Annales Societatis Geologorum Poloniae (1997), vol. 67: 13—23.
PALEOMAGNETIC RESULTS FROM THE COVER (HIGH-TATRIC) UNIT AND NUMMULITIC EOCENE IN THE TATRA MTS
(CENTRAL WEST CARPATHIANS, POLAND) AND THEIR TECTONIC IMPLICATIONS
Jacek GRABOWSKI
P olish G eological Institute, D epartm ent o f G eophysics, R akow iecka 4, 00-975 Warszawa, P o la n d
Grabowski, J., 1997. Paleomagnetic results from the cover (High-Tatric) unit and nummulitic Eocene in the Tatra Mts (Central West Carpathians, Poland) and their tectonic implications. Ann. Soc. Geol. Polon., 13-23.
A bstract: Paleomagnetic studies o f the Mesozoic and Eocene sedimentary rocks from the High-Tatric (para- autochthonous and Czerwone Wierchy units) and Paleogene cover formations o f the Polish Tatra Mts were carried out. In the Middle Jurassic-Lower Cretaceous limestones a normal polarity pre-thrusting (pre-Senonian) compo
nent was identified (5 sites, 32 samples, 92 specimens). Its occurrence also in several localities o f the Lower Jurassic-Upper Jurassic rocks of the Kriźna unit in Poland and Slovakia indicates the possibility o f the regional remagnetization which took place between 119 and 88 my (Middle Cretaceous). Another component o f reversed polarity (2 sites, 17 samples, 28 specimens) is compared with the magnetization o f the Middle Miocene andesites from the Pieniny Klippen Belt. The inclination of the Middle Cretaceous component accounts for proximity o f the Central West Carpathian (CWC) region to the European plate in that time. Declinations in the para-autochthonous unit are rotated about 23° (±6°) clockwise from the coeval reference European paleomagnetic direction.
A bstrakt: Przeprowadzono badania paleomagnetyczne skał osadowych mezozoiku w Tatrach Polskich na obsza
rze wierchowej jednostki para-autochtonicznej i jednostki Czerwonych Wierchów oraz eocenu numulitowego. W skalach węglanowych od środkowej jury po dolną kredę (5 odsłonięć, 32 próby ręczne, 92 próbki) stwierdzono występowanie namagnesowania o normalnej polarności, utrwalonego przed ruchami plaszczowinowymi w późnej kredzie. Podobny kierunek paleomagnetyczny został już wcześniej stwierdzony w kilku miejscach w Polsce i na Słowacji w skałach dolnej-górnej jury jednostki kriżniańskiej. Ponieważ kierunek ten występuje na znacznym obszarze w skałach różnego wieku i ma niemal wyłącznie normalną polarność, może on być regionalnym przemagnesowaniem które nastąpiło między 119 a 88 min lat temu (środkowa kreda). Inny kierunek o odwrotnej polarności (2 odsłonięcia, 17 prób ręcznych, 28 próbek) porównano z namagnesowaniem neogeńskich andezytów z Góry Wżar (Pieniński Pas Skałkowy). Inklinacja składowej kredowej świadczy o bliskości obszaru Wewnętrz
nych Karat Zachodnich i płyty europejskiej, przynajmniej na pograniczu wczesnej i późnej kredy. Deklinacja tego kierunku w para-autochtonie wierchowym wykazuje 23° (±6°) rotacji zgodnej z ruchem wskazówek zegara w stosunku do deklinacji kierunków kredowych z obszaru “stabilnej Europy” .
Key words: Central West Carpathians, Tatra Mts, Mesozoic, High-Tatric units, Eocene, paleomagnetism.
Manuscript received 23 April 1996, accepted 3 January 1997
INTRODUCTION
Paleom agnetic d ata from the M esozoic rocks o f the C entral W est C arpathians (C W C ) are less num erous as com pared w ith other W estern T ethyan regions. S edim entary Ju
rassic rocks o f the K riźna nappe in P oland and S lovakia y ielded pre-folding directions com patible w ith Jurassic re f
erence directions from th e E uropean Platform , w ith som e lo
cal tecto n ic rotations (K ądziałko-H ofm okl & K ruczyk, 1987; K ru c zy k e t al., 1992). H ow ever these results w ere not related to paleom agnetic d ata base for T ethyan realm (i.e.
M arton & M auritsch, 1990) and th eir paleotectonic signifi
cance w as not fully understood. R ecently it w as established
(G rabow ski, 1995a; 1995b) th at th e M esozoic p aleom ag
netic directions from the C W C reveal sim ilar tren d (m ostly clockw ise rotations) as the directions from th e N orthern C alcareous A lps (M auritsch & B ecke, 1987; C hannel et al.
1992a; M auritsch & M arton, 1995). O n the other h and they differ from the coeval directions from the T ransdanubian C entral M ts (M arton & M arton, 1983) and other A pulian fragm ents (i.e. L ow rie, 1986; C hannel e t al., 1992b).
In this paper new p aleom agnetic results from th e M eso
zoic H igh-Tatric unit and n u m m ulitic E ocene o f th e Tatra M ts in Poland are presented. S om e paleotectonic problem s
14
J. GRABOWSKII Foreland (European and M oesian platform ) MM pieniny Klippen B ell
Neogene m olasse Intem ldes
i s : s S Ä r d ing i s r - p o s t-o ro 9 e n ic
] Inner/O uter Dacides and Southern Carpathians [v, v] Neogene volcanics
Fig. 1 Structural map o f the Carpathians (after Winkler and Ślączka 1994). Box indicates the area presented in Fig. 2
i O - 1 crystalline (“ I I para*autochtonous 1---1 core 1-1— unit
I C ze rw o ne W ie rch y l|||p ri Giew ont unit
' u n it a - sedim en tary rocks
b - crystallin e rocks S iro k a unit ' | K r iin a unit |^ j ^ | C h o ć unit I I P aleo g ene
Fig. 2 Structural map o f the Tatra Mts with sampling sites (numbering according to the Tab. 3)
graphical review o f th e investigated profiles w as published by L efeld et al. (1985).
such as distribution o f o ceanic dom ains in the northern C ar
pathian are a and paleogeographic affinities o f the region are briefly discussed. P relim inary results from sites 7, 9 and 12 (see Tab. 3) w ere published by G rabow ski (1995b).
