International Journal of Earth Sciences

, Volume 99, Issue 8, pp 1805–1825 | Cite as

Local shear zone pattern and bulk deformation in the Gran Paradiso metagranite (NW Italian Alps)

Original Paper

Abstract

The Gran Paradiso nappe of the northwestern Alps mostly consists of augen gneisses derived from the Alpine deformation of Permian granitoids. The regional foliation of the augen gneisses developed at lower amphibolite facies conditions and is associated with a top-to-west sense of shear. The granitoid protolith is preserved in the kilometre-scale low-strain domain of the Piantonetto Valley and mainly consists of a porphyritic metagranite including joints, leucocratic dykes and biotite-rich schlieren. In this low-strain domain, the Alpine deformation is mainly localized in discrete ductile shear zones within weakly foliated metagranite. The shear zones mostly dip towards S–SE in a shallow (shear zones1) to steep inclination (shear zones2). The shear zones show typical features that can be explained by reactivation of pre-existing joints and planar compositional heterogeneities. Palaeostress and strain analysis indicate that shear zones and the metagranite foliation both formed in the presence of a strong component of flattening. The kinematics of individual shear zones depends on the orientation of the original heterogeneities (acting as nucleation planes) and by partitioning of strain components at the kilometre-scale with concentration of the flattening component to the Piantonetto low-strain domain. The strain geometry and the kinematics of individual shear zones within Piantonetto are not directly connected to the top-to-west sense of tectonic transport observed elsewhere in the Gran Paradiso nappe. However, the bulk stress ellipsoid reconstructed for the incipient shear zone network within very weakly deformed granites is oriented consistently with the bulk direction of tectonic transport within the Gran Paradiso massif. We conclude that the shear zone network of the Piantonetto Valley is representative of the incipient stages of ductile deformation of a granite nappe. Even if its architecture is determined by the arrangement of pre-existing structural and compositional heterogeneities, aspects of the large-scale bulk strain can be derived from this local shear zone pattern.

Keywords

Nucleation of shear zones Deformation of granites Strain analysis Flattening Gran Paradiso Western Alps 

