A Car bon if er ous/Perm ian, calc-al ka line, I-type granodiorite from the Ma³opolska Block, South ern Po land:
im pli ca tions from geo chem i cal and U-Pb zir con age data
Andrzej ¯ELAZNIEWICZ, Magdalena PAÑCZYK, Jerzy NAWROCKI and Mark FANNING
¯elaŸniewicz A., Pañczyk M., Nawrocki J. and Fan ning M. (2008) — A Car bon if er ous/Perm ian, calc-al ka line, I-type granodiorite from the Ma³opolska Block, South ern Po land: im pli ca tions from geo chem i cal and U-Pb zir con age data. Geol. Quart., 52 (4): 301–308.
Warszawa.
A granodiorite from bore hole WB-102A in the Dol ina Bêdkowska, the Ma³opolska Block (MB), South ern Po land, yielded a mean U-Pb zir con age of 300 ±3 Ma with SHRIMP II. No in her ited older com po nent was de tected. Geo chemically, it is a K-rich, I-type, calc-al ka line granodiorite with su pra-subduction char ac ter is tics (neg a tive Nb and Ti anom a lies). Silicic ig ne ous rocks are abun dant at the MB mar gin along the Kraków–Lubliniec Fault Zone (KLFZ) across which it ad joins to the Up per Silesian Block (USB) where such rocks are scarce.
Both blocks be long to the Variscan fore land. Gra nitic rocks can not, how ever, gen er ate at fore land set tings. Thus, the hy poth e sis is put for ward that the par ent melt for the silicic rocks was de rived from the thick ened lower crust of the Variscan orogenic belt ow ing to extensional de com pres sion melt ing, and trans ported away to wards pull-apart open ings de vel oped along the crustal-scale fault zone (KLFZ) that un der went a com plex strike-slip his tory around the Car bon if er ous/Perm ian bound ary.
Andrzej ¯elaŸniewicz, In sti tute of Geo log i cal Sci ences, Pol ish Acad emy of Sci ences, Podwale 75, PL-50-449 Wroc³aw, Po land; e-mail:
pansudet@pwr.wroc.pl; Magdalena Pañczyk, Jerzy Nawrocki, De part ment of Deep Struc tures Geo log i cal Map ping, Pol ish Geo log i cal In sti tute, Rakowiecka 4, PL-00-975 Warszawa, Po land; e-mails: magdalena.panczyk@pgi.gov.pl; jerzy.nawrocki@pgi.gov.pl; Mark Fan ning, Re search School of Earth Sci ences, Aus tra lia Na tional Uni ver sity, Can berra ACT 0200, Aus tra lia (re ceived: July 01, 2008;
ac cepted: Oc to ber 10, 2008).
Key words: Brunovistulia, Up per Silesian Block, Kraków–Lubliniec Fault Zone, SHRIMP, Variscan fore land, strike-slip.
INTRODUCTION
In South ern Po land, the NW-trending, crustal-scale Kraków–Lubliniec Fault Zone (KLFZ) sep a rates, in the subsurface, the Up per Silesian Block (USB) of the com pos ite Brunovistulian Block (BB) from the SW from the Ma³opolska Block (MB) to the NE, both con cealed un der Me so zoic-Ce no - zoic plat form cover and Carpathian nappes (Fig. 1). The two blocks dif fer mark edly in the ve loc ity struc ture of the crust as shown by seis mic re frac tion pro file CEL-02 of the CELEBRATION 2000 ex per i ment (Malinowski et al., 2005).
Such seis mic data is con sis tent with ear lier in ter pre ta tions of the Kraków–Lubliniec Fault Zone as a terrane bound ary (Brochwicz-Lewiñski et al., 1986; Harañczyk, 1994; Dadlez, 1995; Bu³a et al., 1997, Nawrocki et al., 2004). Based on dif - fer ent lines of ev i dence, this prom i nent crustal fea ture is as - sumed to have orig i nated in Neoproterozoic-Cam brian times and then re peat edly re ju ve nated dur ing the Palaeozoic (Dudek, 1980; Dadlez, 1995; ¯elaŸniewicz, 1998; ¯aba, 1999;
Nawrocki et al., 2004). On the pre-Me so zoic sur face, the fea - ture is con fined to a ca. 500 m wide zone of in tensely brit tle de - for ma tion (Bu³a et al., 1997; ¯aba, 1999) ob served in Palaeozoic rocks of the MB and USB. An other con spic u ous subsurface man i fes ta tion of the KLFZ is a de mar ca tion of the Lower to Mid dle Cam brian shal low-wa ter sand stone suc ces - sion on the Up per Silesian Block (Bu³a, 2000) which does not pass across the fault (Fig. 1A). In con trast, on the MB side, unmetamorphosed to anchimetamorphosed Neoproterozoic pelites (Jachowicz, 1994; Jachowicz et al., 2002), over lain by Or do vi cian and Si lu rian car bon ates and pelitic to psam mit ic rocks, ad here to the Kraków–Lubliniec Fault Zone (Bu³a, 2000). On the two blocks, De vo nian car bon ates are cov ered by Car bon if er ous clastic rocks. The Kraków–Lubliniec Fault Zone, which dips steeply to the NE or SW (¯aba, 1999) in its near-sur face sec tions, likely be comes a widely dis trib uted fea - ture deeper in the crust (Malinowski et al., 2005).
