New 40Ar-39Ar age constrains for magmatic and hydrothermal activity in the Holy Cross Mts. (southern Poland)

Geo log i cal Quar terly, 2013, 57 (3): 551–560 DOI: http://dx.doi.org/10.7306/gq.1117

New

Ar-

Ar age con strains for mag matic and hy dro ther mal ac tiv ity in the Holy Cross Mts. (south ern Po land)

Jerzy NAWROCKI¹, Sylwester SALWA² and Magdalena PAÑCZYK^1, *

1 Pol ish Geo log i cal In sti tute – Na tional Re search In sti tute, Rakowiecka 4, 00-975 Warszawa, Po land

2 Pol ish Geo log i cal In sti tute – Na tional Re search In sti tute, Holy Cross Mts. Branch, Zgoda 4, 25-523 Kielce, Po land

Nawrocki J., Salwa S. and Pañczyk M. (2013) New ⁴⁰Ar-³⁹Ar age con strains for mag matic and hy dro ther mal ac tiv ity in the Holy Cross Mts. (south ern Po land). Geo log i cal Quar terly, 57 (3): 551–560, doi: 10.7306/gq.1117

New ⁴⁰Ar-³⁹Ar iso tope ages of diabase in tru sions from the Holy Cross Moun tains (Po land) con firm the pres ence of at least two events of Pa leo zoic mag matic ac tiv ity in the study area. The old est, lat est Si lu rian/ear li est De vo nian (ca. 424–416 Ma) ep i sode is re corded by a diabase from the Bardo Syncline (Zarobiny PIG-1 bore hole) in the Kielce Re gion. A youn ger, Serpukhovian (ca. 331–323 Ma) event is doc u mented by a diabase from the Milejowice-1 bore hole drilled in the £ysogóry Re gion. The diabase in tru sion pen e trated by the Wzorki-1 bore hole, also lo cated in the £ysogóry Re gion, is most prob a bly of the same age. It pro vided, how ever, con sis tent mid-Tri as sic (243 Ma) ⁴⁰Ar-³⁹Ar iso to pic age re flect ing its per va sive hy dro - ther mal al ter ation. The first stage of the post-Cal edo nian hy dro ther mal ac tiv ity in the Holy Cross Mts. which pro duced polymetallic cop per and iron-bear ing min er ali sa tion may be linked with the youn ger mag matic phase de fined here. The sec - ond stage of post-Cal edo nian hy dro ther mal ac tiv ity in the Holy Cross Mts., as so ci ated with the lead-zinc min er ali sa tion, may be cor re lated with the Mid dle Tri as sic hy dro ther mal event re corded in the Wzorki diabase. Sug ges tions of tem po ral re la tion - ships be tween mag matic/hy dro ther mal ac tiv i ties and min er ali sa tion events should, how ever, be con strained by fur ther de - tailed geo chem i cal and min er al og i cal stud ies.

Key words: Ar-Ar geo chron ol ogy, diabases, min er ali sa tion, Holy Cross Mts.

INTRODUCTION

In some places, Pa leo zoic sed i men tary rocks of both tectono-strati graphic units of the Holy Cross Mts. (HCM), i.e. of the Kielce and £ysogóry re gions (Fig. 1A), are cut by scat tered small to me dium size mag matic in tru sions rep re sented by dykes and sills of ba saltic com po si tion (Fig. 1B; e.g., Czarnocki, 1919; Ryka, 1957; Kardymowicz, 1967). The ages of these mafic in tru sions re main a mat ter of con tro versy. They range from Late Si lu rian to Car bon if er ous. The HCM subvolcanic rocks have a dis tinct sig na ture of anorogenic magmatites, typ i - cal of con ti nen tal extensional set tings, and they rep re sent tholeitic melts gen er ated prob a bly as a re sult of the ther mal ef - fect of a man tle plume on the base of the sub con ti nen tal litho - sphere (Krzemiñski, 2004).

The me dium-grained rocks of ba saltic com po si tion of this study should, ac cord ing to stan dard ig ne ous rock clas si fi ca tion, be named as microgabbros. How ever, due to the wide spread us age of the tra di tional name diabase for ba saltic dykes and sills from the Kielce and £ysogóry re gions, we con tinue to use this lo cal name.

