Tec ton ics of the Chêciny Anticline (Holy Cross Mts., Cen tral Po land) in the light of new car to graphic data and cal cite vein anal y sis
Edyta JUREWICZ and Urszula STÊPIEÑ
Jurewicz E. and Stêpieñ U. (2012) – Tec ton ics of the Chêciny Anticline (Holy Cross Mts., Cen tral Po land) in the light of new car to - graphic data and cal cite vein anal y sis. Geol. Quart., 56 (1): 95–106. Warszawa.
The Variscan orog eny of NE–SW com pres sion has folded the Pa leo zoic core of the Holy Cross Moun tains (Cen tral Po land). The Chêciny Anticline, formed dur ing this tec tonic event, is lo cated in the south west ern part of the Kielce Unit. This pa per pres ents struc tural data from two newly found out crops of Cam brian rocks that mod ify the geo met ric re con struc tion of the Chêciny Anticline, es pe cially within its south ern limb that is sub di vided into two sec ond-or der struc tures: the Rzepka Syncline and the Wrzosy Anticline. The east ern part of the Chêciny Anticline has been re con structed, pin point ing its frag men ta tion into a se ries of blocks (horsts and grabens) sep a rated by faults semi-per pen dic u lar to the anticline axis. New map ping data re veals deep, pre-Tri as sic ero sion of folded Variscan base ment, un - cov er ing Cam brian rocks out crop ping in the hinge of the Wrzosy Anticline. In the Chêciny Anticline, fold ing-re lated short en ing has been ac com pa nied by along-strike ex ten sion and the for ma tion of syn-tec tonic cal cite veins, which filled frac tures ori ented per pen dic u - lar to the fold axis. The mag ni tude of ex ten sion has been es ti mated along a 215 m long main quarry wall of Rzepka Hill, ap prox i mately par al lel to the Variscan struc tures and lo cated within the south ern limb of the Chêciny Anticline. The to tal thick nesses of veins fill ing ex - ten sion frac tures and spaces be tween clasts in tec tonic brec cia were summed and in di cate 8.4% of strike-par al lel ex ten sion (~120o) in the Chêciny area. This value was com pared to ca. 30% of fold ing-in duced short en ing, re lated to NE–SW late Variscan com pres sion. We hence ob tain a strain ra tio of 30:8.4 = 3.5. This high value of strain ra tio in di cates that lon gi tu di nal ex ten sion was a sig nif i cant com po - nent con trib ut ing to the late Variscan de for ma tion in the Kielce Unit.
Edyta Jurewicz, Fac ulty of Ge ol ogy, Uni ver sity of War saw, ¯wirki i Wigury 93, 02-089 Warszawa, Po land, e-mail:
edyta.jurewicz@uw.edu.pl; Urszula Stêpieñ, Pol ish Geo log i cal In sti tute – Na tional Re search In sti tute, Rakowiecka 4, 00-975 Warszawa, Po land, e-mail: urszula.stepien@pgi.gov.pl (re ceived: July 20, 2011; ac cepted: Oc to ber 4, 2011).
Keywords: Holy Cross Mts., Variscan fold ing, cal cite veins, extensional frac tures, faults, tec tonic brec cia.
INTRODUCTION
The Holy Cross Moun tains are com posed of a Pa leo zoic core de formed as a re sult of Variscan fold ing (e.g., Czarnocki, 1919; Filonowicz, 1973) and a Permo-Me so zoic cover folded dur ing Lara mide oro gen esis (op. cit.). The Pa leo zoic core com - prises two main tectono-strati graphic units (Fig. 1) – the
£ysogóry and the Kielce units (Czarnocki, 1919, 1957;
Po¿aryski, 1978; Stupnicka, 1992). The south ern part of the Kielce Unit is the Chêciny–Klimontów Anticlinorium (Samsonowicz, 1926; Znosko, 1962; Mizerski and Or³owski, 1993), which is di vided into tec tonic blocks bounded by trans - verse faults. Within the wes tern most block there are the Zbrza Anticline, the Chêciny Anticline, the Ga³êzice–Bolechowice Syncline and the Dyminy Anticline (e.g., Czarnocki, 1938;
Filonowicz, 1973; Konon 2006).