In both walls of the Kraków–Lubliniec Fault Zone, ig ne ous rocks are in ev i dence (Fig. 1). They are much less abun dant on the USB side. K-rich rhyolites to dacites in truded in the form of
laccolith into Car bon if er ous mudstones that lo cally crop out WNW of Kraków in the Up per Silesian Block (Fig. 1). These were dated at 295 ±3 Ma (U-Pb zir con, Nawrocki et al., 2008).
In bore holes lo cated along the SW mar gin of the Ma³opolska Block, gran ites, por phy ritic dacites and rhyolites, and mi nor mafic rocks have been en coun tered for up to some 10 km from the Kraków–Lubliniec Fault Zone dur ing ex ten - sive sur vey ing aimed at pros pect ing firstly, Pb-Zn and then for Cu, Mo, and W ore min er al iza tion (Dol ina Bêdkowska, where
the bore hole WB-102A is lo cated, Pilica, Zawiercie, Myszków and ¯arki ar eas; Fig. 1A). The Kraków–Lubliniec Fault Zone co in cides with a marked grav ity gra di ent and mag netic anom a - lies ow ing to the min er al iza tion of the ig ne ous rock masses (Królikowski and Petecki, 1995; Podemski, 2001). There is an ar ray of low grav ity anom a lies, stretched in a NW–SE di rec tion be tween Lubliniec, Myszków and Kraków on the Ma³opol ska Block, which re flects the ex ten sive pres ence of fel sic ig ne ous rocks at up per crustal lev els. As some of these rocks in truded
Fig. 1A — geo log i cal map of the Kraków–Lubliniec Fault Zone area (af ter Bu³a and Habryn, 2008, mod i fied): TTZ — Teisseyre-Tornquist Zone, USB — Up per Silesia Block, VDF — Variscan de for ma tion front (af ter Po¿aryski and Karnkowski, 1992; B — lo ca tion of the KLFZ
area in Po land (af ter Mazur and Jarosiñski, 2006, mod i fied; Po¿aryski et al., 1992); C — sim pli fied log of bore hole WB-102A
De vo nian car bon ates, their late Palaeozoic age has been long, if im pre cisely, known. A few at tempts of dat ing (K-Ar, Ar-Ar, Re-Os) yielded whole-rock or min eral ages be tween 312 Ma and 290 Ma (Jarmo³owicz-Szulc, 1984, 1985; G. Ol i ver in Harañczyk, 1989; Chaffee et al., 1997; Podemski, 2001; Stein et al., 2005). This pa per re ports the first U-Pb SHRIMP II anal - y ses of zir cons from a gra nitic rock of the Dol ina Bêdkowska area, some de tails of the geo chem is try of this rock, and the im - pli ca tions of the new data.
PETROGRAPHY AND GEOCHEMISTRY
In the Dol ina Bêdkowska area, some 30 km NNW of Kraków (Fig. 1), granodiorites were en coun tered in the bore - holes DB-5 and WB-102A at a depth of 1198 and 1091.5 m re - spec tively, be neath an up per most Neoproterozoic (Ediacaran) suc ces sion of anchimetamorphosed clastic rocks (Fig. 1C). The two bore holes are 270 m apart which is the min i mum size of the con cealed gra nitic body. A core re trieved from bore hole WB-102A from a depth of 1186–1188 m (Fig. 1C), is of an unfoliated, coarse-grained granitoid with vir tu ally no fab ric (Fig. 2). It is note wor thy that a lack of fab ric is char ac ter is tic of all the Ma³opolska granitoids and re lated subvolcanic rocks.
The WB-102A granodiorites are grey ish red to rarely grey - ish green, gen er ally holocrystalline, mas sive, me dium-grained rocks. They are char ac ter ized by por phy ritic tex ture with me - dium- and even coarse-grained plagioclase and fine-grained crys tals of quartz, al kali feld spar and mafic min er als rep re - sented by bi o tite and am phi bole. Zir con, ap a tite and ti tan ite are pres ent as ac ces sory min er als. In modal com po si tion, rock-form ing min er als oc cur in var i ous pro por tions:
plagioclase 42–55 modal per cent, quartz 24–38%, al kali feld - spar 3–20%, bi o tite 3–9%, and am phi bole (Mg-hornblende) 0.4–3.2% (Markiewicz, 2006). Sub hedral or euhedral tab u lar crys tals of plagioclase are dom i nant within the rock.
Plagioclase with con spic u ous re cur rent zonation are com - monly ob served (Fig. 2). The cores were iden ti fied as an de sine, whereas the outer rims are oligoclase and al bite. Most plagioclase crys tals are slightly al tered (sericitisation, carbonatisation, albitisation and rarely epidotisation). Al kali feld spar forms anhedral crys tals which are oc ca sion ally re - placed by kaolinite. Biotites which form coarse- and me - dium-grained crys tals (Fig. 2), very of ten with in clu sions of zir con and ap a tite, are only rarely chloritised.