A pos si ble link be tween hy dro ther mal vein min er ali sa tion and mag matic events in the HCM has been sug gested by sev - eral au thors (Czarnocki, 1950; Rubinowski, 1962, 1971), on the as sump tion that mag matic in tru sions and the Variscan epigenetic min er ali sa tion had the same deep mag matic source (Kardymowicz, 1967; Rubinowski, 1971). A sec ond ary hy dro - ther mal or i gin was in ferred for the post-Tri as sic lead-zinc for - ma tion (Rubinowski, 1971). The oc cur rence of epigenetic min - er ali sa tion con tain ing dif fer ent met als is com mon in the HCM.

The sys tem of cross cut ting veins rep re sents sev eral events with dif fer ent types of min er ali sa tion, and some ore-bear ing zones have been ex ploited for sev eral cen tu ries. Since the last cen tury they have also been a fo cus of sci en tific stud ies (e.g., Czarnocki, 1950, 1956; Rubinowski, 1971). Three ore as sem - blages: iron-bear ing, cop per-bear ing and lead-zinc-bear ing, were dis tin guished by Rubinowski (1971) who also de fined two stages of hy dro ther mal ac tiv ity in the Holy Cross Mts. – pre-Perm ian and post-Tri as sic.

Dur ing the pre-Perm ian stage the polymetallic cop per as - sem blages was formed. Apart from cop per it con tains nickel, co balt, sil ver and gold (Rubinowski, 1971; Balcerzak et al., 1992; Muszer et al., 1995). This type of min er ali sa tion is cor re - lated with low to me dium tem per a ture hy dro ther mal ac tiv ity and linked with the Variscan fault zones of the west ern part of the Kielce Re gion (Rubinowski, 1971). Rel a tively large oc cur - rences of cop per-bear ing min er ali sa tion are only known from two sites of long-last ing min ing in Miedzianka and Miedziana Góra (Czarnocki, 1956; Rubinowski, 1971).

* Corresponding author, e-mail: magdalena.panczyk@pgi.gov.pl Received: January 18, 2013; accepted: July 18, 2013; first published online: September 12, 2013

The iron-bear ing for ma tion, which oc curs in the £ysogóry Re gion only, is also re garded as Variscan. This age es ti ma tion is based on the oc cur rence of py rite, he ma tite and sid er ite peb - bles in lo cal Perm ian con glom er ates (Samsonowicz, 1934;

Rubinowski, 1971). The larg est ore body con tain ing py rite, he - ma tite and sid er ite was found at Rudki and was mined un til the early 1970s. Smaller oc cur rences of iron-bear ing min er ali sa tion were noted in Zagnañsk (Czarnocki, 1950), £¹czna and Wzdó³-Kamieniec (Osika and Ekiertowa, 1958). In all cases the iron-bear ing min er ali sa tion oc curs as a sys tem of veins de vel - oped along tec tonic dis con ti nu ities.

Cal cite veins up to tens of metres thick lack ing of metal- bear ing min er ali sa tion and de fined as pre-Perm ian oc cur main - ly in the west ern and cen tral parts of the Kielce Re gion (Rubinowski, 1967, 1971). A pre-Perm ian age for this min er ali - sa tion is in ferred be cause peb bles of cal cite veins have been found in Perm ian con glom er ates (Rubinowski, 1971). Some au thors, how ever, pos tu late a dif fer ent, i.e. post-Perm ian age of the cal cite and quartz min er ali sa tion in the HCM. Migaszewski et al. (1996) as signed the main cal cite min er ali sa tion phase to the lat est Perm ian and mid/late Early Tri as sic. Quartz oc cur - rences, noted in the De vo nian car bon ate se quences of the HCM, were linked by Migaszewski et al. (1996) with the Visean/Serpukhovian phase. Ac cord ing to Salwa (2006), quartz min er ali sa tion in the HCM has a polycyclic na ture.

Decimetre-scale quartz vein formed in pre-De vo nian and pre-Perm ian time be cause peb bles de rived from quartz veins have been found within the Perm ian and Lower De vo nian con - glom er ates (Salwa, 2006).

An other type of vein min er ali sa tion in the Kielce Re gion con tains the lead-zinc as so ci a tion. This has been re garded as post-Tri as sic in age and epigenetic in or i gin (Rubinowski, 1970, 1971). This min er ali sa tion fills dif fer ent sys tems of fis sures de - vel oped in Mid dle and Up per De vo nian car bon ates and im preg - nates the Buntsandstein strata.

