Palaeomagnetic Studies of Polish Rocks. III. Neogene Igneous Rocks of the Pieniny Mountains, Carpathians

r o c z n i k p o l s k i e g o t o w a r z y s t w a g e o l o g i c z n e g o

A N N A L E S D E L A S O C I E T f i G £ O L O G I Q U E D E P O L O G N E

T o m ( V o l u m e ) X X X V I I I — 1968 Z e s z y t ( F a s c i c u l e ) 4 K r a k ó w 1968

KRZYSZTOF BIRK ENM AJER \ A L A N E. M. N A IR N 2

STUDIA PALEOMAGNETYCZNE SKAŁ POLSKICH III. NEO G EN SK IE SKAŁY OGNIOWE PIE N IN

(8 fig., 4 tab.)

Palaeomagnetic Studies of Polish Rocks

III. Neogene Igneous Rocks of the P ieniny M ountains, Carpathians

(8 Figs., 4 Tabs.)

STRESZCZEN IE

O pracow anie zaw iera w yniki pom iarów k ie ru n k u n aturalnego m ag­

n etyzm u szczątkowego w neogeńskich skałach ogniowych Pienin. O rien­

tow ane próby do bad ań la b o ra to ry jn y c h pobrano z ponad trzydziestu stanow isk. P o m iary elem entów m agnetyzm u szczątkowego dały dobre w yniki jedynie w p rzy p ad k u dajek andezytow ych góry W żar koło Czorsz­

tyna, które w y k azały k ie ru n e k nam agnesow ania szczątkowego odw rotny w stosunku do obecnego pola m agnetycznego Ziemi. W andezytach okolic Szczaw nicy i Szlachtow ej, k tó re są uw ażane za starsze od andezytów W żaru, stw ierdzono k ieru n ek nam agnesow ania szczątkowego zarów no norm alny, ja k i odwrócony.

P ró b n a k orelacja paleom agnetyczna andezytów W żaru z mioceńskim i skałam i ogniowym i Słow acji w skazuje, że dajki andezytow e pierw szej g eneracji na W żarze m ogą odpowiadać andezytom pierw szej fazy (dolny tor ton) centralnosłow ackiej prow incji w ulkanicznej, d ajk i zaś andezy­

tow e drugiej generacji na Wżarze — starszym andezytom drugiej fazy (granica to rto n u i sarm atu ) tej prow incji w ulkanicznej.

*

* *

A b s t r a c t . Oriented sa m p les w ere collected from about th irty sites in the P ien in y M ountains, Carpathians. R outine m easu rem en ts and stab ility tests in d icated co n sisten t resu lts from th e an d esite dykes exposed on W żar m ount only. O nly reversed m agn etization w as recorded. A ten ta tiv e correlation of th e resu lts w ith th e igneous rocks o f S lovak ia w ou ld equate th e W żar in tru sion s w ith th e first p h a se and lo w er part of th e second p h ase a n d esites of th e C en tral S lovak ian province. From th e sites in th e region of S zczaw nica and Szlachtow a th ere is an in d ication of both norm al and reversed directions of m agn etization in an d esites older than th ose found on W żar m ount.

1 L aboratory of G eology, P o lish A cad em y of S ciences, K raków , ul. S en ack a 3.

2 D epartm ent o f G eology, Case W estern R eserve U niversity, C levelan d (Ohio).

— 476 —

INTRODUCTION

The p re se n t pap er is a f u rth e r contribution to th e palaeom agnetic stu d y of P olish rocks begun in 1961 ( B i r k e n m a j e r , N a i r n , 1964, 1965; B i r k e n m a j e r , K r s , N a i r n , 1968; B i r k e n m a j e r , G r o ­ c h o l s k i , M i l e w i c z , N a i r n , 1968). The p re se n t re p o rt details the palaeom agnetic stu d y of th e Neogene volcanics, andesites and b asalt of th e P ieniny M ountains, in th e P olish C arp ath ian s (Fig. 1). A lthough about th ir ty sites w ere visited, only those on W żar m o u n t gave positive results.

Andesites east of Czorsztyn at Szczawnica (2 sites), on J a r m u ta m ount (4 sites) and on K ru p ian k a m ount (1 site), and th e basalt at Biała Woda w ere sam pled w ith o u t obtaining an y consistent results.

