FLUIDS AND PETROGENESIS
Learning outcomes of the course unit
The rock formation is the result of a series of processes related to extremely different conditions and environments. In all cases, the presence of fluids strongly affects any type of process (magmatic, metamorphic and sedimentary). The aim of the course is to understand how to recognize, through microscopic observation and knowledge of the rock chemistry, the role of fluids in their formation.
At the end of the course, the student must be able to:
- understand the effect of the fluids on the genesis and evolution of a magmatic rock through its petrographic and mineralogical characteristics
- recognize the succession of reactions in a metamorphic rock through the graphic representation of the mineralogical associations
- understand if the mineralogical association of a metamorphic rock is controlled by the fluid or by the rock itself
- trace the conditions of rock formations through thermodynamic calculations
- reconstruct the diagenetic evolution of a sedimentary rock through microscope observation
Knowledge of Mineralogy, Petrography, Geochemistry is required
Course contents summary
The course aims to highlight the importance of fluids in the formation and evolution of any type of rock.
A first part describes how fluids (H2O, CO2, S, Cl and F) are dissolved in magmas, the effects of fluids on the physical characteristics of magmas and on the processes of melting and crystallization of magmas.
A second part describes how to recognize metamorphic reactions and their graphical representation in the presence of fluids; the buffering capacity of the system by the composition of the rock or by an external fluid, considering the equilibria between mineral associations, composition of minerals and fluids; methods of material transfer by metamorphic fluids.
The third part considers the equilibria between solid and fluid phases to identify the formation conditions (T, P, oxygen fugacity and fugacity of other fluids) with examples of calculation of T, P, oxygen, water and carbon dioxide fugacity.
The last part highlights the importance of fluids in various diagenetic environments, particularly for carbonate and silicoclastic rocks, and the relationships between the environment and the characteristics of the infiltrating fluid.
1. Role of volatile in magmas. Presence of volatile components. Solubility of some volatile components (H2O, F and Cl, CO2, S). Effect of volatiles on some physical properties of magmas such as density and viscosity. Effect of volatiles on melting and fractional crystallization processes.
2. Effect of fluids on metamorphic reactions. Recognition and trend of metamorphic reactions. Transportation of matter during metamorphism. Influence of H2O-CO2 fluids on metamorphic reactions. Relationships between fluid composition and metamorphic associations. Buffering and internal control of the fluid composition. Infiltration and external control of the fluid composition.
3. Geothermometry and geobarometry. Fundamental concepts and general equation. Geothermometers. Geobarometers: loading pressure, oxygen fugacity and fugacity of other fluids. Buffers and buffer reactions. Role of oxygen fugacity in phase equilibria.
4. Fluids and diagenesis. Relations between diagenesis and sedimentation environment: composition and characteristics of the fluid, type of sediment, pH and redox conditions. Fluid evolution during diagenetic processes. Diagenetic transformations: physical and chemical compaction (pressure solution), carbonate cementation, siliceous cementation, neomorphism, dissolution, substitution, autigenesis. Dolomitization.
Philpotts A.R., Ague J.J. (2009) Principles of igneous and metamorphic petrology. Cambridge University Press, Cambridge
Winter J.D. (2010) Principles of igneous and metamorphic petrology. Pearson Prentice Hill.
Boggs S. Jr. (2009) Petrology of sedimentary rocks. Cambridge University Press, Cambridge.
Scholle P.A., Ulmer-Scholle D.S. (2003) A color guide to the petrography of carbonate rocks: grains, textures, porosity, diagenesis. AAPG Memoir 77
Lectures on basic theoretical topics and microscopic observations for identifying the described processes.
The teaching material is provided personally to the student or posted on Elly after each lesson.
Assessment methods and criteria
Oral exam with verification of the theoretical knowledge, their application to real cases and verification of the logical-deductive skills (normally performed face-to-face or remotely with the Teams platform if necessary).
The final evaluation of the oral exam is immediately communicated at the end of the exam itself.
Online registration for the exam session is mandatory