Palaeomagnetism of the Lower Palaeozoic rocks from the Western Sudetes, SW Poland - preliminary report

Geological Quartcrly, Vol. 40, No.3. 1996, p. 337-352

}en), NAWROCKI, Aoo=:j iELAZNIEWICZ

Pa laeomagnetism of the Lower Palaeozoic rocks from the Western Sudetes, SW Poland - preliminary r eport*

Palneomagnctic studics of the LowerOrdovicillll rnc:tagranites an mct3volcanic rocks from the I~crll-Knrkonosl'.ll Block and G6ry Kaclawskie. !'eS]lC(:tively, revealed the ])f'CScncc of two charactcristic directions with their poles located on the App;lrent Polar Wander Paths (APWp) ofEastcm Avalonia and Baltica. None of the poles filS to thcAPWPof Annorica Block, evcn ancr possible tc:ctonicconmions. The polc K obtained from the izcrngrnnitc of Kotcic.lniki quarry fits to the Late Ordovician·EarI), Silurian segmenl of Baltica and Eastern Avalooia paths.

Md the pole /of isoI:lled from the Kaczawa metavolcanic rock of Mm:inicc hill is located 011 their Middle CarlIonifel'OUS seement.

n.c

pa1:Icopole M was recorded most probably during the Visean mctllmOrphism of tile Kac:tuwa complcJl;.

n.c

paJacopolc K could have been recorded during "soft" collisioo of Bahica and Eastern AvaloniL On thcothcr hand pa.!:lCopolc K is loc.:.tcd in the Early Ordovician segment of the APWP of Avalonia.

if we l!.S.5umc a modcrnlc (301 northw:ml till of the Izera unit. The obtained <lat.:. do not allow to speak about separation ortlle Izera nnd Kncuwa tcmllCS during the Ordovici:m.

INTRODUCTION

'The Western Sudetes, occupyi ng the northeastern part of the Bohemian Massif (Fig.

I), are recentl y accounted for by highly controversial geody namic models. While many workers see Ihem as an eastern conti nuation oflhe Saxolhuring ian Zone and thus an integral part of the Variscides (W. Franke el al., 1993; A. i.elainiewicz, W. Franke, 1994), some olbers propose a collage of Caledo nian terranes and subsequent Hercynian reworking (G . J. H. Oliver et al. , 1993; Z. Cymerman, M. A. J. Piasecki, 1994). Palaeontological evidence pointing to continuities within a nd across the stratigraphic boundaries of the Palaeozoic systems in several Ordovician-Lower Carboniferous successio ns of the Sudetes make the Caledon ian model hardly tenable (Z. Urban ek, 1 975; J. Haydukiewicz, 1990; 1. Chlupat,

1993; A. Zelainiewicz, S. Cwojdzinski, 1 996).

·Conlribulion to the EUROPROBE meeting, Wroclaw·Ksi~ April 1996.

338 len)' Nawrocki, Andncj Zclainicwic1.

[K2} " -,

Fig. I. Geological sketch of the Western Sudetcs wilh location of samples for paJueomagn~ljc investigations (crossed circles); imc!: the Sudetes in the Bollt:mian M:lSSif

1 - Upper Carbonifcl'Qus-Mcsoll.oic cover: 2 - V.?Jisc:m granitoids; 3 - Devonian of Ihe Morava - Silesian Zone; 4 - unmclamorphosed synorogenic deposits of Latc Dcvoni:m-E:lrly Carboniferous age: 5 - Ordovician- LowcrCarbonifcrous metasediments; 6-Sudcticophiolilc; 7 - metabasites: 8 -LowcrOrdovkian granitoi(,]s:

9 - Ncoprotcrozoic-LowcrC:unbri:ll1 mct:unorphicsucccssion; 10- Lusatinn gmywaclcc of Vendian age: 11- Upper Prolcrowicgranitoids: 12- faults; 13 - "Moldanubian" Thrust: 14- Lusalian Thrust; EfZ- Elbe Faull Zone: FSB - Fore-Sudetic Block; lKB - Ilenl - Karkonosze Block: ISS - Intm-Sudetic Depression; GB - G6ry Bardzkie MIS.; GSS -G6ry Sowie Block: GK - G6ry Kanawskie MIS.; SO - Swicbodticc Depression;

K - Koociclniki; Ka -Karczmisko crag ncar Mystow; KM - K1od7.kO ITIcl:llTlorphic massif; M - Marcinicc hill: MtF- Main Intra-Sudetic Fauli; MZ- Moldaflubian Zone; OPZ-Odra Fault Zone; P- Pilchowice dilm;

