AgeAge andand structurestructure ofof thethe StolzalpeStolzalpe nappenappe -- EvidenceEvidence forfor VariscanVariscan metamorphism,metamorphism, EoalpineEoalpine top-to-the-WNWtop-to-the-WNW thrustingthrusting andand top-to-the-ESEtop-to-the-ESE normalnormal faultingfaulting (Gurktal(Gurktal Alps,Alps, Austria)Austria)
Geological Survey of Austria C. IGLSEDER1,*) , B. HUET1,*) , G. RANTITSCH2,*), L. RATSCHBACHER3,*) & J. PFÄNDER3,*)
INTRODUCTION: OVERVIEW:
17° 16° 15° 14° 10° 11° 12° 13° Tectonic map of the Alps Passau S.M. Schmid, B. Fügenschuh, E. Kissling and R. Schuster , 2004 Donau Inn In the Gurktal Alps (Austria,) the Drauzug-Gurktal nappe system represents the Graphics : S. Lauer Wien 5° 6° 48° 48° 7° München 8° 9° 5240000
Rhein
Basel
Zürich uppermost tectonic part of the Upper Austro-Alpine nappe stack. The Stolzalpe Nappe Besancon
47° 47° Graz
Bern
Maribor
± Drava
(s. str.) is its uppermost unit. It consists of interbedded metasedimentary rocks of the Genève
46° 46°
Rhone T Zagreb agliamento Sava 5230000
Trieste
Milano Venezia Verona Padova Spielriegel Complex, overlain by metavolcanic rocks of the Kaser-Eisenhut Complex. Grenoble Torino 45° 45° Po 17° Po 16° 15° 14° 100 km 11° 12° 13°
Both are covered by the Pennsylvanian clastic Stangnock Formation. In the Genova
44°
Durance
5° 6° Nice 7° 8° 9° 10° investigated area, located at UTM-map sheet Radenthein (NL-33-04-06), the 5220000 Stolzalpe Nappe tectonically overlays the Stangnock Formation belonging to the Tectonic map of the investigated area
Königstuhl Subnappe, also part of the Stolzalpe Nappe. 5210000 Drauzug-Gurktal nappe system Drauzug nappe GEOCHRONOLOGY Stolzalpe nappe 5200000 Königstuhl subnappe 0,084 data-point error ellipses are 2σ data-point error ellipses are 2σ O1 0,095 O2 Pfannock nappe 0,080 LA-ICPMS
5190000 Ackerl nappe 480 0,085 0,076 500 U-Pb zircon Nesselbach subnappe U U 0,075 238 0,072 238 Pb/ 440 Pb/ Murau nappe 206 206 0,065 400 5180000 0,068 Ar/Ar Basal mica schist nappe(s) 0,064 400 Concordia Age = 448.3 ± 4.3 Ma 0,055 Concordia Age = 452.7 ± 4.8 Ma white mica 2σ, MSWD = 0.052; n=14 2σ, MSWD = 3.9; n=16 Ötztal-Bundschuh nappe system Propability = 0.82 Propability = 0.048 0 2,5 5 10 15 20 0,060 0,045 5170000 Koralpe-Wölz nappe system 0,44 0,48 0,52 0,56 0,60 0,64 0,68 0,35 0,45 0,55 0,65 0,75 Kilometers 207Pb/235U 207Pb/235U 400000 410000 420000 430000 440000 450000 460000 470000 480000 Silvretta-Seckau nappe system 110 100
320 V1 A1 A2 100 90 MAP
300 90 80 TGA = 314.22 ± 0.3 Ma WMA = 316.4 ± 1.2 Ma TGA = 92.46 ± 0.15 Ma TGA = 88.38 ± 0.15 Ma 1200 Age (Ma) Age (Ma) Age (Ma) MSWD = 0.0084 80 WMPA = 92.75 ± 0.27 Ma; MSWD = 0.37 70 WMPA = 88.50 ± 0.29 Ma; MSWD = 0.14
IIA = 93.6 ± 1.4 Ma; MSWD =0.42 IIA = 88.83 ± 0.66 Ma; MSWD =0.13 1900 280 2100
2200 2000 youngest step ~274 Ma 70 60 2100 5205000
2300 2000 260 Kilnprein 2400 60 2100 50 1300 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 2000 39 39 39 Cumulative Ar Fraction Cumulative Ar Fraction Cumulative Ar Fraction 1800 2200
1800 PROFILES and RAMAN MICROSPECTROSCOPY 2200 A2
2100
1400
2300 5202500
2200 ESE WNW 2200 1500 ESE WNW ESE WNW ESE WNW 1900 Turrach A1
1900 2100
2300 1600 2200 2400 Bockbühel Eisenhut
2100 5200000
2300 2000 Nesselbach O1 AREA1 at 5.200.000 North AREA1 2200 2300 SSE NNW O2 1800 ESE WNW