GEOLOGY
T he T atra M ts contain th e northernm ost occurrence o f
“ core m ountains” in th e C W C (Fig. 1). It is a horst o f crys
talline pre-M esozoic rocks covered by sedim entary se
quence o f E arly T riassic—L ate C retaceous (Turonian) age (see K siążkiew icz, 1977 and references herein). The Late C retaceous (pre-S enonian) orogeny resulted in the form a
tion o f a nap p e pile thru sted northw ard. The H igh-Tatric (C over) and S ub-Tatric (low er - K rizna and upper - C hoć) units are distinguished (Fig. 2). Term s such as Tatricum , Fa- tricum and H ronicum are also w idely used for H igh-Tatric, low er and u pper S ub-T atric units, respectively (Biely, 1990). T he H igh-T atric units w ere subjected to only m inor horizontal displacem ents. T h ey are divided into para-auto- chthonous unit, w hich is a roughly in situ sedim entary cover o f the crystalline rocks and several detached units. A m ong them the m o st im portant are (from w est to east): C zerw one W ierchy, G iew ont and Ś iroka units. T he S ub-Tatric units w ere detached, transported from the south and thrusted over the H igh-T atric units. P aleogene rocks overlay discordantly the M esozoic and the crystalline core. T he T atra M ts and other m assifs in the C W C w ere uplifted during N eogene (K ovac e t al. 1994) prod u cin g “ core m ountains” surrounded by basins filled w ith T ertia ry sedim ents. A ccording to Piotrow ski (1978) the N eo g en e uplift o f the T atra M ts w as rotational w ith am plitude greater in th e southern than in the nortnern p art o f the m assif. T he axis o f rotation by about 20°
w as ro ughly horizontal and latitudinal. M ore detailed de
scription o f geological structures in the Polish and Slovak T atra M ts can be found in R abow ski (1959), K otański (1961), K siążkiew icz (1977), and M ahel (1968). Strati-
PALEOGEOGRAPHIC SETTING AND EXPECTED PALEOMAGNETIC
DIRECTIONS
A ccording to a com m on view th e C entral W est C arp a
thians area during M esozoic and T ertiary w as situated b e
tw een the E uropean and A frican p lates in the W estern Tethys dom ain (B urchfiel, 1980; R icou et a l. , 1986; G ealey, 1988). N um erous paleogeographic reconstructions differ in details. W ieczorek (1995) assum es th at in th e T riassic and E arly Jurassic T atricum belonged to th e southern, passive m argin o f the E uropean plate. T he T atricum w as separated from A pulia by M eliata ocean (K ozur, 1991) w hich w as opened during th e M iddle T riassic and closed in the Late Ju rassic. In the M iddle Jurassic riftin g occurred north o f the T atricum and V ahic (P ieniny) ocean (M ahel, 1981, B irken- m ajer, 1986, W inkler & Ślączka, 1994, P laśienka, 1995) h ad developed w hich w as closed by the L ate C retaceous. On th e other h and T ollm ann (1990) in series o f paleogeographic m aps does not introduce oceanic dom ains in th e C W C and O uter C arpathians area. H e accepts th e existence o f V ardar ocean betw een the A u stro -A lp in e units and S outhern Alps and prolongates it south o f the C W C .
The “expected” paleom agnetic directions should indi
cate the position o f the C entral W est C arpathians as inter
m ediate betw een A frica and Europe. It should be p ossible to determ ine paleom agnetically the p aleogeographic (i.e A fri
can versus E uropean) affinity o f the T atric area. T he m o v e
m ent betw een A frica and E urope w as so distinct that M eso
zoic/E arly T ertiary paleom agnetic poles an d directions ob tained from these tw o plates differ significantly. D uring last 240 m .y. A frica w as situated alw ays south o f Europe, so the A frican inclinations o f th e characteristic paleom agnetic di
rections should be low er than th e inclinations o f coeval di
rections from E urope (see T abs 1, 2). D ifferences in pa- leodeclination should also be noted. D uring th e M esozoic A frica rotated 30° counter-clockw ise, w hile th e sense o f ro tation o f E uropean plate w as opposite (Tabs 1, 2).
PALEOMAGNETIC RESULTS FROM THE TATRA MTS
15
Table 1 Table 2
“E xp ected ” paleodirections for th e T atra M ts, as i f they w ere part o f th e E uropean Plate, calculated from p aleopoles for the geographical coordinates 20°E, 49°N . D ata 0 -2 0 0 M a after B esse and C ourtillot (1991), T riassic
data after V an der V oo (1993).
“ Expected” paleodirections for th e T atra M ts, as i f they w ere part o f the A frican Plate, calculated from paleopoles for th e geographical coordinates 20°E , 49°N . D ata 0 -2 0 0 M a after B esse and C ourtillot (1991), T riassic
data after V an der V oo (1993).
Age (m.y.) Declination Inclination
245-233 (Early Triassic) 30.0 35.4
232-216 (Late Triassic) 39.1 44.2
200 Sinemurian 32.2 62.3
180 (Bajocian) 34.5 59.4
160 (Oxfordian) 17.7 51.8
140 (Berriasian) 9.7 51.5
120 (Barremian) 356.5 53.5
100 (Albian) 0.8 55.2
80 (Campanian) 0.3 54.7
60 (Paleocene) 5.3 57.5
40 (Eocene) 10.9 61.6
20 (Miocene) 8.5 62.6
0 (Recent) 0 68
Age (m.y.) Declination Inclination
245-233 (Early Triassic) 328.3 36.9
232-216 (Late Triassic) 330.8 41.5
200 Sinemurian 341.6 48.9
180 (Bajocian) 344.6 45.7
160 (Oxfordian) 334.4 36.4
140 (Berriasian) 329.3 36.4
120 (Barremian) 323 40.5
100 (Albian) 337.7 44.9
80 (Campanian) 346 46.7
60 (Paleocene) 354 52
40 (Eocene) 3.4 58.6
20 (Miocene) 5.8 61.5
0 (Recent) 0 68
SAMPLING AND LABORATORY METHODS
R esults from 14 sites in 3 tectonic units are described.