R~tZ - Rhenooorcyniafl Zone; SMF - Sudetic MarginaJ Fault; STZ- SnxOlhuringiafl Zone

Sz).::ic gcologiczny Sudelow Zacllodnich z zaznaC'LC/Iiem micjsc pobrlllli:!. prObek do badilli paicomagnctyclllych (pnekreJlonc k6/ka); w prostokqeic; Sudety na tic masywu czeskicgo

I - pokrywa g6rnokarbol'isko-mezowicllla; 2 - grnniloidy waryscyjskic: 3 - !lewon mornwsko-~l"ski; 4- niczmctDmorli7-Clwanc synorogcnicznc osady pcif.ncgo dcwonu-wcw.~ncgo karbonu: 5 - ZUlClolllOrfi7-ClWana sukccsja ordowicko-dolnokarboriska; 6 - olio!il sudecki; 1 -mctab.lzyly: 8 - granitoidy dolnoonlowickic; 9 - zmc!amorlizowana sukccsja ncoprolerozoicl.Il(I-dolnok'runbryjsk3; 10 - wcndyjskic s1.uroglazy lu1yckic; II - granitoidy gomoprocerozoiczne; 12 - uskoki; 13 _ nruuni~cic "moldanubskic"; 14 _ nasuni~cie lu1yckic;

EFZ - strefa uskokowa t.aby; FSB - blok przcdsudccki; IKB - blok karkonosko·i1.cllki: ISB - dcpresja

!rOdsudccka; GB - Gory B:rrd1.kie; GSB - bioI: Gor Sowich: GK - Gory Kaczilwskic; SO - dcpresja Swicbodzic; K - Ko$cielniki; Ka - skalka K:!~misko kolo Mystowa; KM -mclilmorfik kto-d7.ki; M - wzgor/.c Marciniec; MrF - glowny uskok ~r6dsudccki; MZ - strefa motdanubsk3;

on -

Sirefa uskokow::l Odry; r- lama Pilchowicc: RHZ- strefa re6sko-hcrcy6ska; SMF - sudccki uskok brzctoy; STZ - Slrcfa silksonsko-Iu- ryngska

On the other hand, there are three occurrences of the Upper Devonian conglomerates

with pebbles dcrived from easy indenlifiab le sources nearby (G6ry Sowie Block, Klodzko

metamorphic massif, ophiolitic rocks). U sing that as one o f arguments.

J.

Don (1990)

proposed Ihe Main Intra-Sudetic Fau lt

(MrF)

as a major frac ture boundary between the

Caledonian a nd Variscan elements in the Sudetes. G. J. H. Oli ver

et af.

( 1993) and J . D.

Palaeomagnetism orlhe Lower Palaeozoic rocks ...

'"

Johnston etal. (1994) went on yet further and took the MIF as a colli sion suture between Baltica and a variety of tcctonostratigraphic terranes originally derived f rom Gondwana.

This model neglects, among others, the above-mentioned stratigraphic continuities in the Palaeozoic successions throughout the Sudetes and hence is criticized (P. Aleksandrowsk.i, 1994; A. :lelatniewicz, W. Franke. 1994). Moreover, speculative designation of the Sudetic suscpect terranes differ widely between proponents, wh ich makes the concept difficult to accept uncritically.

Palaeomagnetic data may potentially help in unravelli ng palaeogeographic position of rocks of the same age, and thus terrtln es embodying them, by determining their separation, veloc ity and direction of drift and sense ofrotatien. Unfortunately, palaeomagnetic studies on rocks from polyphase orogenic zones like the Sudetes are very difficult. This is due to widespread remagnetizations caused by multiple th ermal and mineralizat.ion events. More- over, pa laeomagnetic directions obtained from the deformed rocks even of determined age could have been obscured by rotation removing them from their position at the lime of magnelic acqui sition (see e.g. D. Seliabudidaya et at., 1 994). Therefore caution must be exereised while intClpreling Ihe palaeomagnetic data.

Having in mind the potential of the MlF 10 weld lithospheric plates or terranes, separated during the Ordovician by ca. 3000 km wide Tornquist Sea, we have attempled 1 0 get some relevant information rrom palaeomagnetic measurements made on the Ordovician rocks lying on either side of the MlF, i.e. on the opposite sides of the Tornquist Sea (Fig. I).

GEOLOGICAL SETTING

Wc collected samples from gneisses of the Izera - Karko nosze Block (IKS) occurring to thc soulh ofthc MIF, considered a critical plate suture (G. J. H. Oliver

et

at., 1 993), and from acid volcanic rocks of Ihe G6ry Kaczawskie Mts. (GK) to the north of it. The sampled localities were selected to have the TKB and GK rocks on twO different terranes designed by Z. Cymerman andM. A. J. Piasccki (1994).

