PETROGRAPHY
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- Versione italiana
- Academic year
- 2016/2017
- Teacher
- MASSIMO COLTORTI
- Credits
- 9
- Didactic period
- Secondo Semestre
- SSD
- GEO/07
Training objectives
- The course is aiming at providing the petrological and geological knowledges to allow the student to:
- Know the composition and the structure of the Earth in its three fundamental shells: Crust, Mantle and Core, their physical state and the exchange relationships of matter and heat between them;
- Understand which are the mechanisms able to produce different primary magmas from a unique source;
- Understand which are the differentiation mechanisms leading to a large variety of magmas with different mineralogical and chemical composition;
- Recognize and classify the intrusive, effusive and metamorphic rocks;
- To frame the rocks and their chemical-physical features in relation to different geotectonic settings and their distribution in Italy;
- Understand how the main geotectonic settings may produce magmas with different composition.
At the end the student will:
- know structure and composition of our planet and which are the mechanisms that constrain its chemical and mineralogical differentiation;
- acquire all the knowledge necessary for recognize and classify the magmatic and metamorphic rocks as well as their distribution over the Italian territory. This will constitute a fundamental tool to attend with profit, among the others, the course of Geological Survey and the numerous geological excursions organized within the Degree Course;
- know the genetic mechanisms that are at the base of the production and differentiation of magmas and frame them in the right tectono-magmatic setting. This knowledge will be a fundamental requirement to follow, among the others, the course of Vulcanology and petrogenesis and Mineral Deposits, as well as the comprehension of natural volcanic phenomena that occur on the Earth surface.
This knowledge represents the essential expertise of a geologist not only for its application to the professional world, but also for the every-day more necessary dissemination required by the public community. Prerequisites
- The student approaching Petrography should have a general geological basic knowledge, acquired during the Geology I course. This will allow him to constrain the distribution of magmatic and metamorphic rocks within the right framework. He/She should also have the basis of Chemistry and Physics for the comprehension of the mechanisms responsible for magma forming and differentiation thanks to melting and crystallization processes. Compulsory is also the knowledge of Mineralogy, since rocks are made of minerals (and amorphous phases). Similarly for Geochemistry where the behavior of major and trace elements during magmatic processes is taught.
Part of the exercises will be realized by using an Excel spreadsheet. By consequence a basic knowledge of this tool is highly recommended. Course programme
- The teaching is mainly developed with theoric lessons (including identification of rocks) for a total of about 8 CFU, that is 64 h. The remaining CFU (10h) is used for practical petrological exercises (weight %, mol%, Mode, CIPW norm, Spidergrams). The issues addressed in the course are as follows:
a) Drifting of continents, Oceanic floor expansion, Plate tectonics as unifying framework of the petrogenetic processes at global scale (0,25 CFU).
b) Structure and lithological composition of the Earth. Oceanic and continental crust. Lithospheric and asthenospheric mantle. Geological and petrological evidences for a peridotitic vs eclogitic compositions of the Earth’s mantle. Maximum depth of direct sampling of mantle material (0,5 CFU).
c) Convective movements within the mantle. Single vs double layer modeling. Petrological meaning of the 670 km (Upper to Lower Mantle) and 2900 km (CMB, Core Mantle Boundary) discontinuities (0,5 CFU).
d) Geothermal and geobaric gradients. Mineralogical and geochemical composition of the mantle. Melting mechanism of the Earth’s Mantle. Classification of the ultrafemic rocks. Depleted and enriched mantle through melting and metasomatic processes (0,5 CFU).
e) Modal and non modal partial melting. Composition of primary magmas also in relation to geotectonic settings. Fe/Mg distribution between olivine and melt. Primary and differentiated magmas (1 CFU).
f) Mechanisms for magmatic differentiation. Emplacement of magmatic rocks, volcanics and intrusives. Classification and mineralogical composition of effusive and intrusive rocks. Magmatic series. TAS and double triangle of Streckeisen. CIPW Norm. Variation diagram (1,25 CFU).
g) Physical-chemical features of magmas. Phase rule and state diagrams. Representative binary and ternary systems and their application to magmatic processes. Solid solution and system with eutectic or peritectic. Melting and crystallization processes with eutectic and peritectic. Stability fields of the main magmatic phases in relation to T, P, X, pH2O, fO2 (1 CFU).
