Geo log i cal Quar terly, 2013, 57 (2): 325–334DOI: http://dx.doi.org/10.7306/gq.1084

The Niemcza diorites and monzodiorites (Sudetes, SW Po land): a re cord of chang ing geotectonic set ting at ca. 340 Ma

Anna PIETRANIK1, *, Craig STOREY2 and Jakub KIERCZAK1

1 In sti tute of Geo log i cal Sci ences, Uni ver sity of Wroc³aw, M. Borna 9, 50-204 Wroc³aw, Po land

2 School of Earth and En vi ron men tal Sci ences, Uni ver sity of Portsmouth, Portsmouth PO1 3QL, United Kingdom

Pietranik A., Storey C. and Kierczak J. (2013) The Niemcza diorites and moznodiorites (Sudetes, SW Po land): a re cord ofchang ing geotectonic set ting at ca. 340 Ma. Geo log i cal Quar terly, 57 (2): 325–334, doi: 10.7306/gq.1084

Gran ites sensu lato in the Sudetes in truded in sev eral ep i sodes dur ing the Variscan orog eny re cord ing dif fer ent stages ofcrust and man tle evo lu tion. Cor re lat ing pre cise ages with geo chem is try of the Variscan gran ites pro vides in for ma tion on theevo lu tion of these sources within the Variscan orogen. The Variscan in tru sive rocks from the Niemcza Zone (Bo he mian Mas -sif, Sudetes, SW Po land) in clude undeformed dioritic to syenitic rocks and magmatically fo li ated granodiorites. In this studywe ana lysed low SiO2 (48–53 wt.%) monzodioritic rocks from Przedborowa and KoŸmice. The monzodiorites con tainlate-mag matic zir cons with ages of 341.8 ± 1.9 Ma for Przedborowa and 335.6 ± 2.3 Ma for KoŸmice, in ter preted as em place -ment ages of the dioritic mag mas. Older Przedborowa rocks are lower in K, Mg, Rb and Ni than the KoŸmice rocks and sim i -lar compositional trend is also ob served in the Cen tral Bo he mian Plutonic Com plex. The im pli ca tion is that the man tleun der ly ing the Niemcza Zone be came more en riched from ca. 342 to ca. 336 Ma, prob a bly fol low ing the col li sion of theSaxothuringian and Moldanubian/Lugian do mains. The magmatism re lated to the col li sion oc curred ca. 12 Ma later than thatin the Cen tral Bo he mian Plutonic Com plex, but was ac com pa nied by a sim i lar change in magma chem is try from high-K(Przedborowa) to shoshonitic (KoŸmice, Koœmin en claves) and prob a bly to ultrapotassic (Wilków Wielki).

Key words: Bo he mian Mas sif, Niemcza Zone, diorites, LA-ICPMS zir con age, potassic magmatism.

INTRODUCTION

Variscan granitoid magmatism in the Sudetes spans fromca. 350 to ca. 295 Ma (Mazur et al., 2007 and ref er encestherein). Re cent zir con dat ing pro vides pre cise ages and showsthat the magmatism in the Sudetes oc curred in three ma jor ep i -sodes:

– ca. 340 Ma ep i sode, which in cludes em place ment ofgranodioritic and monzonitic mag mas in the Odra FaultZone (344 ± 1 Ma; Dörr et al., 2006), granodioritic anddioritic rocks in the Niemcza Zone (336 ± 3 Ma to 342 ±2 Ma; Ol i ver et al., 1993) and leucocratic gran ite bod ieswithin the Gogo³ów-Jordanów ser pen tin ite mas sif (337 ± 4 Ma; Kryza, 2011);

– ca. 320 Ma ep i sode, which in cludes the KarkonoszeGran ite (322 ± 3 Ma; Kryza et al., 2012) and theBo¿nowice tonalite from the Strzelin Mas sif (324 ± 4 Ma;Oberc-Dziedzic et al., 2010);

– ca. 300 Ma ep i sode, which in cludes gra nitic to tonaliticrocks in the Strzelin Mas sif (306 ± 3 Ma to 294 ± 3 Ma;Oberc-Dziedzic et al., 2010; Oberc-Dziedzic and Kryza,2012) and the Strzegom-Sobótka gran ites (294–310 Ma;Turniak et al., 2005).