The m ain conclusions from th e stu d y of th e W żar andesites w ere rep o rted at the V llth Congress of the C a rp a th ia n -B alk a n ian Association of Geologists, in Sofia ( B i r k e n m a j e r , N a i r n , 1965).

OUTLINE OF GEOLOGY (WŻAR MOUNT)

The igneous rocks of th e W żar m ount n ea r C zorsztyn are for th e most p a rt am phibole-augite andesites ( M a ł k o w s k i , 1958). According to B i r k e n m a j e r (1961, 1962) th e y belong to tw o generations of dyke intrusions. The firs t generation is rep resen ted b y a series of sub-parallel dykes w hich change in strik e from E-W on th e e a ste rn slopes of th e hill, to ENE-W SW near th e crest, and to ESE-W NW on th e w estern flanks (see Fig. 2). T he dykes are found m ainly in th e L ow er Palaeogene core of an anticline in the M agura Flysch (Fig. 3). T here is slight contact m etam orphism . According to B i r k e n m a j e r (1963) th e dykes dip tow ards the core of the anticline as if following tension joints developed during folding and prio r to the intrusions. T heir age is not know n w ith any certitude b u t on regional geological grounds B i r k e n m a j e r (1960, 1962) suggested an early Miocene age (close to th e S avian phase). H ow ­ ever, a Middle Miocene age cannot be excluded ( B i r k e n m a j e r , N a i r n , 1965). T h eir in tru sio n appears to be synchronous w ith a series of NW -SE faults.

The second generation dykes cut the first generation dykes approxi­

m a te ly at rig h t angles following generally th e line of fau lts w hich displace the first generation dykes. The older dykes are th e rm a lly altered by th e younger intrusions and th e re are zones of brecciation som etim es found following th e contacts of th e second generation dykes in w hich frag m en ts of th e firs t generation andesites and altered sed im en tary rocks are found. The age of the second generation dykes on regional geological grounds is Low er Miocene ( B i r k e n m a j e r 1960, 1962) b u t again a Middle Miocene (Tortonian) age cannot be ru led out.

The general geological p ictu re of W żar m ount w as generally confirm ed by the m agnetom etrie survey of M a ł o s z e w s k i (1961, 1963), who assumed, how ever, the dips of th e first generation dykes opposite to those indicated by B i r k e n m a j e r (1963). S everal authors, M o r o - z e w i c z , M a ł k o w s k i and M i c h a l i k (cf. M a ł k o w s k i , 1958;

B i r k e n m a j e r , 1962), considered th e m ajo r p a r t of th e W żar a n d e ­

sites as form ing a laccolith, as does K o z ł o w s k i (1961 a, b, 1965)

whose opinions of th e geological stru c tu re differ m ark e d ly from B i r ­

k e n m a j e r and M a ł o s z e w s k i .

— 477 —

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Pig. 1.Distributionofthe Neogene igneousrocks in the PieninyMountains,l — Andesite; 2 — Basalt; 3 — Southern and northerntectonicborders ofthe Pieniny KlippenBelt; B —■Bryjarkamt.; BW— BiałaWoda; J — Jarmuta mt.; K — Krupianka mt.; W — Wżar mt.

— 4 7 8 -

Fig. 2. L okalizacja m ie jsc pobrania prób do badań p aleom agn etyczn ych na górze W żar koło Czorsztyna. B udow a geologiczna w ed łu g B i r k e n m a j e r a (1962), uproszczona. 1 — a n d ezyty pierw szej generacji; 2 — an d ezyty drugiej generacji;

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B rek cje an d ezytow o-o sad ow e i strefy zm ian term icznych w sk ałach o sa d o w y ch n ie zostały zaznaczone

Fig. 2. L ocation of d yk e sam pling .sites o n th e Wżar m ou n t near Czorsztyn. The g eological m ap is m o d ified from B i r k e n m a j e r (1962). l — F irst generation andesites; 2 — Second generation a n d esites; 3 — M agura san dston e (M iddle Eocene);