Based on geo chem is try (Ta ble 1), the WB-102A rock is a metaluminous, K-rich, calc-al ka line granodiorite. On the Ba-Rb-Sr plot (El Bouseily and El Sokkary, 1975), it also ap - pears in the granodiorite field. The A/CNK in dex of 0.9 al lows as sig na tion to an I-type gran ite with a K/Rb ra tio of 268 and high K2O+Na2O. Such char ac ter is tics re sem ble A-type gran ites, how ever the Ga/Al ra tio of 2.1 as well as rel a tively high CaO, Ba, Sr but low Zr con tents are not con sis tent with such an af fin - ity (Whalen et al., 1987). Al though some A-type sim i lar ity is not sur pris ing in view of the geo log i cal po si tion of the granodiorite in the Ma³opolska Block, the neg a tive Nb and Ti anom a lies strongly in di cate a suprasubduction af fin ity, which is in line with rel a tively low Th con tents (<10 ppm). On the Pearce et al.
(1984) di a grams, the granodiorite plots per sis tently in the field of VAG and on the mod i fied Rb-(Y+Nb) plot (Pearce, 1996) it also lies in the field of post-col li sion gran ites. LREE con tents are 10–60 times chondrite and the REE pat tern is mod er ately frac - tion ated (La/Yb ra tio). A lack of Eu anom aly, rel a tively high con tents of Sr (>200 ppm) and Ba (> 800 ppm), and undepleted Rb and Cs sug gest that plagioclase was not left at the source and con se quently the melt could only be mod er ately frac tion ated and evolved (SiO2 <70%). The high Ba and rel a tively low Rb (<100 ppm) also in di cate in sig nif i cant feld spar frac tion ation (Blevin and Chappell, 1992). Uti liz ing some A-type re sem - blance, the melt may be thought to have been of crustal der i va - tion as sug gested by Y-Nb-Ce and Y-Nb-3Ga plots (Eby, 1992).
The ra tio CaO/Na2O of 0.8 seems to speak in fa vour of par tial melt ing of metapsammitic or granodio ritic to tonalitic pre cur sor rather than pelitic rocks (Jung and Pfänder, 2007). In the R1–R2 di a gram (Bat che lor and Bowden, 1985), it plots close to the bor - der be tween the fields of pre-plate col li sion and post-collisional up lift. The lack of fab ric in this rock cor re sponds well with the post-collisional sig na ture and does not con tra dict a post-tec tonic or anorogenic event in the re gion. How ever, in Zr+Nb+Ce+Y ver sus FeOt/MgO and (K2O+Na2O)/CaO dis crim i na tion di a - grams (Whalen et al., 1987), the WB-102A granodiorite plots in the field of unfractionated gran ites (OGT), far from the field of A-type gran ites.
Fig. 2. Mi cro pho to graph of granodiorite WB-102A Pl — plagioclase, Qtz — quartz, Bt — biotite
More de tailed study of the geo chem is try of the fel sic rocks from the Ma³opolska Block is be yond the scope of this pa per. Geo chem i cal cor re la tions with fel sic rocks from other oc cur rences in the Ma³opolska Block are lim ited, as most pub lished anal y ses from this re gion only show lim its of con - tents of el e ments ex cept for the pa per by Markiewicz (2002) which re fers to ma jor and some trace el e ments. Com par i sons based on avail able data re veal that the chem is try of three granitoids from the Myszków area re sem bles that of the stud - ied sam ple WB-102A.
GEOCHRONOLOGY
ANALYTICAL METHODS
Zir cons were sep a rated us ing con ven tional heavy liq uid and mag netic tech niques. The sam ple was an a lyzed by the SHRIMP II at the Re search School of Earth Sci ences, Aus tra - lian Na tional Uni ver sity, Can berra. Zir con stan dard FC1 (zir - con from the Du luth Gab bro) was used to cor rect Pb/U ra tios for in stru men tal frac tion ation. All grains were im aged in cathodolumine scence (Fig. 3) and pho to graphed in both trans -
Ma jor el e ments ox ides
[wt.%] Trace el e ments
[ppm]
SiO2 68.19 Ba 843 Th 9.39 Eu 0.967
Al2O3 15.39 Co 85 Tl 0.60 Gd 3.29
Fe2O3 3.35 Cs 2.7 U 2.78 Tb 0.47
MnO 0.039 Ga 17 V 60 Dy 2.54
MgO 1.28 Ge 1.5 W 509 Ho 0.51
CaO 3.23 Hf 3.2 Y 15.6 Er 1.47
Na2O 4.07 Nb 9.3 Zr 119 Tm 0.221
K2O 3.20 Pb 9 La 21.8 Yb 1.40
TiO2 0.585 Rb 99 Ce 45.9 Lu 0.225
P2O5 0.14 Sn 1 Pr 4.54
LOI 0.65 Sr 373 Nd 16.8
To tal 100.12 Ta 0.93 Sm 3.21
T a b l e 1 Geo chem is try of the granodiorite stud ied
Fig. 3. Zir cons in cathodoluminescence with lo ca tions of the an a lyzed spots marked
mit ted and re flected light prior to SHRIMP anal y sis to iden tify cores and overgrowths and crack- and in clu sion-free ar eas. An - a lyt i cal pro ce dures fol lowed the meth ods de scribed in Compston et al. (1984) and Wil liams and Claesson (1987). The data were re duced in a man ner sim i lar to that de scribed by Wil - liams (1998, and ref er ences therein), us ing the SQUID Ex cel Macro of Lud wig (2000). All ages in this study are cal cu lated us ing the weighted av er age of the 206Pb/238U ages as nor mally pre ferred for Phanerozoic sam ples be cause the 207Pb/206Pb ages are sen si tive to the com mon Pb cor rec tion. The plots of SHRIMP re sults, us ing ISOPLOT/EX (Lud wig, 2003) in clude:
(1) a Tera-Wasserburg plot 238U/206Pb ver sus 207Pb/206Pb us ing data cor rected for com mon Pb; Tera and Wasserburg (1972) as out lined in Wil liams (1998) which al lows a vi sual as sess ment of the data to de ter mine which data points should be used for the age cal cu la tion, (2) a stacked his to gram, and (3) a weighted av er ages plot of 206Pb/238U ages (us ing the 207Pb-com mon Pb cor rec tion method: Compston et al., 1984). In di vid ual anal y ses (Ta ble 2) are pre sented as 1 sigma er ror el lip ses on con cordia plots and un cer tain ties in mean ages are quoted at the 95% con - fi dence level (2 sigma).