The term “site” describes an outcrop o f several m eters height and w idth. 108 h and sam ples o f M esozoic and T erti
ary sedim entary rocks, m ainly lim estones, w ere collected from the P olish part o f the T atra M ts (Fig. 2). 27 sam ples w ere taken from the num m ulitic E ocene and 81 from the H igh-T atric units (para-autochthonous and C zerw one W ier
chy unit) in th e w estern p a rt o f the T atra M ts w here the m ost com plete profiles o f sedim entary series occur. T he M eso
zoic collection consisted o f L ow er T riassic quartzitic sand
stones and th e M iddle T riassic, M iddle/U pper Jurassic and L ow er C retaceous lim estones. H igh-Tatric series, except sites 5 and 11, w ere sam pled along th e K ościeliska V alley and in som e sm aller v alleys in its vicinity. Sites 5 and 11 w ere situated in the G ąsienicow a V alley. U nfortunately the studied form ations dip uniform ly to th e north (Tab. 3), so the fold test in the H igh-T atric units could not be applied.
The conglom erate test w as perform ed at the field o f b oul
ders at W antule (upper p art o f the M iętusia V alley, site N o.
14). T he boulders resulted from a large rockfall during the last glacial epoch (R abow ski, 1959). T hree localities o f the E ocene num m ulitic lim estones w ere sam pled along the northern edge o f the T atra M ts (Fig. 2).
C ylindrical specim ens, 20 m m in diam eter and 22 m m
height, w ere drilled from the hand sam ples. U sually 2 -4 specim ens w ere obtained from each hand sam ple. N atural rem anent m agnetization (N R M ) w as m easured b y m eans o f th e JR-5 spinner m agnetom eter w h ile m agnetic susceptibil
ity w as m onitored w ith K L Y -2 bridge. The ro ck specim ens w ere therm ally dem agnetized w ith the M M T D non-m ag- netic oven. A lternating field dem agnetization w as carried out in a 2-axis tum bler p roduced b y the Institute o f G eo
physics, Polish A cadem y o f S ciences. D em agnetization ex
perim ents and the N R M m easurem ents w ere perfo rm ed in
side a H elm holz coils that reduced th e geom agnetic field by 95% . C haracteristic directions w ere calcu lated using the principal com ponent analysis (K irschvink, 1980) and in few cases the H o ffm a n -D a y m ethod (H offm ann & D ay, 1978).
M agnetic m inerals w ere identified by m eans o f ther- m om agnetic analysis. It relied on therm al dem agnetization o f isotherm al rem anence (IR M ) acquired in th e field o f about 1 T (the first curve in appropriate figures). Then the sam ple was cooled, m agnetized and dem agnetized again (the second curve in the figures). T his m ethod gives values o f blocking tem peratures for m agnetic m inerals and show s w hat new m inerals originate in the rock due to its heating in the air.
16
J. GRABOWSKITable 3
L ist o f sam pled localities
No Site Age Tectonic unit Bedding N
1 Pod Capkami 356/40 12
2 Mata Łąka Eocene Tertiary cover 0/30 7
3 Lejowa 384/40 8
4 Ornak T l 45/36 9
5 Żółta Turnia Tl 10/32 6
6 Kominy
Tyłkowe T2 21/71 5
7 Wąwóz
Kraków J2
High-Tartic 16/62 3
8 Wąwóz
Kraków J2/J3
para- autochthonous
unit
16/62 4
9 Raptawicka
Turnia J3/K1 34/54 12
10 Wąwóz
Kraków KI 45/54 12
121 1
Hala
Gąsienicowa KI 345/46 4
12 Brama
Kraszewskiego J2/J3 High-Tatric Czerwone Wierchy unit
24/10 8
13 Wielka
Swistówka J3 20/30 11
14 Wantule J3
Quaternary field of boulders
- 7
T - Triassic, J - Jurassic, K - Cretaceous, (1 - lower, 2 - middle, 3 - upper,) N - number o f hand samples taken from the site
PROBLEM OF TECTONIC CORRECTION FOR MESOZOIC ROCKS
Q uestion o f tectonic correction is o f fundam ental im portance for dating the paleom agnetic com ponents. C om m on w ay is to estim ate th eir age in relation to folding p ro c
esses i.e. to establish w h eth er they are post-folding, synfold- ing or pre-folding features.
In the T atra M ts there w ere tw o tectonic events that could change th e position o f the M esozoic sedim entary rocks. F irst it w as a L ate C retaceous nappe thrusting and second w as th e N eogene up lift o f the Tatra M ts referred fur
ther to as a tilting event. E specially the effects o f the latter are d ifficult to estim ate in th e rocks o f H igh-T atric and Sub- T atric series. It is very likely that som e deform ations and d isplacem ents o f M esozoic rocks took place in T ertiary (B ac-M oszaszw ili, 1995). A logical consequence o f the m odel o f rotational up lift o f the T atra M ts during the N e o gene (Piotrow ski, 1978; B ac-M oszaszw ili e t al., 1984;
S pem er 1996) is that all sedim entary sequences w hich now dip at th e angle 2 0 -3 0 ° to the north w ere resting subhorizon-
IRM/IRM0 W K15 a
IRM2/IRM1 = 2 0
IRM/IRMq WK21
b
IRM2/IRM1 = 22
Fig. 3. Thermal demagnetization o f the isothermal remanent magnetization (IRM). a - red sandy limestone (site 7); b - grey limestone (site 10); squares — first heating curve, diamonds — second heating curve; IRM2/IRM1 ratio indicates the increase of the IRM intensity after the first heating
tally from the late C retaceous to early M iocene (for exam ple som e strata in the para-autochthonous H igh-T atric or low er Sub-Tatric unit, see B ac-M oszaszw ili et al., 1984, fig. 8b).