References

  1. Angelier J (1990) Inversion of field data in fault tectonics to obtain the regional stress-III. A new rapid direct inversion method by analytical means. Geophys J Int 103:363–376. doi:10.1111/j.1365-246X.1990.tb01777.x CrossRefGoogle Scholar
  2. Arbaret L, Burg J-P (2003) Complex flow in lowest crustal, anastomosing mylonites: strain gradients in a Kohistan gabbro, northern Pakistan. J Geophys Res 108(B10):2467. doi:10.1029/2002JB002295 Google Scholar
  3. Bailey CM, Simpson C, De Paor DG (1994) Volume loss and tectonic flattening strain in granitic mylonites from the Blue Ridge province, central Appalachians. J Struct Geol 16:1403–1416. doi:10.1016/0191-8141(94)90005-1 CrossRefGoogle Scholar
  4. Baird GB, Hudleston PJ (2007) Modeling the influence of tectonic extrusion and volume loss on the geometry, displacement, vorticity, and strain compatibility of ductile shear zones. J Struct Geol 29:1665–1678. doi:10.1016/j.jsg.2007.06.012 CrossRefGoogle Scholar
  5. Ballèvre M (1988) Collision continetale et chemins P–T. L’unite Pennique du Grand Paradis (Alpes Occidentales). Memoires et Documents du Centre Armoricain d’Etude Structurale des Socles 19Google Scholar
  6. Berthè D, Choukroune P, Jegouzo P (1979) Orthogneiss, mylonite and non-coaxial deformation of granites: the example of the South Armorican shear zone. J Struct Geol 1:31–42. doi:10.1016/0191-8141(79)90019-1 CrossRefGoogle Scholar
  7. Bertrand J-M, Paquette J-L, Guillot F (2005) Permian zircon U–Pb ages in the Gran Paradiso massif: revisiting post-Variscan events in the western Alps. Schweiz Mineral Petrogr Mitt 85:15–29Google Scholar
  8. Borghi A, Compagnoni R, Sandrone R (1996) Composite P–T paths in the Internal Penninic Massifs of the Western Alps: petrological constraints to their thermo-mechanical evolution. Eclogae Geol Helv 89(1):345–367Google Scholar
  9. Brouwer FM, Vissers RLM, Lamb WM (2002) Structure and metamorphism of the Gran Paradiso massif, western Alps, Italy. Contrib Mineral Petrol 143:450–470CrossRefGoogle Scholar
  10. Burg JP, Laurent P (1978) Strain analysis of a shear zone in a granodiorite. Tectonophysics 47:15–42. doi:10.1016/0040-1951(78)90149-X CrossRefGoogle Scholar
  11. Callegari E, Compagnoni R, Dal Piaz GV (1969) Relitti di strutture intrusive erciniche e scisti a sillimanite nel Massiccio del Gran Paradiso. Boll Soc Geol Ital 88:59–69Google Scholar
  12. Carreras J, Casas JM (1987) On folding and shear zone-development: a mesoscale structural study on the transition between two different tectonic styles. Tectonophysics 135:87–98Google Scholar
  13. Christiansen PP, Pollard DD (1997) Nucleation, growth and structural development of mylonitic shear zones in granitic rock. J Struct Geol 19:1159–1172. doi:10.1016/S0191-8141(97)00025-4 CrossRefGoogle Scholar
  14. Compagnoni R, Elter G, Lombardo B (1974) Eterogeneità stratigrafica del complesso degli “Gneiss Minuti” nel massiccio cristallino del Gran Paradiso. Mem Soc Geol Ital 13:227–239Google Scholar
  15. Crawford ML (1966) Composition of plagioclase and associated minerals in some schists from Vermont, U.S.A. and South Westland, New Zealand, with inferences about the peristerite solvus. Contrib Mineral Petrol 13:269–294Google Scholar
  16. Dal Piaz GV, Lombardo B (1986) Early Alpine eclogite metamorphism in the Penninic Monte Rosa-Gran Paradiso basement nappes of the northwestern Alps. In: Evans BW, Brown EH (eds) Blueschists and eclogites. Geol Soc Am Mem 164:249–265Google Scholar
  17. Dal Piaz GV, Hunziker JC, Martinotti G (1972) La Zona Sesia–Lanzo e l’evoluzione tettonico-metamorfica delle Alpi nordoccidentali interne. Mem Soc Geol Ital 11:433–466Google Scholar