DESCRIPTION OF SAMPLE
Zir cons from the sam ple an a lyzed are gen er ally trans par - ent, pale-col oured and euhedral with short-pris matic to nor -
mal-pris matic and less fre quent long-pris matic mor phol ogy (typ i cal elon ga tion from 2:1 to 4:1 and 7:1). In ter nally, most grains have a sim ple struc ture of char ac ter is ti cally mag matic os cil la tory zon ing and a few grains have pla nar-banded zon ing (Fig. 3). Around one third of grains have a weakly zoned or slightly dif fer ently struc tured euhedral to some what subhedral core in crys tal lo graphic con ti nu ity with a euhedral over growth which dis plays more in tense zon ing.
RESULTS
The grains ana lysed have mod er ate U and Th con tents with a Th/U ra tio of 0.28–1.00 which is typ i cal of zir cons grown un - der mag matic con di tions. 14 grains were an a lyzed in 20 spots (Ta ble 2, Figs. 3 and 4). All 20 anal y ses form a sin gle clus ter around 300 Ma and a spread of ages be tween 311 Ma and 278 Ma, with no re cord of in her ited old com po nents. 10 anal y - ses might ap par ently rep re sent “older” zir cons with a mean age of 304 ±2 Ma (MSWD = 0.89) and 7 anal y ses would rep re sent
“youn ger” grains with a mean age of 294 ±3 Ma (MSWD = 0.44). This would be in ac cord with the pres ence of euhedral to subhedral cores in some grains that might sug gest two stages of zir con growth. How ever, there is no cor re la tion be tween the core or out growth po si tions and the mea sured
206Pb/238U ages. The cores show a range of ages (Nos. 1, 6, 8, 9, 12, 14) be tween 311 to 293 Ma and do not de fine any dis tinct
Grain
spot U
[ppm] Th [ppm] Th/U
206Pb*
[ppm]
204Pb/206Pb f206
[%]
To tal Ra dio genic Age [Ma]
238U/206Pb ± 207Pb/206Pb ± 206Pb/238U ± 206Pb/238U ±
1.1 264 124 0.47 10.6 – 0.05 21.33 0.25 0.0526 0.0011 0.0469 0.0006 295.2 3.5
1.2 280 80 0.28 12.0 0.000629 0.23 20.14 0.27 0.0544 0.0010 0.0495 0.0007 311.7 4.1
2.1 637 338 0.53 24.2 0.000070 <0.01 22.60 0.29 0.0513 0.0008 0.0443 0.0006 279.3 3.5
3.1 297 139 0.47 12.3 0.000193 <0.01 20.76 0.27 0.0520 0.0009 0.0482 0.0006 303.5 3.8
4.1 467 200 0.43 19.2 0.000073 0.09 20.84 0.26 0.0531 0.0007 0.0479 0.0006 301.8 3.7
5.1 203 95 0.46 8.5 0.000369 0.14 20.54 0.37 0.0536 0.0011 0.0486 0.0009 306.1 5.4
6.1 307 109 0.36 13.0 0.000835 <0.01 20.33 0.24 0.0525 0.0010 0.0492 0.0006 309.6 3.6
6.2 187 96 0.51 7.6 0.000391 0.37 21.17 0.27 0.0553 0.0020 0.0471 0.0006 296.5 3.7
7.1 231 145 0.63 9.8 0.000305 0.22 20.29 0.25 0.0543 0.0010 0.0492 0.0006 309.5 3.8
8.1 203 121 0.60 8.5 0.000078 0.01 20.44 0.25 0.0526 0.0011 0.0489 0.0006 307.9 3.8
8.2 462 185 0.40 19.1 0.000140 0.11 20.80 0.23 0.0533 0.0007 0.0480 0.0005 302.4 3.3
9.1 481 249 0.52 19.5 0.000090 <0.01 21.22 0.24 0.0520 0.0007 0.0471 0.0005 296.9 3.3
9.2 195 194 1.00 7.8 0.000050 0.12 21.49 0.27 0.0532 0.0012 0.0465 0.0006 292.8 3.6
10.1 248 124 0.50 10.1 0.000116 <0.01 20.99 0.25 0.0508 0.0010 0.0477 0.0006 300.6 3.6
11.1 344 149 0.43 13.1 0.000281 0.24 22.61 0.27 0.0537 0.0009 0.0441 0.0005 278.3 3.2
12.1 528 232 0.44 21.0 0.000063 0.16 21.63 0.24 0.0534 0.0007 0.0461 0.0005 290.8 3.2
12.2 422 190 0.45 16.9 0.000197 0.18 21.45 0.55 0.0536 0.0008 0.0465 0.0012 293.3 7.4
13.1 812 533 0.66 32.5 0.000081 0.11 21.49 0.23 0.0531 0.0006 0.0465 0.0005 292.9 3.1
14.1 357 122 0.34 14.7 0.000125 <0.01 20.91 0.24 0.0524 0.0008 0.0478 0.0006 301.2 3.4
14.2 216 104 0.48 8.9 0.000434 0.38 20.76 0.31 0.0555 0.0011 0.0480 0.0007 302.1 4.5
Notes:
—un cer tain ties given at the ones level;
—er ror in FC1 Ref er ence zir con cal i bra tion was 0.55% for the an a lyt i cal ses sion (not in cluded in above er rors but re quired when com par ing data from dif fer - ent mounts);
