slip
faults. A third, dextral strike-slip fault (called here the Sinaia
Fault) is constrained south of the Braºov Basin by kinematic
data (site 107-95 on Fig. 2, lower corner) and earthquake fo-
cal mechanism solutions (Fig. 1a).
The Braºov-Gheorgheni basin system
Starting in Pliocene a series of basins (the Braºov, Ciuc and
Gheorgheni basins) were superimposed on Cretaceous-Mi-
ocene structures in the internal part of the Eastern Carpathians
(see Fig. 1a). We performed a kinematic analysis which indi-
cates a general NW-SE direction of extension, based on meth-
ods and data presented in Appendix 1 and Figure 13, and using
the computer programs described by Sperner et al. (1993) and
The Braºov Basin
The Braºov Basin shows a flat topography around 400 m
elevation, surrounded by mountains of up to 1800 m. The ba-
sin sedimentary fill is up to 600 m thick and consists of: (A)
a fluvial-lacustrine association (PlioceneMiddle Pleis-
tocene), divided into a dominant, clastic facies (with gravel,
cross-stratified sand, clay, silt, and lignite deposits), and a
subordinate carbonatic-siliceous facies (with limestone,
marl, diatomite); (B) an alluvial association (Middle Pleis-
toceneHolocene) with coarse, migrating channel and alluvi-
al-fan deposits (Marinescu et al. 1981). At different strati-
graphic levels the lacustrine sediments are interbedded with
andesitic tuffs and lava flows, whose source is in the south-
ern part of the Eastern Carpathian Neogene volcanic chain
(Peltz et al. 1971). The faunal assemblages (Liteanu et al.
1962; Samson & Rãdulescu 1963; Rãdulescu et al. 1965)
and magnetostratigraphy (Ghenea et al. 1979) prove an age
of 3.63.8 Ma for the oldest sediments in the Braºov Basin.
The direction of maximum (
) and minimum (
lated paleostresses are considered parallel to the main direc-
tion of shortening and extension, respectively. Data collected
from Pliocene-Quaternary rocks reveal a NW-SE direction of
extension, with strike-slip motion along the NW-SE oriented
margins of the basin (Fig. 2; see Table 1 for the results of ki-
nematic analysis). The fault-slip data sets from pre-Pliocene
rocks are heterogeneous, indicating different tectonic events.
However, the youngest data sub-sets, separated on overprint-
ing criteria of faults of different relative age, show also a NW-
SE direction of extension. This direction is therefore assumed
to indicate the same deformation event as recorded in the
Pliocene-Quaternary rocks, an assumption supported by pre-
vious paleostress analyses which report no extension in the
southern Eastern Carpathians before Pliocene time (Linzer
1996; Zweigel 1995). The joint data also show a general NW-
Fig. 3. Profile in the Braºov Basin (see location in Fig. 2) based on
well data from Geolex Harghita Exploration Company (a), and
used to assume a listric geometry of an asymmetric basin formed
above a horizontal detachment fault (b).
Fig. 4. a) Area-balanced kinematic model for asymmetric basin for-
mation above a horizontal detachment fault (after Groshong 1989). b)
This model allows calculation of the amount of extension and depth
of the detachment fault, based on simple geometric data: a near-
surface plunge of the main detachment fault; b dip of the antithetic
zone; h basin depth; L basin width; d depth of the detach-
ment fault, d = h(Le)/e; e amount of extension, e = 2h/tan
the Braºov Basin d = 8.7 km and e = 14 %.
