GEOLOGIJA 45/1, 247–253, Ljubljana 2002 Shallow intrusive volcanic rocks on Mt. Raduha, Savinja-Kamnik Alps, Northern Slovenia Plitve intruzivne vulkanske kamnine na Raduhi, Savinjsko – Kamni{ke Alpe Polona KRALJ & Bogomir CELARC Geological Survey of Slovenia, Dimi~eva 14, 1000 Ljubljana, Slovenia Key words: intermediate volcanics, intrusive volcanics, Slovenia Klju~ne besede: vulkaniti srednje sestave, intruzivni vulkaniti, Slovenija Abstract Volcanic rocks occurring in Ladinian (?) marls, interstratified with limestone (Sol~ava beds), at Grohat Alpine Meadow and Lipni plaz, Mt. Raduha, are shallow intrusives bodies with porphyric structure, and basaltic andesitic, acid andesitic and dacitic composition. Abundance of major oxides and trace elements in the studied rocks is similar to those observed in the Tertiary Smrekovec volcanic rocks suggesting contemporaneous formation and close genetic relationship. Kratka vsebina Vulkanske kamnine v ladinijskih (?) laporjih s tankimi vlo‘ki apnencev (sol~avske plasti) na planini Grohat in Lipnem plazu na Raduhi predstavljajo plitva intruzivna telesa s porfirsko strukturo in bazi~no andezitno, kislo andezitno in dacitno sestavo. Vsebnosti glavnih oksidov in slednih prvin v raziskanih kamninah so mo~no podobne tistim v terciarnih smrekov{kih vulkanskih kamninah in ka‘ejo na njihovo medsebojno ~asovno in genetsko povezanost. Introduction Marls with intercalations of thin limestone beds of Ladinian (?) age (Sol~ava beds) at Lipni plaz (fig. 1, loc. 1), Grohat Alpine Meadow (fig. 1, loc. 2) and Je‘ (fig. 1, loc. 3), north-western flanks of Mt. Raduha, locally include smaller bodies of coherent volcanics, emplaced concordantly with the sediment bedding (Plate 1 – fig. 1,2). Their thickness, however, is rather diverse – about 5 m at Grohat, and 0,5 at Lipni plaz. At Grohat, the body length amounts to about 30 m, and grades laterally into a weathered horizon. Both, carbonate rocks and intrusive volcanic bodies have very similar dip towards the South-East (140/40). Location 1 is newly discovered, location 2 is marked only on Working map in the scale 1:25000 for Basic geological map of SFRJ, scale 1:100000, Sheet Ravne na Koro{kem (Mio~ & @nidar~i~ 1983) as Oligocene tuffs and tuffites lying discordantly on Lower Triassic rocks. The same geological situation is presented on location 3. East and South-East of the studied sites, in a distance less than 6 km, Tertiary Smre-kovec volcanic complex occurs. It is composed of lavas and shallow intrusive bodies of andesitic and dacitic composition (Kralj, 1986), and extensive volcaniclastic deposits. Isolated outcrops of basal Tertiary conglom- 19-247-253.p65 17. 09. 02, 16:19 247 Black 248 Polona Kralj & Bogomir Celarc Fig. 1: Simplified map of the studied outcrops of shallow intrusive volcanic rocks on Mt. Raduha erates overlie discordantly Upper Triassic limestone and were found on the top of Mt. Raduha. In the Durce area near by, there are tuffs and tuffites lying on Tertiary conglomerates (Celarc, current research) Stanko Buser (personal communication) believes the presented volcanics are Ladi-nian sills and dykes, similar to those found in the Jezersko area (Buser & Cajhen 1977). Another possibility is, that volcanic rocks are of Tertiary age and are genetically related to Smrekovec volcanic complex. The distance is small, especially if Mt. Raduha is not thrusted. In this contribution, geochemi-cal and petrological characteristics