4 — sub-M agura bods (Lower Eocene); 5 — K lu szk o w ce beds (Lower E ocen e- -P aleocen e); 6 — Sam p lin g sites; 7 — Faults; 8 — L in e of cross-section illu strated in Fig. 3. A n d esite-sed im en ta ry breccias and zones of th erm a l alteration of sedim ents

not indicated

— 479 —

Fig. 4. K ontakt dw óch dajek andezytowyich na górze Wżar. Iga — an d ezyt pierw szej g en era cji (stanow isko 9); 2ga — andezyt drugiej gen eracji (stanow isko 10);

6 — brekcja an d ezytow a

Fig. 4. C ontact of tw o a n d esite d yk es at th e W żar m ount. Iga — First generation a n d esite (Site 9); 2ga — Second generation an d esite (Site 10); 6 — A n d esite breccia

PALAEOM AGNETIC IN V ESTIG A TIO N

1) D i r e c t i o n o f M a g n e t i z a t i o n

As the techniques used are sta n d a rd and have been fre q u e n tly described, for exam ple b y B i r k e n m a j e r and N a i r n (1964) and N a i r n (1966) no m ore th a n an outline will be given here. O riented blocks w ere collected from both n a tu ra l outcrops and quarries. The n u m b e r of sam ples p e r site varied according to th e n a tu re a n d size of th e outcrops, in th e ea rlier collection (1961), ra th e r few w ere ta k e n b u t in the la te r collection (1963) attem p ts w ere m ade to collect six sam ples p e r site. Sam pling inform ation is given in Table 1. C ylinders 2.5 cm in d iam eter and le n g th w ere cu t from th e field blocks. M ultiple m easu re­

m en ts w ere m ade in itially on th e 1961 collection to obtain a sam ple m ean w hich w as th e n used to obtain a site m ean. W ith la rg e r sam ple n u m b ers how ever, only a single core w as m easured p er sam ple w ith o u t perceptible loss in accuracy (see D o e l 1, C o x , 1963). All m easu rem en ts of declination and inclination w ere m ade u n d e r a short period astatic m agnetom eter w ith a sensitivity of about 1X 10-5 emu/cc. A ll cores w ere subjected to progressive dem agnetization in a ltern atin g fields as a sta n d a rd technique. This tests sta b ility a n d also serves to rem ove se­

condary com ponents of m agnetization („m agnetic cleaning”). The fields used in general did not exceed 340 oe, although in a few cases dem ag­

netization was carried up to 850 oe. Typical dem agnetization curves are

<--- --- --- Fig. 3. Przekrój geologiczny góry W żar (w edług B i r k e - n m a j e r a , 1963), 1 — andezyty p ierw szej generacja; 2 — piaskojwiec m agurski (środkow y eocen); 3 — w a rstw y podm agurskie (dolny eocen); 4 — w a rstw y k lu szk o w sk ie (dolny eocen - -paleocen). B rek cje a n d ezytow o-osad ow e i strefy zm ian term icznych w skałach

osad ow ych nie zostały zaznaczone

Fig. 3. G eological cross-section of th e W żar m ount (after B i r k e n m a j e r, 1963).

1 — First generation amdesites; 2 — M agura san dston e (Middle Eocene); 3 — su b- -M agura beds (Lower Eocene); 4 — K luszk ow ce beds (Lower E acen e-P aleocene).

A ndesi'te-sedim entary breccias and zones of th erm al alteration of sed im en ts not indicated

6 Rocznik PTG t. XXXVIII, z. 4

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— 4 81 —

show n in Fig. 6. The site m ean at each dem agnetization stage w as com puted using an electronic com puter w ith a program m e devised b y Dr. L. M o l y n e a u x . The direction of m agnetization a t th e stage a t which th e sc atte r was a m inim um was adopted as th a t best rep resen tin g th e original m agnetization. W here this w as th e N.R.M. stage the condition was imposed th a t the m ean direction should not a lter significantly during dem agnetization.

