METAMORPHIC GEOLOGY WITH FIELD INVESTIGATIONS

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;

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 course consists of 6 CFU for a total of 42 hours divided into lessons in power-point alternating with practical exercises classroom aided by hand samples and thin sections of metamorphic rocks.

Further 3 CFU for a total of 36 hours are instead provided during a four days geological field-trip on metamorphic terrains prevalently located in north-eastern Sicily and southern Calabria. The students are divided into groups of four or five units. Each group has an area of about five square kilometers accompanied by a silent geological map (i.e. without legend). Students have to specify the themes in the legend producing a series of structural stations where they will take a series of structural measurement opportunely related to the recognized deformational phases.

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 AND GEOCHRONOLOGY 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 GIS-, 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

Web Sites

1. http://jm-derochette.be/metamorphic_rocks.htm
2. http://www.uwgb.edu/dutchs/EarthSC202Slides/struslid.htm
3. http://virtualexplorer.com.au/special/meansvolume/contribs/heilbronner/text/00/0000.html
4. http://www3.uakron.edu/geology/mcconnell/structGeo/syllabus/week15.htm#readings14