Three-dimensional geometry and tectonostratigraphy of the Pennine zone, Central Alps, Switzerland and Northern Italy

Abstract Continental collision during Alpine orogenesis entailed a polyphase deformation history (D1–D5) in the Pennine zone of the Central Alps. The regional tectonostratigraphy was basically developed during D1 and D2, characterised by isoclinal, typically north-closing recumbent anticlines, separated by pinched-in synclines, on the scale of tens of kilometres. Later deformation phases (D3 and D4) warped the stack into wavy to open folds. Exhumation of this zone resulted locally in later vertical shortening and folding of already steep fabrics (D5). Three-dimensional models of the nappe pile were constructed, based on geostatistical assessment of the regional foliation field and considering the abundant structural field data. These models indicate the existence of five principal tectonostratigraphic levels developed during D1 and thus equivalent to nappe units s. str.: the Gotthard, the Leventina–Antigorio, the Maggia–Simano (and probably the Monte Leone as well as the Composite Lepontine Series), Lebendun–Soja and Adula–Cima Lunga levels. All these tectonic units formed part of the passive continental margin of Europe prior to the onset of the Alpine orogenesis. Individual isoclinal post-nappe folds reflect relative displacements on the order of 40 km or more. The most prominent D2 post-nappe structure is the Wandfluhhorn Fold, structurally equivalent to the northern closure of the Leventina–Lucomagno Antiform. The Lebendun and Monte Leone folds are of similar magnitudes and also affect the whole nappe pile, whereas the smaller Mogno and Molare synforms only refold the Maggia–Simano nappe internally. Principal D3 and D4 structures are the tight Mergoscia Synform directly north of the Insubric Fault between Bellinzona and Locarno (Southern Steep Belt), the Maggia Steep Zone, forming the steep western limb of the Campo Tencia Synform and subdividing the Lepontine dome into the Simplon and Ticino subdomes, the Chiera Synform steepening the dominant foliation in the north (Northern Steep Belt) and the Vanzone and Claro Antiforms steepening the dominant foliation in the south (Southern Steep Belt). The current geometry of the Northern and Southern Steep Belts reflects an interplay between D4 and D3, involving both fold interference and reactivation/tightening.

[1]  B. Grauert,et al.  Paleozoic migmatites affected by high-grade tertiary metamorphism in the central Alps (Valle Bodengo, Italy) , 1975 .

[2]  G. Tilton,et al.  The geodynamic evolution of garnet-peridotites, garnet-pyroxenites and eclogites of Alpe Arami and Cima di Gagnone (Central Alps) from Early Proterozoic to Oligocene , 1992 .

[3]  O. Merle,et al.  Kinematics of the northern part of the Simplon line (Central Alps) , 1987 .

[4]  J. Hunziker,et al.  Thirty-two years of geochronological work in the Central and Western Alps: a review on seven maps , 1992 .

[5]  V. Thakur.  Events in alpine deformation and metamorphism in the Northern Pennine Zone and Southern Gotthard massif regions, Switzerland , 1973 .

[6]  Ernst Ambühl.  Petrographie und Geologie des zentralen Gotthardmassivs südlich Andermatt , 1930 .

[7]  E. Draganits,et al.  Classification of Refold Structures , 2004, The Journal of Geology.

[8]  D. Grujic.  The Influence of Initial Fold Geometry on Type-1 and Type-2 Interference Patterns - an Experimental Approach , 1993 .

[9]  J. S. Fox.  Three-dimensional isograds from the Lukmanier Pass, Switzerland, and their tectonic significance , 1975, Geological Magazine.

[10]  J. Ramsay,et al.  Strain variation in shear belts , 1970 .

[11]  John G. Ramsay,et al.  The techniques of modern structural geology , 1987 .

[12]  G. Wagner,et al.  Actual and ancient uplift rate in the Gotthard region, Swiss Alps: A comparison between precise levelling and fission-track apatite age , 1975 .

[13]  A. G. Milnes.  Structural Reinterpretation of the Classic Simplon Tunnel Section of the Central Alps , 1973 .

