EXAMINATION PAPER
Exam in:
GEO-3104
Date:
Friday 27th February 2015
Time:
Kl 09:00 – 12:00
Place:
B154
Approved
aids:
Ruler
(linjal),
(vinkelmåler),
stereonet,
compass
calculator,
tracing
paper
(passer),
protractor
ordbok
(engelsk),
(kalkerpapir),
millimeter-paper
The exam contains 6 pages included this cover page
Contact person: Luca Menegon
Phone: +44 7710 651583
NB! It is not allowed to submit rough paper along with the answer
sheets
pin,
NB: Each question of the examination paper will carry equal weight to
the final mark for the paper.
Question 1
N
A. Examine the stereogram above, which illustrates bedding data taken from a
small fold exposed in the coastline near Alta. With reference to the stereogram,
complete the following:
a) Label the NE dipping limb of the fold and estimate the amount of dip.
b) Sketch in the profile plane of the fold.
c) Estimate the dip direction / dip of the fold axial plane, and sketch a great
circle to illustrate this on the stereogram.
d) Estimate the plunge/trend of the fold axis and label this on the stereogram.
e) Estimate the inter-limb angle of the fold and annotate the stereogram to
show how you have reached this estimate.
f) In the space below, draw a sketch section through the fold and label the
orientation of the section at the top left and top right of your sketch.
UiT / Postboks 6050 Langnes, N-9037 Tromsø / 77 64 40 00 / [email protected] / uit.no
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Geological mapping of the region that includes the small fold described above
reveals that it is a minor (parasitic) fold related to a kilometer scale regional
synform. The plunge and trend of the fold axis is identical to the minor fold.
However, the larger fold differs in that it has a rounded fold profile, an inter-limb
angle of 60º, and a vertical axial plane. Using the blank stereogram below,
produce a fully labelled and annotated sketch to illustrate the following:
g) Ten poles to bedding planes that were measured around the fold, from
limb to limb and including the hinge zone.
h) A great circle representing an axial planar cleavage observed and
measured in the hinge zone of the fold.
Question 2
Folding mechanisms: Explain briefly the difference between orthogonal flexure
and flexural shear folding. Use sketches.
Question 3
a) Describe and interpret the structural features shown in Figure 1a and 1b
(detail of 1a).
b) Comment on the principal stress directions indicated by the structures
shown, and state the direction of extension implied. Note that the photos
are oriented (North is shown).
c) Annotate the photos in Fig. 1a and 1b to show those directions.
d) Figure 2 shows a fault plane oriented 86°/150° (dip/strike, right-hand rule),
with slickenside striae that pitch at 10° SE. Plot on a thumbnail stereonet
the fault plane (as a great circle) and the striae. Explain, using a sketch,
how the fault plane features indicate the type and sense of slip.
UiT / Postboks 6050 Langnes, N-9037 Tromsø / 77 64 40 00 / [email protected] / uit.no
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N
Figure 1a
N
Figure 1b
UiT / Postboks 6050 Langnes, N-9037 Tromsø / 77 64 40 00 / [email protected] / uit.no
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Figure 2
Question 4
With reference to Figure 3, describes the effect of confining pressure,
temperature and strain rate on rock strength. Your answer should be illustrated
with examples of structures and fault rock types that are relevant to each of the
process that you describe.
Figure 3: Stress-strain relationships for rocks under a variety of
experimental conditions. From Twiss&Moores (2007) and Fossen (2010).
UiT / Postboks 6050 Langnes, N-9037 Tromsø / 77 64 40 00 / [email protected] / uit.no
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Question 5
a) Construct the Mohr-Coulomb failure envelope considering a material with
cohesion of 40 MPa and a coefficient of internal friction of 0.7.
b) On the same diagram draw a Mohr circle at a confining pressure of 250
MPa (using Pc=3 as confining pressure) and a differential stress of 150
MPa. Is the material in a stable or in a critical state of stress?
c) Which pore fluid pressure is required to bring the rock to failure at a
differential stress of 150 MPa?
d) Construct the frictional sliding envelope using a coefficient of frictional
sliding of 0.25. Consider the Mohr circle constructed in b). Which is the
angle between the reactivated fractures and 1?
UiT / Postboks 6050 Langnes, N-9037 Tromsø / 77 64 40 00 / [email protected] / uit.no
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