All the rele v an t d a ta is sum m arised in Table 1, and illu stra te d in Fig. 5, from w hich it can be seen th a t th e first and second g en eratio n andesite dykes cannot be separated on the basis of th e ir directions of m agnetization. Inspection of Table 1 also indicates th e large circles of confidence about the m ean values and some would norm ally be excluded as unsatisfactory. T h at this is p a rtly due to th e sm all sam ple size is

N

Fig. 5. Stereogram k ieru n k ó w m agn etyzacji an d ezytów góry Wżar. L iczby odpo­

w iad ają stanow isk om w y m ien io n y m w tab eli 1

Fig. 5. S tereogram sh ow ing the direction of m agnetization o f th e W żar m ount andesi'tes. N um bers correspond to sites in T able 1

6^*

— 4812 —

evidenced b y th e sm aller values found w hen m ore sam ples w ere collected.

N evertheless it rem ains tr u e th a t the confidence lim its are large w hen com pared to m a n y o th e r results. The reason for this is not clear. F or com pleteness all th e m easurem ents are given.

2) I n t e n s i t y o f M a g n e t i z a t i o n

The in te n sity of m agnetization w as generally low and even w ith in a site, values w ere scattered. It can be seen from th e inspection of Table 1 th a t even a t th e stage of m inim um sc atte r in th e directions of rem anence th e in te n sity values rem ain dispersed. This can also be seen in th e b ehaviour of dem agnetization curves from d ifferen t sam ples from th e sam e site (see Fig. 6). The dispersion of th e in te n sity can be illu strate d b y show ing th e cum ulative distrib u tio n of in te n sity values, using all th e sam ple values (not site m ean values). Fig. 7 shows th a t th is dispersion b o th a t th e N.R.M. stage and th e in te n sity a t th e stage of m inim um s c a tte r of directions follows v e ry closely a log norm al distribution. The n e a r p arallel condition of th e two curves im plies th a t th e ratio of p rim a ry to secondary m agnetization is about th e same independent of the m a g n itu d e of th e m agnetization.

/ \ / \ / I

Demagnet i zi ng field (gauss)

F ig . 6. T yp ow e k rzy w e od m agn esow yw an ia próbek w polach zm iennych. Z m ienność lo k a ln a podana w k ilk u p rzykładach n a różnych próbkach pobranych w tym sam ym o d słon ięciu (np. stan ow isk a 14, 15). N um ery p u nk tów pobraniia próbek — jak

iw talbeli 1

F ig . 6. T yp ical curves o f d em agn etization in a lt e r n a t in g field s. S o m e m ea su re of v a ria b ility per siite is g iv e n b y reproducing dem agnetization curves fo r sev era l sam p les at the sa m e site (e.g. S ites 14, 15). S ite num bers correspond to T able 1

— 483 —

D E M A G

Fig. 7. W ykres n atężen ia p ola m agn etyczn ego (naturalny m agn etyzm szczątk ow y NRM i po odm agnesow yw andu) an d ezytów góry Wżar w p ostaci k rzy w y ch lo g

norm alnych

Fig. 7. Graph of d istrib u tion of in ten sity (NRM and after d em agnetization) of m agn etization of th e W żar m ou n t an d esites as lo g n o rm a l curves

D ISC U SSIO N OF R ESULTS

1) D y k e T r e n d

T here is a change in tre n d of th e firs t generation dykes, w hich could be th e re s u lt of the accum ulation of sm all m ovem ents of slices b etw e en p airs of faults. This is illu stra te d diagram m atically in Fig. 8. Because of th e sc atte r betw een th e site m ean directions and th e sm all n u m b e r of sites b etw een a n y p a ir of fau lts th e m agnetic declinations m e asu red cannot contribute to th e problem . The im provem ent on com puting an overall m ean direction b ro u g h t about b y assum ing a 20° ro tatio n is m inim al (see Tab. 2).

T a b l e 2 O verall site m ean o f th e first gen eration an d esites o f the W zar m ount

D I ^a K

A ssu m in g no rotation 191.5 —73.2 9.4 17.5

A ssu m in g 20° rotation 200.6 — 72.6 9.1 18.6

— 4 8 4 —

— 485 —

2) M a g n e t i c I n c l i n a t i o n

T here is a v e ry large v ariatio n in th e v alue of th e m agnetic inclinations recorded am ounting to some 40°. As th e intrusion of th e second ge­

neration dykes is th e last geologically significant event, th e average declination value of ab o u t 74° m ay be regarded as a sta n d a rd of com­

parison. If this is done, th e n an ap p a re n t correlation can be seen betw een th e inclination value and geographic position (the large confidence lim its of most sites preclude definite statem ents). The largest d e p a rtu re s are found on the low er slopes of th e hill, in th e central region values are in general close to the adopted standard. Thus, although palaeom agnetism can contribute nothing to the tectonic arg u m e n t involving ro tatio n betw een pairs of faults, th e inclination values do suggest th a t th e blocks betw een faults m ay have tilted independently, and not necessarily alw ays in the same sense, some to the north-w est, others to the south-east. The com bination of both tectonic and inclination argum ents is th en to suggest rotation about an inclined axis.