T herefore it is im portant to distinguish betw een pre-tilting and pre-thrusting m agnetization. T he age o f the latter is con
strained as pre-C oniacian. P re-tilting m agnetization in such case w ould im ply pre-N eogene age o f paleo m ag n etic com ponent.
ROCK MAGNETISM
M agnetic susceptibility o f th e investigated specim ens w as rather low and did not exceed 100 x 10-6 SI units. The m agnetic fabric is not well developed. T herm om agnetic analysis reveal m agnetite and hem atite as m agnetic m iner
als. O nly in the site 7 hem atite w ith o u t m agnetite adm ixture w as found (Fig. 3a). T he IRM o f the grey lim estones o f H igh-T atric unit is based upon m agnetite (Fig. 3b) but the presence o f m aghem ite can not be excluded. Second heating curve in both figures (3a,b) and increase o f the IRM inten
sity indicates th at secondary m agnetite originates during heating w hich w as typical o f all th e sam ples investigated.
PALEOMAGNETIC RESULTS
N R M intensities o f grey M esozoic and T ertiary lim e
stones w ere betw een 0,2 and 9 * 1 0 ^ * A /m . R ed L ow er T ri
assic sandstones and U pper Jurassic lim estones had higher intensities close to 10" A /m . T he results from sites 4, 5, 6 and 11 w ere rejected because the N R M vectors w ere dis-
PALEOMAGNETIC RESULTS FROM THE TATRA MTS
17
Table 4
D irections o f the low stability com ponent R
Site D 1 Dc Ic <X95 k n/N
1 341 65 349 26 5 12 54/12
2 10 72 4 42 8 21 17/7
3 348 55 348 15 9 26 11/3
8 14 69 15 7 5 54 16/4
9 348 71 17 20 5 28 33/11
10 354 63 22 26 7 42 10/5
13 356 68 9 39 6 33 16/8
14 12 63 - - 10 42 18/6
D 1 GC9 5 k Dc Ic « 9 5 k
Mean 357 65 5 103 8 24 12 24
Present day field (PDF): D = 0 , 1 = 68
D, I - declination, inclination before tectonic correction; Dc, Ic - declination, inclination after tectonic correction; (X9 5, k - Fisher statistics parameters; n(N) - number o f specimens (samples) used for calculation o f characteristic direction
p ersed and dem agnetization did n o t im prove th e clustering o f directions.
M ost o f the E ocene sam ples (sites 1,2,3) revealed the presence o f a com ponent w hich w as dem agnetized at low fields (up to 20m T ) and low tem peratures (up to 300°C, see Fig. 4a). T hat com ponent (labelled R ) in the present (geo
graphical) coordinates system is sim ilar to th e present-day local geom agnetic field (P D F ) direction (Tab. 4, Fig. 5). A f
ter rem oving the com ponent R the internal consistency be
tw een sam ples and sites w as lost, th e intensity o f m agnetiza
tion fell dow n to about 10% o f the initial N R M and no other characteristic m agnetization o f h igher stability could be iso
lated. T he R com ponent should be considered as post-tilting (i.e. post-N eogene) b ecause after tectonic correction (Tab.
4) its inclination is m uch low er than the predicted Eo- c e n e -M io c e n e inclinations for E uropean and A frican plates (Tabs 1 ,2 ).
B athonian red sandy lim estones o f the para-autochtho
nous unit (site 7) from the K raków G orge revealed a single com ponent w hich w as stable up to 620°C (Fig. 4b). A fter tectonic correction (understood as restoring b eds to the hori
zontal position) th e com ponent is situated in the I quadrant o f the stereo n et w ith m oderately steep inclination (Tab. 5, Fig. 6a, b).
T he overlying C allovian/O xfordian red nodular lim e
stone (site 8) had m ore com posite m agnetization. T he low stability R com ponent (T ab. 4) w as rem oved after d em ag
netization steps o f 2 0m T and 250°C . Interm ediate com po
nent o f norm al polarity w as observed betw een 450 and 515°C . In som e sam ples this com ponent could be defined
Table 5
D irections o f the high stability com ponents A , B and C.
E xplanations as in th e Tab. 4
Site D I Dc Ic OC95 k n/N Comp
7 173 66 30 49 5 70 13/3 A
8 183 74 21 44 9 22 13/4 A
9 228 72 21 52 6 23 25/8 A
10 282 72 20 53 6 26 23/10 A
D I CC9 5 k Dc Ic (X95 k
Mean A: 211 76 17 29 23 50 6 256
Site D I Dc Ic OC95 k n/N Comp
12 301 50 312 48 5 48 18/7 B
10 70 -57 181 -71 7 25 16/8 C
13 69 -79 179 -66 9 22 12/9 C
Mean C: 70 -68 180 -69 - -
using the H o ffm a n n -D a y m ethod (Fig. 7). B efore tectonic correction it is situated in the south-w estern q uadrant o f the stereonet w ith steep inclinations (Tab. 5, Fig. 6a). A fter tec
tonic correction the com ponent is placed in the north-east
ern quadrant w ith m oderately steep inclination (Tab. 5, Fig.
6b). A t higher tem peratures a rev ersed com ponent appeared b ut the increase o f m agnetic susceptibility during therm al dem agnetization precluded its isolation.
A nother com ponent o f m agnetization w as discovered in th e red C allovian/O xfordian lim estone o f th e overthrusted C zerw one W ierchy unit (site 12). It w as stable betw een 380 and 600°C (Fig. 4c) and its declination w as rotated over 60°
counter-clockw ise (Tab. 5, Fig. 6a, b). T he ro ck s at this site lay alm ost horizontally (Tab. 3) so th e position o f this com ponent before and after tectonic correction does not change very m uch.