Pre cise dat ing and rec og ni tion of mag matic ep i sodes is im -por tant for larger scale cor re la tions of chang ing tec tonic set -tings dur ing the Variscan orog eny. For ex am ple, ca. 340 Mamagmatism is wide spread in the Bo he mian Mas sif and is rep re -sented by ultrapotassic rocks (340 ± 8 Ma to 343 ± 6 Ma –Holub, 1997; 337 ± 1 Ma – Janoušek and Gerdes, 2003; 342 ±3 Ma – Kusiak et al., 2010; 335.12 ± 0.57 Ma – Kotková et al.,2010), which in clude nu mer ous bod ies of high-Mg, high-Kmela syenites to melagranites (Wenzel et al., 1997). The mainsce nario for high-K, high-Mg magmatism in volves in ter ac tionbe tween crustal and en riched man tle sources cou pled with frac -tional crystallisation (Janoušek and Holub, 2007; Parat et al.,2010). Pin point ing the crustal source in volved in the ultra -potassic rocks’ gen e ses strongly de pends on pre cise and ac cu -rate dat ing of the magmatism (Janoušek and Holub, 2007;Kotková et al., 2010).

Leichmann and Gawêda (2002) sug gested that theNiemcza Zone intrusives can be cor re lated with the ultra po -tassic rocks from other lo cal i ties in the Bo he mian Mas sif and byim pli ca tion they could have been formed in a sim i lar geo -tectonic set ting. How ever, ages of the Niemcza Zone dioriticrocks and their de tailed geo chem i cal char ac ter is tics have beenso far in suf fi cient to ver ify this hy poth e sis. Pre vi ous dat ing ofthe KoŸmice granodiorite by ID-TIMS (iso tope di lu tion – ther mal ion iza tion mass spec trom e try) of zir con yielded a Con cordiaage of 338 +2/–3 Ma (Ol i ver et al., 1993) sim i lar to that of otherultrapotassic rocks (e.g., Holub, 1997; Janoušek and Gerdes,2003; Kotková et al., 2010; Kusiak et al., 2010). Peg ma titic am -phi boles from Przedborowa yielded a sim i lar age of 335 ± 5 Ma

* Corresponding author: anna.pietranik@ing.uni.wroc.pl

Received: January 28, 2013; accepted: March 21, 2013; firstpublished online: April 15, 2013

by the 40Ar/39Ar method (Dudek et al., 2000). In this pa per, wepres ent the first ages for zir cons from monzodioritic rocks fromKoŸmice and Przedborowa. We com pare the geo chem i calcom po si tion of the rocks with oth ers of sim i lar age in the Bo he -mian Mas sif in or der to see if sim i lar sources were pres ent at are gional scale dur ing the Variscan orog eny.

GEOLOGICAL SETTING

The Niemcza Zone is lo cated in the Bo he mian Mas sif (Fig.1A), in the Sudetes at the east ern mar gin of the Góry SowieGneissic Block, and forms a N–S elon gated shear zone (Fig.1B) pre dom i nately com posed of mylonitised gneiss es of theGóry Sowie Mas sif (Mazur and Puziewicz, 1995; Fig. 2). TheNiemcza Zone also com prises small bod ies of mafic-ultra maficrocks be long ing to the Cen tral Sudetic Ophiolite formed at ca.400 Ma (U-Pb zir con SHRIMP age; Kryza and Pin, 2010) andsmall in tru sions of granodioritic and dioritic rocks formed at ca.338 Ma (U-Pb zir con ID-TIMS age; Ol i ver et al., 1993; Fig. 2).The ca. 338 Ma in tru sive rocks can be di vided into two groups:dioritic rocks, called the Przedborowa type and gra nitic rockscalled the Koœmin type (Dziedzicowa, 1963).

The dioritic rocks (Przedborowa type) form fine-graineddikes com pris ing monzodiorites, quartz diorites, quartz sye -nites and tonalites. They are com posed pre dom i nately of pla -gioclase, am phi bole and bi o tite with mi nor clinopyroxene andK-feld spar (Dziedzicowa, 1963; Puziewicz, 1987, 1988, 1990).The ini tial 87Sr/86Srat338 is 0.70598 for diorites from Przed -

borowa (Lorenc, 1998; Lorenc and Kennan, 2007, 87Sr/86Srat338, re cal cu lated us ing 87Rb de cay con stant of Nebel et al., 2011).

