GEOL 221 Final, Fall 1995

J. : oN. as The Ameri i F ms : erican University of Beirut ae a ia PRp Final Examination " NN Petrology (221) Feb. 2, 1996 Department of Geology Time: 2 hours A. M. Abdel-Rahman Exam rules apply Part I @Q@ Answer ail questions of Part I @ x (MARKS ) (15) 1. (a) Concisely describe the following terms: 2 i) spilite ii) rhythmic layering :- iii) filter pressing iv) lamprophyres e (b) What is the difference between the norm and the mode of a rock? (c) What is a pegmatitic rock, and what is a leuco- gabbro? Using silica content as a _ base for the igneous rocks, give the SiO, intermediate rock, and (15) 2. (a) classification of ~ range of an ultrabasic rock, a basalt. "carbonatite" rocks, and (b) Briefly describe environment of comment on their tectonic emplacement. gram a typical (c) Illustrate by means of a dia label all. section of an ophiolite sequsence; (15) 3. (a) What textural evidence do you expect to see under the microscope to indicate a fractional crystallization origin of a rock? ing diagrams along (b) Describe these textures us perlitic with text; ophitic texture, myrmekite, texture, and perthite. rigin of the Sierra Neveda batholith (western us), in the context of plate tectonics. Note that this batholith is a typical calc-alkaline plutonic suite. (c) Briefly describe the o ne of the fields on the attached (15) 4. Indicate in which o P-T diagram each of the following minerals would most likely be found. Do so py writting the name of the minerals in the appropriate field; Hornblende Staurolite Biotite chlorite Actinolite Hypersthene Glaucophane Plagioclase (An 25) Epidote Andalusite Wollastonite Almandine Albite Prehnite Diopside Tale (a) Define the so-called "metamorphic facies". (b) The muscovite breakdown reaction is an important reaction occurring at the boundary between the amphibolite~, and the granulite facies: write this reaction. (c) What is meant by the term "skarn", and by the term "migmatite". (d) How does the An content of plagioclase vary with increasing grade of metamorphism. (a) Write a metamorphic reaction that occurs at the boundary between greenschist-, and amphibolite facies. (b) Name two minerals that are most characteristic of the low pressure part of the amphibolite facies, and another two most characteristic of the high pressure part of the same facies. (c) Do you expect to find a special type of slate produced as a result of metamorphism within the granulite facies conditions? Why? Part II Answer only two out of three questions in Part II 7. Use the phase diagram given below to; i) Describe the crystallization path of a melt of composition "a", and ii) Describe the melting path of a rock of composition "y", and name such a rock. 2100 (7) Two liquids qa | ! ! [ | | { i | I i \ i \ H \ i a i \ t \ ! \ \ W713 + $° Enstatite | Liquid + i\ + liquid 1695 + Se forsterite | \ | | Cristobalite + liquid d Temperature, °C L | ; jb 1543 + 2° 1557 + 2°) © - "i | Enstatite + cristobalite je { o Forsterite | 1470 + 10 + enstatite! 1400 i + Mg:SiO, mgsio, © Y¥) SiO2 {Forsterite) (Enstatite) {Cristobalite, tridymite) 4 Enstatite + tridymite (10) (10) Construct a fully labelled diagram to indicate the relationship between the various metamorphic facies and an Andean-type (subduction) tectonic environment. (a) Plot the following equilibrium assemblage on one appropriate diagran: Grossularite + wollastonite + diopside + quartz (b) To which facies does this assemblage belong? (c) Give a reaction that leads to the formation of wollastonite and another that forms diopside.