  18. Fitz Gerald JD, Stünitz H (1993) Deformation of granitoids at low metamorphic grade. I. Reactions and grain size reduction. Tectonophysics 221:269–297. doi:10.1016/0040-1951(93)90163-E CrossRefGoogle Scholar
  19. Fossen H, Tikoff B (1993) The deformation matrix for simultaneous simple shearing, pure shearing and volume change, and its application to transpression–transtension tectonics. J Struct Geol 15:413–422. doi:10.1016/0191-8141(93)90137-Y CrossRefGoogle Scholar
  20. Fusseis F, Handy MR, Schrank C (2006) Networking of shear zones at the brittle-to-viscous transition (Cap de Creus, NE Spain). J Struct Geol 28:1228–1243. doi:10.1016/j.jsg.2006.03.022 CrossRefGoogle Scholar
  21. Gabudianu Radulescu I, Rubatto D, Gregory C, Compagnoni R (2009) The age of HP metamorphism in the Gran Paradiso Massif, Western Alps: a petrological and geochronological study of “silvery micaschists”. Lithos 110:95–108Google Scholar
  22. Gapais D (1989) Shear structures within deformed granites: mechanical and thermal indicators. Geology 17:1144–1147. doi:10.1130/0091-7613(1989)017<1144:SSWDGM>2.3.CO;2 CrossRefGoogle Scholar
  23. Gapais D, Bale P, Choukroune P, Cobbold PR, Mahjoub Y, Marquer D (1987) Bulk kinematics from shear zone patterns: some field examples. J Struct Geol 9:635–646. doi:10.1016/0191-8141(87)90148-9 CrossRefGoogle Scholar
  24. Goodwin LB, Tikoff B (2002) Competency contrast, kinematics, and the development of foliations and lineations in the crust. J Struct Geol 24:1065–1085Google Scholar
  25. Grapes RH, Otsuki M (1983) Peristerite compositions in quartzofeldspathic schists, Franz Josef-Fox Glacier Area, New Zealand. J Metamorph Geol 1:47–61Google Scholar
  26. Guermani A, Pennacchioni G (1998) Brittle precursors of plastic deformation in a granite: an example from the Mont Blanc massif (Helvetic, western Alps). J Struct Geol 20:135–148. doi:10.1016/S0191-8141(97)00080-1 CrossRefGoogle Scholar
  27. Handy MR, Stünitz H (2002) Strain localization by fracturing and reaction-weakening—a mechanism for initiating exhumation of subcontinental mantle beneath rifted margins. In: De Meer S, Drury MR, De Bresser JHP, Pennock GM (eds) Deformation mechanisms, rheology and tectonics: current status and future perspectives, vol 200. Geological Society of London Special Publication, pp 387–407Google Scholar
  28. Hirth G, Tullis J (1992) Dislocation creep regimes in quartz aggregates. J Struct Geol 14:145–159. doi:10.1016/0191-8141(92)90053-Y CrossRefGoogle Scholar
  29. Hobbs BE, Mühlhaus HB, Ord A (1990) Instability, softening and localization of deformation. In: Knipe RJ, Rutter EH (eds) Deformation mechanisms, rheology and tectonics, vol 54. Geological Society of London, Special Publication, pp 143–165Google Scholar
  30. Inger S, Ramsbotham W (1997) Syn-convergent exhumation implied by progressive deformation and metamorphism in the Valle dell’Orco transect, NW Italian Alps. J Geol Soc Lond 154:667–677. doi:10.1144/gsjgs.154.4.0667 CrossRefGoogle Scholar
  31. Kassem OK, Ring U (2004) Underplating-related finite-strain patterns in the Gran Paradiso massif, western Alps, Italy: heterogeneous ductile strain superimposed on a nappe stack. J Geol Soc London 161:875–884. doi:10.1144/0016-764903-159 CrossRefGoogle Scholar
  32. Le Bayon B, Ballèvre M (2006) Deformation history of a subducted continental crust (Gran Paradiso, western Alps): continuing crustal shortening during exhumation. J Struct Geol 28:793–815. doi:10.1016/j.jsg.2006.02.009 CrossRefGoogle Scholar
  33. Le Bayon B, Pitra P, Ballèvre M, Bohn M (2006) Reconstructing P–T paths during continental collision using multi-stage garnet (Gran Paradiso nappe, western Alps). J Metamorph Geol 24:477–496. doi:10.1111/j.1525-1314.2006.00649.x CrossRefGoogle Scholar
  34. Le Goff E, Ballèvre M (1990) Geothermobarometry in albite-garnet orthogneisses: a case of study from the Gran Paradiso nappe (Western Alps). Lithos 25:261–280Google Scholar