of shal- low intrusive volcanic rocks at Grohat and Lipni plaz are presented, and the idea of their origin discussed. Petrography and chemical composition The samples from Mt. Grohat and Lipni plaz are very similar according to petrologi-cal characteristics, and they closely resemble the Smrekovec coherent volcanic rocks (Kralj, 1996). They are plagioclase-mag-netite vitrophyres which consists of glassy groundmass, phenocrysts, microphenocrysts and microlites (Plate 1 – Fig. 3, 4). Seriate Plate 1 – Tabla 1 1. Outcrop of shallow intrusive volcanic rock at Lipni plaz 2. The same as Fig. 1, closer view 3. Shallow intrusive vocanic rock from Grohat under plane polarised light. The texture is volcanic, with glassy groundmass and plagioclase phenocrysts of various size. Plane polarised light, magnification 23 x 4. The same as Fig. 3, crossed nicols 5, 6. Clastic character of the rock from Je‘ (location 3). The rock is probably a peperite. Plane polarised light, magnification 23 x 19-247-253.p65 17. 09. 02, 16:19 248 Black 19-247-253.p65 Cyan 17. 09. 02, 16:19 249 19-247-253.p65 Magenta 17. 09. 02, 16:19 249 19-247-253.p65 17. 09. 02, 16:19 249 Yellow Shallow intrusive volcanic rocks on Mt. Raduha, Savinja-Kamnik 249 19-247-253.p65 17. 09. 02, 16:19 1 2 3 4 5 6 249 Black 250 Polona Kralj & Bogomir Celarc texture is commonly observed. Phenocrysts are plagioclases, twinned and zoned, and extensively replaced by albite, less commonly to calcite and a filosilicate mineral, most probably interlayered chlorite/smectite. Glassy groundmass is devitrified and commonly replaced by authigenic albite, mi-crocrystalline quartz and yellowish-green fi-losilicate minerals. Magnetite occurs as mi-crophenocryst and some ten µm sized xeno-morphic grains, dispersed throughout the rock. The sample taken at Je‘ (location 3), along the road from Spodnje Sleme to the Bistra Valley, is just a fragment in a weathered rock and was not analysed chemically. The rock is probably an altered peperite (Plate 1 – Fig. 5, 6). Chemical composition of the studied shallow volcanic rocks is shown in Table 1. At a glance, the rocks can be classified according to the silica content as andesites and dacite. Yet, a closer view to the ignition loss and high calcium and sodium content reveals the influence of rock alteration, particularly calcitisation and albitisation of the primary constituents. Table 1:Chemical composition of shallow intrusive volcanic rocks. R1A – Lipni plaz, G2CA, G1B, Grohat. Oxide/ Element Unit R 1A G2Ca G 1B SiO2 % 51,4 63,7 59,3 TiO2 % 0,903 0,802 0,794 Al2O3 % 15,3 16,4 16,1 Fe2O3 % 4,78 5,45 FeO % 3,6 MnO % 0,14 0,06 0,08 MgO % 1,79 2,25 2,03 CaO % 10,7 2,99 4,13 Na2O % 5,43 4,68 5,12 K2O % 0,45 1,47 1,22 P2O5 % 0,23 0,15 0,14 CO 2 % 6,83 0,66 2,00 L.O.I. % 7,85 2,25 3,50 Li ppm 68 77 89 Be ppm 2,1 1,9 1,0 B ppm 16 23 26 Sc ppm 12,5 11,8 12,1 V ppm 50 111 117 Cr ppm 17 14 6 19-247-253.p65 250 Black Co ppm 12 17 20 Ni ppm 5 3 5 Cu ppm 4,5 9,1 8,8 Zn ppm 61,3 55,2 53,6 Ga ppm 9 12 10 Ge ppm <10 <10 10 As ppm 2 <2 45 Se ppm <5 <5 <5 Br ppm 1 1 1 Rb ppm 12 37 29 Sr ppm 435 441 514 Y ppm 43 31 29 Zr ppm 116 132 125 Nb ppm 11 10 9 Mo ppm 1 1 2 Ag ppm 0,3 <0,2 <0,2 Element Unit R 1A G2Ca G1 B Cd ppm <0,2 <0,2 <0,2 In ppm <0,5 <0,5 <0,5 Sn ppm 4 4 4 Sb ppm 0,4 <0,2 0,9 Cs ppm 5 <3 8 Ba ppm 166 251 221 La ppm 23,7 20,7 20,9 Ce ppm 47,1 37,7 39,2 Pr ppm 6,7 4,6 4,8 Nd ppm 27,9 20,1 20,0 Sm ppm 5,9 4,4 4,6 Eu ppm 2,00 1,01 1,14 Gd ppm 5,5 3,9 3,8 Tb ppm 1,0 0,7 0,7 Dy ppm 6,9 4,9 4,2 Ho ppm 1,53 0,97 0,98 Er ppm 4,3 3,2 2,7 Tm ppm 0,6 0,5 0,4 Yb ppm 3,8 2,8 2,6 Lu ppm 0,55 0,50 0,40 Hf ppm 23 28 26 Ta ppm 5 3 1 W ppm 37 61 51 Au ppm <2 <2 9 Hg ppm <5 <5 <5 Tl ppm <0,1 0,1 0,1 Pb ppm <2 10 26 Bi ppm <5 <5 Th ppm 5,3 6,1 3,7 U ppm 2,7 2,6 1,2 17. 