The gra nitic rocks (Koœmin type) lo cally show ef fects of duc -tile dextral shear ing (Puziewicz et al., 1992, Aleksandrowski etal., 1997) in ter preted as mag matic de for ma tion (Puziewicz,1992). The rocks are me dium-grained, rich in dioritic en clavesand com prise granodiorites, quartz monzonites, quartz monzo -diorites and rare gran ites. They are com posed of var i ous pro -por tions of quartz, feld spars, bi o tite and am phi bole (Puziewicz,1992; Puziewicz and Oberc-Dziedzic, 1995; Lorenc, 1998;Lorenc and Kennan, 2007). A pet ro log i cal study of the KoŸmicegranodiorite gave es ti mates of magma crys tal li za tion tem per a -ture of 730–850°C and the pres sure of em place ment at 4 ±1 kbars (Puziewicz and Radkowska, 1990; Puziewicz, 1992).The ini tial 87Sr/86Srat338 is 0.7077–0.7079 for the granodiorites in Koœmin (Lorenc,1998; Lorenc and Kennan, 2007).

The gra nitic rocks were emplaced con tem po ra ne ously orlater than the dioritic rocks (Puziewicz, 1992). The dioritic rocksare undeformed and the gra nitic rocks are weakly fo li ated andare char ac ter ized by N–S and E–W trending fo li a tion anddextral shear ing (Puziewicz, 1992). Lack of de for ma tion in thedioritic rocks as well as dif fer ent shear sense re corded in thegra nitic rocks com pared to that in the sur round ing mylonites(dextral ver sus sinistral) in di cate that the in tru sive rocks wereyoun ger than the per va sive de for ma tion in mylonites (Mazurand Puziewicz, 1995). Al ter na tively, the in tru sive rocks mayhave sur vived un af fected by the later sinistral shear ing (Aleksa -ndrowski et al., 1997).

326 Anna Pietranik, Craig Storey and Jakub Kierczak

Fig. 1. Gen er al ised map of (A) the Bo he mian Mas sif and (B) the East ern Sudetes show ing the lo ca tion of the Niemcza Zone and the stud ied area (small square in Fig. 1B see Fig. 2)

A – CBPC – Cen tral Bo he mian Plutonic Com plex, MO – Moldanubian Zone, NP – North ern PhylliteZone, RH – Rhenohercynian Zone, SX – Saxothuringian Zone

The Niemcza diorites and moznodiorites (Sudetes, SW Poland): a record of changing geotectonic setting at ca. 340 Ma 327

Fig. 2. Geo log i cal map show ing sam pling sites of the dioritic/syenitic rocks ana lysed in this study (mod i fied af ter Trepka and Gawroñski, 1957; Badura and Dziemiañczuk, 1981; Cwojdziñski

and Walczak-Augustyniak, 1983; Cymerman and Walczak-Augustyniak, 1986)

ANALYTICAL METHODS

ZIRCON DATING

Ap prox i mately 3 kg of fine grained, dioritic rocks from thePrzedborowa and KoŸmice quar ries were crushed and sieved.Heavy min eral con cen trates were sep a rated from the sievedfrac tions by pan ning and zir cons were hand picked andmounted in an ep oxy ring. The grains were ex am ined in chargecon trast im ages. U-Pb anal y ses of zir con were car ried out atthe Uni ver sity of Bris tol us ing a Thermo-Sci en tific El e ment sin -gle-col lec tor ICP–MS (In duc tively Cou pled Plasma – MassSpec trom e try) cou pled to a New Wave 193HE la ser ab la tionsam pling sys tem. The sin gle mea sure ment com prised: 20 s ofgas blank mea sure ment, 40 s of zir con mea sure ment and1 min ute of wash ing out. Data were cor rected for U-Pb frac tion -ation and in stru men tal mass bias by stan dard brack et ing withre peated mea sure ments of the Plešovice zir con with an ac -cepted 206Pb/238U age of 337.13 ± 0.37 Ma (Sláma et al., 2008).Dur ing the ses sion 15 anal y ses of the Plešovice zir con yieldeda 206Pb/238U con cordia age of 338.1 ± 1.1 Ma show ing goodwithin-run reproducibility. Data re duc tion was car ried out withthe soft ware pack age GLITTER® (GEMOC – The ARC Na -tional Key Cen tre for Geo chem i cal Evo lu tion and Metallogenyof Con ti nents). The plot ting and con cordia age cal cu la tion wasdone by Isoplot (Lud wig, 1999), all er rors are plot ted and allages are quoted at the 2 s un cer tainty level.