3) A g e o f t h e I n t r u s i o n s

The local geological evidence for the age of th e intrusions based upon the w ork of B i r k e n m a j e r (1960, 1962) w hich leads to th e suggestion of a Low er or Middle Miocene age, has alread y been sum m arised. In a b ro ad er sense, the change in tre n d of the firs t generation dykes is tectonic and th u s re la te d to the last stages of th e C a rp a th ia n orogenic activity. In th e E x tern al C arp ath ian zone this activity is placed w ith in the T ortonian (cf. K s i ą ż k i e w i c z , 1963), w hich th erefo re is te n ta ­ tively regarded as th e m ost probable age for th e W żar dykes.

It is now possible to a tte m p t to rela te the sign of m agnetization to a sequence established in th e andesites and rhyolites of th e C entral and E ast Slovakian volcanic provinces w hich N a i r n (1966, 1967) a ttem p ted to correlate w ith resu lts from Japan, New Zealand and F rance. The reversed m agnetization of th e W zar dykes suggests correlation w ith

<--- Fig. 8. R ekonstrukcja ew o lu cji strukturalnej góry Wżar. A — stadium przed rotacją,

an d ezyty pierw szej g en era cji posiadają k ierun k i W^E; B — rotacja an d ezytów pierw szej .generacji w centralnej partii góry W żar jako efek t su m ow an ia się m ałych p rzesunięć w zdłuż praw osk rętnych u skoków i tw orzenie siię brekcjd an d ezy to w o - -osadow ych , przede w szy stk im w zdłuż głów n ej strefy rozłam u; C — stad iu m po rotacji (stadium o'becne). A nd ezyty drugiej gen eracji in tru d ow ane w zdłuż strefy g łów n ego rozłamu.

O b j a ś n i e n i a : 1 — an d ezyty drugiej generacja; 2 — an d ezy ty pierw szej g en e­

racji; 3 — brekcja andezytow o-osad ow a; 4 — p iask ow iec m agu rski (środkow y eocen) i warsitwy pod m agursk ie (dolny eocen) na skrzydłach a n ty k lin y W żaru;

5 — w a r stw y k lu szk o w sk ie (dolny eocen-p aleocen ) w jądrze a n ty k lin y W żaru;

6 — uskoki; 7 — przybliżony przebieg osi an tyk lin aln ej

Fig. 8. R econstruction o f structural evolution of th e W żar m ount. A — P re-rotation stage, the first gen eration andesiite dykes trending W -E; B — R otation o f first gen eration andesiite dykes in th e central part of Wżar m ou n t due to accum ulation of sm all m o v em en t along d extral fa u lts, and form ation of andesi'te-sedim entary breccias m ain ly along th e m ajor fractu re zone; C — Rost^rotation stage (the p resen t stage) w ith the second gen eration andesiite dykes intruded along th e m ajor fractu re zone.

E x p l a n a t i o n s : 1 — Second gen eration an d esites; 2 — First generation andesites; 3 — A n d esite-sed im en ta ry breccia; 4 — M agura san d ston e (M iddle Eocene) and sub-M agura beds (Dower Eocene) on th e lim bs of the W żar m ou n t a n ticline; 5 — K luszk ow ce beds (Low er E ocen e-P aleocene) in th e core of th e W żar m ou n t anticline; 6 — Faults; 7 — A p p roxim ate course of th e an ticlin a l a xis

— 486 —

first and low er second phase andesites of th e C en tral Slovakian province.

However, all th e T ortonian rocks save those in th e highest T ortonian- -low est S a rm a tia n are rev ersely m agnetized, and u n til m ore detailed sam pling can be carried out, th e possibility th a t this is an arte fa c t of the sam pling cannot be elim inated. The correlation is given in Table 3.