—f206 [%] de notes the per cent age of 206Pb that is com mon Pb;
—cor rec tion for com mon Pb made us ing the mea sured 238U/206Pb and 207Pb/206Pb ra tios fol low ing Tera and Wasserburg (1972) as out lined in Wil liams (1998) T a b l e 2 Re sults of SHRIMP U-Pb anal y ses of zir cons for the Dol ina Bêdkowska granodiorite, sam ple WB-102A
in de pend ent event of zir con crys tal li za tion. More over, in two grains (Nos. 6 and 9), the cores ap pear youn ger than the rims (Fig. 3). There fore, any ap par ent dis tinc tion within the en tire group has no real sig nif i cance, as con firmed by the Tera-Wasserburg con cordia di a gram (Fig. 4). Two anal y ses plot to the right of the group and are thought to pos si bly re flect Pb loss. Dis card ing these two youn gest ages, 18 anal y ses yielded ages rang ing from 311 to 293 Ma, with a mean age of 300 ±3 Ma (Ta ble 2, Fig. 4) which re cords the main zir con crys tal li za tion event in the granodioritic magma. This is taken to date magma em place ment at the Car bon i f er ous/Perm ian bound ary (Gradstein et al., 2004).
DISCUSSION
The time in ter val, 311–293 Ma, is very sim i lar to that ob - tained by other meth ods for the Ma³opolska fel sic rocks to the north of the Dol ina Bêdkowska area, which is near est to the rhyolitic laccolith area of the Up per Silesian Block (Fig. 1). The mean age of 300 ±3 Ma of the WB-102A granodiorite over laps within er ror with a mean age of 295 ±3 Ma for the Zalas rhy o - lite (Nawrocki et al., 2008). It fol lows that the ig ne ous in tru - sions in the Ma³opolska Block and the Up per Silesian Block of Brunovistulia were con tem po ra ne ous, strad dling the Car bon if - er ous/Perm ian bound ary. In view of the sim i lar tim ing and their pres ent-day prox im ity, their der i va tion from the same source is likely though not cer tain. More iso to pic stud ies are re quired to re solve this ques tion. A strik ing dif fer ence lies in the ab sence of min er al iza tion in the Up per Silesian rocks, which is in marked con trast to those on the Ma³opolska side of the Kraków–Lubliniec Fault Zone. Bore hole log pro files show that the outer por tions of the granodiorite body(ies) and the en vel - op ing coun try rocks are min er al ized (Cu-Mo-W) and in clude calc-al ka line por phyry cop per-type de pos its (Podemski, 2001).
In the case of the WB-102A and DB-5 bore holes, such min er - al iza tion likely de vel oped to wards the end of the mag matic ac - tiv ity in the area, and the bulk of the granodiorite body hav ing re mained bar ren.
Lo cal iza tion of the ig ne ous in tru sions mainly in the NE wall of the Kraków–Lubliniec Fault Zone and a lack of any fab - ric in the granitoids and re lated subvolcanic rocks sug gest some con trol of the crustal-scale fault zone on the dis tri bu tion of the high-level mag matic bod ies in the re gime with nearly zero deviatoric stress. Alternatively, the fel sic mag mas may have in - truded as a mush with a low per cent age of crys tals, that might have pre vented them from ac quir ing any di rec tion ally pre - ferred ar range ment at the time of em place ment. This is in line with the nearly 15 m.y. long time in ter val when zir cons crys tal - lized in the granodiorite magma that must have been in a pro - tracted mol ten state, al low ing for dis so lu tion of all older zir - cons as no in her ited com po nent sur vived in the new zir con pop u la tion. The high tem per a ture of the in trud ing mag mas, al - though still re quir ing quan ti fi ca tion, is clearly shown by wide ther mal ha los around the ig ne ous bod ies, and cor rob o rated by con tact meta mor phism up to migmatitic stage (Heflik and Piekarski, 1992; Moryc and Heflik, 1998).
