Final Examination Igneous Petrology EOSC321 (83 Points Total)
Student name ______Student Number______
Final Examination Igneous Petrology EOSC321 (83 points total)
1. Define the norm of a rock (1 pt). Think about the bulk composition and the mineralogy of carbonatites and explain why carbonatites, of all igneous rocks, show the strongest mismatch between the modal and normative mineralogy (1 pt).
2. Why is the Clapeyron slope of the CO2-saturated liquidus of anorthite at P Total = P CO2 = 1 kb negative (1 pt)? Write the melting reaction of anorthite at these conditions (1 pt).
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3. Write the Batch Melting Equation (1 pt). What is the highest possible value for the degree of melting F for the terrestrial melting conditions (1 pt)?
4. Define an incompatible element (1 pt).
5. List at least 2 mineralogical differences between alkaline and tholeiitic basalts (2 pts).
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6. The Ba-SiO2 plot below shows the liquid line of descent (indicated by the arrow) for a suite of volcanic rocks produced by the simultaneous fractional crystallization of two minerals. Compositions of phenocryst minerals A, B and C that might be involved in the fractional crystallization are plotted on the diagram.
On the diagram below, mark a composition of a bi-mineral mix, which controls the evolution of magma from composition D to composition E (1pt). Note that this question has two correct answers, choose any one of them.
What are the proportions of minerals A, B and C in this bi-mineral mix you have chosen (1 pt)?
Show your Lever Rule constraints for the previous question on the plot (1 pt).
How much of this bi-mineral mix needs to be fractionated for the magma to evolve from composition D to composition E? (1 pt)
Show your Lever Rule constraints for the previous question on the plot (1 pt).
3 24-Nov-17 Student name ______Student Number______
7. Draw a schematic phase diagram T(temperature)-X(composition) for a binary eutectic system and label all T-X fields on the diagram with phases that exist at the temperatures and the compositions of the fields (5 points).
8. Thermobarometry is a powerful technique commonly used by petrologists to calculate pressures or temperatures of rock formation. Explain the principle of thermobarometry based on the application of the Phase rule to an igneous system (1 pts). Write the isobaric Phase rule (1 pt) and define all variables in it (3 pts).
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9. On the diagram below, draw schematic REE patterns for A) partial melt produced by low-degree melting of the primordial plagioclase-bearing undepleted mantle (1 pt), and (B) refractory residue left after the melt extraction of the low-degree melt from the primordial plagioclase-bearing undepleted mantle (1 pt). Explain why each curve is shaped the way it is (2 pts).
10. All igneous rocks can be subdivided into three series, tholeiitic, calc-alkaline and alkaline. What is the most abundant series out of the three (1 pt)? In what tectonic settings do we most often find alkaline rocks (1 pt)? What magma series shows the Fe enrichment for the intermediate evolved compositions (1 pt)?
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11. Two melting events occurred almost simultaneously at 2 Ga in the primordial mantle. Melting below the southern part of the Pangea continent produced alkaline mafic partial melts with Sm/Nd =0.11, whereas melting beneath the Northern Pangea produced tholeiitic mafic partial melts with Sm/Nd = 0.15. Basalts in what part of Pangea, southern or northern, have higher Nd ratios (present-day 143Nd/144Nd) now? (1 pt) Draw a 143Nd/144Nd -Time diagram with evolution lines for the basalts and the primordial mantle to illustrate your answer (3 pts).
12. Carbonatites are commonly found in complex, multi-phase igneous plutonic bodies, which also contain alkali silicate rocks. Why do these rocks and carbonatites show identical Sr-Nd isotope ratios (1 pts)? On a schematic diagram below, plot Sr-Nd isotope ratios for a carbonatite and an alkali silicate phase of the multi-phase igneous plutonic body if both carbonatite and an alkali silicate rocks have an asthenospheric origin (1 pt).
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13. Is it possible for a magma produced in the crust to be primary? (1 pt) Explain your answer (1 pt). What are the three elements whose concentrations can be used as the criteria for the primary character of magma? (3 pts)
14. Describe the petrological evidence for the formation of oceanic island basalts in the undepleted, primodial asthenospheric mantle (2 pts).
15. List three Large Igneous Provinces you know (3 pts).
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16. Fill out the table below to contrast oceanic magmas of different tectonic settings (21 pts total)
Mid-ocean ridge Ocean island Island Arc Dominant volcanic rock type (1 pt)
Dominant plutonic Not applicable Not applicable rock type (1 pt)
Cause for melting and magma generation (1 pt)
Show the position of the geotherm (or the adiabate) with respect to the mantle solidus (2 pts) in the P-T space during melting
Where do the rocks plot on the Sr-Nd isotopic diagram (1 pt)
Schematic REE pattern for volcanic rocks (1 pt)
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17. What is the importance of the gabbro-peridotite contact in ophiolitic massifs (1 pt)? Define an ophiolite (1 pt).
18. What is the expected relationship between the crustal thickness and the abundance of the bimodal suite volcanics in Large Igneous Provinces? Explain your answer (2 pts).
19. What is the common morphology of kimberlite bodies (1 pt)? In what tectonic setting does kimberlite form (1 pt)?
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20. What role does water play in the formation (2 pts) and evolution (3 pts) of subduction zone magmas?
21. Draw a schematic cross-section through a typical continental arc. The cross-section should include a mantle wedge (1 pt), a subducted slab (1 pt), a batholith belt (1 pt), a volcanic arc (1 pt), isotherms (1 pt), source regions for magma generation (2 pts) and typical crust thicknesses (1 pt).
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