The Izera - Karkonosze Block in ils northern part, from which our samples have come, consists mostly of (meta)granites emplaced during the Early Ordovician 515-480 Ma interval as shown by U-Pb multigrain

(A.

Korytowski eral., 1993; S. Ph ilippe et at.,

1995)

and Pb-Pb single grain zircon ages (A . Kr6ner

el

at., 1994), roughly consistent with Rb-Sr who le rock (errochrone) ages of 500-460 Ma provided by M. Borkowska et ai. (1980).

These granites. widely retaining their original igneous tex tures, became laler heteroge- neously deformed in superposed, generally subverucal zones of localized ductile shearing (A. Zelatniewicl., 1996). The age of this polyphase sheari ng remain s largely und ctennined.

However, younger dextral tra nspressiona l regime well seen in the MlF 7.one mu st have occurred under greenschist facies co nditions during the Visean, after the deposition of the Visean limestones in the GK but before the intrusion into the middle of the IKE of the Variscan Karkonosze Granite that yielded a Rb-Sr whole rock isochron age of 324±1I Ma (C. Pin et 01., 1988). On intruding the granite exerted some contact effect on its country rock within

It

ca. 500 m wide thermal aureole.

The G6ry Kaczawskie succession of (Cambrian?) Ordovician-Early Carboniferous age

consists of the Ordovician sandstone-sha le sediments passing upwards into th e Silurian-

S

340

Koocielniki

KS-2b s

~

Q

1m_ 00=

00 ~~""OOO""-"c'OO~"c-"

Man:iniec M-la

"

^{(X lo-JAhn)}

Q Oo~

I m _ I

W

"

w

"

E

s

lcn:y Nawrocki, Andrzej Zelatniewic~

KoSciclnikj

_"'-4b

s

(><IO"Mo)

~

I I

" Oo~

""'_

S

Q

Q

Marciniec M-4a S

•

^{(~ lli'Nm)}

/"

:?'

S

~

Q Innl!lItlII ^Oo~

"

I

Pilchowice PI-Je

s

'"

2

j)

(~ IO"Ahn)

j

00=

"",0=

00

_{200 400·C}

Karczmisko K-Sa

s '"

(x IO.JAIrn 20

w

"

Oo~

1=-

() 0 200 400 6OO·C

W

Palaeomagnetism of the Lower Pa1:1COz.oie rocks ...

341

Middle to Upper Devonian pelagic clayey-siliceous deposits s ubjected during the Early Carboniferous to widespread turbiditic redeposition within sedimentary-tectonic melanges (Z. Ba ranowski et al .• 1990; Z. Urbanek et aL, 1995). The Ordovician-Silurian sedi menta- tion was acco

mpanied by

bimodal volcanis m bearing a within-plate. alkaline signature, maturing with time toward N-MORB pillow basalts. Although the basallic volcanis m has not been dated more closely as yet, the acid element of this bimodal volcanogenic sui te yield ed aU-Ph multigrain zircon age of 5

11±39 M

a (unpublished data of C. Pin, cf. R.

Kryza, A. Muszy nski, 1992).

The G6ry

Kaczawskie s uccession experienced some blueschist metamorphism at P >

12

kb and 300-400' C followed by regional greenschist overprint at P < 8 kb and

T

350-450'C (R. Kryza,

\996). T

he unpublished geochronological data of H. Maluski are consistent with the Ar-Ar ages obtained for the Zelezny Brod metabasi

lcs

in

the Sou

th Karko nosze (Rychory MIS.), yielding ca. 360 and 340 Ma for blueschi st and greenschist me tamorphism, respectively (H. Maluski, F. Patoeka, 1996). The greenschist event swept also the lJ<B rocks in Ihe MIF zonc at the dextral tra

nspressional contact

with the G6ry Kaczawsltie succession (A. Zelatniewicz, 1996).

SAMPLING AND LABORATORY METHODS

20 hand oriented samples were taken from the (meta)granites of the Izera - Karkonosze Block

in twO localities. One is an abandoned quarry east of Ko~cielniki

(12 samples), the other is a craggy cliff near the Pilchowice dam (8 samples).

In

both cases, in spite of proximity to the MIF. the sampled rocks are very little deformed and have well preserved texture of a coarse-grained porphyritic granite. The granite from Koscielniki is dated at 500±12 Ma (V-Pb mu

ltigrain abraided zircon age: S. Philippe.

personal communication).