At the Car bon if er ous/Perm ian boundary, the Ma³opolska wall of the Kraków–Lubliniec Fault Zone was sub ject ei ther to an over all ex ten sion or to wrench ing that might have given room for an ar ray of ig ne ous in tru sions, pos si bly emplaced in pull-apart con di tions. In deed, a com plex strike-slip re gime comprising dextral transtension, fol lowed by dextral transpression and then nor mal fault ing with a sinistral slip com - po nent is sug gested to have con trolled the KLFZ evo lu tion in lat est Car bon if er ous through Perm ian times (¯aba, 1999). Such con di tions are very likely to have fa cil i tated the fel sic in tru - sions, es pe cially the dextral transtensional event that was thought by ¯aba (1999) to be the one that fa voured magma rise and fi nal em place ment of the granodiorite bod ies in the Ma³opolska Block in late Westphalian times. Our new SHRIMP data on zir cons shows the event (300 ±3 Ma) ac tu ally
Fig. 4. U-Pb SHRIMP anal y ses of zir cons from granodiorite WB-102A
A — Tera-Wasserburg con cordia di a gram; B — prob a bil ity den sity dis tri - bu tion plot; C — fre quency plot
strad dled the Car bon if er ous/Perm ian bound ary, by ref er ence to the GTS2004 scale (Gradstein et al., 2004).
Late- to post-collisional fel sic magmatism of sim i lar age oc curred in the Variscan orogenic belt in Cen tral Eu rope at ca.
310–290 Ma (Bonin, 1998; Fin ger and Steyrer, 1990; Fin ger et al., 1997; Franke, 2000). How ever, the Ma³opolska in tru sions oc cur out side the orogenic belt (Fig. 1) and granitoids are un - likely to gen er ate in fore land set tings. There fore, we pro pose a hy poth e sis that the par ent melt for the Ma³opolska and Up per Silesian silicic rocks was de rived from the thick ened lower crust of the Variscan orogenic belt ow ing to extensional decompressional melt ing near the crust/man tle bound ary. The su pra -subduction sig na tures in her ited from the orig i nal set ting were writ ten in the chem i cal mem ory of the gra nitic melts which were de rived from be low the orogen that was un der go - ing ther mal re lax ation. They were likely driven by the hy drau - lic gra di ent and trans ported from their place of or i gin, in the west erly lo cated orogenic root with rem nant subduction zone, to wards the not-too-dis tant pull-apart open ings de vel oped along the wrenched Kraków–Lubliniec Fault Zone in the rel a - tively low ve loc ity crust of the Ma³opolska Block (see Malinowski et al., 2005). The high tem per a ture gra nitic magma prob a bly trav eled as a crys tal mush which kept it from form ing a fab ric align ment or, al ter na tively, the mag matic flow was tur bu lent. Advective heat ing in the crustal zone of the Kraków–Lubliniec Fault Zone is consitent with ex ten sive con - tact meta mor phism in the area (in clud ing skarns de vel oped in
over ly ing De vo nian car bon ates) and sub se quent ex ten sive hy - dro ther mal pro cesses around the Car bon if er ous/Perm ian bound ary. Fur ther geo chem i cal and geo chron ol ogi cal stud ies are nec es sary to test this hy poth e sis.
CONCLUSIONS
1. Silicic calc-al ka line magmatism oc curred in the Variscan fore land par al lel to the Kraków–Lubliniec Fault Zone be tween 310 Ma and 290 Ma, which was co eval with post-collisional gran ite in tru sions in the Cen tral Eu ro pean Variscides.
2. The magmatism was ge net i cally con nected with the Variscan orogen from which the fel sic magma was likely driven by the hy drau lic gra di ent and mi grated to wards the fore - land.
3. In tru sions of fel sic rocks were fa cil i tated by the com plex strike-slip and nor mal re gime ac tive along the crustal-scale Kraków–Lubliniec Fault Zone.
4. Al though broadly co eval, granodiorites ap par ently in - truded ear lier than as so ci ated hypa bys sal rocks in both the Ma³opolska Block and the Up per Silesian Block.
Ac knowl edge ments. This is a con tri bu tion to the re search pro ject “Palaeozoic Ac cre tion of Po land” (PCZ-07-21). Two anon y mous re view ers are ac knowl edged for con struc tive re - marks.
REFERENCES
BATCHELOR R. A. and BOWDEN P. (1985) — Petro gen etic in ter pre ta - tion of granitoid rock se ries us ing multicationic pa ram e ters. Chem.
Geol., 48: 43–55.
BLEVIN L. B. and CHAPPELL B. W. (1992) — The role of magma sources, ox i da tion states and frac tion ation in de ter min ing the gran ite metallogeny of east ern Aus tra lia. Trans. Royal Soc. Ed in burgh: Earth Sc., 83: 305–316.
BONIN B. (1998) — Orogenic to non-orogenic mag matic events: over - view of the Late Variscan mag matic evo lu tion of the Al pine Belt. Tr. J.
Earth Sc., 7: 133–143.
BROCHWICZ-LEWIÑSKI W., VIDAL G., PO¯ARYSKI W., TOMCZYK H. and ZAJ¥C R. (1986) — Pre-Perm ian tec tonic po si - tion of the Up per Silesian Mas sif (S Po land) in the light of stud ies on the Cam brian. C. R. Acad. Sc., Ser., II, 303, (16): 1493–1496.
BU£A Z. (2000) — Dolny paleozoik Górnego Œl¹ska i zachodniej Ma³opolski. Pr. Pañstw. Inst. Geol., 171.
BU£A Z. and HABRYN R. eds. (2008) — At las geologiczno-strukturalny pod³o¿a paleozoicznego Karpat Zewnêtrznych i zapadliska przedkarpackiego. Pañstw. Inst. Geol. Warszawa.