The Chêciny Anticline (Figs. 1 and 2) is lo cated within the south east ern part of the Pa leo zoic core of the Holy Cross Moun -
tains (Czarnocki, 1938; Hakenberg, 1971a; Filonowicz and Lindner, 1986). It is lim ited to the south by the Permo-Me so zoic cover (op. cit.). Sec ond-or der folds, made up of the Rzepka Syncline and the Wrzosy Anticline, out crop in the south ern limb of the Chêciny Anticline. The Wrzosy Anticline is for the first time de fined in this pa per, based on newly rec og nized out crops of Cam brian rocks (Fig. 2). Rzepka is the name of a hill lo cated south of Chêciny town, where an aban doned quarry is lo cated. This quarry, with a 215 m long wall run ning al most par al lel to the re - gional trend of the late Variscan fold axes, en abled the de tailed struc tural anal y sis de scribed in this ar ti cle. Our anal y sis was di - rected at es ti mat ing the sig nif i cance and value of lo cal ex ten sion in duced by the late Variscan fold ing in this re gion. We also used new car to graphic data re gard ing Cam brian out crops to ana lyse the ge om e try of the south ern part of the Chêciny Anticline where the sec ond-or der Rzepka Syncline and Wrzosy Anticline are lo cated.
This re con struc tion al lowed rec og ni tion of the block-like ar chi tec - ture of the Chêciny Anticline, with in di vid ual, fault-lim ited blocks be ing up- and down-thrown with re spect to each other. More over,
new map data dem on strate that deep, pre-Tri as sic ero sion reached Cam brian rocks within the core of the Chêciny Anticline.
GEOLOGICAL SETTING
The Pa leo zoic core of the Holy Cross Moun tains was ex - ten sively (and ad mi ra bly) sur veyed by Czarnocki (1919, 1927). How ever, the tim ing and geodynamics of fold ing of the Pa leo zoic core of the Holy Cross Moun tains still re main con - tro ver sial. Ac cord ing to Kowalczewski (1965, 1971) and Znosko (1999, 2000) the first fold ing event was late Cal edo - nian in age and pro duced re verse faults and thrusts. This was when in ten sive ero sion, mainly of Si lu rian and Or do vi cian rocks, took place. Ac cord ing to an other group of re search ers, the late Cal edo nian event was less sig nif i cant than the Variscan de for ma tion (G³azek et al., 1981; Or³owski and Mizerski, 1998; Lamarche et al., 1999, 2003 and oth ers).
An im por tant role in the tec tonic evo lu tion of the Holy Cross Moun tains was played by Al pine oro gen esis. This tec tonic event was re spon si ble for de for ma tion of the Permo-Me so zoic cover and diapiric-like re-ar range ment of the Variscan anticline struc - tures. The ef fects of this de for ma tion can be ob served in e.g., the Chêciny Anticline with duc tile rocks in its core (Cam brian thin-bed ded sand stone, mudstone and shale; G³azek and Kutek 1970; Jaroszewski, 1972; Stupnicka, 1972; Kowalski, 1975).
Due to the com plex geo log i cal his tory of the Chêciny Anticline and its fring ing struc tures in the vi cin ity of Chêciny, sev eral struc tural anal y ses have been con ducted in this area (Stupnicka, 1972; Kowalski, 1975; Mastella and Konon, 2002;
Dêbowska, 2004; Konon, 2004, 2006, 2007 among oth ers).
Cal cite min er al isa tion has also been stud ied in the Chêciny Anticline (Wrzosek and Wróbel, 1961; Migaszewski et al., 1996; Wierzbowski, 1997 and oth ers) and, fur ther more, nat u ral re sources re lated to ore min er al isa tion have been ex am ined (Morozewicz, 1923; Rubinowski, 1954, 1955, 1962, 1971 among oth ers).