The granite from Pilchowice is undated, but nearby locality of the same rock up the course of the Kwisa river has rocks with U-Pb zircon age of 514±

l

l Ma (A. Kory

towski

et al .•

1993).

In the G6ry Kaczaws kie Mts. sampled were acid metavolcanic rocks occurring on the so uthwestern slope of the Marciniec hill (15 samples) and in the crag Kan:zmisko

(5

samplcs). The Ma

rciniec rock

is foliated and folded. and coarse-grained Karczmisko ke

ratophyre has much

poorer record of pene trative deforma tio n, yet it is much s teepened by almost 90'

likewise the surrounding

metasediments. It is the rock f TOm M arcinicc that

Fig. 2. Results of dem~gllCtiz:l1ion (orIlKIgonal platsand intensity decay curvcs)arEarly P:lIacoz.oie magm:Uie rocks fram lhe western part of SudelCS

x, y, z - the planes of tile projection. '/lrm - the intensity of tile natural remanent m3gllCtizalion. 'rm - the intensity of the remonent rT1lIgnctiuuion afterdemagllCtization; onhngonnl plots were prepared i" situ coordinates Wyniki rozmagncsawnnin (diagramy artogonalne onn: knywe spOOku natct.enia) wezcsnopaleowietnych skal IIl:1gfTIQwych t taehodniej C7~ci Sudct6w

x, y, l - p!asu:tytny projekcji. "mn - na!;:tenie natur.llnej porosto!oki magnetYU.IIej, IT/II - nJIt;"U:nic po7.QStaloki magoetyeUlej po i"ozm;J.gncsowaniu; projckeje ortogonalne wykooano w ukladzic bel korekeji lcktoniewej

342

" 1!

~

t -

,-

^~

~~

^{~ ~}

~

:;

%

^N ~

::l •

~

-

'"

~

•

_Z

.. ^N

.,;

-

0

~

::l

_~

11

^{M ~}

- ^•

^~

'" ^~

~ @

~ ~

~

~

• -

" -

~ ~

"

_~

0

"

^'S

I

f ^~

^{~ "}

,2

q -;

-

~

g

~

•

^M

-

~

~ ~

~

~

~ N

~

'"

^~

~

M N

~

~

~

~

-

~

•

'"

~

"

!i

~

~

"

E

"

,"

'~

~

~

- ~

0 ~

•

~

•

•

N

~ ~

~

~ M

'"

^{M M}

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..

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~

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~

:g

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.2 ~

Jeny N;lwrocki, Andn.ej Zclatniewi~

yielded the above·mentioned

U~Pb

zircon age of ca. 5 11 Ma. Keratophyrcs of Karcz rnisko re main undated. Accordi ngly, both the T KB

gneisses and GK acid metavolcanic rocks are of

the s ame Ea rl y Ordo vic ian c rystal- lizati onallemplacemcnt age.

Accordingly, it may be assumed that the magne tic carriers were primarily magnetized during the

Early

Ordovician at the lime of in·

trusion and extrusion, oflhe IK.8 and GK rocks, respectively. In both cases remagnetization is to be

expected during the Visean greenschi st metamorphism , in panicular in the Kaczawa rocks which were defonned at that ti me.

Unfortunately, the position of the palaeo- horizo ns in the sa mpled rocks at the time of magnetizatio n is difficult to determine. For the GK samp les tectonic correc tion was made ac- cording to the attitude of the bedding foliat ion plane obse rved in the neighbouring metasedi- ments. In the Izera granite o utcrops there is no rel iable geolog ical ev idence for a tectonic tilt, yel some authors assume some northward tiltar the Izera rocks caused by the ascent of the Karkonosze Grani te (S. M azur, R. Kryza, 1994),

Seve ral co re speci m ens wi th 2.2 e m

d iameter and 2.2 cm le nght were drilled from

each sam pIe. Eachspecimen has bccnsubjected

to stepwise demagnetization in nonm agnelic

oven with mimetal screens. Th e natural reman-

ent ma gne tization (NRM) of specime ns was

measured by means of lR-5 spinner magne-

tometer. Demagnetization a nd measurements

werccarried

OUI

in a cage reducing the ambient

field by about 95%. Magnetic susceptibility

was measured us in g KLY-2 suscepti b ility

bridge. Th e thermomagnetic method, in which

the saturation remanence versus temperature is

observed, was used to detenn ine the nature of

mag netic carriers. The principal compone nt

ana lys is as presented by J . L. Ki rschvink ( 1980)

was used to detennine the components ofNRM

and their unblocking temperature spec tra.

Pabeom3Jlnelism of tile Lower Pa!aeoloic rocks ...