V ery interesting results w ere obtained from w eakly m agnetized grey lim estones o f th e M alm -N e o co m ian and N eocom ian age from the sites 9, 10 and 13. In all these sites the low stability R com ponent (Tab. 4) constituted 8 0 -9 0 % o f the initial N R M intensity (Fig. 4d). A fter its rem oving, usually in the tem perature interval 3 5 0 -4 5 0 °C th e norm al polarity com ponent w as observed (Tab. 5, Fig. 4d). This di
rection w as encountered in the sites 9 and 10. A lik e in the sites 7 and 8 this com ponent before tectonic correction re
vealed steep dow nw ard inclinations w ith the south-w esterly declinations (Tab. 5, Fig. 6a). A fter tectonic correction the declinations becam e north-eastern w hile inclinations are about 50° (Fig. 6b). In som e sam ples from the site 10 and in m ost sam ples from the site 13 a rev ersed p o larity com po
nent w as revealed, unblocked betw een 2 5 0 -3 5 0 °C (Fig. 4e, Tab. 5). In som e sam ples from the site 10 the rev ersed com ponent occurred together w ith h igher stability norm al co m ponent and th eir unblocking tem perature spectra w ere sepa
3 — Annales...
18
J. GRABOWSKIa L5C
N
WK13D
D ow n
I NRM - 1 .5 x 10"4 A /m
R48A
1^ 1= 1 .6 4 x 1 0 ''A /m (60% Intcm)
I nrm - 7.04 x lO -“ A /m
WK24Y
BK3B
N
•Si
AtfTC at i3 5 0 °C / A n j 2 5 " C 200" C f
‘ 5 1
20° CO!..
vz D o w n &
Inrm= 7,76 X 10 * A /m
f W 1 B
(1 7% I m u m ) D o w n
Indm = 6.52 x 10“1 A /m
Fig. 4. Demagnetization diagrams o f typical specimens, a - grey nummulitic limestone (site 3); b - red sandy limestone (site 7); c - red limestone (site 12); d - grey limestone (site 9); e - grey limestone (site 10); f - grey limestone (site 14); (a) and (f) before tectonic correction, (b)-(e) - after tectonic correction; xy, xz, yz - the planes of projection, units are in 10-4 A/m
rate. It reveals steep up w ard inclinations before as w ell as after tectonic correction (Tab. 5, Fig. 6a, b). “In situ” d ecli
nation is abo u t 70° w hile after tectonic correction it is close to 180°.
Fig. 5. Stereographic projection of the component R before tectonic correction
Stability test
S im ilarity o f th e com ponent R (Tab. 4) to th e PD F di
rection could suggest th at it represents th e recen t viscous re
m anent m agnetization (V R M ). A lternative explanation that com ponent R is due to a N eogene rem agnetization is also possible. Fission track ages o f apatites from th e crystalline core o f the T atra M ts yielded ages betw een 10 and 23 M a (B urchart, 1972). This w as in terpreted as the last therm al event related to the post-orogenic up lift o f the T atra m a ssif and erosional rem oval o f the sedim entary cover.
In order to establish the age o f th e p o st-folding com po
nent R a conglom erate test w as p erform ed at th e site 14 (W antule). 7 h and sam ples w ere taken from independent blocks o f grey U pper Jurassic lim estones. M agnetite w as the only carrier o f m agnetization in th ese rocks. T herm al de
m agnetization w as applied to m o st o f specim ens (Fig. 4f).
O ne specim en from each h and sam ple w as treated w ith the A F dem agnetization. The N R M consisted o f tw o com po
nents o f separate unblocking tem p eratu re spectra. L ow sta
bility (LS ) com ponent w as rem oved up to 300°C . Its direc
tion in all sam ples is close to the PD F d irection (Tab. 6).
H igh stability (H S) com ponent is rem oved betw een 525 and 575°C. It clustered w ell w ithin a single h and sam ple but v ar
ied betw een sam ples. (Tab. 6) A F dem agnetization w as not effective in separation o f the tw o com ponents. Interm ediate
PALEOMAGNETIC RESULTS FROM THE TATRA MTS
19
Fig. 6. Stereographic projection o f the components A, B and C;
a - before tectonic correction, b - after tectonic correction; num
bering o f sites corresponds to that in the Table 3
directions betw een th e low and high stability com ponents w ere observed.
T he results o f th e conglom erate test are obvious. The LS com p o n en t is a rec en t V R M acquired during last 20 000 years. It corresponds to th e low stability R com ponent ob
tained in m o st sites (Tab. 4). The HS com ponent is an older m agnetization o f M esozoic or T ertiary age.
Age of characteristic magnetizations
T he low stability com ponent R is a recent viscous m ag
netization, as confirm ed b y th e conglom erate test.
T he higher stability com ponents are divided into three groups: A , B and C (Tab. 5, Fig. 6a,b). G roup A is ch arac
terized by norm al p olarity and north-eastern déclination af
ter tectonic correction. It can be reasonably assum ed th at the com ponents A are pre-tiltin g (i.e. pre-N eogene). T h eir dec
lination an d inclination in the post-tilting coordinates (Tab.
5) w ould require the location o f the studied area in the southern p olar region in th e N eogene or later w hich is very unlikely. M oreover the com ponents A from various sites cluster b etter after than before tectonic correction (Tab. 5, Fig. 6a, b).
G roup B (site 12 only) reveals norm al polarity and counter-clockw ise ro tated north-w estern declination. This
N
Fig. 7. Determination o f characteristic magnetization using Hoffmann-Day method, site 8. Stereographic projection of the differential vectors (dots) and demagnetization planes (great cir
cles) after tectonic correction. Black dots and continuous line - lower hemisphere projection, white dots and broken line - upper hemisphere projection. Intersection point o f demagnetization planes (large dot) indicates the characteristic direction
Table 6
R esults o f conglom erate test in th e W antule site
Sample Dl s Il s «95 k n Dh s Ih s CC95 k n
W1 22 62 14 29 4 11 -9 14 46 4
W2 358 67 - - 2 236 -38 - - 1
W3 14 68 10 163 3 170 -11 6 366 3
W4 26 46 17 56 3 7 28 13 85 3
W6 332 64 23 17 4 153 58 15 67 3
W7 23 64 - - 2 215 -25 - - 1
Mean: 12 63 10 42 6 - - - - -
DLS, (ILS) - declination (inclination) o f the low stability compo
nent; DHS, (IHS) - declination (inclination) of the high stability component; n - number o f entries
com ponent is also considered as pre-tilting. Its inclination fits the expected Jurassic—E arly T ertiary inclinations o f A f
rican and E uropean plates after tectonic correction.