09. 02, 16:19 Shallow intrusive volcanic rocks on Mt. Raduha, Savinja-Kamnik 251 In the silica-total alkali diagram (L e B a s e t a l . 1986), the studied shallow intrusive rocks fall in the fields of basaltic trachyan-desite, andesite and dacite (fig. 2). Based on classification using immobile elements Zr/ TiO2 – SiO2 (Winchester & Floyd 1979), the rocks are andesites and dacite (fig.3), close to Tertiary volcanic rocks from the Smrekovec, Roga{ka Slatina and Rogatec areas. Based on the diagram of K2O/SiO2 contents after Ewart (1979), the rock samples belong to calc-alkaline basaltic andes-ites, acid andesites and dacites. In general, variations of trace elements and some of their ratios (table 2) are well in the variation span of orogenic andesites (Gill 1981), dacites (Ewart 1979), Tertiary volcanic rocks from the Smrekovec, Roga{ka Slatina and Rogatec areas (Kralj, 1996; this volume), and South Pannonian basin (Pami} & Balen 2001). One outstanding exception is lithium, which is much higher than expected for andesites and dacites, although still in the variation span for dacites. We believe that lithium could originate from the action of deuteric fluids or partial incorporation of the enclosing marl in to magma during its emplacement to the host rock. Rubidium is relatively low with respect to the data for dacites (E w a r t 1979), but closer to the data of Pami} & Balen (2001) for andesite formations in South Pannonian basin. Barium is low, too. Both, low rubidium and barium could be related to alteration of plagioclase feldspars. On the other hand, strontium is very high and suggests that it could be partially derived from an external source, probably carbonate. Table 2: Some trace element ratios for intrusive volcanic rocks from Mt. Raduha Ratio R 1A G2Ca G1 B K/Rb 308 330 348 Ba/La 7,0 12,1 10,6 Zr/Nb 10,5 13,2 13,9 La/Th 4,5 3,4 5,6 La/Nb 2,15 2,07 2,32 La/Yb 6,24 7,4 8,0 Ce/Yb 12,3 13,5 15,1 Zirconium, zinc and rare earth elements (REE) with yttrium are well in the variation span for andesites and dacites. Chondrite Fig. 2. The silica-total alkali diagram (L e B a s e t a l . 1986) for the studied shallow intrusive volcanic rocks from Mt. Raduha 19-247-253.p65 17. 09. 02, 16:19 251 Black 252 Polona Kralj & Bogomir Celarc Fig. 3. Classification using immobile elements Zr/TiO2 – SiO2 (W i n c h e s t e r & F l o y d 1977). Shallow intrusive volcanic rocks from Mt. Raduha – closed diamonds; Smrekovec volcanics – open circle, squares, triangles; Roga{ka Slatina – closed square; Rogatec (Trli~no) – closed triangles normalised (Nakamura 1974) REE patterns are very similar for all analysed samples of shallow intrusive volcanic rocks (fig. 4, R 1A, G1 B, and G2Ca). Ligt rare earth elements (LREE) are moderately enriched with respect to heavy rare earth elements (HREE). Very small negative cerium and europium anomalies can be observed. The REE plots are similar to those observed for the Smrekovec volcanics (Kralj, 1996) and acid andesite from Zagaj at Roga{ka Slatina (Kralj, this volume). Fig. 4. Chondrite normalised REE abundance for the samples from Mt. Raduha. R 1A, Lipni plaz, G1 B and G2Ca, Grohat 19-247-253.p65 17. 