[14]  N. Mancktelow.  The Simplon Fault Zone , 1990 .

[15]  Secondo Casasopra.  Studio petrografico dello Gneiss granitico Leventina , 1940 .

[16]  C. Davidson,et al.  Symmagmatic folding of the base of the Bergell pluton, Central Alps , 1996 .

[17]  T. Baudin,et al.  Rb-Sr mica ages in the Alpine shear zones of the Truzzo granite: Timing of the Tertiary alpine P-T-deformations in the Tambo nappe (Central Alps, Switzerland) , 1994 .

[18]  A. Milnes.  Structure of the Pennine Zone (Central Alps): A New Working Hypothesis , 1974 .

[19]  V. Köppel.  The Lepontine Area, a Geochronological Summary , 1993 .

[20]  A. Milnes,et al.  Structural development of the Infrahelvetic complex, eastern Switzerland , 1977 .

[21]  P. Jeanbourquin.  The lower Penninic nappes in the western Alps: the link between Helvetic and penninic , 1995 .

[22]  U. Ring.  The Alpine geodynamic evolution of Penninic nappes in the eastern Central Alps , 1992 .

[23]  H. Pfeifer,et al.  Zermatt-Saas and Antrona Zone: a petrographic and geochemical comparison of polyphase metamorphic ophiolites of the West-Central Alps. , 1989 .

[24]  B. W. Evans,et al.  Petrogenesis of garnet lherzolite, Cima di Gagnone, Lepontine Alps , 1978 .

[25]  G. Alan.  Structure and history of the Antigorio nappe (Simplon group, north Italy) , 1965 .

[26]  A. Steck.  Le massif du Simplon ― Réflexions sur la cinématique des nappes de gneiss , 1987 .

[27]  N. Chatterjee.  The Alpine metamorphism in the Simplon area, Switzerland and Italy , 1962 .

[28]  U. Schärer,et al.  Alpine and pre-Alpine magmatism in the root-zone of the western Central Alps , 1996 .

[29]  P. Heitzmann,et al.  Deep Structure of the Swiss Alps: Results of NRP 20 , 1997 .

[30]  P. R. Cobbold,et al.  Development of sheath folds in shear regimes , 1980 .

[31]  W. Weber.  Zur Geologie zwischen Chiavenna und Mesocco , 1966 .

[32]  Quartz c-axis fabric development and large-scale post-nappe folding (Wandfluhhorn Fold, Penninic nappes) , 1988 .

[33]  R. Trümpy.  An outline of the geology of Switzerland , 1980 .

[34]  A. Milnes.  Structural zones and continental collision, Central Alps , 1978 .

[35]  A. Milnes,et al.  Sequence and style of major post-nappe structures, Simplon—Pennine Alps , 1981 .

[36]  A. Steck,et al.  The Tertiary structural and thermal evolution of the Central Alps—compressional and extensional structures in an orogenic belt , 1994 .

[37]  R. Steiger.  Dating of orogenic phases in the central Alps by K-Ar ages of hornblende , 1964 .

[38]  M. Schumacher.  Geological interpretation of the seismic profiles through the Southern Alps (lines S1–S7 and C3-south) , 1995 .

[39]  M. Liniger,et al.  Early to mid Tertiary crustal extension in the Central Alps: The Turba Mylonite Zone (Eastern Switzerland) , 1996 .

[40]  P. Choukroune,et al.  Orthogneiss, mylonite and non coaxial deformation of granites: the example of the South Armorican Shear Zone , 1979 .

[41]  S. Schmid,et al.  Ascent, emplacement and exhumation of the Bergell Pluton within the Southern Steep Belt of the Central Alps , 1996 .

[42]  Neil S. Mancktelow,et al.  The Simplon line: a major displacement zone in the western Lepontine Alps , 1985 .

[43]  B. Grasemann,et al.  Two-dimensional thermal modelling of normal faulting: the Simplon Fault Zone, Central Alps, Switzerland , 1993 .

[44]  T. Baudin,et al.  Shear zone patterns and strain distribution at the scale of a Penninic nappe: the Suretta nappe (Eastern Swiss Alps) , 1996 .

