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Download IgPetrolFinal11 - Department of Earth and Planetary Sciences
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Francis - 2011 Faculty of Science Final Examination December 9, 2011, room 315, 2 pm Earth and Planetary Sciences EPSC-423 Igneous Petrology Examiner: Don Francis No books, notes, communication, etc. allowed! Francis - 2011 Igneous Petrology EPSC-423 Final Exam December 9, 2011 Answer 7 out of the 9 following questions. Each question is worth ~7 of your final mark out of 100. 1. With the aid of a diagram, write an essay describing how the olivine – clinopyroxene – quartz liquidus projection can be used to formulate a simplistic genetic model relating the Earth’s peridotitic mantle, basaltic oceanic crust, and granitic continental crust. Use your diagram to predict the crystallization sequence and the liquid line of descent a magma ocean crystallizing on the early Earth whose composition was that of the Earth’s present day mantle. How would the case of fractional crystallization differ from that of equilibrium crystallization. 2. Making use of explicit examples, discuss the usefulness of the concept of acidic and basic components in predicting the response of simple phase equilibria to the presence of additional chemical components. Go on to explain how these concepts form the basis of the 2 lattice thermodynamic model for silicate melts, with explicit reference to predicting the crystallization of olivine using Fe-Mg partitioning between olivine and silicate melt. 3. Define and describe the “Hawaiian Paradox”, and then go on to discuss its implications for nature of the mantle source(s) of Hawaiian tholeiites? 4. Describe the similarities and differences between E and N MORB lavas, and then go on to discuss their implications for the relationship between, and origins of, E-MORB and N-MORB. 5. Describe the controversy concerning the relative importance of magma mixing versus crystal fractionation in the production of subduction-related andesites along continental margins, making explicit reference to observations and calculations in Labs 10 and 11 on the Eocene Sifton Range volcanics and granitoids of the northern Canadian Cordillera. 6. Characterize the range of “basaltic” lava types seen in the Fort Selkirk area (Lab 4) of the central Yukon, and go on to discuss the implications of their compositional variation for the petrogenesis of the Fort Selkirk magmatic suite. Speculate on any possible implications of similarities to Hawaiian magmatism. 7. Making use of explicit examples, discuss the implications of the fact that interpretations based on incompatible trace element variations in lavas commonly appear to disagree with those based on compatible trace element and/or major element variations. Go on to explain how one can use trace elements to distinguish between the roles of partial melting and fractional crystallization processes in producing the compositional variation of a suite of volcanic rocks 8. Reproduce a plot of 87Sr/86Sr versus 143Nd/144Nd in which the approximate isotopic compositions of the following reservoirs are shown: depleted mantle, primitive mantle, continental crust, N-MORB, EMORB, EM1, and EM2. Describe and compare the long-term trace element compositions, and possible origins, of each of these reservoirs. 9. Describe the differences between volcanic suites exhibiting tholeiitic versus calc-alkaline liquid lines of descent. What are the origins of these differences and how do they explain the different tectonic settings in which these volcanic suites are found. Speculate on possible implications for the origin of the Earth’s continental crust.