POST-OROGENIC UPLIFT-INDUCED EXTENSION: A KINEMATIC MODEL 319
Fig. 5. Geological map of the Ciuc and Gheorghieni Basins (after Alexandrescu et al. 1968; Sãndulescu et al. 1968) and directions of ex-
tension recorded in Pliocene-Quaternary rocks or separated as the youngest recorded deformation in pre-Pliocene rocks (see Table 1 for
results of the kinematic analysis). The fault planes are graphically represented in equal area, lower hemisphere stereonets as great circles,
with arrows showing the direction of slip of the hangingwall. The joint planes are plotted in equal area, lower hemisphere stereonets as
poles. The calculated stress tensor from fault slip data is defined as the orientation and magnitude of principal stresses
the main direction of shortening is parallel with
and the main direction of extension is parallel with
SE direction of extension in places, but some joint sets have
varying orientation (see Fig. 12) which indicates a stress re-
gime with radial extension. The relative age relationship be-
tween these structures suggests that the joint sets with
varying orientation are older than the normal faults.
Well data of a Romanian exploration company (Geolex
Harghita) were used to infer the geometry of the Braºov Basin.
The profile in Figure 3 shows an asymmetric basin shape and
tilted blocks, characteristic for listric fault geometry. Therefore,
we used a model of asymmetric basin formation along listric
faults and above a horizontal detachment fault (Fig. 4a; Gros-
hong 1989) to calculate the amount of extension and the depth
of the detachment fault in the Braºov Basin. Figure 4b shows
the geometric elements of this model. The basin asymmetry re-
sults from the difference between the dip a of the main listric
fault on one basin margin and the dip b of the so-called anti-
320 GÎRBACEA, FRISCH and LINZER
Table 1: The results of the kinematic analysis of data collected in the Braºov
Basin (fault-slip and joint data). Ages: Pz Paleozoic; J Jurassic; Cr
Cretaceous; Mc Miocene; Pl Pliocene; P Pleistocene; H Holocene;
E Early; L Late.
Data sets consisting exclusively of joints are those
is given, as the direction of maximum density of joint poles.
is the ratio between the stress magnitudes [R = (
)]. R defines the
regime of deformation, as: plain strain, with R = 0.5 (deformation occurs
only parallel to
= 0); axial extension (constriction),
with R=1 (shortening occurs parallel to both
); axial shortening
(flattening), with R=0 (extension occurs parallel to both
cates the average value of the differences between the measured striae on fault
planes and the orientation of the calculated maximum compressive stress (
Lat. N/Long E
45°46'38"/25°40'30" 054/12 4 074/11 325/59 170/29 0.546 10°
45°48'00"/25°40'27" 220/12 61
45°52'27"/25°36'32" 124/07 11 124/76 247/08 338/02 0.307 16°
45°51'03"/25°37'42" 128/10 36
45°52'24"/25°54'31" 284/37 49
3 347/76 252/1 162/14 0.499 1°
45°57'39"/24°48'56" 125/46 46
45°52'30"/25°46'38" 119/05 8 100/86 234/3
45°52'30"/25°46'38" 119/05 32
45°55'22"/25°59'00" 021/16 35
45°58'46"/26°00'52" 274/70 9 307/84 59/2
45°58'46"/26°00'52" 274/70 22
46°00'04"/26°01'10" 199/24 33
46°01'52"/26°02'02" 215/61 24
3 163/15 3/74
46°03'01"/26°01'48" 234/55 28
46°03'01"/26°07'54" 291/24 4 144/77 48/2
317/18 0.504 2°
46°02'56"/26°07'54" 291/24 28
46°04'59"/26°09'55" 283/19 18
45°53'32"/25°36'02" 293/60 23
46°04'42"/25°36'49" 102/15 25
46°06'50"/25°34'31" 128/16 16 226/89 41/1
45°54'18"/25°28'32" 140/65 9 308/89 47/0
45°54'18"/25°28'32" 140/65 10 129/22 284/63 34/10
45°51'22"/25°29'00" 230/17 12 150/86 47/1
45°51'22"/25°29'00" 230/17 12 295/2 29/86
45°50'02"/25°27'08" 135/19 11 253/85 51/5
45°50'02"/25°27'08" 135/19 8 300/6 44/67 208/20 0.261 13°
45°33'21"/25°18'10" 160/47 12 206/65 19/48
45°33'21"/25°18'10" 160/47 9 156/14 31/66 251/19 0.556 9°
9 127/79 238/4 329/11 0.377 10°
13 19/78 243/98 151/8
23 105/28 313/59 202/12 0.358 21°
thetic zone on the opposite basin margin. At the first
increments of strain the conjugate fault (BC) to the
main listric fault (ADCG) is formed, and extension
moves the segment BC to a new position JG. The fold-
ing of the footwall initiates with BC and JG as axial sur-
faces. This model is area-balanced when the area of
ABC equals the area of DIJEGC. From this condition
one obtains the amount of simple shear extension (and
total displacement on the horizontal detachment fault)
as e = 2h/tan
. The depth of the detachment fault is
d = h(Le)/e. For the Braºov Basin a calculation along
the line AA (shown in Fig. 2) with L = 16.5 km,
h = 1222 m, and a assumed to be 50
(from field obser-
vation) yields a minimum value of extension e =
2 km and depth of the detachment fault d = 8.7 km. A
value of 14 % extension is calculated from the
stretched length L of 16.5 km after 2 km extension.