RESULTS OF DEMAGNETlZATION AND

MAGNETIC SUSCEPTlBn...ITY ANISOTROPY fNVESTIGA TlONS

GRANITOIDS

343

KoScielniki. The NRM intensities flucluated here from 0.3 1 02.5 x JO-"Alm. In most of specimens only one component ofNRM ( label led

K)

with maximum blocking tempera- tures o f about 575 " C was isolated (Fig. 2). A little fluc tuation of this component during subsequent heating is a permanent feat ure observed on the demagnetization path but all the obtained high-temperature cha racteri stic directions are very well clustered (Tab. 1, Fig. 3).

In some specimens low-temperature components also occurred. Unfortun ately, they are very scattered (Fig. 3). The degree of An isotropy of Magnetic Susceptibility (AMS) P ranges from 1.039 to

t

.065, The mainaxcsofanisotropy are dispersed (Fig. 3). Hardly some characteristic directions correspond to the minimum anisotropy axes obtained for the same specimen. These features are consistent with the obvious lack of tectonic fabric and metamorphic overprint in the sampled granite and emphasize the significance of the component

K

possibly acqui red at the time of intru sion or du ring its cooling.

P ilchowice. The NRM intensities of Pilc howice gran ite varied from 0.4 to 3.6 x 1 0-4A1m. MajordecreaseoftheNRM intensities during thermal demagnetization took p lace at temperature range of 300-350'C (Fig. 2). At those temperatures component with shallow inclinat ion (labe lled P) was removed. Most of specimens revealed also the presence of low te mperature components with steep incl inations , most probably of recent(?) origin. The main axes of the AMS are grouping very well (Fig. 3) but no ne of them corresponds to the directio n

P.

The degree of anisotropy varies from 1.037

10

1.084. Equatorial va lues of inclination may show that lheacquisi lion of the component

P

mostly likely occurred during the Carboniferous overprin t at the MIF zone. The pronounced AMS corresponds well with the foliation-norma l shortening during the Visean dextral transpression.

METAVOLC~CROCKS

Marciniec. TheNRM intensities were here much higher tha n those observed in the Izera granite and fl uc tua ted from 6.5 to 18 x 10-3 Aim, During thermal demagnetization, a fter removing a low temperature component , at the temperature range of 250--630' C only one component (labelled

M)

was observed (Fig. 2). Alternati ng field demagneti zation experi- menl revealed also the presence of the component M (Fig. 2), whose internal homogeneity a t the sample and local ity levels is very good (Tab. I). The magnetic susceptibility anisotropy axes are grouping d isti nctly al the rig ht angle to the structura l grain of the GK produced by the SSW-vergentoverall shortening of the Kaezawa co mp lex during the Early Carboniferous times. Yet the direction

M

does nOI correspond to th e AMS (Fig. 3). Th e degree of anisotropy P varies from [.034 to 1.069.

Karczmisko. The intensities of NRM of me lakeratophyre from the Karczmisko c rag

were sl ightly lower than those noted in the sampl es from Marcini ec, and varied from 1.8 to

5.6 x 10-3Aim. Alt hough in single specimens the charac teristic directio ns. separated at the

•

,.

Jcrzy Nawrocki, Afldl7.cj Zclaf.niewicz

KOSCIELNIKI

PIlCHOWICE

KARCZMISKO

MARCINIEC

•

, . _•

c-t-h--j-

f-H:OO;8-+-j-

PnJru:omagnetism orLIle Lower P:Iloeozoic rocks ...

345

temperatures

up to630'C. are very

distinct (Fig. 2), theirclusteringal the sample

and locality level

is very poor (Fig.

3). The degree of magnetic susceptibility an

isotropy P nuctuated

between 1.045 and

1.162.

TheanisolrOpy axes (Fig. 3)arecl

ustered in the way characteristic for the secondary tectonic deformation

when so-called "pencil" s

tructures

are formed (R.

Kligfield et al., 1983).

MAGNETIC CARRIERS

Theml0magnetic curves prepared for the metavolcani

c rocks from the Karczmisko crag and the Marciniec hill show the presence of hematite with blocki

ng temperatures of about

675'C (Fig.

4). Significant decrease of isothermal

remanence at lower temperatures indi- cates the likely presence of another magnetic mine ral. Duri

ng the demagnetization experi- ment

the largest decrease of the NRM intensity was observed at th e temperature range of 400--550

'C and in

the demag

netizing field

nOI hi gher than 50 mT (Fig. 2). Therefore it is very probable that magnetite is also an important magnetic carrier in th e inves

tigated rocks.