R eversed polarity com ponents in th e sites 10 and 13 w ere included to the group C (Fig. 6a, b). T h ey should be interpreted as pre-tilting too. I f they w ere p o st-tilting a 8 0 -1 1 0 ° counter-clockw ise ro tatio n w ould be required to m atch them w ith Late T ertiary/Q uaternary d eclinations o f A frica and Europe. A fter tectonic correction th e am plitude o f rotation is no m ore than 30°.
It is not certain w hether th e com ponents A are prim ary.
A lthough the sam pled rocks co v ered th e tim e span betw een B athonian and N eocom ian, reversed com ponents w ere not observed. The reversed m agnetizations in sites 10 and 13
20
J. GRABOWSKIo
Fig. 8. Paleopole A at the background o f the European Appar
ent Polar Wander Path (after Besse and Courtillot, 1991). A ’ indicates the position of paleopole A after 23° clockwise rotation of the Tatra Mts around local vertical axis. Age o f paleopoles in m.y.
(com ponent C ) revealed low er blocking tem peratures and steeper inclinations than those o f com ponent A. So, the com ponent C can not be considered as the reversed counter
part o f the com ponent A. M oreover the com ponents A seem to have a regional significance. P re-folding com ponents that could be assigned to the A group w ere obtained from the variegated B athonian to K im m eridgian rocks o f the K riźna nappe in the W estern T atra M ts and B elianske T atry (K ą- d ziałko-H ofm okl and K ru czy k , 1987, K ruczyk et al., 1992, G rabow ski, 1995a). T hey are all (except one at D olina F i
lipka, see K ądziałko-H ofm okl and K ruczyk, 1987) o f nor
m al polarity, too. Single polarity n ature o f the com ponent A could m ay indicate its secondary character because betw een M iddle Ju rassic and E arly C retaceous num erous reversals o f the geom agnetic field to o k p la ce (H ailw ood, 1989; O gg et al., 1991 ; Ju arez et al. , 1995). A question arises w hether this com ponent could be pre-thrusting. T he evidence o f p re thrusting origin o f the com ponent A com es from the G ładkie U płaziańskie tectonic slice (G rabow ski, 1995a) belonging to the K riźna unit in the W estern T atra M ts. R ed radiolarian lim estones o f Late Jurassic age revealed the presence o f p re
folding com ponent A. T he strata in this site dip steeply ( 6 0 - 80°) to the north w hile th e K riźna thrust plane is dipping only gently to the north (B ac-M oszaszw ili et al., 1984, fig.
8a) and obliquely cuts the bedding so that folding obviously pre-dates thrusting. Thus the com ponent A m ight have been acquired later than early A ptian (upper age lim it o f the rocks containing this com ponent, site 10) and before the Conia- cian (term ination o f the Late C retaceous thrusting) in a long p eriod o f exclusively norm al polarity o f geom agnetic field (H ailw ood, 1989). The age constraints for acquisition o f the com ponent A w ould be 119 -8 8 m .y., w hat roughly corre
sponds to th e boundary betw een E arly and Late C retaceous.
The pole o f the com ponent A falls close to the Late Jurassic segm ent o f the E uropean A pparent P olar W ander Path (A P W P , Fig. 8). A fter 23° counter-clockw ise rotation it could be m atched with th e C retaceous paleopoles. This m o vem ent corresponds to 23° (±6°) clockw ise rotation o f
th e T atra M ts around th e local v ertical axis after E arly A p
tian. P ossibility o f such ro tation w as suggested in th e earlier paper (G rabow ski, 1995b). T he am plitude and sense o f ro ta tion correspond to th at inferred for the L ow er S ub-Tatric nappe in th e w estern T atra M ts (1 7 -3 0 ° clockw ise, see G rabow ski, 1995a).
N orth-w esterly directed com p o n en t B w as encountered in the overthrust C zerw one W ierchy u n it only (site 12). The com ponent is also interpreted as pre-thrusting. T he counter
clockw ise rotation, induced from the N W deviation o f the characteristic rem anent m ag netization m u st have taken place during th e thrusting o f the C zerw one W ierchy unit over th e para-autochthonous H igh-T atric cover.
T he interpretation o f reversed p olarity com ponent C is difficult. Its inclination is steeper than any expected M eso zoic inclination. The com ponent C after tectonic correction becom es very sim ilar to the ch aracteristic m ag netization ob
tained in the M iocene andesites from the Polish sector o f the P ieniny K lippen B elt at M t. W żar (B irkenm ajer & N aim , 1968) - about 25 km to th e no rth -east from th e W estern T a
tra (Tab. 5). The radiom etric age o f y o u n g er p hase o f the in
trusions w as established b y B irkenm ajer e t al. (1987) as 12.6 m .y. (Sarm atian) w hile the o lder phase is regarded as E arly B adenian (1 6 -1 3 m .y.). T he age o f com ponent C could correspond to the fission track ages from the cry stal
line core (1 0 -2 3 m .y. - B urchart, 1972) w hich indicate the age o f p o st orogenic uplift o f the T atra m assif. T he com po
nen t C w ould be an exam ple o f p re-tilting m agnetization w hich postdates the thrusting.
GEOLOGICAL IMPLICATIONS
It w as already p ointed out by K ądziałko-H ofm okl and K ruczyk (1987) that the characteristic paleom agnetic direc
tions from the T atra M ts are closer to the E uropean rather than A pulian or A frican reference directions. T his conclu
sion w as confirm ed by further studies in S lovakia (K ruczyk e t al., 1992) and P oland (K ruczyk & K ądziałko-H ofm okl, 1988; G rabow ski, 1995a; 1995b;). T hese results are listed in th e T able 7. M ost declinations reveal clockw ise rotations.
