Karawanken tonalite pluton

from Wikipedia, the free encyclopedia

The Karawanken tonalite pluton , sometimes just Karawanken tonalite , is an Oligocene intrusive body along the Periadriatic seam in Carinthia and Slovenia .

geography

The Karawanken tonalite pluton is a 43 kilometers long and a maximum of 2.2 kilometers wide lamella made of tonalite that strikes immediately north of the Periadriatic Seam (locally referred to as the Remschenig fault ) in an east-southeast-west-northwest direction (N 115). The intrusion starts in the east near Plešivec in Slovenia . It then moves to Austrian territory, sweeps south of Eisenkappel through the Remschenig Valley and ends in the west just before the Vellach . A small isolated lens appears further west south of Villach near Susalitsch in the Karawanken .

geology

The valley low around St. Margarethen is underlain by the Karawanken tonalite. In the background the north walls of the Uschowa from the southern Alpine Triassic.

The Periadriatic Seam, also known in Slovenia as the 50 to 60 kilometer long Smrekovec Lineament , represents an important Terrang boundary and was created due to dextral (right-shifting) transpression between the Eastern Alps in the north on the one hand and the Southern Alps in conjunction with the External Dinarides in the south on the other . It disappears in the east below tertiary sediments of the south-western Pannonian basin and probably continues in a north-easterly direction in the Balaton lineament of Hungary . Two further branches cross the southern Pannonian Basin east of the Zagreb-Zemplen Lineament while maintaining the same east-south-east direction and follow the Drava and Sava Depression ( Sava Fault ). In the surrounding basement of the Pannonian Basin, paleogenic granitoids with overlying andesites and dazites were found. The Šoštanj Fault , southeast section of the Smrekovec Lineament, is cut off by the dextral Labot Fault south of the Bacher Mountains and shifted to the southeast.

The Karawanken tonalite pluton is accompanied further north by a second, similarly steep, 45 kilometer long granitoid lamella, the Karawanken granite pluton . This is much older with 224 to 216 million years and comes from the Upper Triassic ( Carnian ). Between the two plutonite lamellae is Austroalpine basement, consisting of cordierite- bearing metamorphic paleozoic era ( paragneiss , microblade gorge , phyllonites , amphibolites and cordierite knot schist). Hornfelse reveal the contact metamorphic heating caused by the tonalite.

Further north, wedged between two dextral lateral shifts, follows the lamella of the Eisenkappel diabase as well as internally overlapping, north-vergent platform limestone from the Central and Upper Triassic , which in turn is pushed onto the Late Miocene / Pliocene Sattnitz conglomerate of the Klagenfurt Basin . The Klagenfurt Basin is a flexure basin with more than 1000 meters of sediment filling. Its age ranges from the Serravallian ( Sarmatian ) to the upper Messinian ( Pontian ), the hillside conglomerates are Pliocene, possibly even Pleistocene .

South of the Periadriatic Seam, the Karawanken tonalite pluton is in abnormal contact with Paleozoic and Triassic formations of the northwestern Dinarides and the Southern Alps. The Paleozoic is mostly absent or not open-minded. The Triassic, shifted to the north, begins with the Werfen strata , followed by the gray Dolomites, banked limestone and flaser limestone. In Slovenia, the south side of the Smrekovec lineage and the Šoštanj fault is built up by the Smrekovec volcanic rocks - Oligocene / Miocene andesites, basaltic andesites and dazites and their volcaniclastic equivalents.

The fault is more or less vertical and is characterized by cataclasites , mylonites and ultramylonites. The Karawanken in Eisenkappel thus represent a total of a so-called flower structure is ( English flower structure ) as is characteristic of Transpressionsgürtel.

Petrography

The medium to coarse-grained Karawanken tonalite pluton was captured by a very strong dynamometer metamorphosis along the periadriatic seam and ductile deformed so that it now has a clearly pronounced two-dimensional parallel structure ( foliation ). That is why it was previously referred to as tonalite gneiss. A lineation can also be clearly seen on this main schisto surface , which is defined by elongated hornblende , biotite and elongated mafic inclusions. It falls at 13 ° to the east-southeast.

The pluton contains numerous mafic inclusions of dioritic composition and is interspersed with light aplitic and dark mafic veins and ducts.