h) Trace element distributions during magmatic processes. Compatible and incompatible elements. Spidergrams. Enriched and depleted patterns in relation to different sources, partial melting and differentiation degrees. Negative and positive anomalies in spidergrams and their geodynamic and petrogenetic significance (0,75 CFU).
i) Magmatic associations and parental magmas genesis in different geodynamic settings. Mid-ocean ridge, suprasubduction, within-plate and active or passive rifting magmatisms. Comparison with ophiolites (0,75 CFU).
j) Metamorphism and metamorphic processes: factors and thermobarometric conditions of the various metamorphic facies. Metamorphisms and geodynamic settings. Index minerals and metamorphic zone. Prograde and retrograde metamorphism. The coupled metamorphic belts. The metamorphic facies and the reactions which constrains their boundaries: cornubianites, green schists, anphibolites, blu schists, eclogites and granulites. Migmatites and anatectic processes (1,5 CFU).
During the exercises the following procedures will be taught:
Chemical analyses expressed as weight %, mol % and atom %. Determination of afu in the most common minerals for magmatic petrology. Determinations of factors to transform oxide in element. Preliminary mass balance calculations and its application to modal estimations. Calculation of CIPW norm. Projection in the triangle diagrams and in the spidergrams. Didactic methods
- The course is developed thanks to both theoric lessons and exercises. During the lessons transparencies and slides are projected to allow the student to better follow the treated issues. National and international geological situations are continuously referred in order to keep awake the attention of the student. The teacher keeps inviting the students to consult Internet, as well as the reviews and the books made available thanks to our University both in paper and digital. Similarly he stimulates them to assume an active behavior during the lessons with the aim to form a geological perception that allow to discriminate by himself among the numerous theory and models that can be found within the scientific literature.
Part of the lessons are based on the recognition of the magmatic and metamorphic rocks. This is developed by the teacher and his assistants showing the numerous samples available in the room also thanks to a magnificent glass (10X). Their classification will be then included in the right geological and geodynamic context, in order to make this part of the course more appealing.
Exercises are held with some examples first on the dashboard or through slides projection. Afterward the teacher, helped by PhD students and Fellows, walk between the desk and verify the level of understanding of the proposed calculations for each single students.
Excursions represent a fundamental step for a fruitful development of the petrographic and geological knowledge of the student, taking into account that rocks and their setting at local and regional scale cannot be adequately shown in a classroom. To this purpose every year an excursion is organized in geological and petrologically meaningful localities, where in a rather limited area it would be possible to observe the rocks and their mutual relationships in the most fruitful way. Localities that have been visited during various years are as follows: Sicily (Mts. Peloritani and Etna); Tuscany (Elba Island, Vulsini); Piemonte e Lombardia (Ivrea-Verbano Zone, Ossola and Formazza valleys); Trentino Alto-Adige (Caoria and Cima d’Asta, Rolle Pass, Fassa valley); Liguria ed Emilia-Romagna (Ophiolitic series of Internal and External Ligurides); Sardinia (Dorgali, Aghero, Sulcis, Sant’Antioco). Learning assessment procedures
- The examination consist of a written and an oral part.
In the written test the chemical composition of a rock is provided both in terms of major and trace elements and its classification is required as effusive and intrusive case, the serial affinity and its geodynamic settings. To this aim the student will develop the CIPW norm calculations, by means of a spreadsheet, and will use a series of diagrams provided by the teacher. Trace element analyses should be normalized and projected onto a spidergram.
Once the written test is passed the oral exam will start with the analysis of the errors that could have been done in the written test and after having ascertain that the student has understood the mistakes he made. Afterwards the recognition of a rock is proposed, by means of describing its peculiar characteristics, such as color index, structure and textures and mineralogical compositions, also discussing possible genetic mechanism of that rock. The exam will then continue on the topics treated during the course.
Starting from the necessary basic knowledge, the main purpose of the examination is to ascertain the capacity of the student to develop a reasoning that demonstrate his/her petrological and geological mature development.
A score is attributed to both tests, although the final judgment will be formulated in critical and reasonable manner that will take into account the final level at which the student is arrived at the end of his/her pathway. Generally speaking this usually does not correspond to the simple arithmetic averaged value. Reference texts
- D'Amico C., Innocenti F., Sassi F.P. 1987."Magmatismo e Metamorfismo", UTET
Morbidelli L. 2003. "Le Rocce e i loro costituenti", BARDI Editore