For the whole width of the Braºov Basin the amount of
extension is probably not larger than 5 km.
The Ciuc and Gheorgheni basins
Both basins show the same type of sedimentary
fill: a fluvial-lacustrine facies with gravel sand, clay
and coal, with an important amount of volcano-sedi-
mentary deposits; and an alluvial facies, with river
terraces and recent alluvium. The sedimentary pile
reaches up to 800 m thickness in the Ciuc Basin and
1000 m in the Gheorghieni Basin, with an age of
PlioceneEarly Pleistocene for the fluvial-lacustrine
facies and Middle PleistoceneRecent for the alluvial
facies (Bandrabur & Codarcea 1974). K/Ar dating of
the youngest lava flow situated below the first sedi-
ments deposited in the Ciuc Basin yielded an age of
4.0±0.4 Ma (Pécskay et al. 1995).
Similar to the Braºov Basin, the kinematic analysis
indicates NW-SE extension, with strike-slip motion
along the NW-SE oriented basin margins (Fig. 5).
North of the Trotuº Fault the subsidence in the East-
ern Carpathians foreland occurred only in Sarmatian
time. South of this fault the subsidence started in Early
Sarmatian (Sãndulescu et al. 1981) and continued until
Quaternary time. During this period the foreland for-
mations record a change from silty, sandy and gravelly
to gravel-dominated sedimentation (Marinescu et al.
1981; Sãndulescu et al. 1981). The deposition rate in-
creased from up to 5000 m thickness in Early Sarma-
tianPliocene time (with a mean value of 0.42 mm/a
between 13.61.9 Ma), to 3000 m in the Pleistocene
(1.6 mm/a, after Liteanu et al. 1972). The age and
thickness of sediments deposited in the Eastern Car-
pathians foreland were used by Artyushkov et al.
(1996) to infer an uplift curve (Fig. 6) with a very rap-
id rate during PlioceneQuaternary time. The young
POST-OROGENIC UPLIFT-INDUCED EXTENSION: A KINEMATIC MODEL 321
uplift of the southern Eastern Carpathians is indicated
also by fission-track data which yielded 2 Ma for the
youngest cooling ages (Sanders et al. 1997).
The foreland area situated between the Trotuº and
the Intramoesian faults was folded in PliocenePleis-
tocene time, during the Valachian Phase (Sãndules-
cu 1984). The absence of good exposure in this area
makes a paleostress analysis, based on fault-slip data,
impossible; but published geological maps (Motaº et
al. 1967; Dumitrescu et al. 1968a; Dumitrescu et al.
1968b) show NNE-SSW (in the N) to ENE-WSW (in
the S) trending regional fold axes (Fig. 1a) which indi-
cate a general NW-SE oriented shortening.