Two sites with polymetallic min er ali sa tion, and con tain ing marcasite, py rite, uraninite and sid er ite, were found at Rudki and Wzdó³-Kamieniec of the £ysogóry Re gion (Osika and Ekiertowa, 1958, Rubinowski, 1971; Szecówka, 1987). A tar get of the past min ing in the HCM was also the bar ite de posit. Sev - eral prom i nent bar ite veins have been ex ploited in the west ern part of the HCM where they cut Pa leo zoic to Mid dle Tri as sic strata (Czarnocki, 1936).

The aim of this study is to de fine pre cise and cred i ble iso to - pic ages for se lected mafic in tru sions of the HCM. Pre cise ages of magma em place ment are im por tant in re con struct ing the Late Cal edo nian and Variscan tec tonic re gimes in that area.

These data could also help in de ter min ing the sources and chro nol ogy of epigenetic min er ali sa tion in the HCM.

Fig. 1A – lo ca tion of the Holy Cross Moun tains on a tec tonic sketch map of Cen tral Eu rope (af ter Winchester and the Pace TMR Networkteam, 2002, mod i fied); B – geo log i cal sketch map of the Holy Cross Moun tains (af ter Filonowicz, 1981; Romanek, 1988;

Kowalczewski et al., 1990) with bore holes yield ing the ⁴⁰Ar-³⁹Ar age es ti ma tions marked

BVT – Brunovistulian Terrane, CDF – Cal edo nian De for ma tion Front, HCD – Holy Cross Dis lo ca tion, KLFZ – Kraków–Lubliniec Fault Zone, KR – Kielce Re gion, £R – £ysogóry Re gion, MPT – Ma³opolska Prox i mal Terrane, TTZ – Teisseyre-Tornquist Zone

INTRUSIONS STUDIED

BARDO DIABASE

The most ex ten sive ig ne ous in tru sion of the HCM oc curs in the Bardo Syncline in the cen tral part of the Kielce Re gion (Fig. 1). This diabase in tru sion pen e trates the Si lu rian rocks of this syncline, close to the strati graphic bound ary be tween Lower Lud low graptolite shales and Up per Lud low grey - wackes. The over all thick ness of the in tru sion var ies from 10 to 30 m. Tec tonic and strati graphic ob ser va tions sug gest a Late Lud low–Siegenian age in ter val for the Bardo diabase (Kowalczewski and Lisik, 1974). How ever, pre lim i nary iso - tope stud ies have not ex cluded a Variscan age (Migaszewski, 2002). A palaeomagnetic study of the Bardo diabase pro vides a pre-fold ing palaeomagnetic pole con cor - dant with the lat est Si lu rian seg ment of the ap par ent po lar wan der path for Baltica (Nawrocki, 2000). The re sults of the palaeomagnetic cor re la tion are con sis tent with those of sub - se quent ⁴⁰Ar-Ar³⁹ de ter mi na tions of plagioclase grains de - rived from the diabase (Nawrocki et al., 2007). Both age es ti - ma tions are, how ever, not suf fi ciently pre cise. The ⁴⁰Ar-Ar³⁹ sam ple stud ied re vealed the pres ence of two pla teaus for the low and high tem per a ture steps, which were 432 ± 2 Ma and 425 ± 11 Ma, re spec tively. On the other hand, the step size weight ing in di cated that the sec tion of the age spec trum from the step-heat ing run, from 0.4 to 0.97, was 424 ± 6 Ma (Nawrocki et al., 2007). Ac cord ing to Krzemiñski (2004) the Bardo diabase in tru sion may re cord a de tach ment of the Ma³opolska Block from Baltica, and its trans la tion along the craton mar gin dur ing Late Lud low–Emsian times up to its pres ent-day po si tion (see also Narkiewicz, 2002). How ever, this tec tonic trans la tion is not sup ported by any ex ist ing palaeomagnetic data (Nawrocki, 2000; Schätz et al., 2002).

It should be noted that Si lu rian (438 ± 16Ma) mag matic ac tiv - ity has been also doc u mented through K-Ar dat ing of a ba - salt vein in trud ing into the Brunovistulian base ment (Pøichystal, 1999).