The core of the Chêciny Anticline is made of lower Cam - brian rocks (Fig. 2C) – claystones as well as mudstones with
quartzitic sand stone in ter ca la tions, in tensely de formed by tec - tonic pro cesses (Czarnocki, 1928, 1929, 1947; Jaroszewski, 1965; Kowalski, 1975; Stupnicka, 1986; Lamarche et al., 2003 and oth ers). The thick ness of lower Cam brian rocks has been es ti mated at ca. 800 m (Hakenberg, 1971a, b; Filonowicz and Lindner, 1987). The limbs of the Chêciny Anticline are com - posed of Emsian sand stones, at tain ing a thick ness of a few metres, and Mid dle and Up per De vo nian lime stones and dolomites ca. 600 m thick (Hakenberg, 1971a, b; Filonowicz and Lindner, 1987). Thick-bed ded, mas sive and reef lime - stones pre dom i nate, lat er ally pass ing into banded dolostone.
The youn gest De vo nian strata, of Frasnian age, are marls and marly shales. To wards the south, the Chêciny Anticline is fringed by Perm ian and Tri as sic rocks, ly ing un con form ably over De vo nian rocks and be long ing to the Permo-Me so zoic cover of the Holy Cross Moun tains.
The Chêciny val ley, be ing a text book ex am ple of mor pho - log i cal in ver sion (a val ley at an anticline crest), is mainly filled with Pleis to cene gla cial de pos its (Fig. 2A). Pleis to cene de pos its oc cur also to the south of the hills made up of De vo nian rocks – Zamkowa Hill and Rzepka Hill (Fig. 2A). The thick ness of the Pleis to cene at tains a few to over a dozen metres.
MAPPING DATA
Two new Cam brian out crops were found out side Chêciny val ley, i.e. out side the Chêciny Anticline core. A new ar ti fi cial out crop is lo cated to the east of Rzepka Hill at a petrol sta tion where earth works un cov ered regolith con tain ing abun dant quartzitic sand stone frag ments, the li thol ogy of which in di cates that they are Cam brian. In the out crop lo cated to the west of Rzepka Hill, regolith with abun dant quartzitic sand stone frag - ments has a con tact to wards the west with weath ered red - dish-grey dolomites, whose li thol ogy in di cates that they are Eifelian. This con tact be tween Cam brian and De vo nian rocks (be tween blocks no. 3 and 4 in Fig. 2B) is tec tonic and is due to a trans verse fault. The pres ence of a fault zone to the west of Rzepka Hill had al ready been pointed out by Stupnicka (1972),
Fig. 1. Lo ca tion of the study area in the Holy Cross Mts. (based on Kutek and G³azek, 1972)
Fig. 2. Sim pli fied geo log i cal maps and pro file of the study area (based on Hakenberg, 1971a, b, changed by pres ent au thors) A – su per fi cial ge ol ogy, black rect an gle – lo ca tion of Fig ure 7A; B – bed rock ge ol ogy; C – lithostratigraphic pro file;
lithostratigraphic units: TK – Keuper + Rhaetian, TM – Muschelkalk, TB – Buntsandstein, Pz – Zechstein
how ever, our new data sug gests that this zone is com posed of two faults be tween which a nar row belt of mainly Qua ter nary de pos its (over ly ing Cambrin) may be ob served (Fig. 2A, B).
South of Rzepka Hill abun dant quartzitic sand stone clasts, the li thol ogy of which in di cates that they are Cam brian, were found disconformably on Buntsandstein (Tri as sic) cover (Fig. 3). These clasts are usu ally well-rounded and their sizes vary be tween 0.5 and 10 cm. Clasts within the basal part of Buntsandstein con glom er ate also in clude abun dant lime stone and do lo mite frag ments, both rounded and an gu lar. An gu lar frag ments are of ten of vein cal cite of dif fer ent sizes (a few to over a dozen cm). The an gu lar ity in this case is due to the large (and eas ily cleav ing) crys tals. Rounded clasts of white and pink vein cal cite, up to 2 cm in di am e ter, are also abun dant and a few rounded lydite clasts have also been found (Fig. 3B). The ma - trix in the Buntsandstein con glom er ate is made of quartz sand and ac com pa nied by mica. The ce ment is cal car e ous and its red col our is due to he ma tite (Rubinowski, 1962).
