95807 - GEOLOGIA STRUTTURALE E TETTONICA (7 CFU)

Learning outcomes

This course will offer students the possibility to grow the knowledge and skills necessary to recognise, describe and interpret structural and tectonic features at all scales of observation. Also, students will know how to use structural geology to constrain teconic and geodynamic scenarios recorded in the rock record. In more detail, after completing the course, students will be able to: - recognise, measure and plot the geometric features of a significant variety of geological structures, from the outcrop to the regional scale; - understand the mechanics of deformation and assess the dynamic and kinematic framework within which deformation and strain localization have taken place; - reconstruct modes and timing of deformation; - decipher the geodynamic environments that govern the first-order evolution of our Planet.

Course contents

-General introduction and pedagocic approach to the course

-Description and quantification of strain in rocks, with practical exercises aiming to have the students familiarize with the most common methods of strain analysis (center to center, Fry method, Rf/fi).

-Mechanics of rock deformation. Lithostatic and hydrostatic pressure, Pascal law, confining pressure. Mean stress, differential stress, deviatoric stress. Common stress states in the crust. In situ stress determination.

-Mechanics of faulting, inputs from experimental rock deformation. Upper crustal brittle deformation. Mohr diagram. Failure envelope and detailed analysis thereof. Andersonian stress conditions. Optimally oriented faults vs. misoriented faults. Pore pressure and effective stress.

-Fracturing modes (Mode I, II and III) and associated structures. Joints, hybrid and sear fractures.Numerical exercises to practice the application of the Mohr diagram to natural faulting examples and geomechanics problems.

-Strong vs. weak faults.

-Tension gashes and veins. Vein crystallization mechanisms, en echelon geometries, brittle-ductile deformation zones.

-Strain localization, seismic cycle and stick-slip behavior.

-Strain localization mechanisms under upper crustal conditions. Fault classification, fault dynamic-, geometric- and kinematic classification. Fault architecture, nucleation and propagation mechanisms. Dip-, oblique- and strike-slip faults.

-Faults within strike-slip, compressive and extensional environments. M/Y, P, R, R' and T ffractures and faults. Restraining and releasing bends.

-Passive margins, active margins, transcurrebt margins and leaky margins.Extension by McKenzie and Wernicke's models listric normal faults, principles of seismic section interpretation, core complexes. Fold and thrust belts, orogenic wedges, critical taper, overthrusts and inverse faults, duplexes, tectonic windows and klippe, piggy-back basins, foreland and hinterland domains, in-sequence and out-of-sequence thrusting. Thin- and thick-skinned tectonics. Strike-slip systems, positive and negative flower structures. Indentation tectonics.

-Rheology and shear strength litospheric profiles. Analysis of end-member rheological behavious (elastic, viscous, plastic, viscoelastic, elastoplastic, etc). Torsion experimental deformation up to high gamma values, power-law creep, secondary creep, deformation domains in the lithosphere.

- Folds and folding mechanisms. Transposition, fold classification and geometric characterization. Interference patterns, fold vergence, relationships between S0 and S1, 2, etc. Bending vs. buckling. Biot equation and implications thereof on the analysis of folded layers.

- Viscosity and ductile deformation. Power-law creep, microstructural analysis as a gauge to read phisical conditions of deformation. Deformation mechanism maps. Linear and point defects in crystals. Dislocation types and dislocation movement mechanisms. Cataclastic flaw, pressure-solution, dislocation glide and creep.

- Strain recovery, Regime 1,2 and 3 for quartz by Hirth and Tullis, SGBM, SGRR, FGBM. CPO and SPO in dynamically recrystallized minerals, Critical Resolved Shear Stress, AVA maps, EBSD and universal stage.

- Strain localization mechanisms in mono- and polymineralic rocks.

- Kinematic analysis of mylonites, oriented samples, kinematic indicators.

-Planar and linear fabrics.

Readings/Bibliography

Structural Geology, II edition, 2016, Haakon Fossen, 524 pp., Cambridge University Press.

Microtectonics, 2005, Cees W. Passchier e R. A. J. Trouw, 366 pp., Springer.

Teaching methods

The course is based on a combination of theory lessons, practical sessions and one excursion to deformed areas of the Northern Apennines.

Assessment methods

Students will be evaluated by a combination of a 3 hr written exam and an oral examination.

Office hours

See the website of Giulio Viola