The pluton has the following mineral inventory:

The accessories take up a total of 3 percent by volume and contain early apatite and zircon , late allanite and sphene , possibly also monazite , and as opaque ore minerals ilmenite , magnetite and pyrite . Secondary formations are chlorite , epidote , clinozoisite , sericite , kaolinite and carbonates . Rarely occurring almandine can be regarded as a xenocrystal.

The rather small-grain, xenomorphic quartz is gray in color and arranged in lines. It shows pores and occasionally contains small inclusions of ilmenite and zircon. The plagioclase, which is a few millimeters in size and zoned with oscillations, appears pure white. The cores are very rich in anorthite (An 90 to An 65 ), in the mantle and shell the anorthite content drops to An 30 , even to An 25 . Plagioclase can contain clinozoisite and light mica, with the latter usually also adding biotite. The xenomorphic alkali feldspar is probably orthoclase with weak triclinization. Myrmekite is found on the border between plagioclase and alkali feldspar. Its quartz wart stems protrude convexly into the alkali feldspar. The pleochroic biotite occurs in black panels up to 7 millimeters in size, which agglomerate to form aggregates. It can decompose into chlorite with the excretion of sphen. It contains idiomorphic plagioclase as inclusions. The prismatic, also pleochroic hornblende is dark green to black in color and can be up to 20 millimeters long. As with biotite, inclusions of idiomorphic plagioclase confirm the priority of plagioclase in the crystallization sequence. The prismatic, 0.3 millimeter long apatite forms inclusions in biotite, hornblende and feldspar. The sometimes zoned epidote is up to 0.6 millimeters in size and is often found on the edges of the hornblende. Chlorite is a secondary formation after hornblende and biotite.

The appearance of Myrmekite refers to metasomatic processes in the already solidified rock.

Petrology

Main elements

The following table is intended to illustrate the chemical main element composition of the Karawanken tonalite pluton:

Oxide
wt.%		 Tonalit 1 Tonalit 2 Tonalit 3 Tonalite /
granodiorite		 Granodiorite Standard mineral
weight%		 Tonalit 1 Tonalit 2 Tonalit 3 Tonalite /
granodiorite		 Granodiorite
SiO 2 58.90 60.72 62.40 64.20 68.10 Q 19.50 18.40 22.40 20.30 28.10
TiO 2 0.83 0.52 0.60 0.58 0.35 C. 1.50 2.70 3.40
Al 2 O 3 17.00 17.25 18.00 15.50 17.20 Or 8.50 11.90 10.50 1.70 14.10
Fe 2 O 3 3.05 1.79 1.21 1.80 0.90 From 19.30 23.60 23.10 30.80 29.70
FeO 4.63 3.93 4.07 3.55 2.08 On 32.50 25.10 24.80 20.40 14.80
MnO 0.17 0.16 0.14 0.11 0.14 Tuesday 0.25 5.50
MgO 3.35 3.99 2.99 2.25 1.90 En 8.40 10.10 7.50 4.10 4.70
CaO 6.80 5.35 5.09 5.64 3.16 Fs 4.90 5.20 5.80 3.10 2.80
Na 2 O 2.25 2.75 2.71 3.62 3.51 Mt 4.50 2.60 1.80 2.60 1.30
K 2 O 1.42 1.98 1.76 1.96 2.38 Il 1.60 1.00 1.10 1.10 0.70
P 2 O 5 0.20 0.27 0.11 0.17 0.13 Ap 0.50 0.60 0.30 0.40 0.30
LOI 1.80 0.89 1.45 0.11 0.66

The sub-alkaline tonalites have a calcareous character with a medium potassium content (English medium-K ). They also belong to the granitoids of type I. The SiO 2 values ​​vary between 58 and 68 percent by weight, the tonalites are therefore intermediate , andesite-equivalent plutonic rocks. Their TiO 2 values ​​are quite low.

The tonalites are also quartz-normative and consequently oversaturated with quartz . The partial occurrence of normative corundum points to the peraluminous character of the rocks , of normative diopside to a metaluminous character.