No 204Pb cor rec tion was ap plied to the data. 204Pb was mea -sured dur ing the ses sion to gether with 204Hg and Hg cor rec tionwas ap plied to 204Pb re sult ing in val ues be low de tec tion limit for204Pb. The ref er ence zir con 91 500 with an ac cepted age206Pb/238U of 1062.4 ± 0.8 (Wiedenbeck et al., 1995) was ana -lysed as un known to check for data qual ity. The 206Pb/238U agefor the 91 500 zir con mea sured in this study is 1065 ± 4.6 Ma (n = 14, MSWD = 0.8), in agree ment with the age pub lished byWiedenbeck et al. (1995). Also, at the same ses sion, zir consfrom the Gêsiniec tonalite were ana lysed and yielded a Con -cordia age of 294.7 ± 1.5 Ma (n = 10, MSWD = 0.7), which isiden ti cal to the SHRIMP age of 294.7 ± 2.8 Ma ob tained re centlyfor the tonalite (Oberc- Dziedzic and Kryza, 2012). Cor rect val ues for 91 500, Gêsiniec zir con as well as Con cordia ages for ana -lysed zir cons from the Niemcza Zone sug gest that no 204Pb cor -rec tion was re quired along with the fact that 204Pb could not bede tected.

CHEMICAL ANALYSES

Whole rock geo chem i cal anal y ses for ten sam ples weredone in the ACME An a lyt i cal Lab o ra tory (4 from Przedborowa,2 from KoŸmice and 4 of en claves from Koœmin). Ma jor el e -ments were ana lysed by ICP-ES (In duc tively Cou pled PlasmaEmis sion Spec trom e try) and trace el e ments were ana lysed byICP-MS fol low ing fu sion of sam ples in LiBO2/Li2B4O7. The an a -lyt i cal reproducibility (2SD), as es ti mated from 10 anal y sis ofstan dard SO18/CSC is be low 0.8% for ma jor el e ments, andfrom 0.8 (Nd) to 8% (La) for trace el e ments at 95% con fi dencelim its. An a lyt i cal ac cu racy (2SD), as es ti mated from the realcon cen tra tion in the stan dard SO18/CSC is be low 4% for ma jor

el e ments and from 4 (U) to 26% (Y) for trace el e ments at 95%con fi dence lim its.

An ad di tional 6 sam ples were ana lysed for ma jor el e mentsat the lab o ra tory of the In sti tute of Geo log i cal Sci ences, Uni ver -sity of Wroc³aw, Po land by a com bi na tion of AAS (Atomic Ab -sorp tion Spec tros copy) and ti tra tion.

RESULTS

MONZODIORITE FROM KOZMICE:PETROLOGY AND GEOCHEMICAL COMPOSITION

The monzodiorite from KoŸmice crops out in the quarry onStrach Hill. The monzodiorite is in a sharp in tru sive con tact withgranodiorite, the lat ter was dated by Olivier et al. (1993) at 338+2/–3 Ma. Recrystallisation of monzodiorite at the con tact withgranodiorite in di cates that the granodiorite magma in truded intoal ready crys tal lised, older monzodiorite (Puziewicz, 1992). Thepe trol ogy of monzodiorite was de scribed in de tail by Puziewicz(1988, 1992) and it is sum ma rized here. The monzodiorite(called also vaugnerite) is fine-grained, undeformed and is com -posed of plagioclase, bi o tite and pyroxene. Zir con oc curs withinbi o tite, of ten at its rims (Fig. 3A). Pyroxene is re placed by am phi -bole close to the con tact with granodiorite. Three sam ples of themonzodiorite were ana lysed in this study (two within ap prox i -mately 20 cm of the con tact and one a few metres from the con -tact with granodiorite). Zir cons were sep a rated from the sam plecol lected far ther away from the con tact. This sam ple con tainsless Si, Cr and Ni and slightly less K and Mg than the sam plescol lected near the con tact, other el e ments con cen tra tions aresim i lar (Ap pen dix 1*). The dated sam ple has 52 wt.% SiO2 andmod er ate amounts of K2O (~3 wt.%). It is also char ac ter ized bylow Ni (8 ppm) and mod er ate Rb (150 ppm).