[45]  A. Steck.  Structures et déformations tertiaires dans les Alpes Centrales (Transversale Aar-Simplon-Ossola) , 1984 .

[46]  G. Schreurs.  Structural analysis of the Schams nappes and adjacent tectonic units; implications for the orogenic evolution of the Penninic Zone in eastern Switzerland , 1993 .

[47]  W. Leu.  Lithostratigraphie und Tektonik der nordpenninischen Sedimente in der Region Bedretto-Baceno-Visp , 1986 .

[48]  F. Neubauer,et al.  Pre-Mesozoic Geology in the Alps , 1993 .

[49]  N. Froitzheim.  Origin of the Monte Rosa nappe in the Pennine Alps—A new working hypothesis , 2001 .

[50]  D. Schmatz,et al.  Tertiary metamorphic conditions in the eastern Lepontine Alps , 1995 .

[51]  Laurentius Zawadyński.  Geologisch-petrographische Untersuchungen in der Valle Onsernone (Tessin) , 1952 .

[52]  R. Holdsworth,et al.  Geological Society Special Publications , 2005 .

[53]  B. Chadwick.  Deformation and Metamorphism in the Lukmanier Region, Central Switzerland , 1968 .

[54]  Peter Knup.  Geologie und Petrographie des Gebietes zwischen Centovalli-Valle Vigezzo und Onsernone , 1958 .

[55]  J. Ramsay.  Folding and fracturing of rocks , 1967 .

[56]  E. Vesco.  Genesi e metamorfosi delle rocce basiche e ultrabasiche nell'ambiente mesozonale dell'orogene pennidico , 1953 .

[57]  D. Grujic,et al.  Structure of the northern Maggia and Lebendun nappes, central Alps, Switzerland , 1996 .

[58]  W. Hall.  The structural geology and metamorphic history of the lower Pennine Nappes, Valle di Bosco, Ticino, Switzerland , 1972 .

[59]  R. Trümpy.  PALEOTECTONIC EVOLUTION OF THE CENTRAL AND WESTERN ALPS , 1960 .

[60]  G. Schreurs,et al.  The significance of the Schams nappes for the reconstruction of the paleotectonic and orogenic evolution of the Penninic zone along the NFP-20 East traverse (Grisons, eastern Switzerland) , 1990 .

[61]  D. Gebauer,et al.  The mafic-ultramafic rock association of Loderio-Biasca (lower Pennine nappes, Ticino, Switzerland): Cambrian oceanic magmatism and its bearing on early Paleozoic paleogeography , 2002 .

[62]  A. Heim,et al.  Les nappes de recouvrement des Alpes pennines et leurs prolongements structuraux . Die grosse Eiszeit in der Nordschweiz . Zur Tektonik des Flysches in den östlichen Schweizeralpen . Beobachtungen aus der Wurzelregion der Glarnerfalten : (helvetischen Decken) , 1911 .

[63]  H. Becker.  Garnet peridotite and eclogite Sm-Nd mineral ages from the Lepontine dome (Swiss Alps): New evidence for Eocene high-pressure metamorphism in the central Alps , 1993 .

[64]  J. Ramsay,et al.  Folds and fractures , 1987 .

[65]  O. Merle,et al.  Tertiary kinematics in the Lepontine dome , 1989, Geological Society, London, Special Publications.

[66]  O. Merle,et al.  The building of the Central Swiss Alps: an experimental approach , 1989 .

[67]  T. Baudin,et al.  Métamorphisme et déformation dans la nappe de Tambo (Alpes centrales suisses): évolution de la substitution phengitique au cours de la déformation alpine , 1993 .

[68]  P. Jeanbourquin,et al.  Les métasédiments du Pennique inférieur dans la région de Brigue-Simplon. Lithostratigraphie, structure et contexte géodynamique dans le bassin Valaisan , 1991 .

[69]  M. Handy,et al.  The kinematics of movements along the Insubric Line and the emplacement of the Ivrea Zone , 1987 .

[70]  F. Albarède,et al.  238U/206Pb-235U/207Pb-232Th/208Pb zircon geochronology in alpine and non-alpine environment , 1974 .