STRUCTURAL ANALYSIS
The Rzepka Syncline and Wrzosy Anticline to gether form a sub or di nate (sec ond-or der) fold within the south ern limb of the Chêciny Anticline, the lat ter stretch ing be tween Miedzianka Hill in the NW and the Radkowice vil lage vi cin ity in the SE. The Rzepka Syncline is a lo cal struc ture, pres ent
only to the south of Zamkowa Hill and at Rzepka and Sosnówka hills. It does not con tinue to wards the NW, where in stead sev eral faults, re spon si ble for the com plex tec tonic struc ture of Zegzela Hill and ¯ebrownica are pres ent (Kutek and G³azek, 1972). The Chêciny Anticline is di vided into trans - verse, fault-bounded blocks. These are usu ally nor mal faults that give way to el e va tions and de pres sions. Five fault-bounded blocks can be dis tin guished in the part of the Chêciny Anticline in ves ti gated. Start ing from the SE and con tin u ing to wards the NW these blocks are named (Fig. 2B): Zamkowa Hill (1), Rzepka Hill (2 + 3), Korzecko (4) and Sosnówka Hill (5). A map view shows that within Zamkowa and Rzepka hills the an - ti cli nal axis plunges to wards the NW (Fig. 2B). The Korzecko block is the most el e vated, pro duc ing wid en ing of the band of Cam brian out crops. Most of this block is cov ered by Qua ter - nary de pos its. More over, the con sid er able width of the val ley cut ting through the south ern limb of the Chêciny Anticline, and the great thick ness of gla cial (Pleis to cene) de pos its, in di cate a lack of De vo nian in the val ley base ment. Ac cord ing to Kowalczewski (1963) trans verse faults cut ting the Chêciny Anticline are of pre-Zechstein or i gin.
This sug ges tion is sup ported by the fact that the trans verse faults are ori ented coplanar to extensional frac tures, which later on (dur ing block-like ver ti cal move ments) were trans formed into faults. De pres sions, which orig i nated due to ver ti cal move - ments along fault hang ing walls, are of ten filled with Buntsandstein de pos its. Buntsandstein de pos its pre served in tec tonic grabens de lin eate pre-Tri as sic re lief and in di cate the pre-Tri as sic age of the transverse faults.
The Rzepka Syncline is slightly oblique to the main (Chêciny) Anticline, which is eas ily un der stand able in the case of such a small fold, plung ing and dy ing-out to wards the NW (Fig. 4). Most of the extensional frac tures are geo met ri cally re - lated to the Rzepka Syncline. When our work be gan, we first di - vided these frac tures into groups based on vein fill min er al ogy (pure cal cite, Fe-cal cite and he ma tite). How ever, the re sults showed that the frac ture ori en ta tion is in de pend ent of min er ali sa - tion type (see Okamato et al., 2006). There fore, our mea sure - ments are shown on only two con tour di a grams in Fig ure 5:
non-min er al ised (Fig. 5A) and min er al ised (Fig. 5B). These di a - grams re veal 2 groups of extensional frac tures: lon gi tu di nal (L) and trans verse (T) to the fold struc tures. A geo met ric anal y sis of the frac ture sys tem in di cates that, within both min er al ised and non-min er al ised frac ture types, a frac ture set ori ented trans verse to the fold axis pre dom i nates (Fig. 5A, B). Many of these frac - tures be came non-ver ti cal, their an gle of dip be com ing ca. 80o SE. This can be at trib uted to fold axis plunge. The plunge of the Rzepka Syncline and Wrzosy Anticline axes to wards the NW is clear in plan view, be cause Cam brian rocks crop out at the south-east edge of the Wrzosy Anticline (Figs. 2 and 4). Trans - verse frac tures (T) are layer-per pen dic u lar and cal cite-min er al - ised (Fig. 5B). Their dom i nant ori en ta tion is al most par al lel to the com pres sion di rec tion (~13°). The sec ond set of frac tures (L) that can be dis tin guished in ste reo grams (Fig. 5) – the frac tures par al lel to the fold axis (lon gi tu di nal) – are re lated to the bend ing of a large fold hinge and the de vel op ment of extensional frac - tures semiparallel to the ax ial plane above a neu tral sur face of the hinge re gion. The mean strike of the (L) frac ture set is 135° and frac tures dip steeply at 75–90° to wards the S (Fig. 5).