C ounter-clockw ise rotations in th e overthrust C zerw one W ierchy unit in th e T atra M ts and in th e K riźn a u nit o f M ala F atra m ight be o f local character. A lso th e values o f inclina
tions fit the expected E uropean M esozoic inclinations and they are significantly higher than the inclinations from T ransdanubian C entral M ts o r S outhern A lps (Fig. 9). Thus, i f com ponent A is ten tatively regarded as the p o st-early A p- tian/pre-C oniacian (1 1 9 -8 8 m .y.) rem agnetization the fol
low ing conclusions can be draw n:
- during acquisition o f the com ponent A the T atricum and F atricum (sensu B iely, 1990) o f th e C entral W est C ar
pathians are related to the southern m argin o f the E uropean Plate. The total w idth o f three hypothetical oceanic dom ains (e.g. V ahicum , M agura and Silesian basins, see M ahel, 1981; B irkenm ajer, 1986; 1988; W inkler & Ślączka, 1994;
P laśienka, 1995) betw een the C W C and the E uropean plate around th e E arly/L ate C retaceous boundary is below the resolution o f the current p aleom agnetic data. It should be stressed th at existence o f w ider oceans in th e E arly C reta
Table 7
PALEOMAGNETIC RESULTS FROM THE TATRA MTS
21
C haracteristic directions from the M esozoic rocks o f the Central W esy C arpathians. N - num ber o f sites
Locality and age of rocks D I N CX95 k References
Pieniny Klippen Belt, Niedzica unit,
Bathonian-Callovian 16 52 1 7 57
Kiuczyk &
Kądziałko-Hofmokl (1988)
Tatra Mts, High-Tatric para-autochton
(Bathonian-Neocomian) 23 50 4 6 256 tis paper
Tatra Mts, High-Tatric Czerwone Wierchy unit
(Callovian-Oxfordian) 312 48 1 5 48 this paper
Tatra Mts, Kriźna unit
(Bajocian-Kimmeridgian) 22 59 7 4 198 Kądzialko-Hofmokl &
Kruczy k (1987)
Tatra Mts, Kriźna unit, (Oxfordian) 37 53 4 9 108 Grabowski (1995a)
Belianske Tatry, Kriźna unit, (Middle-Upper Jurassic) 40 59 4 8 118 Kruczy k ef n/. (1992)
Choć Hills, Kriźna unit, (Lower Jurassic) 39 63 3 12 104 Kruczy k et al. (1992)
Nizke Tatry, Kriźna unit, (Middle Jurassic) 2 56 4 14 73 K ruczykefa/. (1992)
Magura Spiäska, Kriźna unit, (Middle Jurassic) 75 46 3 12 114 Kruczy k et al. (1992)
Mala Fatra, Kriźna unit, (Middle-Upper Jurassic) 321 44 21 3 96 Kruczyk et al. (1992)
Mean inclination: 53°, (± 8°)
ram eters o f m ean inclination o f the com ponent A from the T able 7 and m ean Eurasian E arly /L ate C retaceous pa- leopoles o f B esse and C ourtillot, 1991);
- clockw ise rotation o f the com ponent A (23°, ± 6°) suggests that th e T atra M ts particip ated in the Late Creta- cous or later tectonic m ovem ents w hich have changed their position in relation to the E uropean Platform . T he nature o f these m ovem ents is unknow n and can n o t be inferred at the present stage o f investigation. T his could be eith er a clock
w ise tectonic rotation around the local v ertical axis, strike- slip m ovem ent or com bination o f both. S inistral strike-slip m ovem ent along the faults b ordering the P ieniny K lippen B elt on the south w ere suggested b y B irkenm ajer ( 1985) and clockw ise rotation o f th e com ponent A does n o t contradict the proposed m odel;
V ery interesting are geological consequences o f pre- folding age o f com ponent C. I f its M iocene age w as proved (m ore data is required) it w ould be an evidence that dips o f bedding and thrust planes in th e H igh-T atric series w ere in
deed changed during the N eogene uplift o f the T atra M ts.
CONCLUSIONS
I. The M iddle Ju ra ssic -L o w e r C retaceous sedim entary rocks in the T atra M ts reveal p ost-and pre-fo ld in g m agneti
zations. The post-folding com ponent R is a rec en t viscous rem anent m agnetization as confirm ed by conglom erate test.
The pre-folding norm al polarity com ponents A and B w ere acquired before the Late C retaceous thrusting. B ecause they occur in the rocks o f B a jo c ia n -E a rly A ptian age it is sug
gested that they m ay represent the post-early A ptian/pre- ceous and M iddle/L ate Jurassic can not be excluded. M axi
m um am ount o f tectonic shortening during the Late C reta
ceous com pression in the region from F atricum in the south to the southern edge o f the E uropean platform in the north (including the subduction o f oceanic crust and intra-conti- nental overthrusts) did not exceed 1200 km (sum o f a.95pa-
Fig. 9. Comparison o f the inclination o f the characteristic com
ponents from the Central West Carpathians (full dot, inclination value plotted after Tab. 7) and Transdanubian Central Mts (open dots, after Marton and Marton, 1983) with expected paleoinclina- tions for the European (full squares, after Besse and Courtillot, 1991) and Adriatic plates (open squares, after Channel 1992b).
Inclinations are recalculated from the pole positions for the geo
graphical coordinates 20°E, 49°N. 95% confidence error bars for all data and age error for the component from the CWC are indicated
22
J. GRABOWSKIC oniacian rem agnetization (1 1 9 -8 8 m .y.). T he reversed com ponent C could be contem poraneous w ith M iocene an- desite intrusions in the P olish part o f th e P ieniny K lippen Belt.
2. M ean inclination o f th e pre-thrusting com ponents in the T atra M ts, other C W C m assifs (M ala Fatra, C hoć H ills, N izk e T atry, M agura S piśska) and P ieniny K lippen B elt in
dicates th e ir proxim ity to th e E uropean plate at least in the p o st E arly A ptian/pre-C oniacian tim e span. T he w idth o f hypothetical oceanic dom ains betw een th e C W C and E uro
p ean P latform in this tim e is below the resolution o f current paleom agnetic data.