MONZODIORITE FROM PRZEDBOROWA: PETROLOGY AND GEOCHEMICAL COMPOSITION

Pe trol ogy of the quartz monzodiorite, the dom i nat ing rock inthe Przedborowa Quarry, was de scribed in de tail by Dzie -dzicowa (1963) and Puziewicz (1990) and is sum ma rised here.The monzodiorite forms an ap prox i mately 100 m thick, unde -formed dike within am phi bo lites. The rock is fine-grained andcom posed pre dom i nately of plagioclase, am phi bole (horn -blende), bi o tite and al kali feld spar with mi nor quartz. Two dom i -nat ing types of the monzodiorite in clude: equigranular monzo -diorite and por phy ritic monzodiorite (with bi o tite pheno crysts).Two sam ples of each type were ana lysed in this study for ma jorand trace el e ments and two sam ples of the equigranular typewere ana lysed for ma jor el e ments only (Ap pen dix 1*). Zir conswere sep a rated from the equigranular type. Zir con oc curs within hornbende and bi o tite, usu ally close to their rims (Fig. 3B). Thepor phy ritic type con tains more Si and K and less Fe, Mg, Ca, Tithan the equigranular type (Ap pen dix 1). It is also richer in in -com pat i ble el e ments, such as Rb, Cs, Ba, Hf, U, Zr, but notLREE. The low-SiO2 sam ples (51–52 wt.%) have mod er ateamounts of K2O (2–3 wt.%). They are also char ac ter ized by lowNi (6–9 ppm) and Rb con cen tra tions (50–80 ppm).

328 Anna Pietranik, Craig Storey and Jakub Kierczak

* Supplementary data associated with this article can be found, in the online version, at doi: 10.7306/gq.1084

The Niemcza diorites and moznodiorites (Sudetes, SW Poland): a record of changing geotectonic setting at ca. 340 Ma 329

Fig. 3A, B – mi cro scope view of KoŸmice and Przedborowa monzodiorite dated in this study (plane po lar ized light),typ i cal oc cur rence of zir con grains is marked by ar rows; C–F – charge con trast im ages of zir cons; the lin ear pits

rep re sent the ma te rial ab lated for dat ing; C, D – KoŸmice; E, F – Przedborowa

Bt – bi o tite, Hbl – hornblende, Kfds – po tas sium feld spar, Pl – plagioclase, Qtz – quartz, Zrn – zir con

MONZODIORITIC ENCLAVES FROM THE KOŒMINQUARRY AND OTHER ROCKS

Four monzodioritic en claves were col lected fromthe Ko œmin Quarry in or der to com pare their geo -chem is try to that of Przedborowa and KoŸmice. Theen claves are por phy ritic (pla gio clase pheno crysts)and are com posed of plagioclase, am phi bole, bi o tite, K-feld spar, pyroxene and quartz. The en claves arelow in SiO2 (50–52 wt.%) and high in MgO(6–10 wt.%) and K2O (~4 wt.%). They are also char -ac ter ized by high Rb (150–250 ppm) and high Ni(21–165 ppm), but low Zr (113–168 ppm).

Ma jor el e ment com po si tion was also ana lysed indioritic rocks from other lo cal i ties in the NiemczaZone (Ap pen dix 1): (1) quartz syenite from Pi³awa,com posed of am phi bole, al kali feld spar, plagioclaseand quartz (Puziewicz, 1987), (2) quartz diorite fromK³oœnik com posed of plagio clase, bi o tite, am phi bole, pyroxene and quartz and (3) syenite from WilkówWielki com posed of al kali feld spar, bi o tite, am phi -bole, plagioclase, quartz and ap a tite. The rock fromWilków Wielki is chem i cally dis tinct from other rockshav ing low SiO2 and Al2O3 and high MgO, CaO, K2Oad P2O5 (Ap pen dix 1).

ZIRCON AGES

Zir cons from both dioritic sam ples are euhe draland short to nor mal pris matic (Fig. 3C–F). Theyshow weak os cil la tory zon ing in charge con trast im -ages. The grains from Przedborowa are larger (ap -prox i mately 100 mm or more in the di am e ter per pen -dic u lar to z axis) than the grains from KoŸmice (lessthan 100 mm in the di am e ter). Ten zir con grains from Przedborowa and nine grains from KoŸmice wereana lysed (one anal y sis per grain, Fig. 3C–F, allgrains). All ages are Con cordia within ± 5%, none ofthe anal y ses were re jected (Ap pen dix 1). The zir -cons from Przedbo rowa yield a sin gle Con cordia age of 341.8 ± 1.9 Ma (Fig. 4A). All nine grains fromKoŸmice do not yield a Con cordia age, as two of thegrains (Koz-1, Koz-8) are older with an age of ca.350 Ma (Ap pen dix 1). The re main ing seven grainsyield a Con cordia age of 335.6 ± 2.3 Ma (Fig. 4B).Ten grains from Przedborowa and se ven grains from KoŸmice yield a sin gle Con cordia age of 339.2 ±1.9 Ma, but with an MSWD of 3.1.

DISCUSSION

NIEMCZA MAGMATISM: OVER 10 MY OF MAGMA EMPLACEMENT?