A new sam ple for the whole rock ⁴⁰Ar-Ar³⁹ stud ies was taken from the west ern part of the Bardo Syncline where the diabase in tru sion was pen e trated by the new Zarobiny PIG-1 bore hole (lat i tude: 50°46’44.9”N, lon gi tude: 20°55’44.7”E). A fresh piece of rock was col lected from the bore hole at a depth of 84.8 m (Fig. 2). The Bardo diabases are char ac ter - ized by a fine-grained subophitic tex ture (Fig. 3A). The main min eral com po nents are plagioclase laths of lab ra dor ite-an - de sine com po si tion and clinopyroxene (augite) crys tals. In - di vid ual megacrysts of plagioclase (lab ra dor ite), which ex - ceed 2 mm in length, are also spo rad i cally found (Fig. 3B).

Ore min er als such as skel e tal titanomagnetite and titanohematite crys tals are com mon, whereas tiny crys tals of py rite and chal co py rite are scarce (Fig. 3C). The rocks are mod er ately al tered (sec ond ary quartz, cal cite, kaolinite;

chloritization of augite) and cut by microveins filled with cal - cite and chlorite (Fig. 3D).

New ⁴⁰Ar-³⁹Ar age constrains for magmatic and hydrothermal activity in the Holy Cross Mts. (southern Poland) 553

Fig. 2. Sam pling sites with ⁴⁰Ar-³⁹Ar age de ter mi na tions vs. sim pli fied lithological logs of the bore hole

cores ana lysed

MILEJOWICE DIABASE

The diabases ana lysed from the £ysogóry Unit are rep re - sented by two va ri et ies of rock: the Milejowice diabase and the Wzorki diabase, which dif fer in min eral paragenesis, tex ture and in ten sity of al ter ation. The Milejowice diabase from the

£ysogóry Re gion forms a nar row zone (max. 20 m wide) of long dykes cut ting folded Late Or do vi cian to lat est Si lu rian shales and greywackes. They were prob a bly in truded dur ing the late Gedinnian–early Siegenian (Kowalczewski, 2004). Ac cord ing to Krzemiñski (2004) the Milejowice diabase can be con sid ered as a post-tec tonic mag matic event as so ci ated with the ex ten - sion of the Baltica pas sive mar gin at the fi nal, Late Si lu rian stage of its col li sion with East Avalonia.

A sam ple for whole rock ⁴⁰Ar-Ar³⁹ age de ter mi na tions was taken from the Milejowice-1 bore hole at a depth of 96.4 m. The Milejowice-1 bore hole was lo cated at 50°50’17”N lat i tude and 21°13’50”E lon gi tude. The diabases (microgabbro?) from this depth are char ac ter ised by a me dium-grained subophitic tex - ture (Fig. 3E). The rocks con tain mainly clinopyroxene (augite) crys tals and plagioclase laths of lab ra dor ite-an de sine com po si - tion. Titanomagnetite, il men ite and ti tan ite are com monly ob - served. Ore min er als are rep re sented also by very small crys - tals of chal co py rite (Fig. 3F). Slightly chloritised bi o tite oc curs scarcely. Ad di tion ally, ac ces sory min er als are rep re sented by ap a tite, which forms in clu sions within bi o tite crys tals. The augite as well as sub or di nate bi o tite are some what chloritised.

WZORKI DIABASE

Sev eral dis tinct mag netic anom a lies mea sured by Paw³owski (1947) near the vil lage of Œwiêta Katarzyna–Psary in di cated the pres ence of pre vi ously un rec og nized diabase in - tru sions in that area of the £ysogóry Re gion. A diabase in tru - sion about 50 m thick was pen e trated by the Wzorki-1 bore hole lo cated at 50°54’57.8”N lat i tude and 20°53’10.5”E lon gi tude.

The diabase cuts across the Ludlovian shales and mudstones.

A sam ple for the ⁴⁰Ar-Ar³⁹ study was taken from the bore hole at a depth of 72.4 m. The fine-grained subophitic Wzorki diabase is ev i dently al tered. The rock con tains strongly al tered plagioclase laths (pre vi ously of lab ra dor ite-an de sine com po si - tion) and chloritised clinopyroxene (augite) crys tals (Fig. 3G).