The Perºani volcanics
Alkali basaltic volcanism was active in the Perºani
Mts., NW of the Braºov Basin (Fig. 1a), during
PlioceneQuaternary time. K/Ar analyses yielded ages
of 2.250.35 Ma for the volcanic activity (Casta 1980;
Mihãilã & Kreutzer 1981; Downes et al. 1995). The ki-
nematic analysis of fault-slip data collected from the
Perºani basalts shows a general NW-SE direction of ex-
tension (Fig. 7), expressed in outcrop-scale normal
faults, domino and horst-and-graben structures (Fig. 8).
The ubiquitous distribution of these extensional struc-
tures within the volcanic chain and their constant orien-
tation excludes, in our opinion, the possibility that they
were formed due to non-tectonic processes, for in-
stance caldera collapse or updoming due to shallow in-
trusions (as argued by Seghedi & Szakács 1994). The
calculated direction of extension and the NE-SW orient-
ed alignment of the eruption centres indicate the em-
placement of the basalts along a NE-SW-trending crust-
The kinematic model
Our kinematic data prove that the extension initiated
in the Braºov Basin through jointing, because the
joints are older than the normal faults. According to
general accepted genetical interpretations for joints
Continuation of Table 1
Lat. N/Long E
8 138/14 337/75 229/5
°15'53"/25°58'39" 144/43 10 106/87 208/1 298/3 0.443 14°
°05'42"/25°04'22" 111/16 20
12 340/1 232/86
7 327/8 210/74 59/14
5 323/3 203/84
8 136/13 331/76 227/3
12 336/3 239/69 67/21
9 90/15 242/73 358/8
17-96 LMc- 46
9 111/20 262/67 17/10
25 245/86 48/4
6 359/85 220/4
12 123/85 232/2
11 188/40 347/48 88/11
Y ear, Mo, Dy
MB, MS, ML
s, d, r
s, d, r
1960, 01, 04
1967, 02, 27
1969, 04, 18
1975, 02, 08
1975, 03, 07
Table 2: Seismological data of earthquakes occurred along the Trotuº, Sinaia, and Intramoesian strike-slip faults. The data were provided by
M.C. Oncescu (Karlsruhe University), and calculated after the P wave first motion signs. Each focal mechanism solution is accompanied by
an information set, consisting of: earthquake number, used to identify the plot on the map in Figure 1a; date when the earthquake
occurred, (year, month, day); epicenter co-ordinates (in decimal values); focal depth; magnitude (MB body wave magnitude;
MS surface wave magnitude; ML local magnitude, based on duration of seismic oscillations); focal plane data: strike (s), dip (d),
and rake (r) of the nodal planes, and orientation of the P, B, and T axes (a azimuth, p plunge). The P and T axes are assumed parallel to
the directions of the maximum shortening and extension, respectively.
322 GÎRBACEA, FRISCH and LINZER
(see Ramsay & Huber 1987, and references therein), we
suggest that regional uplift was the driving mechanism for
the formation of the vertical extensional fractures in the
Braºov Basin. The potential energy stored in rocks in a re-
gion subjected to uplift increases with increasing elevation
and, later, a deviatoric horizontal stress will result from the
potential energy contrast between the uplifted area and the
surroundings (Houseman & England 1986). When the up-
lift-induced horizontal deviatoric stress is large enough to
exceed rock strength, extension begins in terms of gravity
spreading (Neugebauer 1978), due to gravitational mass
transfer from the area with higher potential energy towards
the area with lower potential energy. For the Braºov Basin
we suggest that the magnitude of extensional strain was ini-
Fig. 6. Uplift curve in the Eastern Carpathians (after Artyushkov
et al. 1996). The presence of 3000 m thick Pleistocene formations
in the Eastern Carpathians foreland basin (Liteanu et al. 1972)
suggests a higher pre-Quaternary elevation of the Eastern
Carpathians than the present elevation.