The in ter pre ta tion of zir con ages re quiresknowl edge of when the zir con crys tal lised dur ingmagma evo lu tion. Dioritic rocks are low in sil ica and zir co niumand, there fore, undersaturated in zir con un til late in thecrystallisation his tory (Wat son and Har ri son, 1983). The in her -ited com po nent in dioritic zir con is scarcely pres ent and thatmakes in ter pre ta tion of zir con ages more stra ight for ward. Thetem per a ture of zir con sat u ra tion cal cu lated in this study (fol low -ing zir con sat u ra tion ther mom e ter of Wat son and Har ri son,

1983) is be low 700°C for Przed borowa and be low 660°C forKoŸmice, much lower than the typ i cal liquidus and also sol i dustem per a tures for quartz diorite mag mas (Pietranik et al., 2009).Af ter ap prox i mately 70% of crystallisation, zir con sat u ra tion isaround 800°C in the stud ied com po si tions. The im pli ca tion isthat zir con in monzodioritic mag mas crystallises late and its age should be in ter preted as the age of the em place ment of

330 Anna Pietranik, Craig Storey and Jakub Kierczak

Fig. 4. Con ven tional con cordia di a grams for zir consfrom Przedborowa (A) and KoŸmice (B)

Black cir cles rep re sent ages ac cepted for the con cordia age (see text for the dis cus sion)

magma. It is con sis tent with the struc tural po si tion of zir con inKoŸmice and Przedborowa, which forms euhedral grains en -closed in the rims of mafic min er als (Fig. 3A, B).

The Con cordia ages for the Przedborowa and KoŸmicemonzodiorites are ca. 342 ± 2 Ma and 336 ± 2 Ma sug gest ingthat the Przedborowa in tru sion might be older. How ever, onlyseven out of nine zir cons from KoŸmice yielded a con cordiaage, whereas two grains are older (ca. 350 Ma), which makesthe age in ter pre ta tion for KoŸmice am big u ous. There fore, thebest con straint on the age of the monzodiorite em place ment isca. 342 ± 2 Ma ob tained from zir cons from Przedborowa.

In ter est ingly, the age dis tri bu tion is sim i lar to that from theKoŸmice monzodiorite and was noted by Kryza (2011) for leuco -granite from the Gogo³ów-Jordanów ser pen tin ite mas sif (datedby U-Pb, SHRIMP). The zir cons from the leucogranite also in -clude a main age pop u la tion around 337 Ma and a sin gle zir congrain with an age around 350 Ma. The slight “smear ing” of agesalong the con cordia plot for both the KoŸmice monzodiorite andGogo³ów-Jordanów leucogranite may sug gest that the real agefor both in tru sions is older and the ages were af fected byPb-loss. How ever, it would be sur pris ing if both the monzodioriteand leucogranite, mag mas with dis tinct ther mal his to ries and zir -con sat u ra tion tem per a tures, were sim i larly af fected by Pb-loss.Also, the KoŸmice grains are small and ho mog e nous, sim i lar tograins crys tal lised in quickly cooled, low Si mag mas. They do not show any fea tures typ i cal of hy dro ther mal al ter ation (Kusiak etal., 2009) or Pb-loss (Kryza et al., 2012). Al ter na tively, the336–337 Ma age could be the age of em place ment for both theKoŸmice and Gogo³ów-Jordanów in tru sions and the older

350 Ma zir cons are in her ited. The older grains from KoŸmicehave sim i lar col our and mor phol ogy to the youn ger, clus teredanal y ses and sim i lar char ac ter is tics of 350 Ma and youn gergrains were also noted for the Gogo³ów-Jordanów leucogranite(Kryza, 2011). In this case the in her ited sig nal is real, as might be sug gested by the oc cur rence of sim i lar grains in two lo cal i ties,the 350 Ma old grains prob a bly come from a pluton, ini tiallyempla ced be low the level of the KoŸmice and Gogo³ów- Jor -danów in tru sions em place ment. The in jec tion of new magma atca. 336 Ma could have dis in te grated the older, al ready so lid i fiedrocks. Remelting of this older ig ne ous source could have alsopro duced leucogranitic melts, such as those which in truded theGogo³ów- Jordanów mas sif (Kryza, 2011). Re cy cling of in her itedzir con grains, only a few Ma older than the in tru sion age, is ob -served in other in tru sions world-wide (e.g., Coleman et al., 2004).