Trace elements

Table with trace elements :

Trace element
ppm		 Tonalite /
Granodiorite 1		 Tonalite /
Granodiorite 2
Cr 91 110
Cs 2.8 2.4
Zr 175 154
Nb 9.0 7.0
Nd 23.4 14.2
Rb 64.0 74.0
Sr 280 240
Ba 343 318
Th 12.20 5.09
Ta 0.92 0.84
Hf 4.90 4.10
La 31.6 13.8
Ce 62.4 30.0
Sm 4.32 3.44
Eu 1.02 0.89
Tb 0.551 0.497
Yb 2.06 1.90

The trace element concentrations of the Karawanken tonalites are quite comparable to the granodiorites of the Pohorje pluton, but are usually somewhat lower. There is also an indisputable similarity to the Re-di-Castello group of the Adamello pluton and the Bergell pluton . This applies in particular to the trace elements hafnium , zirconium , yttrium , thorium and uranium , but also to most rare earths. The elementary ratios Ba / Sr, Ba / La, Nb / Th and Nb / U also show good agreement.

In the case of rare earths , a very clear enrichment of the LREE compared to the HREE can be observed. When applied, the LREE show a very steep and consistent dip, which indicates the fractionation of hornblende. Europium has a weakly pronounced negative anomaly, which indicates only moderate fractionation of feldspars. The HREE are very flat and low in concentration, which in turn implies the fractionation of clinopyroxene.

The incompatible trace element ratios K / Ba (34 to 55), K / Rb (265 to 295), Ba / Sr (1.2 to 1.3) and Rb / Cs (22.9 to 30.8) are very high and typical of granites and andesites of the continental margin. High ratios of Ba / Nb (38 to 45) and Ba / La (11 to 23) and a low Nb / Th ratio (0.7 to 1.4) indicate contamination by continental crust.

Rb-Hf-Ta triangular diagrams show that the Karawanken tonalites come to lie in the transition area between the granitoids of the island arc and the continental collision area.

Chondrite-normalized trace element diagrams confirm the medium-K, calcareous character of the rocks. It can therefore be assumed that liquids were pressed out of the subducted oceanic rocks, which then migrated into the overlying mantle wedge and, with the accumulation of LILE and LREE, caused it to melt.

Isotope ratios

Position of the Karawankentonalite (K) compared to the magmatites of the Pohorje pluton (P) in the δ 18 O- 87 Sr / 86 Sr diagram. The tonalites are much more heavily contaminated by crustal magma.
Isotope ratio Tonalit 1 Tonalit 2
87 Sr / 86 Sr 0.708122 ± 2 0.707920 ± 8
εSr 43.4 43.5
δ 18 O 8.1 8.3

The isotope ratio 87 Sr / 86 Sr is relatively high with a range of variation from 0.707385 to a maximum of 0.710066 - higher than that of the neighboring granodiorites of the Pohorje pluton. The δ 18 O values ​​are also increased. Taken together, both factors point to significant contamination of the tonalite magma by crustal magma.

Structural structure

The pluton consists spatially of a more or less vertical tonality table, which runs parallel to the periadriatic seam. To the north, the angles of incidence of the foliation flatten noticeably and an arched vault is formed that dips towards the south. Preserved roof areas of the pluton above the flatter vault indicate that the intrusion forms a bulging dome structure within the surrounding Austroalpine. The axis ratio X / Z (English aspect ratio ) of magmatic inclusions rarely exceeds 3: 1 and is therefore likely to have been created above the solidus - as less strongly deformed plutons suggest. The current axis ratio of the entire tonalite pluton is 18: 1. In a Flinn diagram, the inclusions come to lie in the flattening field and indicate a transpressive deformation. The flat surfaces parallel to the main fault turn more and more into the horizontal with increasing distance. Parallel to the main disorder, there are also some secondary disorders, mostly also steep and with the same, sometimes also antithetical, shear sense.

tectonics

The all-pervading foliation, which was already created in the igneous state, was again ductile overprinted under the conditions of the lower green schist facies. The temperature of the tonalitic magma is estimated at 750 to 800 °. The maximum temperatures in the cladding rocks were around 300 ° C. Assuming a high temperature gradient, this corresponds to a space depth of 8 to 10 kilometers or an ambient pressure of 0.35 to 0.5 GPa . On the south side of the periadriatic seam, however, only brittle deformations took place - this means that the periadriatic seam in the Karawanken as well as in the central Alps represents a brittle / ductile transition.