The largest

dec

rease

of

isothermal magnetization of the Izera

granite samples takes pl ace at temperatures below 600·C. although a small hematite " tail"

is also observed

(Fig. 4).

However, the shape of

demagnetization c

urves

(Fig. 2) indicate that magnetite is the main carrier of

remanence in the Kogcielniki

granite. A significant increase of isothermal

rcmanence after the first healing

was noted in the sample from

Pilchowice (Fig.

4). This

increase together with a sharp decrease of

the NRM

intensity

at the temperature ran ge of 300-330· C (Fig. 2) may indicate that ferric sulph ide (pyrrothite?) is the main NRM carrier

in

^thi

^{s grani toid.}

DISCUSSION

QFTHE RESULTS

The palaeopoles

K and M

taken

in situ or tectonica

lly corrected

fit well thc Appare

nt

Po

lar Wander Paths (APWP) ofBahiea and Eastern A

valonia (Fig. 5). None of palaeomag-

netic poles isolated here fits the APWP of

Armorica.

It should be stressed, however. that

the APWP of Armorica is as yet very tentative (see V.

Bachtadse

et al.,

1

995).

The

palaeopole P is located away fTOm the two mentioned paths. This fact may be related either to local tectonic rotati on on the MlF zone during the Visean dextral transpression, or taken as artefact. However. so

me Permian palaeopoJes from the Sudetes have been found ro

tated

Fig. 3. Stereogrnphic projections or tile characteristic components orille ~m:mcnt rnagnetiullion (on the left) nmJ Lhe main axes of magnetic susceptibility obtained from the Sudetic Lower Palaeozoic rocks

The low tcmpcr.lturecomponcnlS from Ko.§ciclniki:rnd maximumsusccptibilily axCSllJ'e marked by squ:u-es; in the susceptibility graplls circles m:u-k the minimum suscep(ibilily n~cs, trinngles- inlermcdi.ue susceplibility axes Projekeje st~ografiezne sklndowych chamlacrystyc7.1lYch pozostalo!ci mngm:l)'t:znej (z lewej $Irony) onl.1;

gl6wnyeh osl podatnoki mngnct)'t:zllej otn:ymanych z sudeckich, doloopalcozoio.ll)'t:h skat magmowyeh Niskotempcrnlurowt: skl:KIowc z Ko.fcidnik omz osie m3ksyrnalncj podntno.fci z.:lznnczooo kw;]drntnmi; nn projekejneh osi podaLnoki magnetycz.ncj k61kami Z3.l.nnczono os;e minimalnej podnmo.fei, natomia.<;1 tr6jk:Ullmi - osie po§redniej podaLnooei

346

Jerzy Nawrocki, Andrzcj Zelatniewic7.

Irm/Jrm"

Kokielniki, sample KS4

IMiInno Pilchowiee, sample PL3

.. ..

.. ..

" "

.. ..

" "

" ,.

.. _"

.. ..

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• ,.

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^~

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_{- -}

Irrn2IIrm 1- 1.3 ^{T~C) Irm2Ilnnl" 18 T("e)}

I"""~ Karczmisko, sample K4 Marciniee. sample M4

InnIIrn> •

.. . ^.

^"

" ..

..

^'''f''- .".".~".~-.•.. :-.

J ..

"",

" "

..

^.,',

^. ',' ..

" "

"

^···1

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.. ..

.. ..

" " • •

• •

• ,.

^lrm2Il

-

rml" 1.1^~

-

5 ^~ T("C)

-- ^{• '.}

lnn2/Innl-

^-

^~

0.8 ^{- -}

^{T(G C)}

- ^-

first heating (pierwsze grzanie) ... - second heating (druCic gnanic)

Fig. 4. Examples of intensity decay cu~ of isothermal remanence (s.as.umted 10 1 Tesln field) during healing of Early Pmaco:wic

magmatic

rocks from the western part ofSudclCS

{,trio - iSOIhcrrnal remanence before heating. 1m - isothermal

remanence

durillg heating. 10111-isotherm:!!

refI1llllcncc before firs! healing. 1mQ.-isothermal remanence before second heating

Przyklady Icrtywych sJXldku natcicnia pozosla!o~ci iw\crmiczncj (nasyooncj w polu I tesli) z biegiem w)'grzewania wczcsnopalcOloicUlych ~IUU magmowych 1. zachodniej ct¢ki SUdclOW

/rmc - pOl:OSta/~ izolcnniczna przcd grzaniern, Irm _ pozosuUo~(! izolcrmiczna ^W trakcic grLllnia, Irml -

P07.ostalO~ izotermicznll prz.cd pierwszym grzaniem, frrrll-pozostlll00(! iZotcmUC'ZlIa prlcd drugim gr7.1lnicm

antidockwise by 15 ' from the expected positions

(J.

