Deformation History

Structural analysis carried out in the Tuscan Nappe (TN) in the southeastern sector of the Apuan Alps highlights a structural evolution much more complex than that proposed so far. The TN has been deformed by structures developed during four deformation phases. The three early phases resulted from a compressive tectonic regime linked to the construction of the Apenninic fold-and-thrust-belt. The fourth phase, instead, is connected with the extensional tectonics, probably related to the collapse of the belt and/or to the opening of the Tyrrhenian Sea.

CITATIONS 25 READS 122 3 authors: Some of the authors of this publication are also working on these related projects: Master degree thesis: Tectonometamorphic evolution of the Massa Unit in Punta Bianca area (Northern Apennines, Italy) View project Evolution of the Lanterman-Mariner tectonic melange: evidences for the geodynamic of the paleo-Pacific margin of Gondwana and numerical models View project

In severe plastic deformation processes, ultimate aim is to achieve high efficiency in grain refinement in every stage of deformation. One of the most efficient ways to gain this efficiency is introduction of different component of deformation e.g. different route in equal channel angular extrusion. In this research, newly developed severe plastic deformation named Multi-axial Incremental shearing (MAIS) and simple shear process are analyzed via crystal plasticity modelling to compare grain refinement achievements in two types of severe plastic deformation process. The results show that due to the introduced complex deformation history in MAIS process, more slip systems are activated compared to simple shear and this leads to more efficiency in grain refinement. It is also concluded that modes of deformation other than primary mode are more activated in MAIS process compared to simple shear.

Detailed microstructural analysis of inclusion trails in hundreds of garnet porphyroblasts from rocks where spiral-shaped inclusion trails are common indicates that spiral-shaped trails did not form by rotation of the growing porphyroblasts relative to geographic coordinates. They formed instead by progressive growth by porphyroblasts over several sets of near-orthogonal foliations that successively overprint one another. The orientations of these near-orthogonal foliations are alternately near-vertical and near-horizontal in all porphyroblasts examined. This provides very strong evidence for lack of porphyroblast rotation.

Leventina Nappe represents one of the lowermost exposed units in the Alpine nappe stack and corresponds to a slice of the European margin that was entrained into the Alpine continental accretionary prism during the tertiary tectonic event. this study yields details regarding the tectonic and metamorphic history of the Leventina Nappe, through detailed analysis of structures and shear zone patterns, and the examination of the si-content of white mica along a north-south profile. the Leventina Nappe underwent three phases of ductile deformation. Foliation s1 is mostly sub-parallel to the regionally dominant structural fabric (the s2 foliation). s2 foliation is penetratively developed in the structurally higher portions of the Leventina Nappe toward the simano Nappe, while it is only weakly developed in the core of the Leventina Nappe. A 50 to 200 m wide mylonite zone, with a D2 top-to-NW sense of shear marks the boundary to the simano Nappe. throughout the Leventina Nappe only small-scale D2 shear bands (mm to cm wide) are observed, showing a top-to-NW sense of shear. Deformation phase D3 locally generated a vertical axial plane foliation (s3) associated with the large-scale D3 Leventina antiform. Microtextural evidence and phengite geobarometry were used to constrain the temperature and pressure conditions of equilibration of the Leventina Gneisses. Highest si (pfu) values are preserved in the core of phengitic micas and reflect pressure and temperature conditions of around 8 kbar at 550 °c and 10 kbar at 650 °c in the northern and southern parts of the Leventina Nappe, respectively. Lower si (pfu) values from the rims of white micas correspond to a metamorphic pressure of ca. 5 kbar during the exhumation of the unit. these metamorphic conditions are related to the underthrusting of the thinned European margin into the continental accretionary prism during late Eocene time. these new data allow us to propose a kinematic model for the Leventina Nappe during the tertiary Alpine tectonics. ZusAMMENFAssuNG Die Leventina-Decke stellt eine der tiefsten Einheiten dar, welche im alpinen Deckenstapel aufgeschlossen ist. sie entspricht einem teil des europäischen Kontinentalrandes, welcher während der alpinen Kontinentalkollision in den Akkretionskeil einbezogen wurde. Die detaillierte Analyse der strukturelemente und der scherzonenverteilung sowie die untersuchung von si-Gehalten in metamorphen Hellglimmern entlang eines Nord-süd-Profiles ergeben neue Erkenntnisse zur tektonischen und metamorphen Geschichte der Leventina-Decke. Drei Deformationsphasen werden in der Leventina-Decke beobachtet. Die schieferung s1 ist mehrheitlich sub-parallel zur regional vorherrschenden schieferung (s2). s2 ist in den höheren teilen der Leventina-Decke zur simano-Decke hin penetrativ ausgebildet, wogegen sie im Kern der Leventina-Decke nur schwach ausgeprägt ist. Ein 50 bis 200 m mächtiger Mylonit-Horizont mit einem NWgerichteten D2-schersinn stellt im Hangenden die Grenze zur simano-Decke dar. In der ganzen Leventina-Decke werden nur feine D2-scherbänder (mm bis cm) mit einem top-nach-NW schersinn beobachtet. Die D3-Deformationsphase erzeugte lokal eine vertikale Achsenebenenschieferung s3, welche im Zusammenhang mit der grossmassstäblichen D3-Leventina-Antiform steht. Mikrotexturen und Phengit-barometrie wurden benutzt, um temperaturund Druckbedingungen für die Metamorphose der Leventina Gneise abzuschätzen. Hohe si (pfu)-Gehalte der Kerne von Hellglimmer widerspiegeln metamorphe Druck-und temperaturbedingungen von ungefähr 8 kbar bei 550 °c im Norden und 10 kbar bei 650 °c im süden der Leventina-Decke. tiefere si (pfu)-Gehalte von Hellglimmer-rändern entsprechen einem metamorphem Druck von ca. 5 kbar während der Heraushebung der Einheit. Diese metamorphen bedingungen widerspiegeln das "underthrusting" der ausgedünnten europäischen Kruste in den kontinentalen Akkretionskeil im späten Eozän. Diese neuen Daten erlauben es uns, ein kinematisches Modell für die tertiäre alpine Orogenese zu formulieren.