BU£A Z., JACHOWICZ M. and ¯ABA J. (1997) — Prin ci pal char ac ter is - tics of the Up per Silesian Block and Ma³opolska Block bor der zone (south ern Po land). Geol. Mag., 134 (5): 669–677.
CHAFFEE M. A., EPPINGER R. G., LASOÑ K., ŒLÓSARZ J. and PODEMSKI M. (1997) — A geo log i cal, al ter ation, and geo chem i cal model of the Myszków por phyry Cu-Mo de posit, south ern Po land. In:
Min eral De pos its (ed. H. Papunen): 851–854. Balkema, Rot ter dam.
COMPSTON W., WILLIAMS I. S. and MEYER C. (1984) — U-Pb geo - chron ol ogy of zir cons from lu nar brec cia 73217 us ing a sen si tive high mass-res o lu tion ion microprobe. J. Geoph. Res., 89: B252–B534.
DADLEZ R. (1995) — De bates about the pre-Variscan tec ton ics of Po land.
Stud. Geoph. Geodaet., 39: 227–234.
DUDEK A (1980) — The crys tal line base ment block of the Outer Carpathians in Moravia: Bruno-Vistulicum. Roz. Èes. Akad. Vìd, Ø.
mat-prirod. Vìd, 90: 1–85.
EBY G. N. (1992) — Chem i cal sub di vi sion of the A-type granitoids: petro - gen etic and tec tonic im pli ca tions. Ge ol ogy, 20: 641–644.
EL BOUSEILY A. M. and EL SOKKARY A. A. (1975) — The re la tion be - tween Rb, Ba, and Sr in gra nitic rocks. Chem. Geol., 16: 207– 219.
FINGER F., ROBERTS M. P., HAUNSCHMID B., SCHERMAIER A. and STEYRER H. P. (1997) — Variscan granitoids of cen tral Eu rope: their typology, po ten tial sources and tectonothermal re la tions. Miner.
Petrol., 61: 67–96.
FINGER F. and STEYRER H. P. (1990) — I-type granitoids as in di ca tors of a late Pa leo zoic con ver gent ocean-con ti nent mar gin along the south ern flank of the cen tral Eu ro pean Variscan orogen. Ge ol ogy, 18:
1207–1210.
FRANKE W. (2000) — The mid-Eu ro pean seg ment of the Variscides:
tectono-strati graphic units, terrane bound aries and plate evo lu tion. J.
Geol. Soc., Lon don, Spec. Publ., 179: 35–61.
GRADSTEIN F., OGG J. and SMITH A. (2004) — A Geo logic Time Scale 2004. Cam bridge Univ. Press.
HARAÑCZYK C. (1989) — Wulkanizm rejonu Krzeszowic (in Pol ish).
Przewodnik 60 Zjazdu Pol. Tow. Geol. Kraków, 14–16 wrzeœnia 1989:
51–71. Warszawa.
HARAÑCZYK C. (1994) — Znaczenie sutury terranowej Zawiercie-Rzeszotary dla poznania kaledoñskiego transpresyjnego górotworu krakowidów (in Pol ish). Przewodnik 65 Zjazdu Pol. Tow.
Geol. w Sosnowcu. Pr. Nauk. UŒl., 1431: 69–80.
HEFLIK W. and PIEKARSKI K. (1992) — Con tact meta mor phic rocks from the vi cin ity of Myszków (Up per Silesia). Bull. Pol. Acad. Sc., Earth Sc., 40 (1): 31–42.
JACHOWICZ M. (1994) — O wystêpowaniu mikroskamienia³oœci grupy Acritarcha w utworach starszego paleozoiku pó³nocno-wschodniego obrze¿enia GZW. Prz. Geol., 42 (8): 631--637.
JACHOWICZ M., BOBIÑSKI W., BU£A Z., CWOJDZIÑSKI S., ¯ABA J.
and ¯ELAZNIEWICZ A. (2002) — Geneza i pozycja stratygraficzna podkambryjskich i podorodowickich anchimetamorficznych ska³ w po³udniowej Polsce — przedpole orogenu neoproterozoicznego? Fi nal re port: grant KBN 9T12B03217 (in Pol ish). Centr. Arch. Geol. Pañstw.
Inst. Geol.
JARMO£OWICZ-SZULC K. (1984) — Datowania metod¹ K-Ar ska³ NE obrze¿enia Górnoœl¹skiego Zag³êbia Wêglowego (in Pol ish). Spraw.
Pos. Nauk. Inst. Geol., Kwart. Geol., 28 (3/4): 749–750.
JARMO£OWICZ-SZULC K. (1985) — K-Ar datings of ig ne ous rocks from NE mar gin of the Up per Silesian Coal Ba sin. Kwart. Geol., 29 (2): 343–354.
JUNG S. and PFÄNDER J. A. (2007) — Source com po si tion and melt ing tem per a tures of orogenic granitoids: con straints from CaO/Na2O, Al2O3/TiO2 and ac ces sory min eral sat u ra tion ther mo m e try. Eur. J.
Miner., 9: 859–870.
KRÓLIKOWSKI and PETECKI Z. (1995) — Gravimetric at las of Po land.
Pañst. Inst. Geol. Warszawa.
LUDWIG K. R. (2000) — SQUID 1.00, A User’s Man ual. Berke ley Geochronol. Cen ter Spec. Publ., 2.
