69261 - Structural Geology and Tectonics

Academic Year 2021/2022

  • Docente: Giulio Viola
  • Credits: 8
  • SSD: GEO/03
  • Language: Italian
  • Teaching Mode: Traditional lectures
  • Campus: Bologna
  • Corso: First cycle degree programme (L) in Geological Sciences (cod. 8015)

Learning outcomes

This course is designed to develop a robust understanding of deformation processes and structures produced by displacement and deformation in the Earth's lithosphere at scales ranging from the tectonic plate scale, down to the crystal lattice scale. Students will learn to (1) recognize, describe and characterize the geometry and types of structures produced by crustal deformation histories involving contractional, extensional and wrench regimes, (2) to understand the deformation processes steering the microstructural evolution of deformed rocks, (3) to appreciate the parameters influencing the strength and mechanical behaviour of the Earth's crust and underlying mantle lithosphere, and to understand (5) the large-scale geodynamic processes controlling plate motions.

Course contents

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 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.

-Driving stress ratio for hydrofracturing, strong vs. weak faults, morphological characterization of joints and fracture surfaces..

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

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

-Stereographic projections and application thereof to solve structural geological and geological problems (rotations, retrodeformation of folds, fold axis determination, etc.).

-Strain localization mechanisms in upper crustal conditions. Fault classification, fault dynamic, geometric and kinematic classification. Fault plane modelling. 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.

- Study of orogenic wedges and fold and thrust belts, with particular attention to the Northern Apennines and the Southern Alps and their seismotectonic character.

Readings/Bibliography

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

Selection of scientific papers.

Teaching methods

The course is based on a combination of theory lessons, practical sessions in the laboratory (including triaxial tests) and excursions to deformed areas of the Southern Alps and 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