  35. Mancktelow NS (2002) Finite-element modelling of shear zone development in viscoelastic materials and its implications for localisation of partial melting. J Struct Geol 24:1045–1053. doi:10.1016/S0191-8141(01)00090-6 CrossRefGoogle Scholar
  36. Mancktelow NS, Pennacchioni G (2005) The control of precursor brittle fracture and fluid–rock interaction on the development of single and paired ductile shear zones. J Struct Geol 27:645–661. doi:10.1016/j.jsg.2004.12.001 CrossRefGoogle Scholar
  37. Mancktelow N, Stöckli DF, Grollimund B, Müller W, Fügenschuh B, Viola G, Seward D, Villa IM (2001) The DAV and Periadriatic fault system in the eastern Alps south of the Tauern window. Int J Earth Sci 90:593–622. doi:10.1007/s005310000190 CrossRefGoogle Scholar
  38. Marquer D, Challandes N, Baudin T (1996) Shear zone patterns and strain distribution at the scale of a Penninic nappe: the Suretta nappe (eastern Swiss Alps). J Struct Geol 18:753–764. doi:10.1016/S0191-8141(96)80009-5 CrossRefGoogle Scholar
  39. Maruyama S, Liou JG, Suzuki K (1982) The peristerite gap in low-grade metamorphic rocks. Contrib Mineral Petrol 81:268–276Google Scholar
  40. Massonne H-J, Chopin C (1989) P–T history of the Gran Paradiso (western Alps) metagranites based on phengite geobarometry. In: Daly JS, Cliff RA, Yardley BWD (eds) Evolution of metamorphic belts, vol 43. Geological Society of London Special Publication, 545–549Google Scholar
  41. Meffan-Main S, Cliff RA, Barnicoat AC, Lombardo B, Compagnoni R (2004) A Tertiary age for Alpine high-pressure metamorphism in the Gran Paradiso massif, western Alps: a Rb–Sr microsampling study. J Metamorph Geol 22:267–281. doi:10.1111/j.1525-1314.2004.00512.x CrossRefGoogle Scholar
  42. Menegon L, Pennacchioni G, Stünitz H (2006) Nucleation and growth of myrmekite during ductile shear deformation in metagranites. J Metamorph Geol 24:553–568CrossRefGoogle Scholar
  43. Menegon L, Pennacchioni G, Spiess R (2008a) Dissolution–precipitation creep of K-feldspar in mid-crustal granite mylonites. J Struct Geol 30:565–579. doi:10.1016/j.jsg.2008.02.001 CrossRefGoogle Scholar
  44. Menegon L, Pennacchioni G, Heilbronner R, Pittarello L (2008b) Evolution of quartz microstructure and c-axis crystallographic preferred orientation within ductilely deformed granitoids (Arolla unit, Western Alps). J Struct Geol 30:1332–1347. doi:10.1016/j.jsg.2008.07.007 CrossRefGoogle Scholar
  45. Passchier CW (1998) Monoclinic model shear zones. J Struct Geol 20:1121–1137. doi:10.1016/S0191-8141(98)00046-7 CrossRefGoogle Scholar
  46. Pennacchioni G (1988) Studio geologico del tratto meridionale della dorsale tra Valnontey e Valleile (Cogne, Valle d’Aosta). Mem Sci Geol 40:333–354Google Scholar
  47. Pennacchioni G (1996) Progressive eclogitization under fluid-present conditions of pre-Alpine mafic granulites in the Austroalpine Mt Emilius Klippe (Italian western Alps). J Struct Geol 18:549–561. doi:10.1016/S0191-8141(96)80023-X CrossRefGoogle Scholar
  48. Pennacchioni G (2005) Control of the geometry of precursor brittle structures on the type of ductile shear zone in the Adamello tonalites, southern Alps (Italy). J Struct Geol 27:627–644. doi:10.1016/j.jsg.2004.11.008 CrossRefGoogle Scholar
  49. Pennacchioni G, Mancktelow NS (2007) Nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions. J Struct Geol 29:1757–1780. doi:10.1016/j.jsg.2007.06.002 CrossRefGoogle Scholar
  50. Pennacchioni G, Di Toro G, Brack P, Menegon L, Villa IM (2006) Brittle–ductile–brittle deformation during cooling of tonalite (Adamello, southern Italian Alps). Tectonophysics 427:171–197. doi:10.1016/j.tecto.2006.05.019 CrossRefGoogle Scholar