Age

The Karawanken tonalite pluton could be dated by Scharbert (1975) to be 28 ± 4 and 29 ± 6 million years. Accordingly, it has an Oligocene age (border Rupelium / Chattian ).

Individual evidence

  1. ^ Christof Exner: Geology of the Karawanken plutons east of Eisenkappel, Carinthia . In: Communications from the Geological Society in Vienna . 64th Volume, 1971, pp. 1-108 .
  2. ↑ P. Mioč: Geologija prethodnega obnočja med Južnimi in Vzodnimi Alpami v Sloveniji (doctoral thesis) . University of Zagreb, 1984, p. 182 .
  3. ↑ L. Fodor et al .: Miocene-Pliocene tectonic evolution of the Slovenian Periadriatic Fault: implications or Alpine-Carpathian extrusion models . In: Tectonics . tape 17 , 1998, pp. 690-709 .
  4. ↑ a b E. Faninger: Karavanški tonalit . In: Geologija . tape 19 , 1976, p. 153-210 .
  5. ^ F. Nemes, F. Neubauer, S. Cloetingh and J. Genser: The Klagenfurt Basin in the Eastern Alps: an intra-orogenic decoupled flexural basin? In: Tectonophysics . tape 282 , 1997, pp. 189-203 , doi : 10.1016 / S0040-1951 (97) 00219-9 .
  6. ↑ E. Faninger and I. Štrucl: Plutonic emplacement in the Eastern Karavanke Alps . In: Geologija . tape 21 , 1978, p. 81-87 .
  7. ^ RK Polinski and GH Eisbacher: Deformation partitioning during polyphase oblique convergence in the Karawanken Mountains, Southeastern Alps . In: Journal of Structural Geology . tape 14 , 1992, pp. 1203-1213 , doi : 10.1016 / 0191-8141 (92) 90070-D .
  8. ^ GP Laubscher: The late Alpine (Periadriatic) intrusions and the Insubric Line . In: Mem. Soc. Geol. Ital. tape 26 , 1983, pp. 21-30 .
  9. ↑ C. Miller, M. Thoni, W. Goessler and R. Tessadri: Origin and age of the Eisenkappel gabbro to granite suite (Carinthia, SE Austrian Alps) . In: Lithos . tape 125 , 2011, pp. 434-448 , doi : 10.1016 / j.lithos.2011.03.003 .
  10. ↑ J. Pamić and L. Palinkaš: Petrology and geochemistry of Paleogene tonalites from the easternmost parts of the Periadriatic Zone . In: Mineralogy and Petrology . tape 70 , 2000, pp. 121-141 .
  11. ↑ H. Kagami, P. Ulmer, W. Hansmann, W. Dietrich and RH Steiger: Nd-Sr isotopical and geochemical characteristics of the Southern Adamello (Northern Italy) intrusives: implication for crustal versus mantle origin . In: Journal of Geophysical Research . tape 96 , 1991, pp. 14331-14336 .
  12. ^ NB Harris, JA Pearce and AG Tindle: Geochemical characteristics of collision-zone magmatism . In: MP Coward and AC Ries, Collision tectonics (eds.): Geol. Soc. London Special Publication . tape 19 , 1986, pp. 67-81 .
  13. ↑ CL Rosenberg: Shear zones and magma ascent: A model based on a review of the Tertiary magmatism in the Alps . In: Tectonics . 23, TC3002, 2004, p. 1-21 , doi : 10.1029 / 2003TC001526 .
  14. ↑ C. Exner: The geological position of the magmatites of the Periadriatic Lineament . In: Verh. Geol. Bundesanst. Austria . tape 2 , 1976, p. 3-64 .
  15. ^ W. von Gosen: Fabric developments and the evolution of the Periadriatic Lineament in southeast Austria . In: Geological Magazine . tape 126 , 1989, pp. 55-71 .
  16. ↑ S. Scharbert: Radiometric age determinations of intrusive rocks in the Eisenkappel area (Karawanken, Carinthia) . In: Negotiations of the Federal Geological Institute . tape 4 , 1975, p. 301-304 .