Fig. 7. Geological map of the Perºani Mts. (after Patrulius et al. 1967; Sãndulescu et al. 1968; Seghedi & Szakács 1994) and directions of
extension recorded in Pliocene-Quaternary alkaline basalts. For further explanation, see Figure 5.
POST-OROGENIC UPLIFT-INDUCED EXTENSION: A KINEMATIC MODEL 323
tially small and the extension had rather a radial orientation,
since joints with varying orientation formed; in a later stage
the normal faults developed, accomodating increasing exten-
sional strain due to an increasing topographic gradient. The
dominance of NW-SE oriented extension may be directly re-
lated to the presence of available space in the corner between
the European and the Moesian plates (see Fig. 1a). This avail-
able space is considered a free boundary which allowed mass
transfer from the uplifted area. Thus, the uplift-related exten-
sion from the hinterland was accommodated by shortening in
A kinematic model is presented here (Fig. 9) taking into ac-
count the observed strike-slip faults on the basin borders. In
our model the gravitational, uplift-induced southeastward
motion of a crustal block between the sinistral Trotuº and the
dextral Sinaia strike-slip faults resulted in extension in the
hinterland accommodated by shortening in the foreland. The
calculated amount of extension in the Braºov Basin is e = 14
% (probably not larger than 5 km), above a detachment fault
at ca. 8.7 km minimum depth (our calculation). This
detachment may have been connected with older detachment
horizons at 1015 km depth, shown by ªtefãnescu (1985) in
the Eastern Carpathians flysch nappes (Fig. 10). These
detachment horizons were reactivated in Pliocene time and
transferred the deformation from the hinterland to the foreland.
The present subsidence in the Braºov Basin (up to 4 mm/a af-
ter Cornea et al. 1979) and seismicity along the Trotuº and Si-
naia faults, together with the shallow earthquakes indicating
NW-SE horizontal compression within the fold-and-thrust
belt, fit in this model and can be explained by it.
The NW-SE to N-S oriented Pliocene-Quaternary shorthen-
ing from the outer southern Eastern Carpathians has been re-
lated to a southward displacement of the orogen relative to its
foreland (Hippolyte & Sãndulescu 1996). However this short-
ening may have partly accomodated the extension from the
Braºov-Gheorghieni basins, as we propose in our model.
Rapid uplift in the Eastern Carpathians starting in Pliocene
time resulted in gravity-induced southeastward motion of a
crustal block above reactivated detachment horizons from
the fold-and-thrust belt, in an area between the Trotuº and
the Sinaia strike-slip faults. The motion of this crustal block
resulted in NW-SE oriented extension and the formation of
the Braºov-Gheorghieni basins in the hinterland, accommo-
dated by shortening and folding of the foreland formations in
the foreland, in the available space inside the corner between
the European and Moesian plates. The amount of Pliocene-
Quaternary hinterland extension (and, consequently, of fore-
land shortening) is around 5 km. The zone of folded
Pliocene-Quaternary foreland formations between the Sinaia
and the Intramoesian faults (see Fig. 1a) still can not be ex-
Tectonic structures from the Perºani Mts. indicating NW-SE oriented extension in the Pliocene-Quaternary basaltic/volcano-sedi-
mentary rocks (in quarries): a) Hegheº (outcrop 21-96); b) Mateiaº (outcrop 24-96); c, d) La Brazi (outcrop 22-96).
324 GÎRBACEA, FRISCH and LINZER
Fig. 9. a) Kinematic model for the Pliocene to Recent tectonic evolution of the Eastern Carpathians. The uplift-induced southeastward
motion of a crustal block between the Trotuº and Sinaia strike-slip faults resulted in extension and basin formation in the hinterland, ac-
commodated by coeval shortening and folding in the foreland; b) the crustal motion may have been taken place above a detachment hori-
zon within the fold-and-thrust belt (profile after ªtefãnescu 1985).
