Metamorphic geology and survey

The metamorphic geology course has the aim to give the main principles of the metamorphic and magmatic processes at the base of the continental crust formation in the different geological and geodynamic context. To this aim the student at the end of the course will be able to:

a) understand the basic principles of the solid-state rheology as well as the elastic and mechanical properties of the main rock types constituting the continental crust;

b) describe and classify the different types of deformation structures, reconstructing the setting and the space-time evolution;

c) collect, process, mapping disaggregated structural data, identifying the style and reconstructing the space-time evolution;

d) read and interpret geological maps in the crystalline basement areas;

e) reconstruct the deformation- blastesis relationships occurred during the tectono-metamorphic evolution of metamorphic units;

f) determine, with the integration of opportune geotermobarometric techniques, the changes of pressure and temperature registered by the basement rocks, reconstructing the P-T trajectories;

g) contextualize within the Paleozoic-Oligocene Mediterranean geodynamics the kinematic of the Calabro-Peloritani microplates.

The former part of the course is 6 CFU long and is divided between 42 hours of power-point lectures and practical classroom exercises supported by hand samples and thin sections of metamorphic and plutonic rocks.

Additional 3 CFU are given throughout the course of four days of geological fieldwork on the metamorphic terrains that are primarily found in north-eastern Sicily and southern Calabria. The students are split up into four or five unit groups. Each group contains a region of around three square kilometers and a geological map that is silent (i.e., without a legend). To create a series of structural stations where they will take a series of structural measurements appropriately related to the recognized deformational stages, students must identify the topics in the legend.

• Know the classification principles of igneous and metamorphic rocks;

• Know the principles of optical microscopy for the recognition of fundamental minerals;

• Know the theoretical basis of the use of stereographic projections;

• Know the foundations of the current central Mediterranean geological-geodynamic structure.

Metamorphic geology: 6 credits (42 hours)

FIRST PART

INTRODUCTION

Principles and purposes of the Metamorphic Geology. Description of the main orogenetic processes. The geothermal gradient and its influence on the genesis of crystalline basements.

SECOND PART

MECHANICAL PROPERTIES OF ROCKS

Principles of rheology of the solid state: Analysis of stress and strain. History of the strain: total strain, incremental strain, progressive deformation. Coaxial and non-coaxial deformation. The rheological behaviour of minerals and rocks: Inter and intracrystalline deformation mechanisms; Strain control factors in mono- and Polymineralic rocks. Recovery process. The main flow laws in the solid state rheology. Inter-and intra-crystalline deformational mechanisms. Mineral Preferred Orientation: Shape and Lattice Preferred Orientation and their interrelationships. 

THIRD PART

MESO-MICROSTRUCTURAL INVESTIGATIONS AND STRUCTURAL DATA REPRESENTATION

Foliations and lineations. Description and classification of the folds. Theoretical models of folding. Distribution of strain in the folds. Examples of representation of structural elements through stereographic projections. Concepts of symmetry of structural data set. Rotation and statistical processing of structural data. Dispersion of the structural elements. Geometry and structural types of interference. Methods of structural analysis in areas characterized by poly-deformational evolution. Definition of shear zone. Classification of fault rocks and their location in different crustal levels. The kinematic indicators. Microstructural analysis of cataclastic and mylonitic rocks. The pseudotachylite.  Recognition and interpretation of metamorphic microstructures. 

FOURTH PART

RECONSTRUCTION OF THE BLASTO-DEFORMATIONAL RELATIONSHIPS, THE CONCEPT OF TEXTURAL EQUILIBRIUM, GEOTHERMOBAROMETRY OVERVIEW, P-T-d-t TRAJECTORIES RECONSTRUCTION.

Reconstruction of the blasto-deformational relationships: Chronology of deformational events. Chronology of the blastic events. Chronological relationships between deformation and blastesis also through image analysis techniques (Effective Reactant Volumes (ERV) and Effective Bulk Chemistry (EBC)). Elements of geothermbarbarometry and geochronology: The reconstruction of the P-T-d-t path. Mineralogical renewal during metamorphic processes and the concept of the sequence of paragenesis. Evolution of geothermbarbarometric techniques: thermodynamic databases and calculation of phase diagrams: sections, projections and pseudosections. The reconstruction of the orogenic cycles: thickening and exhumation/denudation processes.