09. 02, 16:19 252 Black Shallow intrusive volcanic rocks on Mt. Raduha, Savinja-Kamnik 253 In the Ce – Ce/Y diagram, volcanic rocks from Mt. Raduha are well aligned in the line for the Smrekovec volcanic rocks, and are different than acid andesite from Zagaj at Roga{ka Slatina and dacite from Trli~no at Rogatec (fig. 5). Fig. 5. The Ce/Y vs. Ce diagram with the volcanic rock samples from Mt. Raduha (closed diamonds), Mt. Smrekovec (open squares, open triangles and open circle), Zagaj at Roga{ka Slatina (closed square) and Trli~no at Rogatec (closed triangle) Abundance of compatible trace elements Cu and Ni is low with respect to the data for dacites (Ewart 1979). Copper is low in comparison with the Smrekovec volcanics, too, but very close to the abundance observed in the lava from Trli~no at Rogatec. Nickel is in the same variation range as in the Smre-kovec, Roga{ka Slatina and Rogatec volcanic rocks. Conclusions Shallow intrusive volcanic rocks from NW flanks of Mt. Raduha are classified as low potassium, calc-alkaline andesites and da-cite. Trace element variations are consistent with the variation span for andesites (Gill 1981) and dacites (Ewart 1979) and are comparable with those observed in the Smre-kovec, Roga{ka Slatina and Rogatec volca- nic rocks. Magmas seem to be emplaced in Ladinian (?) slaty marls during the Smre-kovec volcanic activity owing to their week mechanical resistence and probably increasing lithostatic pressure. Shallow intrusives underwent alteration. In the early stage, it was very possibly related to the activity of deuteric fluids and is reflected in albitisation of plagioclases and somewhat higher sodium content than expected from the silica content. Late-stage alteration possibly involved calcitisation and the formation of clay minerals. References B u s e r , S . & C a j h e n , J . 1977: Osnovna geolo{ka karta SFRJ 1:100000, Celovec (Klagenfurt) L 33-53. – Zvezni geolo{ki zavod, Beograd. E w a r t , A . 1979: A review of the mineralogy and chemistry of Tertiary-recent dacitic, latitic, rhyolitic, and related salic volcanic rocks. In: F. Barker (ed.), Tronhjemites, dacites, and related rocks, Developments in Petrology 6, 13-121, Elsevier, Amsterdam. G i l l , J . B . 1981: Orogenic andesites and plate tectonics. Springer-Verlag, 390 pp, Berlin. LeBas, M. J., LeMaitre, R. W., Streck e i s e n , A . & Z a n e t t i n , B . 1986: A chemical classification of volcanic rocks based on total alkali-silica diagram.- J. Petrology 27, 745-750, Oxford. K r a l j , P . 1996: Lithofacies characteristics of the Smrekovec volcaniclastics, northern Slovenia.- Geologija 39, 159-191, Ljubljana. M i o ~ , P . & @ n i d a r ~ i ~ , M . 1983: Osnovna geolo{ka karta SFRJ, Ravne na Koro{kem L 33-54, 1:100000. – Zvezni geolo{ki zavod, Beograd. P a m i } , J . & B a l e n , D . 2001: Petrology and geochemistry of Egerian-Eggenburgian and Badenian tholeiite-calc-alkaline volcanics from the South Pannonian basin (Croatia). – N.Jb. Miner. Abh. 176, 3, 237 –267, Stuttgart. P e c c e r i l l o , A . & T a y l o r , S . R . 1976: Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, northern Turkey.- Con-trib. Miner. Petrol. 58, 63-81, Berlin. Winchester, J. A. & Floyd, P. A. 1977: Geochemical discrimination of different magma series and their differentiation products using immobile elements.- Chem. Geol. 20, 325-343, Amsterdam. 19-247-253.p65 17. 09. 02, 16:19 253 Black