Fig. 10. Geometric assumptions used for kinematic analysis. For a
given fault plane and striae (with known sense of slip), the shorten-
ing axis P (parallel to
) and the extension axis T (parallel to
in a plane normal to the fault plane, containing the slip line (after
Turner 1953). The B axis (parallel to
) is normal both to P and T
axes. The angle
is a function of the slope of the Mohr envelope.
Fig. 11. Example of kinematic interpretation of joint data (outcrop
3-95): a) graphical presentation of joint planes in equal area, low-
er hemisphere stereonets; b) poles of the joint planes; c) contoured
density intervals using the Kamb method of contouring (Kamb
1959). Maximum density (the black area) is assumed to be parallel
to the main direction of extension (
POST-OROGENIC UPLIFT-INDUCED EXTENSION: A KINEMATIC MODEL 325
Fig. 12. Graphical presentation of fault-slip and joint data collected in the Braºov Basin. The fault planes are represented in equal area,
lower hemisphere stereonets as great circles, with arrows showing the direction of slip on the hangingwall. The joint planes are plotted in
equal area, lower hemisphere stereonets as poles. See data locations in Fig. 2.
326 GÎRBACEA, FRISCH and LINZER
plained with this model. The shortening there may be related
to the general N-S compression recorded in the Moesian
Platform by Bergerat et al. (1995) and Maþenco (1997). An-
other open question remains the mechanism which induced
the accelerated rate of uplift in Pliocene time, 56 Ma after
the Miocene oceanic closure. A model presented by Gîrbacea
& Frisch (1998) suggests delamination of the lower lithos-
pheric mantle, following continental collision and slab
break-off, as the uplift-triggering mechanism.
Acknowledgments: Financial support was given by the
German Science Foundation. We had stimulating discussions
with Horst-Peter Hann, Lothar Ratschbacher, Franz Moser,
Blanka Sperner, and Peter Zweigel. Helpful reviews were giv-
en by Franz Neubauer and Michal Kováè. All this is gratefully
The methods and results of kinematic analysis
The orientation of faults and associated striae can be used to de-
termine the stress tensor, defined as the orientation of principal
and the ratio R between the stress magnitudes
[R = (
)], during a brittle episode of deformation.
Although the kinematic analysis calculates the main directions on
which strain (deformation) occurred, the term stress is used
here (paleostress analysis, stress tensor, stress ratio, etc.) because it
is used in most of the publications, in fact dealing with strain analy-
sis. The geometric assumption used for the kinematic analysis of
fault-slip data is presented in Figure 11. For a given fault plane and
associated striae (defined by their direction and sense of slip), the
axis lies in the plane defined by the slip direction and the normal to
the fault plane. The angle
and the slip direction
(which is, in fact, the angle between the developing fault and the
principal axis of the compression) is a function of the slope of the
Mohr envelope and has a maximum value of 45
due to the Cou-
lomb failure criterion. The fault planes are graphically represented
in equal area, lower hemisphere stereonets as great circles, with ar-
rows showing the direction of slip of the hangingwall. The aim of
the kinematic analysis is to calculate the best fitting stress tensor for
a fault population, applying these geometrical conditions to each
fault (see Allmendinger et al. 1989, and references therein for fur-
ther discussions on this topic).
For the kinematic analysis of joint data the joint planes were plot-
ted in equal area, lower hemisphere stereonets as poles (see Figs. 5
and 12). The maximum density of poles to joint planes was assumed
to indicate the direction of maximum extension, i.e.
. A contour-
ing procedure was applied to each data set to derive the maximum
density of joint poles, following the method of Kamb (1959). This
method calculates the magnitude of standard deviation
relate to stress terminology) for a uniform distribution of points on
ion. The resulting plot shows fields of point density, the
maximum density being assumed to indicate the direction of maxi-
(Fig. 12). The data sets with joints with varying ori-
entation were assumed to indicate a stress regime with radial exten-
sion and flattening geometry (i.e. with extension occurring parallel
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