[71]  M. Sartori,et al.  Geologic framework and structural evolution of the western Swiss-Italian Alps , 1995 .

[72]  H. Steiner.  Radiometrische Alterbestimmungen an Gesteinen der Maggia-Decke (Penninikum der Zentralalpen) , 1984 .

[73]  V. Trommsdorff,et al.  Revised Thermobarometry of Alpe Arami and other Garnet Peridotites from the Central Alps , 2001 .

[74]  D. Marquer,et al.  Subduction and obduction processes in the Swiss Alps , 1998 .

[75]  S. Schmid,et al.  Geophysical‐geological transect and tectonic evolution of the Swiss‐Italian Alps , 1996 .

[76]  A. Steck,et al.  Nappe geometry in the Western Swiss Alps , 1993 .

[77]  C. Davidson,et al.  The Bergell pluton (Southern Switzerland, Northern Italy): Overview accompanying a geological-tectonic map of the intrusion and surrounding country rocks , 1996 .

[78]  M. Pfiffner.  Genese der hochdruckmetamorphen ozeanischen Abfolge der Cima Lunga-Einheit (Zentralalpen) , 1999 .

[79]  Marco Steinmann.  Die nordpenninischen Bündnerschiefer der Zentralalpen Graubündens , 1994 .

[80]  D. Sanderson.  The development of fold axes oblique to the regional trend , 1973 .

[81]  M. Frey,et al.  Alpine Metamorphism of the Central Alps. , 1999 .

[82]  T. Baudin,et al.  Basement-cover relationships in the Tambo nappe (Central Alps, Switzerland): geometry, structure and kinematics , 1993 .

[83]  C. Heinrich.  Eclogite Facies Regional Metamorphism of Hydrous Mafic Rocks in the Central Alpine Adula Nappe , 1986 .

[84]  A. Steck,et al.  La nappe du Lebendum entre Alte Kaserne et le Val Cairasca (massif du Simplon): nouvelles observations et interprétations , 1992 .

[85]  Friedhelm von Blackenburg.  Combined high-precision chronometry and geochemical tracing using accessory minerals: applied to the Central-Alpine Bergell intrusion (central Europe) , 1992 .

[86]  J. Watterson,et al.  Stretching fabrics, folds and crustal shortening , 1974 .

[87]  J. C. Hunziker,et al.  Alpine cooling and uplift , 1997 .

[88]  M. Lemoine,et al.  The western alps: Palaeogeography and structure , 1970 .

[89]  O. Merle,et al.  Post-amphibolitic westward thrusting and fold vergence in the Ticino domain , 1988 .

[90]  P. Cobbold,et al.  Bending anisotropy: A mechanical constraint on the orientation of fold axes in an anisotropic medium , 1981 .

[91]  W. Kurz,et al.  Structural evolution of Adula nappe, Misox zone, and Tambo nappe in the San Bernardino area: Constraints for the exhumation of the Adula eclogites , 2003 .

[92]  C. Lajaunie,et al.  Foliation fields and 3D cartography in geology: Principles of a method based on potential interpolation , 1997 .

[93]  R. Nolen-Hoeksema,et al.  The Lepontine Alps as an evolving metamorphic core complex during a-type subduction: Evidence from heat flow, mineral cooling ages, and tectonic modeling , 1985 .

[94]  S. Schmid,et al.  The role of the Periadriatic Line in the tectonic evolution of the Alps , 1989, Geological Society, London, Special Publications.

[95]  U. Ring.  The kinematic history of the Pennine Nappes east of the Lepontine Dome: Implications for the tectonic evolution of the Central Alps , 1992 .

[96]  P. Heitzmann,et al.  Geological interpretation of the seismic profiles of the Central Traverse (lines C1, C2 and C3-north) , 1995 .

[97]  S. Schmid,et al.  Tectonic map and overall architecture of the Alpine orogen , 2004 .

[98]  N. Mancktelow,et al.  Structure and kinematics of the northern Simano Nappe, Central Alps, Switzerland , 2005 .