Fig. 3. Pho to graphs of se lected frag ments of Lower Tri as sic rocks with clasts of Cam brian quartzitic sand stone (A) and lydite (B)
CHARACTERISTICS OF CALCITE VEINS AND TECTONIC BRECCIAS FROM THE RZEPKA QUARRY
Macrocrystalline cal cite veins trans verse (T) to the fold struc tures are usu ally a few mm to a few cm thick and the num - ber of min eral lay ers within in di vid ual veins is usu ally be tween one and three. More growth zones can be dis tin guished in the thick est vein in the quarry lo cated at the west ern end of the quarry wall (Fig. 6A, B). Most of the veins are sym met ri cal,
with an eas ily vis i ble me dian line. Fibres grew from the vein wall to wards the cen tre, mak ing these syntaxial fi bre veins (Ramsay and Huber, 1983). Veins opened faster than the crys - tal growth rate or by pe ri odic seal ing and frac tur ing (via a mech a nism of crack-seal growth; see Passchier and Trouw, 1998). A lack of cur va ture of the grow ing fibres in di cates no vein-par al lel dis place ment dur ing crys tal growth. In di vid ual cal cite crys tals are a few mm to 2–3 cm long. Most of the veins con tain traces of he ma tite mostly in be tween con sec u tive growth lay ers, which colours the veins red or pink.
Fig. 4. Sche matic 3D block-di a gram of the Chêciny and Wrzosy anticlines and Rzepka Syncline di vided into blocks Ex pla na tions as in Fig ure 2
Fig. 5. Ste reo graphs of frac tures within Givetian dolomites, quarry wall in Rzepka Hill A – frac tures with out min er al isa tion; B – with cal cite and Fe-cal cite min eral veins; (L) – lon gi tu di nal frac tures,
(T) – transverse frac tures; lower hemi sphere, pole to plane
The larg est cal cite vein in the Rzepka quarry, found at the west ern end of the quarry wall, is ca. 85 cm thick and dips at 70o to wards the N, which is an un usual vein ori en ta tion in this quarry (Fig. 6A, B). This is a com pos ite type of vein with 50–60 grow ing fi bre lay ers. Most of the com pos ite veins con - tain traces of he ma tite mostly in be tween con sec u tive growth lay ers, which colours the veins red or pink.
The cal cite (vein) min er ali sa tion of the Rzepka Hill quarry is prob a bly re lated to low-tem per a ture, non-met al lif er ous for -
ma tion, within which rose-type (“ró¿anka”) macrocrystalline cal cite veins were formed (Rubinowski, 1962). These veins oc - cur typ i cally in the SW part of the Kielce re gion, within the Mid dle De vo nian lime stones and dolomites. They are con sid - ered pre-Zechstein and usu ally fill (T) frac tures semi-per pen - dic u lar to re gional fold axes (Fig. 5). An ad di tional ar gu ment in fa vour of their pre-Zechstein age is the fact that some frag ments of “rose”-like cal cite veins are found within the basal part of the Buntsandstein de pos its (see above).
Fig. 6. Pho to graphs of cal cite veins and dolostone brec cia in the Rzepka quarry wall
A – frag ment of the thick est cal cite vein in the W-part of quarry; B – mi nor and less reg u lar vein; C – cha otic brec cia with min - eral ce ments; D – brec cia as so ci ated with cal cite vein; E – extensional vein as so ci ated with Riedel shears, re lated to axis plunge
Tec tonic brec cias are abun dant in the Rzepka quarry (Fig. 6C, D). These fault rocks oc cur in the im me di ate vi cin ity of cal cite veins and rep re sent mo saic or cha otic brec cia types (Mort and Wood cock, 2008). The brec cias in ques tion prob a bly orig i - nated due to hy drau lic frac tur ing (Branquet et al., 1999) and/or ex ten sion re spon si ble for rock frac tur ing and as so ci ated rock im - plo sion (Sibson, 1986; Loucks, 1999). Orig i na tion of these brec - cias would be syn chro nous with mul ti ple ac ti vated pro cesses of extensional frac ture open ing. The in tense red col our of min er als fill ing spaces be tween brec cia clasts is due to Fe com pounds, sat u rat ing De vo nian cal car e ous rocks.
Lo cally extensional veins are as so ci ated with R type brit tle Riedel shears (Fig. 6E; com pare with Wilcox et al., 1973). The for mer might be re lated to fold axis plunge to wards the west as - so ci ated with the di vi sion of the Chêciny Anticline into blocks.