LUDWIG K. R. (2003) — Isoplot/Ex ver sion 3.0. A geo chron ol ogi cal toolkit for Microsoft Ex cel. Berke ley Geochronol. Cen ter Spec. Publ., 1a.
MALINOWSKI M., ¯ELAZNIEWICZ A., GRAD M., GUTERCH A. and JANIK T. (2005) — Seis mic and geo log i cal struc ture of the crust in the tran si tion from Baltica to Palaeozoic Eu rope in SE Po land — CELEBRATION 2000 ex per i ment, pro file CEL02. Tectonophysics, 401 (1–2): 55–77.
MARKIEWICZ J. (2002) — Przejawy kontaktowo-metasomatycznego oddzia³ywania granitoidowej intruzji mrzyg³odzkiej. Biul. Pañstw.
Inst. Geol., 402: 101–132.
MARKIEWICZ J. (2006) — Granitoidowy magmatyzm Doliny Bêdkowskiej (strefa krawêdziowa bloku ma³opolskiego) jako przes³anka wystêpowania z³ó¿ porfirowych Mo-Cu-W. Centr. Arch.
Geol. Pañstw. Inst. Geol.
MAZUR S. and JAROSIÑSKI M. (2006) — Budowa geologiczna g³êbokiego pod³o¿a platformy paleozoicznej po³udniowo-zachodniej Polski w œwietle wyników eksperymentu sejsmicznego POLONAISE’97. Pr. Pañstw. Inst. Geol, 188: 203–222.
MORYC W. and HEFLIK W. (1998) — Meta mor phic rocks in the base - ment of the Carpathians be tween Bielsko-Bia³a and Cra cow. Geol.
Quart., 42 (1): 1–14.
NAWROCKI J., ¯YLIÑSKA A., BU£A Z., GRABOWSKI J., KRZYWIEC P. and POPRAWA P. (2004) — Early Cam brian lo ca tion and af fin i ties of the Brunovistulian terrane (Cen tral Eu rope) in the light of paleomagnetic data. J. Geol. Soc., Lon don, 161: 513–522.
NAWROCKI J. FANNING M., LEWANDOWSKA A., POLECHOÑSKA O. and WERNER T. (2008) — Palaeomagnetism and the age of the Cra cow vol ca nic rocks (S Po land). Geoph. J. Int., 174: 475–488.
PEARCE J. (1996) — Sources and set tings of gra nitic rocks. Ep i sodes, 19:
120–125.
PEARCE J. A., HARRIS N. B. W. and TINDLE A. G. (1984) — Trace el e - ment dis crim i na tion for the tec tonic in ter pre ta tion of gra nitic rocks. J.
Petrol., 25: 956–983.
PODEMSKI M. ed. (2001) — Palaeozoic por phyry mo lyb de num-tung sten de posit in the Myszków area, south ern Po land. Pol. Geol. Inst. Spec.
Pap., 6: 1–88.
PO¯ARYSKI W. and KARNKOWSKI P. (1992) — Tec tonic map of Po - land dur ing the Variscan time, 1:1 000 000. Wyd. Geol. Warszawa.
PO¯ARYSKI W., GROCHOLSKI A., TOMCZYK H., KARNKOWSKI P.
and MORYC W. (1992) — The tec tonic map of Po land in the Variscan ep och. Prz. Geol., 40 (11): 643–651.
STEIN H. J., MARKOWIAK M. and MIKULSKI S. Z. (2005) — Meta - mor phic to mag matic tran si tion cap tured at the Myszków Mo-W de - posit, south ern Po land. In: Min eral De posit Re search: Meet ing the Global Chal lenge: 833–836. Springer.
TERA F. and WASSERBURG G. J. (1972) — U-Th-Pb sys tem at ics in three Apollo 14 bas alts and the prob lem of ini tial Pb in lu nar rocks. Earth Planet. Sc. Lett., 14: 281–304.
WHALEN J. B., CURRIE K. L. and CHAPPELL B. W. (1987) — A-type gran ites: geo chem i cal char ac ter is tics, dis crim i na tion and petro gen - esis. Contrib. Miner. Petrol., 95: 407–419.
WILLIAMS I. S. (1998) — U-Th-Pb Geo chron ol ogy by Ion Microprobe.
In: Ap pli ca tions of microanalytical tech niques to un der stand ing min - er al iz ing pro cesses (eds. M. A. McKibben, W. C. Shanks III and W. I.
Ridley). Rev. Econ. Geol., 7: 1–35.
WILLIAMS I. S. and CLAESSON S. (1987) — Iso to pic ev i dence for the Pre cam brian prov e nance and Cal edo nian meta mor phism of high grade paragneisses from the Seve Nappes, Scan di na vian Caledonides, II. Ion microprobe zir con U-Th-Pb. Contrib. Min eral. Petrol., 97: 205–217.
¯ABA J. (1999) — Ewolucja strukturalna utworów dolnopaleozoicznych w strefie granicznej bloków górnoœl¹skiego i ma³opolskiego. Pr.
Pañstw. Inst. Geol., 166.
¯ELAZNIEWICZ A. (1998) — Rodinian-Baltican link of the Neoproterozoic orogen in south ern Po land. Acta Univ. Carolinae, Geol., 42 (3–4): 509–515.