Titanomagnetite, il men ite and ti tan ite are typ i cal ore min er als, whereas very small chal co py rite crys tals are very scarce.

Relicts of clinopyroxene grains oc cur within a mix ture of al ter - ation prod ucts. The com mon sec ond ary min er als are car bon - ates – an ker ite and sid er ite as well as chlorite and kaolinite.

Pumpellyite and prehnite were also iden ti fied within the Wzorki diabase (Fig. 3H) as prod ucts of in tense metasomatism.

The diabases stud ied from both ar eas con tain ca. 50% of SiO2. On the to tal al ka lis ver sus sil ica (TAS) clas si fi ca tion di a - gram (Fig. 4A; Maitre et al., 1989), all sam ples fall within the ba - saltic field. Plot ted on the clas si fi ca tion di a gram of Winchester and Floyd (1977; Fig. 4B), the com po si tion of the mafic in tru - sions falls within the subalkaline ba salt field.

ANALYTICAL METHOD

All the whole-rock sam ples for ⁴⁰Ar-³⁹Ar geo chron ol ogy were crushed by hand or with a jaw-crusher and sub se quently milled us ing a swing-mill. The sam ples were cleaned and pro - cessed into a range of grain-sizes and the 0.25–0.5 mm frac tion was se lected. Pheno crysts were re moved from the sam ples and, in some cases, the frac tions were sep a rated into one mag - netic and one non-mag netic part. The ⁴⁰Ar-³⁹Ar dat ing was car - ried out at the ⁴⁰Ar-³⁹Ar geo chron ol ogi cal lab o ra tory at the Uni - ver sity of Lund, Swe den. The sam ples se lected for ⁴⁰Ar-³⁹Ar dat ing were ir ra di ated to gether with the TCR sanidine stan dard (28.34 Ma fol low ing Renne et al.,1994) for 24 hours at the Or e - gon State re search re ac tor. J-val ues were cal cu lated with a pre - ci sion of <0.25% and are re ported for each sam ple in the data ta bles. De cay con stants uti lized were those given in Steiger and Jäger (1977). The ⁴⁰Ar-³⁹Ar geo chron ol ogy lab o ra tory at the Uni ver sity of Lund uses a Micromass 5400 mass spec trom e ter with a Far a day and an elec tron mul ti plier. A metal ex trac tion line, which con tains two SAES C50-ST101 Zr-Al get ters and a cold fin ger cooled to ca. –155°C by a Polycold P100 cryo genic re frig er a tion unit, is also pres ent. Whole rock sep a rates were loaded into a cop per plan chette that con sists of sev eral 3 mm holes. Sam ples were step-heated us ing a defocused 50W CO2

la ser. Sam ple clean-up time that made use of the two hot Zr-Al SAES get ters and a cold fin ger with a Polycold re frig er a tion unit was five min utes. The la ser was rastered over the sam ples to pro vide even-heat ing of all grains. The en tire an a lyt i cal pro cess is au to mated and runs on a Macintosh-steered OS 10.2 with soft ware mod i fied spe cif i cally for the lab o ra tory at the Uni ver sity of Lund and de vel oped orig i nally at the Berke ley Geo chron ol - ogy Cen ter by Al Deino. Time zero re gres sions were fit ted to data col lected from 10 scans over the mass range of 40 to 36.

Peak heights and back grounds were cor rected for mass dis - crim i na tion, iso to pic de cay and in ter fer ing nucleogenic Ca-, K- and Cl-de rived iso topes. Iso to pic pro duc tion val ues for the cad - mium lined po si tion in the OSU re ac tor were: ³⁶Ar-³⁷Ar(Ca) = New ⁴⁰Ar-³⁹Ar age constrains for magmatic and hydrothermal activity in the Holy Cross Mts. (southern Poland) 555

Fig. 3. Pho to mi cro graphs of sam ples ana lysed from the Bardo diabase (A–D) and of diabases from the £ysogóry Re gion (E–H) A – fine-grained subophitic tex ture with plagioclase laths and clinopyroxene grains, crossed polars (Zarobiny PIG-1 bore hole, depth 84.8 m);