Such geo met ri cal re or ga ni za tion, giv ing way to block tilt ing, might have been con tem po rary with extensional frac ture for - ma tion and might have led to lo cal shear stress re spon si ble for the or i gin of Riedel-type frac tures.
EXTENSION ESTIMATE BASED ON CALCITE MINERALISATION
CALCITE VEINS
A large aban doned quarry within De vo nian dolomites ex - ists in the study area, pro vid ing a unique op por tu nity to carry out a de tailed struc tural anal y sis (Fig. 7A). Abun dant, nearly ver ti cal, min er al ised extensional frac tures are ex posed in a ca.
215 m long main quarry wall that is ori ented al most par al lel to the re gional struc tural strike. Cal cite veins fill ing these frac -
tures are highly sys tem atic. The thick est veins are ori ented per - pen dic u lar to re gional fold axes and are ex cel lent for geo met ri - cal anal y sis of re la tion ships be tween folds and frac ture sets. In our work we as sume that the summed thick nesses of these cal - cite veins, com pared to the De vo nian do lo mite thick ness along a sec tion al most par al lel to the re gional struc tural pat tern, in di - cate the amount of ex ten sion.
The south ern wall of the Rzepka Hill quarry, the sub ject of our struc tural study, is lo cated on the south ern limb of the Rzepka Syncline (Fig. 7B). The main wall of the quarry is about 10 m high and is ori ented at ca. 120o and is al most 215 m long. Givetian dolomites are ex posed in this wall (Filonowicz and Lindner, 1986, 1987), show ing a monoclinal, gen tle dip to - wards the north (Fig. 5A). The bed ding is clearly vis i ble in the lower level of the quarry. Its up per, better ex posed ex ploi ta tion level, where the tec tonic mea sure ments were taken, is made of mas sive dolomites. A young trans verse fault, found at the west - ern end of the wall, cuts the larg est cal cite vein in the Rzepka quarry, which in di cates the post-min er ali sa tion age of this fault.
Cal cite min er ali sa tion ob served in this quarry may be con - nected with the rose-type, be cause it is per pen dic u lar to re - gional strike of fold axes (Rubinowski, 1962).
To es ti mate elon ga tion along the ex ten sion plane (that is elon ga tion par al lel to a fold axis), the thick nesses of all cal cite veins were summed up along a sec tion per pen dic u lar to vein at ti - tudes. The Rzepka quarry wall is suit ably ori ented for this, be - cause mea sure ments taken along the wall re quired only slight cor rec tion. A hor i zon tal line (al most per pen dic u lar to cal cite vein planes) has been drawn along the wall of the quarry. Along this line, vein thick nesses and at ti tudes were mea sured, and data col lected re gard ing the rel a tive age of min er ali sa tion and frac ture
Fig. 7. Struc tural blockdiagram of the Rzepka Hill area (A) and photo of the quarry wall (B);
view from the south Ex pla na tions as in Fig ure 2
prop a ga tion. Min er al ised frac tures were ana lysed to com pare with all frac ture data col lected in the quarry (Fig. 5).
Be sides mea sur ing the cal cite veins fill ing the extensional frac tures – di la ta tion within tec tonic brec cias, where spaces be - tween clasts were sim i larly filled by cal cite – was also mea sured.
Mea sure ments were taken along the same hor i zon tal line.
TECTONIC BRECCIAS
The mea sure ments of cal cite min er ali sa tion con tent within tec tonic brec cias were based on pho to graphs. Two types of brec cia were dis tin guished: (1) brec cias with where the ce ment col our is lighter than clast col our and (2) those where ce ment col our is darker than clast col our (Fig. 8). The for mer type is made of an gu lar, up to 20 cm large frag ments of De vo nian do - lo mite with a ma trix made of white to pink-white cal cite (Fig. 8Aa). The ma trix fills spaces be tween clasts as well as small cracks within clasts. The sec ond type of brec cia is also made of De vo nian do lo mite clasts, but these are smaller and partly rounded (Fig. 8Ba). The larg est clasts, up to 2–3 cm in di am e ter, are an gu lar. The min eral ma trix is grey and dark grey, darker than the clasts. An gu lar clasts are cut by thin cal - cite veins of the same color and age as the ma trix.
