Francis – 2013
Faculty of Science
Final Examination
Earth and Planetary Sciences EPSC-212
Introductory Petrology
Examiner:
Don Francis
April 25, 2013
6 p.m. - 9 p.m.
Associate Examiner: Andrew Hynes
No books, notes, communication, etc. allowed !
Francis – 2013
Introductory Petrology EPSC-212B Final Exam
April 25, 2013
Answer Question 1; and then 6 out of Questions 2 through 10 with essays 1-2 pages in length! All
questions are equally weighted.
1. Give the exact chemical formulae of each of the following minerals:
diopside
anorthite
nepheline
forsterite
albite
enstatite
fayalite
phlogopite
tremolite
dolomite
Answer 6 of the following 9 questions:
2. With the aid of a diagram, explain how the olivine – clinopyroxene – quartz liquidus
projection can be used to formulate a simplistic genetic model relating the Earth’s mantle,
oceanic crust, and continental crust. Go on to explain why basalt is the dominant crustal
lithology on all the terrestrial planets.
3. Discuss the important role that water plays in igneous petrology. In your discussion be
sure to address the following issues:





melting temperatures of rocks.
composition of the first melt.
stability of plagioclase with respect to other silicate minerals.
liquid line of descent during crystal fractionation.
proportion of felsic lavas to felsic pyroclastic rocks in volcanic suites
4. Define each of the following terms as they are used in igneous petrology and describe the
features (textural, mineralogical, and/or compositional) that you would expect in a rock to
which the term would be applied:
layered cumulate
porphyritic versus oikocrystic
welded tuff
chilled margin
flow banding
5. Describe the sequence of minerals that precipitate from seawater as it is evaporated. How
can this sequence be reconciled with the restricted compositional range and cyclic nature of
most of the Earth’s large evaporite deposits? Go on to propose a possible reason for the fact
that dolomite beds are commonly found beneath evaporite deposits in the sedimentary
record.
Francis – 2013
Introductory Petrology EPSC-212B Final Exam - continued
April 25, 2013
6. Aside from fossil evidence, what sedimentary features would enable you to determine
whether a sequence of sandstones and related rocks were deposited in a sub-aerial
alluvial-fan environment or in a submarine turbidite fan environment? Relate their
differences to the mechanisms of sediment transport and deposition, and depositional
environment.
7. State Walther’s rule of facies succession and discuss its implications for the timetransgressive nature of most lithologic sedimentary beds.
Go on to define the
stratigraphic term “parasequence” and discuss the relevance of Walther’s rule to the
interpretation of the origin of individual parasequences in successions of sedimentary
rocks.
8. With the aid of a sketch, describe the form of the following divariant reaction curve in
temperature - XCO2 space:
A + 3B  D + 2E + CO2 + 3H2O
If a rock that is composed of the minerals A and B has  5% initial fluid with an XCO2 of
 0.7, contrast the evolution of the composition of the fluid as the above reaction
proceeds to the right with increasing temperature under three different conditions:

The system is closed with respect to fluids, and the initial proportion of A with
respect to B is ~ 1/3.

The system is closed with respect to fluids, but contains approximately equal
proportions of A and B.

The fluid composition remains externally buffered at XCO2 = 0.7 as temperature
increases.
What is the effect of these three different situations on the temperature range over
which minerals A and B would coexist with minerals C and D and the maximum
thermal stability of the mineral assemblage A + B?
9. You are on a traverse across a metamorphic terrane comprised of a sequence of
alternating layers of metapelite and metabasalt. Describe the different sequence of
metamorphic minerals that would appear in each of these lithologies as you proceed up
metamorphic grade, making specific correlations between their different mineral
assemblages at equivalent P-T conditions. All other things being equal, which lithology
would begin to melt first with a progressive increase in metamorphic temperature. Why?
10. With the aid of a P-T diagram, explain how the univariant reactions between the three
polymorphs of Al2SiO5 and the univariant reactions for the first appearance of garnet at
the expense of staurolite and for the breakdown of muscovite can be used to constraint the
pressure and thus depth of a metamorphic terrane in the amphibolites facies.