3. In th e Late C retaceous or later T atra M ts w ere either rotated 23° (±6°) clockw ise or translated along a strike-slip fault.
Acknowledgements
Author gratefully acknowledges the financial support o f State Committee for Scientific Research (grant no. 6 6208 92 03). Criti
cal remarks o f Doc. Marek Lewandowski, Doc. Andrzej Żelaźnie- wicz and an anonymous reviewer are appreciated. Thanks are also due to the authorities of the Tatra National Park for permission to carry out the field work.
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S tre s z c z e n ie
REZULTATY BADAŃ PALEOM AGNETYCZNYCH Z SERII W IERCHOW YCH I EOCENU NUM ULITOW EGO TATR (CENTRALNE KARPATY ZACHODNIE, POLSKA) I ICH
TEKTONICZNE IMPLIKACJE
J a c e k G rabow ski
Artykuł prezentuje wyniki prac paleomagnetycznych prze
prowadzonych w Tatrach Polskich (Fig. 1). Przedmiotem badań były wierchowe serie osadowe należące do jednostek para-auto- chtonicznej i Czerwonych Wierchów oraz autochtoniczne osady eoceny numulitowego (Fig. 2). Osady te powstawały na obszarze basenu Tetydy między płytami afrykańską i europejską. Oczeki
wane kierunki paleomagnetyczne z obszaru tatrzańskiego (Tab. 1, 2) powinny wpasowywać się w te ramy geotektoniczne. Opróbo-
wano pełny profil jednostki para-autochtonicznej, od triasu dol
nego po dolną kredę, w rejonie doliny Kościeliskiej i Wąwozu Kraków. Skały dolnego triasu i dolnej kredy pobrano też z rejonu Hali Gąsienicowej. W jednostce Czerwonych Wierchów opróbo- wano wapienie górnej jury w Bramie Kraszewskiego (dolina Koś
cieliska) i w kotle Wielkiej Swistówki (dolina Miętusia). Wapienie eocenu wzięto do badań z odsłonięć w dolinach Lejowej i Malej Łąki oraz w kamieniołomie pod Capkami (Tab. 3).
Pozostałość magnetyczna badanych skał jest oparta na mag
netycie i hematycie (Fig. 3). W skałach eoceńskich oraz w więk
szości szarych wapieni górnej jury i dolnej kredy przeważa współ
czesne lepkie przemagnesowanie (składowa R - Tab. 4, Fig. 4a, f, Fig. 5). Jego wiek został potwierdzony testem na blokach wapien
nych w osuwisku Wantule (Tab. 6). W odsłonięciach skał dolnego i środkowego triasu z profilu Kominów Tyłkowych i Żółtej Turni nie udało się wydzielić żadnych kierunków charakterystycznych.
W rejonie Doliny Kościeliskiej w skałach węglanowych od środ
kowej jury po dolną kredę (5 odsłonięć, 32 próby ręczne, 92 prób
ki) stwierdzono występowanie przedfałdowego namagnesowania (składowa A - Tab. 5, Fig. 4b-d, Fig. 6). W czerwonych wapie
niach jury górnej w Wąwozie Kraków kierunek ten wydzielono stosując metodę Hoffmanna-Day’a (Fig. 7). Podobny kierunek pa
leomagnetyczny utrwalony przed szariażem późnokredowym został już wcześniej stwierdzony w kilku miejscach w Polsce (jed
nostka kriżniańska, jednostka niedzicka) i na Słowacji (Mała Fa- tra, Góry Choczańskie, Niżnie Tatry, Tatry Bielskie, Magura Spis
ka) w skałach dolnej-gómej jury (Tab. 7). Ponieważ kierunek ten występuje na znacznym obszarze w skałach różnego wieku i ma niemal wyłącznie normalną polarność, może on nie być kierun
kiem pierwotnym, a raczej przedsenońskim przemagnesowaniem, utrwalonym między 119 i 88 min lat. Paleobiegun składowej A lokuje się w pobliżu późnojurajskich biegunów płyty europejskiej (Fig. 8). Po rotacji bieguna A o kąt 23° (±6°) wokół lokalnej osi pionowej można go zgrać z biegunami środkowokredowymi. W rejonie Bramy Kraszewskiego (jednostka Czerwonych Wierchów) kierunek paleomagnetyczny jest skręcony 70° przeciwnie do ruchu wskazówek zegara (Tab. 5, Fig. 4c, Fig. 6 - składowa B) co sugeruje lokalną rotację tektoniczną. Inny, niewątpliwie wtórny, przedfałdowy kierunek o odwrotnej polarności (Tab. 5, Fig. 4e, Fig. 6, składowa C - 2 odsłonięcia, 17 prób ręcznych, 28 próbek) porównano z namagnesowaniem neogeńskich andezytów z Góry Wżar (Pieniński Pas Skałkowy). Inklinacja składowej A świadczy o bliskości obszaru Wewnętrznych Karpat Zachodnich i płyty europejskiej, przynajmniej na pograniczu wczesnej i późnej kredy (Fig. 9). Szerokość hipotetycznych oceanów Vahicum, Magur
skiego i Śląskiego w tym czasie jest poniżej rozdzielczości metody paleomagnetycznej. Deklinacja kierunku A na obszarze para-auto
chtonicznej serii wierchowej Tatr wykazuje 23° (±6°) rotacji zgodnej z ruchem wskazówek zegara w stosunku do deklinacji kierunków kredowych z obszaru „stabilnej Europy” . Może to być wynik rotacji tektonicznej wokół lokalnej osi pionowej lub ruchu wzdłuż uskoku przesuwczego. Obecność przedfałdowego namag
nesowania, którego wiek zinterpretowano jako mioceński (skła
dowa C) świadczy, że upady warstw oraz powierzchni nasunięć skał mezozoicznych w Tatrach mogły ulec zmianie w wyniku neo- geńskiego wypiętrzenia.