B – plagioclase phenocryst (lab ra dor ite com po si tion), crossed polars (Zarobiny PIG-1 bore hole, depth 84.8 m); C – plagioclase laths, chloritised clinopyroxene, py rite and chal co py rite and skel e tal titanomagnetite and titanohematite crys tals, back-scat tered elec tron im age (BSE; Zarobiny PIG-1 bore hole, depth 84.8 m); D – diabase cut by microveins filled by two gen er a tions of cal cite and chlorite, back-scat tered elec tron im age (outer parts of veins; Zarobiny PIG-1 bore hole, depth 84.8 m); E – diabase (microgabbro?) with subophitic tex ture with fine plagioclase laths of lab ra dor ite com po si tion par tially en closed by me dium-grained clinopyroxene (augite) crys tals, crossed polars (Milejowice-1 bore hole, depth 96.3–96.5 m); F – pre dom i nant clinopyroxene ac com pa nied by plagioclase and chloritised bi o tite with ap a tite in clu sions, and ore min er als such as titanomagnetite, il men ite, mag ne tite and very small chal co py rite crys tal, back-scat tered elec tron im age (BSE; Milejowice-1 bore hole, depth 96.3–96.5 m); G – strongly metasomatised diabase with relicts of clinopyroxene crys tals and groundmass com posed of a mix ture of sec ond ary min er als, crossed polars (Wzorki-1 bore hole, depth 72.3–72.5 m); H – sec ond ary min er - als: pumpellyite, car bon ates and chlorite, back-scat tered elec tron im age (BSE; Wzorki-1 bore hole, depth 72.3–72.5 m); min eral sym bols af - ter Kretz (1983): Ank – an ker ite, Ap – ap a tite, Cal – cal cite, Chl – chlorite, Cp – chal co py rite, Cpx – clinopyroxene, Ilm – il men ite, Mgt – mag ne tite, Pl – plagioclase, Pmp – pumpellyite, Py – py rite, Sd – sid er ite, Ti-Mgt – titanomagnetite; all BSE im ages and min eral phase iden ti - fi ca tion were per formed at the Microprobe Anal y sis Lab o ra tory (PIG-NRI) in War saw us ing a Cameca SX 100 in stru ment

Fig. 4A – chem i cal clas si fi ca tion of the rocks stud ied on the to tal al ka lis ver sus sil ica (TAS) di a gram of Maitre et al. (1989);

B – chem i cal clas si fi ca tion of mafic in tru sions us ing a Zr/TiO2 vs. Nb/Y di a gram (Winchester and Floyd, 1977)

Fig. 5. ⁴⁰Ar-³⁹Ar age spec tra of diabase whole-rock sam ples from the HCM

Er ror bars of step ap par ent ages are drawn at 1s an a lyt i cal un cer tain ties; pla teau and pseudoplateau ages (±2s er ror) are also listed; MSWD – mean square weight de vi a tion, r – prob a bil ity of oc cur rence

based on Chi Square Ta bles, n – number of steps defining the plateau age

0.000264, ³⁹Ar-³⁷Ar(Ca) = 0 .000695, and ⁴⁰Ar-³⁹Ar(K) = 0.00073. The ⁴⁰Ar blanks were cal cu lated be fore ev ery new sam ple and af ter ev ery three sam ple steps. The blank val ues were sub tracted for all in cre men tal steps from the sam ple sig - nal. The lab o ra tory was able to pro duce very good in cre men tal gas splits, us ing a com bi na tion of in creas ing time at the same la ser out put, fol lowed by in creas ing la ser out put. The age pla - teaus were de ter mined us ing the cri te ria of Dal rym ple and Lamphere (1971), which spec ify the pres ence of at least three con tig u ous in cre men tal heat ing steps with sta tis ti cally in dis tin - guish able ages and con sti tut ing more than 50% of the to tal ³⁹Ar re leased dur ing the ex per i ment. In some places where a sta tis - ti cal over lap of steps is not ob tained, a forced-fit age is given over a cer tain per cent age of gas. The ⁴⁰Ar-³⁹Ar geo chron ol ogy data were pro duced, plot ted and fit ted us ing the ar gon programme pro vided by Al Deino from the Berke ley Geo chron - ol ogy Cen tre, USA.

