Learning objectives
The main objective of this course is to provide a basic understanding of the magma generation in the different geodynamic environments through time and the relations between magmatic/metamorphic processes and plate tectonics
Course unit content
APPLICATION OF TRACE ELEMENT AND ISOTOPE GEOCHEMISTRY TO PETROLOGY
PETRO-TECTONIC ASSOCIATIONS:
Mid-ocean ridge magmatism
Mantle plumes and oceanic islands
Mantle plumes and basaltic plateaux
Arc magmatism
Collisional granitoids
Continental rift magmatism
CASE STUDIES BASED ON FIELD OCCURRENCES:
-EXAMPLES OF FOSSIL OCEANIC LITHOSPHERE (Ligurian ophiolites, N Apennines)
-CRYSTALLINE BASEMENTS AND POST-VARISCAN MAGMATISM (Ivrea-Verbano Zone, southern Alps)
-OROGENIC HIGH PRESSURE METAMORPHISM (Sesia Zone and Pennidic units from western Alps)
Full programme
INTRODUCTION
-Mantle composition and heterogeneity
-Causes of melting and origin of magmas
1-GEOCHEMISTRY OF TRACE ELEMENTS AND RADIOGENIC ISOTOPES: PETROLOGICAL APPLICATIONS
-Principles of geochemistry of trace elements: partition coefficients, compatible and incompatible elements, representation of trace elements (normalizations)
-Geochemical models of crystallization, mixing, AFC, partial melting
-Radiogenic isotopes as tracers of petrogenetic processes: Rb / Sr, Sm / Nd, Lu / Hf, Re / Os, U-Pb-Th systems
-Model ages, internal isochrons, closure temperature
-Carbon in the mantle
2-GEOCHEMICAL CHARACTERISTICS OF MAGMAS AND PETROGENETIC PROCESSES AT DIFFERENT GEODYNAMIC SETTINGS:
DIVERGENT PLATE BOUNDARIES AND MID-OCEAN RIDGES
-structure, composition and lithologies in the modern and fossil oceanic lithosphere
- oceanic lithosphere at fast, slow and ultra-slow spreading-ridges; oceanic core complexes
-mineralogy and geochemistry of MORB and of the lower oceanic crust
-petrogenesis of MORBs, segregation and ascent: from single melt increments to aggregated melts
- geochemical and isotopic heterogeneity in the MORB source
- plume-ridge interactions
- hydrothermal alteration of the oceanic crust
- serpentinization processes and their petrogenetic relevance
MAGMATISM AT CONVERGENT PLATE BOUNDARIES
-distribution, type and structure of magmatic arcs
- magmatic series in intra-oceanic arcs: petrographic, mineralogical and geochemical characters (FAB, boninites, adakites, arc tholeiites, shoshonites, leucitites..)
-sources of magmas and their evolution
-melting/ dehydration of subducted lithosphere
-melting of the mantle wedge
-release of fluids / melts from the slab and transfer of components from the slab to the mantle wedge: experimental studies and HP-UHP metamorphic rocks as natural laboratories
-role of serpentinites
-new petrogenetic models involving diapiric ascent and melting of melanges from the subducted slab
-isotopic tracers of arc processes (Sr, Nd, Pb, B, Be)
-continental arcs: magmatic series and the role of the continental lithosphere; examples from the Andes and the Cascade Range
-origin of granitic magmas: processes of differentiation, anatexis (fluid-present and fluid-absent melting), hybridization
OCEANIC INTRAPLATE MAGMATISM AND MANTLE PLUMES
-Global distribution and tomographic images of hotspots and of subducted plates
-type of OIB magmas
-isotopic variations of Sr, Nd, Hf, Pb, Os and mantle reservoirs (“geochemical geodynamics and the mantle zoo”)
-relationships between mantle plumes and crustal recycling processes
-nature and origin of components in the sources of OIB magmas
-role of pyroxenites
-Sobolev model and Di-CaTsch-Fo-Qtz system
-structure and melting in a mantle plume
-example of Hawaiian magmatism
CONTINENTAL INTRAPLATE MAGMATISM
-basaltic plateaux
-composition and origin of carbonatitic magmas
-ultrapotassic magmas
3- CASE STUDIES:
-ophiolites of the Internal Ligurian Units (N Apennine) as example of oceanic lithosphere formed at a slow/ultra-slow spreading ridge
-ophiolites of the External Ligurian Units (N Apennine) as example of oceanic lithosphere originated at an ocean-continent transition zone
- continental rifting and oceanization processes
- post-Varisic magmatism and the crustal section of the Ivrea area (Southern Alps)
- Notes on the architecture of the Alpine chain and the main magmatic and metamorphic events in the Alps (with particular reference to W Alps)
Bibliography
TEXTBOOKS
- John D. Winter (2010), Principles of igneous and metamorphic petrology, Ed. Prentice Hall
-H. Rollinson (1998) - Using geochemical data (cap. 4 e 6)
- M.G. Best and E.H. Christiansen, Igneous Petrology (Blackwell Science)
- A. Philpotts and J. Ague, Principles of Igneous and Metamorphic Petrology (Cambridge University Press)
LECTURE NOTES AND ARTICLES PROVIDED BY THE LECTURER
Teaching methods
-1. Lectures
- 2. Optical microscope observations * of thin sections related to specific case studies treated during the course (magmatic and mantle rocks from ophiolitic sequences; mantle xenoliths affected by metasomatic processes)
- 3. Field excursions*: 5 days of fieldwork on selected and well known outcrops from the N Apennine and W Alps which will provide examples of oceanic lithosphere, mantle heterogeneity, continental lower crust and orogenic metamorphism
* if 2-3 could not be realized due to Covid-19 emergency, they wil be replaced by images and detailed field guides
Assessment methods and criteria
Oral examination including:
- discussion of a scientific article from the recent literature on a topic of the course chosen by the student
- 1question concerning trace element and radiogenic isotope geochemistry
-2 questions about magmatic associations and related geodyamic settings
- 1 question about case studies from Alps and Apennines