An at tempt has been made to es ti mate cal cite mineralisation con tent within both types of brec cias. To do so, the col our con - trast be tween ma trix and clasts was used. Such cal cu la tion meth ods, based on pho to graphs and us ing a sim ple nu meric pro ce dure, are be com ing more com mon (e.g., Heilbronner, 2000; Clark and James, 2003; Heilbronner and Keulen, 2006).
In this work, the sim plest nu merical method was used, based on the anal y sis of mono chro matic pho to graphs and grey shade distribution.
The first step was to trans form each pho to graph into a grey-scale pic ture (Fig. 8Ab, Bb). This was done in the pop u lar graphic soft ware pack age CorelPhotoPaint. The best trans for - ma tion ef fects were at tained when sep a rat ing a pic ture into RGB chan nels. In both cases of tec tonic brec cia types the best con trast was seen in the green chan nel (G). Sub se quently, in or - der to better dif fer en ti ate be tween clasts and ma trix, bright ness, con trast and in ten sity lev els were ad justed and the im ages were saved in tiff for mat (with out com pres sion). By this means, the pho to graphs were pre pared for fur ther anal y sis in ArcGIS.
Then, his to grams were cal cu lated, show ing the dis tri bu tion of grey shades in the pho to graphs, where 0 sig ni fied black and 255 was white. In both cases the dis tri bu tions were skewed and in di cated less min er ali sa tion than clast con tent. How ever, the first type of tec tonic brec cia con tains more min er ali sa tion (com pared to clasts) than the sec ond type of tec tonic brec cia.
The next step was the best pos si ble de lim i ta tion be tween rock frag ments and ma trix (Fig. 8Ac, Bc), to be able to trans form the pho to graphs into one-bit maps. Such a trans for ma tion al lowed cal cu la tion of the rel a tive pro por tions of clasts and ma trix. Two main classes were pro posed, one con tain ing clasts and the other ma trix, the limit be tween them be ing set at the dom i nant value.
Con trast ing – black and white – colours were as signed to these two classes. Then ad di tional classes were set up be low and above the mode. A sub se quent step ana lysed these classes to as sign each one to a cor rect, pre vi ously as sumed main class.
Each time, a black-and-white out put was com pared to a bench -
mark grey-scale brec cia pho to graph, by over ly ing im ages (Fig. 8Ad, Bd).
To in crease the con trast be tween min er al isa tion and clasts in bench mark pho to graphs, pixel val ues were raised to the sec - ond or third power. This densifying method was used to best rep re sent both brec cia types in black-and-white (one-bit) im - ages. Pre cise cal cu la tion of min er al isa tion con tent in % in both brec cia types was pos si ble thanks to the de scribed im age pro - cess ing pro ce dure. Thus, the first type of brec cia con tains as much as 44% of min er al isa tion and sec ond type con tains 31%.
Over all, brec cias make up ca. 2.5% of the en tire mea sured quarry wall length, and min er al isa tion con tained within them makes up al most 1% of this length.
Tak ing into ac count cal cite vein thick nesses and cal cite min - er al isa tion within tec tonic brec cias, min er al isa tion was found to con sti tute ca. 8.4% (ca. 18 m) of the to tal wall length (215 m).
DISCUSSION AND CONCLUSSIONS
The Wrzosy Anticline has been dis tin guished within the south ern limb of the Chêciny Syncline, pre vi ously known as the Rzepka Syncline (Czarnocki, 1938; Hakenberg, 1971a;
Filonowicz and Lindner, 1986). These two struc tural el e ments are lo cal, sec ond-or der folds that do not con tinue far to wards the NW. In stead, in the NW of the in ves ti gated area, they are prob a bly sub sti tuted by tec toni cally com pli cated struc tures on
¯ebrowica and Zegzela hills, where over turned lay ers of Pa leo - zoic rocks could be ob served (Kutek and G³azek, 1972). The Chêciny Anticline as well as both sec ond-or der folds on its south ern limb are up right, open folds with semivertical ax ial planes (Figs. 4 and 7). Ac cord ing to Konon (2006), the Rzepka Syncline is an ex am ple of a footwall syncline, the or i gin of which could pre cede fault prop a ga tion. Ac cord ing to our new data, the dis tinc tion of the Wrzosy Anticline south wards of the Rzepka Syncline, both be ing sym met ri cal in na ture, seems to pre clude such an in ter pre ta tion in the area stud ied.