In this light, the age of ca. 342 Ma ob tained for ho mo ge -neous zir con pop u la tion in Przedborowa seems to be a goodap prox i ma tion of the em place ment age for dioritic mag mas inthe Niemcza Zone, but the sec ond ep i sode of mag matic ac tiv ity could have taken place sev eral mil lion years later. Also, themagmatism in the area could have started be fore 350 Ma andcould be rep re sented by a hid den pluton.

GEOCHEMISTRY OF THE NIEMCZA ZONE ROCKS: FROM HIGH-K TO ULTRAPOTASSIC MAGMATISM

The geo chem i cal com po si tion of dioritic rocks from theNiemcza Zone shows that they are mostly shoshonitic (Fig. 5A;

The Niemcza diorites and moznodiorites (Sudetes, SW Poland): a record of changing geotectonic setting at ca. 340 Ma 331

Fig. 5. Ma jor el e ment com po si tion of rocks from the Niemcza Zone com pared with other

in tru sive rocks of sim i lar ages from the Bo he mian Mas sif

Data sources for the Czech rocks: Janoušek et al. (2000, 2004; Kotková et al., 2010; Parat et al., 2010) A – clas si fi ca tion af ter Peccerillo and Tay lor (1976)

Peccerillo and Tay lor, 1976), with scarce high-K (Przed borowa)and ultrapotassic rocks (Wilków Wielki and one en clave fromKoœmin). Com par ing rocks with low SiO2 con tent (48–53 wt.%)shows that Przedborowa has gen er ally lower K2O, MgO, Rb andNi from all other diorites in the Niemcza Zone. The im pli ca tion isthat if the age dif fer ence be tween Przedborowa and KoŸmice isreal it cor re lates with a change in magma chem is try from high-Kto shoshonitic over ap prox i mately 5 Ma. In ter est ingly, a sim i larchange was ob served in other in tru sive rocks from the Bo he mian Mas sif (Janoušek et al., 2000). Mag matic rocks with ages of375–335 Ma are wide spread in the Cen tral Bo he mian Mas sifand they are in ter preted as re lated to the subduction and thesub se quent col li sion of the Saxothuringian plate un der theTeplá- Barrandian unit (Schulmann et al., 2009; Žák et al., 2011).Be tween 354 and ca. 340 Ma, the magma chem is try changedfrom nor mal high-K calc-al ka line (e.g., Sázava pluton at 354 ±4 Ma; Janoušek et al., 2004) to shoshonitic (e.g., Blatná suite346 ± 10 Ma; Holub, 1997; 346 ± 2 Ma; Janoušek et al., 2010 orKlatovy granodiorite 347 +3/–4 Ma; Dörr and Zulauf, 2010) andto ultra potassic (e.g., Tøebic pluton, 341.6 ± 2.8 Ma; Kusiak et al., 2010; or Jihlava pluton, 335.1 ± 0.6 Ma; Kotková et al., 2010).This change in geo chem is try was ob served in both dioritic andgra nitic rocks and for the dioritic mag mas it in di cates a change inman tle geo chem is try as the man tle evolves from slightly de -

pleted at ca. 350 Ma to strongly en riched at ca. 340 Ma(Janoušek et al., 2004; Janoušek and Holoub, 2007). Com par i -son of geo chem i cal com po si tion be tween the dioritic rocks fromthe Niemcza Zone and those from the Cen tral Bo he mianPlutonic Com plex as well as Tøebic and Jihlava plutons (Figs. 5and 6) shows that most of the Niemcza Zone diorites arecompositionally sim i lar to the high-K calc-al ka line to shoshoniticrocks from the Cen tral Bo he mian Plu tonic Com plex that in trudedat ca. 354–346 Ma (high-K calc-al ka line rocks of the Sázavasuite and shoshonitic rocks of the Blatná suite). Nor mal calc-al -ka line rocks also oc cur ring in the Sázava suite were not found inthe Niemcza Zone. So far only the dioritic rock from WilkówWielki and dioritic en clave from Koœmin have geo chem i cal com -po si tion sim i lar to that of the ultrapotassic in tru sions with in tru sion ages around 340–335 Ma. These two rocks were not dated andfur ther age – geo chem is try cor re la tions can not be done.