RESULTS

The Bardo diabase whole-rock subsamples 2063-01 and 2063-02 from the Zarobiny PIG-1 bore hole gave well-de fined Ar-Ar pla teau ages of 412 ± 2 Ma and 415 ± 2 Ma, re spec tively (Ap pen dix 1, Fig. 5), with me dium MSWDs (1.64 and 2.06) and me dium to low (subsample 2063-02) prob a bil i ties of X² dis tri bu - tion. The age spec tra show an ir reg u lar in crease of ap par ent age from the low tem per a ture steps to wards the in ter me di ate tem per a ture steps.

Subsamples 2060-01 and 2060-02 from the diabase in tru - sion drilled in the Milejowice-1 bore hole re vealed the pres ence of whole-rock ⁴⁰Ar-³⁹Ar pseudoplateau ages 322.5 ± 1.1 Ma and 331.0 ± 1.9 Ma, re spec tively. In this case the age spec tra show a reg u lar in crease of ap par ent age from the low tem per a ture steps to ward the high tem per a ture steps.

Very con sis tent pla teau and pseudoplateau ages of 242.7 ± 1.6 Ma and 243 ± 2 Ma, re spec tively were de ter mined for subsamples 2064-01 and 2064-02 taken from the Wzorki-1 bore hole. In con trast to the pre vi ous sam ples, the age spec tra here show a reg u lar de crease of ap par ent age from the low tem per a ture steps to wards the in ter me di ate tem per a ture steps (Fig. 4). In spite of dis tinct age con sis tency, the me dium val ues of MSWDs are ac com pa nied here by rather low prob a bil i ties of X² dis tri bu tion, which are nev er the less ac cept able.

DISCUSSION

The re sults of ⁴⁰Ar-³⁹Ar dat ing re veal the pres ence of two events of mag matic ac tiv ity ex pressed by the diabase in tru - sions in the study area. The old est of these is doc u mented by the Bardo diabase drilled by the Zarobiny PIG-1 bore hole. The rel a tively pre cise age of this in tru sion can be in ferred from the iso tope ages pre sented here and the re sults of the cor re la tion of nor mal po lar ity palaeomagnetic re cord ob tained from the diabase of both limbs of the Bardo Syncline (Nawrocki, 2000) with the global po lar ity-time scale (GPTS; Fig. 6). Even as sum - ing an un cer tainty (non-an a lyt i cal) er ror of iso tope age es ti ma - tions, a Late Lochkovian–Early Emsian age of the Bardo in tru - sion can be ex cluded be cause this time in ter val is rep re sented by a geo mag netic field of re versed po lar ity. The real age of this in tru sion lies the be tween lat est Lud low (age of rocks con tain ing the in tru sion) and ear li est Lochkovian, where the nor mal po lar - ity time in ter val at the GPTS over laps with the ⁴⁰Ar-³⁹Ar ages ob tained here. Thus, the Bardo diabase emplaced in the age in -

ter val en closed be tween ca. 424 and 416 Ma pre ced ing the Late Lochkovian tec tonic event ex pressed by the Miedziana Góra and Gruchawka Con glom er ates, and a tec tonic dis cor - dance (Kowalczewski and Migaszewski, 1993; Malec, 1994).

The youn ger event of the mag matic ac tiv ity in the HCM is man i fested by the Milejowice diabase in tru sion sam pled in the Milejowice-1 bore hole. Ac cord ing to the new iso tope data, this in tru sion was emplaced in the Serpukhovian ca. 331–323 Ma.

The older ⁴⁰Ar-³⁹Ar age (331 Ma) cor re sponds well with the

40Ar-³⁹Ar age of a diabase in tru sion from the Brunovistulian side of the Kraków–Lubliniec Fault Zone drilled in the WB-137 bore - hole (Ta ble 1; see Nawrocki et al., 2010).

The Milejowice and Wzorki diabase in tru sions partly cor re - spond to the ma jor trans verse faults that are al most per pen dic - u lar to the Holy Cross Fault (Fig. 1). The iso to pic stud ies do not show the age of em place ment of the Wzorki in tru sion. The sam - ple stud ied has been strongly af fected by hy dro ther mal pro - cesses. As a re sult of these pro cesses the ⁴⁰Ar-³⁹Ar pla teau and pseudoplateau ages for the Wzorki diabase de fine most prob a - bly the time of its strong hy dro ther mal al ter ation that took place in the Mid dle Tri as sic, at 243 Ma (Anisian). The tec tonic set ting can point to the same Variscan age of the em place ment of the Wzorki-1 diabase as in the case of the Milejowice in tru sion.