Naw rocki, 1995). All the palaeopoles most probably were little affected by tectonic stress, because they are not convergent with the axes of anisotropy of magnetic susceptibility, which otherwise is consistent with low amo unt of strain record in both the I KB and GK rocks. A large scatter of cha racteristic directions in the metavolcanic rock from Karczmisko could be connected with relatively greater degree of anisotropy.

!fthc coincidence of the pa[aeopoles K and M with the APWP of Baltica and Avalonia

is not accidental, we can assume that the paJacopole

M

is of the Visean age and fits the

APWP of Baltica, while palaeopole

K

is of (h.e Late Ordovician age and filS the APWP for

Ava lonia (Fig. 5).

PallIC()magnetism ofthc Lower P:ilaeozoic rocks ... 347

Fig. 5. Apparent Polar WlInder Paths for Sallica (T. H. TOll'vik fillll .. 1992), Eastern AVlllonia (T. H. Torsvik el al., (993) lind Anoorica (T. H. Torsvik fit al., 199(), and pre-Permian palacomagnetic poles from Sudetes Al _ pole from the Sudetic ophiolite (M. lelcibka fit (IL, 1995), K, M. P - poles presenled in Ihis paper, polcs wilh ovals of confidence drown by dashcd line an: shown aflcrlectonic correction; 30' of northward (azimuth IS') tilt of Ihc K~iclniki grnnitc was assumed (sec S. Mazur, R. KryzlI, 1994); numbers in the brackets indicate the palllC()llItimdes ofinvcstigated area calculatcd :ICC(Irding 10 the palaeopo1e; ages in Ma

Scid:l;i powrnej wedrowki paleobicguna charaktcryslyczm:go dla Sa/tiki (T. H. Torsvik i in., 1992), wschodniej Awalonii (T. H. Torsvik i in., 1993) i Armoryk! (T. H. Torsvik i in., 1990) oraz prtedpcrmslde palcobicguny Z Sudct6w

A I _ biegun z oriolitu sudcckiego (M. JeJCI\sl:a i in., 1995). K. M, P - bicguny pncdstawione w Iym artykule;

bicguny 7. owalcm ufnofci wykrcl.lonym lini;t przcrywan<l nnnicsiono po korekcji tcklonic7.ncj; przyjeto,:i.e skiero- wany ku p6lnocy (azymul IS') upad grnnitu

z

Ko~cielnik wynes! 30' (patrz S. Mazur, R. Kryza, 1994); liemy w nawiasach oznaczaj1l palcoszerok~ci gcogmficzrn: miejsca badan odnosZ<\CC sie do danego paleobicgllnB; wick w milionao:::h lat

The l ate Visean ageof lhe palaeopole M is very probable because althat time thest udicd

metavo l canitcs were subjected to greenschist metamorphism (R. Kryza, A. Muszynski,

1992). Poles positioned much alike the pole M werc isolated from the Sudetic ophiolite by

M. Jclciiska el at. (1995, Fi g. 5. pole AI). They have been interprcted as Si lurian ones

because of the isotopic U-Pb zircon data (G. J. H. Ol iver et at., 1993) pointing to

crystallization ti me of the gabbro protolith. However, Silurian and Carboni ferous segments

".

^Je17.y Nawrocki, Andnej Zela1.niewict

of the APWP for Baltica lie very close to each othe r. Therefore the Lute Visean age of the pole A

I

is quile likely as well. The Carboniferous paJaeopoles convergent with

M

and

AI

werc also noted in the other parts of the Variscan orogen (J. B. Edel, F. Wickert, 1991 ).

Mechanism of acquisition of the paJaeopoJe

K

is not clear. If

it

is really of Late Ordovician-Early Silurian age, then ilS acquisition could be connected with "soft" collision of Baltica and Eastern Avalonia that took place

JUSt

at that time (see T. H. Torsvik el al..

1993), However, the solution assuming a moderate ( .. 30°) syn-Variscan nonhward dipping

of stodied granitoids can nOI be excluded. Then palaeopolc

K

corrected in such a way is located in the Early Ordovician segment of Avalonian APWP (Fig. 5), hence close to the emplacement age of the studied granite. This place al least northern part of the Izera-Kar- konosze Block on the Early Ordovician Avalonia and can require collision with Baltica by th e Laic Ordovician when the two APWP paths mel. However, it should not necessary me:m that the

G6ry

Kaczawsk ie Mts. were part of the Baltica. With illegible Early Ordovician directions in our samples. the Kaczawa complex may, in view of the data in hand, by that time belong to either Baltica or Avalonia, if tectonic corrections for the observed folding or the Marciniec rocks are carefully made.