T a b l e 3 T en ta tiv e age and palaeom agn etic correlation of th e P ie n in y M ountains

andesites w ith the ign eou s rocks of th e C entral and E ast S lo v a k ia n P ro v in ces

A g e Central

S lo vak ia

East S lo v a k ia

P ien in y M ountains,

P oland

Upper R - l2nd ph ase

F in a l p h a se J an d esites [ 3ird phase J rh y o lites j

+ N +

| an d esites

M iddle S arm atian

— — 1st p h a se an d esites

R

3rd p h a se J |2 n d p h a se Low er an d esites [

in tru sives 2nd p h a se J

+ + + N + +

J rh yolites

■[Introductory

Upper

an d esites j

- R - J phase andesi­

tes 2nd g en era ­

tio n am p h ib o- le -a u g ite a n ­

desites

T ortonian Middle 2nd p hase rh yolites

Low er 1st p hase an ­

desites - R -

1st gen eration am p h ib ole- -a u g ite an d esites

The geo lo g ica l aspects of th e correlations in S lo v a k ia fo llo w K u t h a n (1948, 1964).

The p alaeom agn etic zonation is from N a i r n (Ii967).

4) M e a s u r e m e n t s o n I g n e o u s R o c k s b e t w e e n K r o ś c i e n k o a n d B i a ł a W o d a

E ast of the W żar m ount th e re are num erous andesite dykes o u t­

cropping betw een Krościenko and B iała W oda (Fig. 1). B etw een K roś­

cienko and Szczawnica all th e andesites exam ined proved to be too bad ly

w eath ered or too poorly exposed for sam pling. A t Szczawnica on the

B ry ja rk a m ount and in th e G rajcarek stream , and near S zlachtow a on

— 4 8 7 —

mounts Jarmuta and Krupianka samples were collected at several sites in amphibole andesite or amphibole-augite andesite which appeared fresh. A small isolated outcrop of olivine basalt was sampled at Biała Woda.

A ll of these samples were weakly magnetized and upon demagnet­

ization did not produce consistent results. As minimum information it appeared that two Jarmuta sites were reversely magnetized and three (on Jarmuta, Grajcarek and Bryjarka) were normally magnetized (Tab. 4).

T a b l e 4 P a laeom agn etic aspect of igneous «rocks b e tw e e n Szczaw n ica and B ia ła W oda

S ite/rock type D I ^a K R

Demagn.

field oe

Sam pling

S zczaw n ica, Bryjarka:

am phibole a n d esite 320.3 + 5.1 53.9 6.3 2.683 170 2/5

S zczaw n ica, G rajcarek

stream : am phibole andesite 306.5 +43.2 32.3 15.6 2.872 85 3/4 Jarm uta (M alinów quarry),

S it e 1: am phibole an d esite 284.8 -7 1 .4 75.8 13.1 1.924 255 2/4 Jarm uta (Pod B ukam i), S i­

te 2: am phibole andesite 55.9 + 73.0 — — — — 1/4

Jarm u ta (SE slope), S ite 3:

amiphi'bole an d esite all too w e a k or inhom ogenous for m ea su rem en t Jarm uta (P ałk ow sk i Potok),

S ite 4: am pbiibole-augite a n ­ d esite

tw o sam ples g a v e no readings, o th er two only NRM at D = ca 240 and I = —45

B ia ła Woda: o liv in e basalt two sam ples g ave no readings, on e sa m p le on ly NRM m ea su rea b le

According to the work of M a ł k o w s k i (1958) the amphibole ande­

sites are the oldest phase of magmatic activity in the Pieniny Mountains.

Confirmation of this view was obtained by K a r d y m o w i c z (1952) who found xenoliths resembling the amphibole andesites within the amphibole-augite andesites of mount Wżar. Their petrological character indicates they cooled at greater depths than the Wżar andesites and their implacement geologically is regarded as contemporaneous w ith the end of the Savian phase (lowest Miocene or uppermost Oligocene — cf. B i r- k e n m a j e r , 1958, 1960). This is consistent with the known occurrence of rocks of both normal and reversed magnetization w ithin the Bur- digalian.

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