Brit tle frac tur ing of De vo nian rocks took place in the late phase of the Variscan orog eny. This pro cess was gen er ally con - nected with lon gi tu di nal ex ten sion per pen dic u lar to the axes of mac ro scopic folds and was re spon si ble for the de vel op ment of extensional vein ing. Struc tural anal y sis, based on mea sure - ments of cal cite min er al isa tion in veins and tec tonic brec cias, per mit ted es ti ma tion of lon gi tu di nal (fold axis-par al lel) ex ten - sion to be 8.4% and to com pare this with fold ing-con trolled short en ing, de ter mined from the cross-sec tion of Hakenberg (1971a), to reach 30%. This way, we ob tain a strain ra tio of 30:8.4 = 3.5. This high value of strain ra tio in di cates that lon gi - tu di nal ex ten sion was a sig nif i cant com po nent, con trib ut ing to late Variscan de for ma tion in the Kielce Unit.
Dur ing the late Variscan deformational stage, af ter the cal - cite veins were formed, the Chêciny Anticline be came frag - mented into fault-bounded blocks (Znosko, 1962; Mizerski and Or³owski, 1993; Konon, 2006). The pre-Tri as sic (pre-Perm - ian? – see Kowalczewski, 1963) age of these trans verse faults can be dem on strated on the south ern slope of the Rzepka Hill where the fault vis i ble in the west part of the quarry wall is cov - ered by Buntsandstein de pos its (Figs. 2B and 7A). Dif fer ent ver ti cal dis place ments along these faults pro duced graben and
c
a
d
Fig. 8. Se lected pho to graphic doc u men ta tion of brec cia anal y sis based on mono chro matic pho to graphs A – brec cia with dark clasts and light min eral ce ment; B – brec cia with light clasts and dark min eral ce ment
horst struc tures and a re gional NW plunge of fold axes. Tec - tonic mo tion could be ac ti vated along trans verse dis con ti nu - ities of dif fer ent or i gins, e.g. extensional frac tures with cal cite min er ali sa tion. El e vated blocks, es pe cially that the Korzecko (no. 4 in Figs. 2B and 4) and the SE part of the Zamkowa block, have been strongly eroded (Kowalczewski, 1971; Stupnicka, 1992). Ac cord ing to Konon (2004) as much as 1 km of Pa leo - zoic rocks were re moved in the course of post-Visean ero sion.
Due to the high el e va tion of the Korzecko block, only Cam - brian rocks are found within it and this is the rea son why the Rzepka Syncline and Wrzosy Anticline can not be traced there (Figs. 2B and 4). Cam brian quarzitic sand stone and lydite clasts within the Buntsandstein de pos its in di cate the range of ero sion within up-thrown tec tonic blocks (Fig. 3). Pre-Tri as sic un cov er ing of Cam brian rocks could also have been re spon si - ble for diapiric-like tec ton ics (G³azek and Kutek, 1970;
Jaroszewski, 1972; Stupnicka, 1972; Kowalski, 1975) and the ero sion-con trolled ge om e try of buckle fold in ter fer ence (Si -
mon, 2005). Due to diapiric-like move ments of eas ily de form - able Cam brian thin-bed ded sand stone, mudstone and shale, a lo cal de tach ment at the bound ary of com pe tent/in com pe tent rocks has formed (Konon, 2006). This means that some de tach - ments con nected with diapiric-like tec ton ics could have started rel a tively early dur ing the late Variscan orogenic stage (Lamarche et al., 2003), in stead of dur ing the early Al pine (Laramian) tec tonic event (Czarnocki, 1947; G³azek et al., 1981). This con clu sion is also sup ported by a Tri as sic stra tal cover over ly ing el e vated blocks as well as to tec tonic bound - aries be tween them (Figs. 2 and 4).
Ac knowl edge ments. This study was sup ported by the In - sti tute of Ge ol ogy, Uni ver sity of War saw. We would like to thank an anon y mous re viewer and Z. Cymerman for stim u lat - ing dis cus sions and com ments and E. Szynkaruk for lin guis tic im prove ment.
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