In the Pilchowice, Marciniec and Karczmi sko samples similar mnxima of the magn etic anisotropy axes (Figs. 3, 5) are probably related to the Visean principal tectonic Stress operating along the SSW- NNE direction . Magnetic lineation observed in the neighbouring, post-orogenic Variscan KarkonOS7.e Gra nite (H. Diot, M. P. Mierzejewski, 1 994) is ob- viously younger and perpendicular to those recognized in the IKB and GK.

It

should be noted that thescatterd AMS pattern observed in the sam ples from Kok icl- niki is completely different from other samples and consistent with little slfain.

CONCLUSIONS

It follows from this study that:

- separation of parts of the Sudetes (suspect lerranes) by the Tornquist Sea du ring the

Ordovician cannot be inferred from the currently obtained palaeomagnetic data;

- no evidence ex ists for any large-scale strike-slip displacements along the MIF zone (alleged Baltica-Gondwana suture of G. J. H. Oliver e/ al., 1 993) at least from the Late Ordovician onwards, which precludes the Caledonian oblique colli sion in the Sudetes;

- by the Carboniferous the Sudetes were all assembled within Baltica and Avalonian segments of the Laurussia;

- during the Ordovician at least the IKB, and possibly both rKB and GK, might be linked to A valonia;

- there is no indication in the Sudetes for connection with Armorica duri ng the whole Palaeozoic;

- limited number of the studied localities and lack of well defined pre-Pennian

structural controls on palaeohori:wns do not allow at the moment

10

draw more precise

conclusions.

Palacom:lgnetism ortne Lower Palaeowic rocks ... 349

Acknowledgements, Grant KBN No.9 S602 030 06pOl from the Co mmittee of Scientific Research, Warsaw, is gratefully ackno wledged. Special thanks

[0

Dr. Stefan Cwojdzit'iski for his participation at prelimi nary stage o f this work.

Zaklad Geofix.yki

Paristwowcgo Instytutu Goologicznego Warsuwa, ul. Rakowic:cka 4 Instytut Nnuk Geologicl.llych Polskiej Akademii Naulr;

Wroclaw, ul. Podwale75 Received: 5.06.1996

Trallslated byaw/wr!

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Pal:lC(lmagnctism of the Lower PaJaeo7.oic rocks ...

Jcrzy NAWROCKI, AndlZCj :2;E"LAZNLEWICZ

I'ALEOMAGNETYZM SKAL DOLNEGO PALEOZOIKU Z ZACHODNIEJ CZFcSCI SUDETOW - KOMUNIKAT WSTF;PNV

Strcsl:c1:cnic

35'

W wyniku badati pnIcomagnclyc1.nych dolnoordowickich mctagrllllil6w i mclawulkanilow z bloku izcrsko-- -karlconoskkgo i Gar KaCQwskich wyod~bniOflO dwa kierunki Chamk~rySIyezne, kl6rych bicguny 1I1okoW31lC 5lI no. ~cictce pozomej wCdr6wki bicguna paJeomagnetYC7.ncgo charakleryslYC7.llego dla wschodnicj Awlllonii i Baltiki. Zadcn z bieglln6w nie nawilp.Ujc do kid.k.i :umorykanskiej, nawel po wykonaniu moiJiwej korekcji lekloniC"£Ilcj. Siegun K, kt6ty otaymano 1: granMw ilcrskich odslMi3jltCych sic w Kokielnikach, palotony jest na pOfnoordowickim-wczesnosyhmkimsegmencidcid.k.i bahycko-awalooskicj. Sicgun M, !::Iory wyod~bniono Z IllClawulkanitow l:ocZllwskich, oprObowanych no. wzgorzu Marciniec, ulokowany jest no. ~rodkowokarbOliskim

segmencie Ie; kie1.k.i. Biegun len wpisal si~ no.jprawdopodobniej w wyniku wizcfiskiego metrunorfizmu, jillci obj:!! kompleks kaczawski. Biegun K mOg/ si~ ulrwaJi~ z }ednej sttOlly w wyniku "mi!;kkiej" koJizji Balliki i wsehodniej Awo.lonii. Z drugicjjednak sirony biegun lco lokujc silO no. wczesnoordowiekim fragmeneie kictld 8walotiskiej,je§1i wtoiymy umiarkowany (30"), pOtnocny upalijednoslki izerskicj.