  51. Perello P, Delle Piane L, Piana F, Stella F, Damiano A (2004) Brittle post-metamorphic tectonics in the Gran Paradiso Massif (northwestern Italian Alps). Geodin Acta 17:71–90. doi:10.3166/ga.17.71-90 CrossRefGoogle Scholar
  52. Poirier JP (1980) Shear localization and shear instability in materials in the ductile field. J Struct Geol 2:135–142. doi:10.1016/0191-8141(80)90043-7 CrossRefGoogle Scholar
  53. Pryer LL (1993) Microstructures in feldspars from a major crustal thrust zone: the Grenville Front, Ontario, Canada. J Struct Geol 15:21–36. doi:10.1016/0191-8141(93)90076-M CrossRefGoogle Scholar
  54. Ramsay JG (1980) Shear zone geometry: a review. J Struct Geol 2:83–99. doi:10.1016/0191-8141(80)90038-3 CrossRefGoogle Scholar
  55. Ramsay JG, Allison I (1979) Structural analysis of shear zones in an alpinised Hercynian Granite (Maggia Lappen, Pennine Zone, Central Alps). Schweiz Mineral Petrogr Mitt 59:251–279Google Scholar
  56. Ramsay JG, Graham RH (1970) Strain variation in shear belts. Can J Earth Sci 7:786–813Google Scholar
  57. Ring U (1998) Volume strain, strain type and flow path in a narrow shear zone. Geol Rundsch 86:786–801. doi:10.1007/s005310050177 CrossRefGoogle Scholar
  58. Ring U, Collins AS, Kassem OK (2005) U–Pb SHRIMP data on the crystallization age of the Gran Paradiso augengneiss, Italian western Alps: further evidence for Permian magmatic activity in the Alps during break-up of Pangea. Eclogae Geol Helv 98:363–370. doi:10.1007/s00015-005-1170-9 CrossRefGoogle Scholar
  59. Robin P-YF, Cruden AR (1994) Strain and vorticity patterns in ideally ductile transpression zones. J Struct Geol 16:447–466. doi:10.1016/0191-8141(94)90090-6 CrossRefGoogle Scholar
  60. Segall P, Pollard DD (1983) Nucleation and growth of strike-slip faults in granite. J Geophys Res 88:555–568. doi:10.1029/JB088iB01p00555 CrossRefGoogle Scholar
  61. Segall P, Simpson C (1986) Nucleation of ductile shear zones on dilatant fractures. Geology 14:56–59. doi:10.1130/0091-7613(1986)14<56:NODSZO>2.0.CO;2 CrossRefGoogle Scholar
  62. Srivastava DC, Lisle RJ, Vandycke S (1995) Shear zones as a new type of palaeostress indicator. J Struct Geol 17:663–676. doi:10.1016/0191-8141(94)00084-D CrossRefGoogle Scholar
  63. Stipp M, Stünitz H, Heilbronner R, Schmid SM (2002) The eastern Tonale fault zone: a ‘natural laboratory’ for crystal plastic deformation of quartz over a temperature range from 250 to 700°C. J Struct Geol 24:1861–1884. doi:10.1016/S0191-8141(02)00035-4 CrossRefGoogle Scholar
  64. Takagi H, Goto K, Shigematsu N (2000) Ultramylonite bands derived from cataclasite and pseudotachylyte in granites, northeast Japan. J Struct Geol 22:1325–1340 Google Scholar
  65. Tikoff B, Greene D (1997) Stretching lineations in transpressional shear zones: an example from the Sierra Nevada Batholith, California. J Struct Geol 19:29–39Google Scholar
  66. Tourigny G, Tremblay A (1997) Origin and incremental evolution of brittle/ductile shear zones in granitic rocks: natural examples from the southern Abitibi Belt, Canada. J Struct Geol 19:15–27. doi:10.1016/S0191-8141(96)00075-2 CrossRefGoogle Scholar
  67. Vauchez A (1987) The development of discrete shear zones in a granite: stress, strain and changes in deformation mechanisms. Tectonophysics 133:137–156. doi:10.1016/0040-1951(87)90286-1 CrossRefGoogle Scholar
  68. Vernon RH (2004) A practical guide to rock microstructure. Cambridge University Press, CambridgeGoogle Scholar
  69. Viterbo C (1959) La composizione chimico-petrografica di alcune rocce tipiche del Gran Paradiso. Rend Soc Mineral Ital 15:255–284Google Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  1. 1.Dipartimento di GeoscienzeUniversità degli Studi di PadovaPadovaItaly
  2. 2.Institutt for GeologiUniversitetet i TromsøTromsøNorway

Personalised recommendations