The pos si ble link be tween hy dro ther mal min er ali sa tion and mag matic events in the HCM pos tu lated by sev eral au thors (Czarnocki, 1950; Rubinowski, 1962, 1971) can be con strained by the new iso tope ages, as sum ing that the mag matic in tru - sions and the epigenetic min er ali sa tion have the same deep source (Kardymowicz, 1967; Rubinowski, 1971). The first stage of post-Cal edo nian hy dro ther mal ac tiv ity in the HCM that pro - New ⁴⁰Ar-³⁹Ar age constrains for magmatic and hydrothermal activity in the Holy Cross Mts. (southern Poland) 557

Fig. 6. ⁴⁰Ar-³⁹Ar ages of diabase in tru sions from the Bardo Syncline (Zalesie Ra vine, Nawrocki et al., 2007; Zarobiny PIG-1 bore hole, this pa per) and NE part of the Up per Silesia Mas sif (Sosnowiec IG 1 bore hole; Nawrocki et al., 2010) vs. a strati - graphic chart with a part of the global po lar ity-time scale (af ter Gradstein et al., 2012)

The Bardo diabase re veals the pres ence of nor mal palaeomagnetic po lar ity only (see Nawrocki, 2000)

duced the polymetallic cop per and the iron-bear ing min eral as - so ci a tions (Rubinowski, 1971) may be linked with the Serpukhovian mag matic phase de fined here. The sec ond stage of hy dro ther mal ac tiv ity, as so ci ated with the lead-zinc min er ali sa tion (Rubinowski, 1971) may be cor re lated with the Anisian when the Wzorki diabase un der went strong hy dro ther - mal al ter ation. It should be stressed, how ever, that any spa tial and tem po ral re la tion ship of min er ali sa tion and mag matic ac tiv - ity should be ex am ined by more de tailed geo chem i cal and min - er al og i cal stud ies.

CONCLUSIONS

1. The new iso to pic ages, partly con trolled by magnetostratigraphy, sub stan tially re fine the ex ist ing strati - graphic set ting of the Holy Cross Mts. diabases. The Bardo diabase is ev i dently older than the Late Lochkovian. The age of its em place ment is en closed be tween the lat est Ludlow and ear li est Lochkovian i.e. be tween ca. 424–416 Ma. The Milejowice diabase in tru sion was formed dur ing the Variscan stage of tec tonic evo lu tion of the Holy Cross Mts. It was emplaced dur ing the Serpukhovian (ca. 331–323 Ma ago).

2. The ⁴⁰Ar-³⁹Ar pla teau ages for the Wzorki diabase de fine the time of its strong hy dro ther mal al ter ation that took place in

the Middle Tri as sic, at 243 Ma (Anisian). The iso to pic stud ies do not al low us to es ti mate the age of em place ment of this in tru - sion, but its tec tonic set ting points to the same Variscan age as for that of the Milejowice in tru sion.

3. The post-Cal edo nian hy dro ther mal ac tiv ity in the HCM that pro duced the polymetallic cop per and the iron-bear ing min - eral as so ci a tions may be linked with the Serpukhovian mag - matic phase de fined here. An other hy dro ther mal ac tiv ity event (pro duc ing the lead-zinc min er ali sa tion) may have taken place in the Anisian when the Wzorki diabase was hy dro ther mally al - tered. Hy poth e ses con cern ing the tem po ral re la tion ships of mag matic/hy dro ther mal ac tiv ity and min er ali sa tion events in the HCM should, how ever, be con strained by fur ther de tailed geo chem i cal and min er al og i cal stud ies.

Ac knowl edge ments. This re search was sup ported by the Min is try of Sci ences and Higher Ed u ca tion (pro ject no.

00.8520.1103.11.0 and de ci sion no. 3982/E-267/SPUB/2012-1) and by the Min is try of the En vi ron ment of Po land from the sources of the Na tional Fund for En vi ron men tal Pro tec tion and Wa ter Man age ment. We sin cerely thank to Z. Migaszewski, J.

Leichman and A. Vozarova for pro vid ing crit i cal and con struc tive re marks. We are grate ful to G. Zieliñski for an a lyt i cal work. Spe - cial thanks go to A. Schersten from Lund Uni ver sity for Ar-Ar anal y sis.

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