FIFTH PART

WESTERN MEDITERRANEAN GEODYNAMICS FROM THE END OF PALEOZOIC TO THE PLIOCENE-PLEISTOCENE PHASES

The geological-geodynamic evolution of the Calabrian Peloritani Orogen  (CPO). The Variscan vs.  Alpine orogenic cycle. The role of crustal-scale shear zones in the present-day structure of the CPO. CPO palinspastic reconstructions up to the Oligocene-Miocene transition.

Field-based module: 3 credits (36 hours)

FIELD TECHNIQUES

Field measurements: arrangement of linear and planar elements. Cartographic representation with an encoded symbology. Stations measurement and processing of structural data. Reconstruction of space-time deformation events. Time-related distinction of structural symbols on thematic maps. Textural and structural characterization of deformation structures. Recognition of mesoscopic paragenetic assemblage in basement rocks. Penetrativity and pervasiveness of deformation structures. Genetics setting of deformation structures. Detection and interpolation of the boundaries between the units. Examples of graphic reconstruction of the limits and the limits on the validity of interpolation. Detection and characterization of the boundaries between plutonic rocks and metamorphic rocks. Elements of geothematic cartography assisted by Drone-, GIS- and, GPS-based techniques.

TECTONIC ELEMENTS

Tectonostratigraphic setting and tectonic-metamorphic evolution of the Calabrian Peloritani Orogen basement units.Styles of tectonic structures. Type and scale of folding systems. Characterization and classification the brittle deformation structures. Influence of brittle tectonic systems (faults and thrust) on the location of the continuity of the basement Units. Relationships between types and timing of emplacement of plutonic bodies within metamorphic units. Reconstruction of structural developments on the map: the trend of fold axes, foliation planes, and lineation diversified per timing generation and style. 

Books

1. Barker J. – Introduction to metamorphic textures and microstructures. (Blackie USA, Chapman & Hall) 1998.
2. Passchier C. W. & Trouw R. A. J. – Microtectonics. (2nd ed. xvi + 366 pp. + CD-ROM. Berlin, Heidelberg, New York: Springer-Verlag). ISBN 3 540 64003 7.
3. Vernon R. H. – A practical guide to rock microstructure. (Cambridge University Press) 2004. 594 pp. ISBN: 9780521891332
4. WINTER (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. 
5. Fossen H. – STRUCTURAL GEOLOGY. (Cambridge University Press) 2010. 463 pp. ISBN: 9780521516648
6. Handouts and notes distributed in class during the course.

The final evaluation relating to the course of Metamorphic Geology provides the possibility (optional) to carry out an ongoing test on the principles of solid-state rheology during the course. At the end of the course, the assessment of the ongoing test will be integrated with the production of an end-of-course work group, normally developed in groups of four or five students, relating to the statistical processing of structural measurements taken autonomously during the field-related surveys in Samo or Palmi (RC) or Scifì (ME), contextualized within the central Mediterranean geological-geodynamic framework from the Palaeozoic to the Oligo-Miocene passage.

This work can be presented either in paper form or with the aid of a power-point presentation.

During and at the end of the presentation of the paper, the teacher will ask the students a whole series of basic theoretical notions, among those dealt with during the course.

The final grade will include a balanced synthesis between the judgment of the synthesis and expository skills demonstrated and the degree of maturity in understanding the theoretical notions underlying the course.

MYlonites and some kinematic indicators. 

The sheat-folds. The low-strain domains.

Fault rocks and their correlations as a function of depth of formation.

Tectono-metamorphic evolution of the Mandanici Unit.

Pencil-strucures and L-tectonites.

The crenulation cleavage.

The rheology of plastic deformation.

Collisional environments.

Mylonites within the Mandanici Unit.

The stereographic projections.

Lineations and foliations.

The tectonite concept and the evolution of the Flinn diagram.

Tectono-stratigraphic setting of the Calabrian-Peloritanian Orogen.

Kinematic indicators;

The stratigraphic structure of the Aspromoment Massif.

The crustal anatexis and migmatites.

Migmatitic layering.

 Strain rate vs. recovery.

 The sheath folds.

 The interference structures.

 Kinematics and evolution of mylonitic structures.

 The concept of vorticity and the kinematic vorticity number.

 Pure shear vs. simple shear.

 Tectono-stratigraphic setting of the Peloritanian Mountains; The Mandanici unit.

 Main, secondary and accessory minerals and their role in reconstructing blasto-deformational relationships.

Geothermalbarometric techniques: a comparison.

Spatiotemporal relationships between the emplacement of granitoid bodies and the metamorphic basement.