1800 2200
2100 Spielriegel 363 316-322 5197500 2000 285 297 Turracher Höhe
2100
2100 10m 1900 2200 2100 305 1800 2000 2300 2300
2000 2300 2200 Bretthöhe PROFILE1 2200 2300 2000 Rinsennock Gruft n = 16 2200 n = 14 n = 12 2200 ESE WNW n = 11
2200 Drauzug-Gurktal nappe 1900 system 5195000 Stolzalpe1600 nappe
2000 2100 V1 Kaser-Eisenhut Komplex 2200 Spielriegel Komplex1500 1400 Königstuhl sub-nappe (s.n.) Werchzirm Formation Raman Microspectroscopy 2100 Stangnock Formation Murau nappe; Nesselbach s.n. Thermometry Data (in °C) „Murau Limestone” PROFILE 1 at 5.195.500 North „Murau Group” 5192500 Gruft Ötztal-Bundschuh nappe 2.5 W Rinsennock Hoazhöhe Bretthöhe O 1800 system Bundschuh nappe 2000 1600 D4-Normal fault 1700 Permo-mesozoic cover 2 295-305 (Stangalm1600 meso. s.str.) 1900 Bundschuh-Priedröf
2200 Komplex D3-Thrust 2300 1700 347-359 1300 Koralpe-Wölz nappe 1.5 system Gstoder nappe 5190000 D3-Axial plane 2300 Ebene Reichenau 2200 Radenthein
2100 283-362 Komplex 1 308 330-373 D2-Axial plane Hinterkoflach Hochrindl 0.5 1600
411 412 413 414 415 416 417 418 419 420 1800
1600
1200 1800 1700 5187500
1700 1600
100 STRUCTURES 1
VARISCAN STRUCTURES (D1 + D2) 1600 D1 isoclinal folds overprinted by D2 folding D2: ENE-verging asymmetric open folds n=271 n=91
2.5%, 5% 5%, 10% 5185000
D3 D31300 thrusting (shear-sense)
1500 1500 1600 D4 D4 normal faulting (shear-sense) 1600
nappe boundary 1000
1800 D1 D2 410000 412500 415000 417500 420000 422500 SW NE E W
n=84 n=166 5 cm 5 cm SYNOPSIS and CONCLUSIONS: 2.5%, 5% 5%, 10% (EO-)ALPINE STRUCTURES (D3 + D4 + D5) D3: W-verging asymmetric tight folds D3: C´-type shear-bands top W LA-ICPMS U/Pb zircon ages ( ) pin the volcanism of the Kaser-Eisenhut Complex to n=54 n=18 5%, 10% Upper-Ordovician (448 ± 4 - 452 ± 5 Ma).
A Lower Pennsylvanian 316±1 Ma 40Ar/39Ar white mica age ( ) in metasedimentary rocks D3 D3 of the Spielriegel Complex and Raman microspectroscopy thermometry on W E carbonaceous material indicate a Variscan peak-temperature of ~350° C. NW SE Most of the structure in the Stolzalpe nappe is Variscan [NW-SE striking isoclinal folding n=65 n=56 5 cm 5 cm 5%, 10% (D1) followed by ENE-verging asymmetric open folds (D2)].
D4: C´-type shear-bands top E D5: isolated open folds n=39 Eoalpine deformation is characterised by W-verging asymmetric tight folds and brittle 1%, 6% ductile top W/NW thrusting (D3), overprinted by top E/SE normal faulting (D4).
40 39 σ 3 Upper Cretaceous 88-92±1Ma Ar/ Ar white mica ages ( ) in the footwall (Permo- σ 1 D4 D5 Mesozoic cover of the Bundschuh Nappe) and Raman microspectroscopy thermometry NW SE NW SE peak values of ~300°C in the Stolzalpe nappe and Königstuhl subnappe are attributed to the Eoalpine event. n=89 2 cm n=20 2 cm σ 5%, 10% 2 Neoalpine shortening (D5) is very limited to isolated open folds.
1,*) [email protected]; [email protected]; Department of Hard-Rock Geology, Geological Survey of Austria; Neulinggasse 38, A-1030 Vienna, Austria
2,*) [email protected]; Department of Applied Geology and Geophysics, Montanuniversität Leoben, Peter-Tunner Straße 5, A-8700 Leoben, Austria PANGEO 2016, Innsbruck
3,*) [email protected]; [email protected]; Department of Geology and Economic Geology, TU Bergakademie Freiberg, Bernhard-von-Cottastraße 2, D-09596 Freiberg, Germany