The gen eral im pli ca tion is that the dioritic magmatism in theNiemcza Zone re cords a change in the chem is try of in tru siverocks sim i lar to that ob served in the Cen tral Bo he mian PlutonicCom plex from 354 to 346 Ma (high-K calc-al ka line to shosho -nitic), but the change in the Niemcza Zone oc curred prob a bly be -tween 342 and 336 Ma ago, ca. 10 Ma later. The geo chem i calevo lu tion of mag mas in the Cen tral Bo he mian Plutonic Com plexis re lated to the subduction of Saxothuringian do main un der the

332 Anna Pietranik, Craig Storey and Jakub Kierczak

Fig. 6. Trace el e ment com po si tion of rocks from the Niemcza Zone com pared with other in tru sive rocksof sim i lar ages from the Bo he mian Mas sif

Data sources for the Czech rocks: Janoušek et al. (2000, 2004), Kotková et al. (2010) and Parat et al. (2010)

Teplá-Barrandian microplate and change in the man tle chem is -try with the fi nal em place ment of ultrapotassic rocks de rived from the underthrusted Saxothuringian con ti nen tal crust and stronglyen riched man tle (Janoušek and Holub, 2007; Žák et al., 2011).By cor re la tion, a sim i lar pro cess could have taken place in theSudetes, also in re sponse to the col li sion be tween two do mains,prob a bly Saxothuringian and Molda nubian. How ever, such acon clu sion should be sup ported by fur ther pre cise dat ing cou -pled with geo chem i cal and pet ro log i cal anal y ses of dioritic rocksfrom Wilków Wielki and en claves from Koœmin as well as otherlo cal i ties of diorities such as K³oœnik and Niemcza. Also, fur thercom par i son of mag matic and subsolidus fab rics in the in tru siverocks of the Niemcza Zone (so far only done for the KoŸmicegranodiorite; Puziewicz, 1992) with well-doc u mented fab rics ob -served in the Cen tral Bo he mian Plutonic Com plex (Žák et al.,2012) could pro vide ad di tional in for ma tion on cor re la tions be -tween tec tonic re gimes in the two ar eas. Pre cise dat ing of thegranu lites from the Orlica- Œnie¿nik Mas sif (Anczkiewicz et al.,2007; Walczak, 2011) should show if they are tem po rally re latedto the ultrapotassic magmatism in the Niemcza Zone sim i larly tothe re la tions ob served for the Cen tral Bo he mian Plutonic Com -plex (Janoušek and Holub, 2007).

CONCLUSIONS

The monzodioritic rocks from the Niemcza Zone re cord achange in geo chem is try from high-K to shoshonitic mag masover less than 10 Ma. Zir con yields magma em place ment agesof 341.8 ± 1.9 Ma for Przedborowa (high-K) and 335.6 ± 2.3 Mafor KoŸmice (shoshonitic). The dif fer ence in chem i cal com po si -

tion of Przedborowa and KoŸmice rocks re flects the in creas ingen rich ment of the un der ly ing man tle from ca. 342 to ca. 336 Ma. Sim i lar evo lu tion of man tle com po si tion is re corded in rocksfrom the Cen tral Bo he mian Plutonic Com plex from ca. 354 toca. 347 Ma, there fore over a sim i lar time-span as that sug -gested for the Niemcza Zone. Chem i cal and tem po ral cor re la -tions be tween the two ar eas sug gest that (1) sim i lar geotectonic set ting de vel oped diachronously in dif fer ent parts of the Bo he -mian Mas sif and (2) the time-span of ca. 6–7 My is re quired toevolve from high-K to shoshonitic magmatism. The ultra potas -sic rocks, such as those which af fected the Czech part of theBo he mian Mas sif at 340–335 Ma, were not dated in this study,but syenites from Wilków Wielki are po ten tial can di dates to con -strain tim ing of the ultrapotassic magmatism in the Sudetes.

Ac knowl edge ments. J. Puziewicz and J. Leichmann arethanked for the field trip dur ing which sam ples were col lectedand for in ter est ing dis cus sion that started work on this pro ject.J. Puziewicz is thanked for help ful com ments on the ear lier ver -sion of this manu script. K. Dymna is thanked for zir con sep a ra -tion. Mas ter the sis of J. Gruszczyñska and A. Winiecka helpedto lo cate rep re sen ta tive sam ples of the Koœmin en claves.M. Kusiak, S. Mazur and J. Žák are thanked for their help fulcom ments and im prove ment of this manu script. AP ac knowl -edges grant no. N N307 105235 by the Pol ish Min is try of Sci -ence and Higher Ed u ca tion. JK ac knowl edges the Pro ject “De -vel op ment of the po ten tial and ed u ca tional of fer of the Uni ver -sity of Wroc³aw - the chance to en hance the com pet i tive ness ofthe Uni ver sity” co-fi nanced by the Eu ro pean Un ion un der theEu ro pean So cial Fund.

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334 Anna Pietranik, Craig Storey and Jakub Kierczak