GEOLOGY HIGHER
Map Exercises
– Answers
Map 1
(a) (i)
(ii)
South-eastern side.
Older gneiss on the South-eastern side of the fault is adjacent to
younger conglomerate on the North-western side. The gneiss must
have been moved up to be at the same level as the conglomerate.
Or
(ii)
(b) (i)
(ii)
The width of the outcrop of the anticline is wider on the South-eastern
side of the fault. When an anticline is faulted the part which has been
moved up has a wider outcrop.
Tear fault.
It has displaced dyke P. Since dyke P is vertical displacement must
have been by sideways movement.
Or
(ii)
The outcrop of the anticline has been displaced with no change to it’s
width. This means that there has been horizontal movement on the
fault.
(iii) The South-eastern side has been moved approximately 285 m
towards the North-east.
Or
(iii) The North-western side has been moved approximately 285 m
towards the South-west.
(c) (i)
(ii)
Thrust fault.
It is a fault of reverse type which has pushed older rock on top of
younger rock. The fault plane dips at a low angle, and a low-angle
reverse fault is called a thrust fault.
(iii) Fault F1 is a normal fault formed by pulling forces. Tension does not
produce the high pressure shear movement required to form
mylonite.
(d)
It is transgressive.
Or
It changes levels within the conglomerate. A lava flow cannot
transgress or change levels.
Map Exercises – Answers
1
(e)
One
(f)
B, E.
(g) (i)
There are no cross-cutting relationships which allow relative ages to
be established.
(ii)
All you can say is that both are older than the thrust fault S. Because
there are no cross-cutting relationships you cannot say what their
relative ages are.
(h)
Topographic profile.
(i)
D, K, B, L, A. C
Map Exercises – Answers
2
Map 2
(a) (i)
(ii)
Southern side.
Older conglomerate with granite boulders on the North side is
adjacent to younger sandstone on the South side. The sandstone
must have moved down to be at the same level as the conglomerate.
Or
(ii)
The width of the outcrop of the core of the anticline is narrower on the
South side of the fault. This narrowing occurs when an anticline is
moved down.
Or
(ii)
The width of the outcrop of the core of the syncline is wider on the
South side of the fault. This widening occurs when a syncline is
moved down.
(iii) Northern side
(iv) Same reasons as above with North/South reversed.
(v)
Igneous rock forms a vertical dyke. Movement on the fault has been
vertical. Vertical movement cannot displace the outcrop of a vertical
structure.
(b)
Unconformity.
(c)
Tuff is the rock formed from volcanic ash.
(d)
A, C
(e)
Topographic profile.
(f)
J, L, K, E, H, G
Map Exercises – Answers
3
Map 3
(a) (i)
(ii)
North side
Older sandstone on the South side is adjacent to younger
conglomerate P on the North side. The younger rocks on the North
side must have moved down to be at the same level as the older
rocks on the South side.
Or
(ii)
(b) (i)
(ii)
The outcrop of the anticline is narrower on the North side of the fault.
Such narrowing takes place when an anticline is moved down.
Tear fault
It has displaced the vertical dolerite dyke. This means that there must
have been sideways movement.
Or
(ii)
The outcrop of the anticline has been moved to the side. Since the
displaced outcrop has not been narrowed or widened there has been
sideways movement only.
(iii) South side has been moved to the East by approximately 140 m
Or
(iii) North side has been moved to the West by approximately 140m
(c)
Two.
(d) (i)
Plunging anticline
(ii)
(e) (i)
North at 10º and South at 10º.
It transgresses or it changes from one level to another in the
conglomerate. Lava flows do not transgress.
Or
(ii)
(f)
It intrudes along the fracture zone of fault F1. Lava flows do not
intrude.
Fault breccia
Map Exercises – Answers
4
(g)
D, E
(h)
Topographic profile.
(i)
B, A, K, F, I, D
Map Exercises – Answers
5
Map 4
(a) (i)
(ii)
North side.
Older mudstone on the North side is adjacent to younger sandstone
on the south side. The older rocks on the North side must have been
moved up to be at the same level as the younger rocks on the South
side.
Or
(ii)
(b) (i)
(ii)
The faulted basin has a narrower outcrop on the North side. Such
narrowing occurs when a syncline or basin has been moved up.
Movement of fault F2 has been vertical so it would not displace the
outcrop of a vertical structure. The outcrop of fault F1 has been
displaced so it cannot be vertical.
Reverse.
(iii) Gneiss has been pushed up to a level about the younger
conglomerate.
(c)
The dyke cuts volcanic ash (and lavas P and Q) and is also partly
covered by volcanic ash. The dyke has been intruded during the
interval between early and late eruptions.
(d)
C, D.
(e)
Topographic profile.
(f)
A, L, K, G, J, H
Map Exercises – Answers
6
Map 5
(a) (i)
(ii)
South side.
The outcrop of the anticline is narrower on the South side. Such
narrowing occurs when an anticline is moved down.
Or
(ii)
(b) (i)
(ii)
The outcrop of the syncline is wider on the South side. Such widening
occurs when a syncline is moved down.
Tear fault.
Vertical dykes of diorite and dolerite have been displaced. The
outcrops of vertical structures are displaced only by sideways
movement.
(iii) The North-east side of the fault has been moved approximately 550m
to the North-west.
Or
(iii) The South-west side of the fault has been moved approximately
550m to the South-east.
(iv) The diorite and dolerite dykes show different displacements. This can
happen only if the fault has moved more than once.
(c)
A, F
(d)
Topographic profile.
(e)
H, F, E, B, I, C
Map Exercises – Answers
7
Map 6
(a) (i)
(ii)
(b) (i)
(ii)
Cone sleet.
Circular outcrop with all-round steep inward dip.
South-east.
The outcrop of the ring dyke is wider on the South-east side than on
the North-west side. A wider part of the cone must have been moved
down to lie adjacent to a lower narrower part of the cone.
(iii) Movement on fault F3 has been vertical. Vertical movement would
not displace the outcrop of a vertical structure. Because the outcrop
of dolerite L has been displaced it cannot be a vertical intrusion.
(c) (i)
(ii)
Tear fault.
It has displaced the outcrop of fault F3. Since fault F3 is vertical,
movement must have been sideways.
4
B, D
5
Topographic profile.
6
G, J, E, H, A, F
Map Exercises – Answers
8
Map 7
(a) (i) Two
(ii) Two
(iii) One
(b)
Accept any reasonable answer, for example:
 During thrust movements the rocks have been twisted through about
90º
 Before thrusting the rocks were twisted round by faulting.
 Before deposition of conglomerate Q the gneiss was folded in the
manner of folding lined paper from corner to corner.
3
D, E
4
Topographic profile.
5
F, B, J, C, H, E
Map Exercises – Answers
9
Map 8
(a) (i)
(ii)
Tear fault.
Fault F2 is vertical. F1 has displaced F2. Such displacement could
have been caused only by sideways movement.
(iii) The outcrop of F1 has not been displaced by movement on fault F3.
Movement on fault F3 has been vertical. Vertical movement would
not displace the outcrop of a vertical structure.
(b) (i)
(ii)
(c) (i)
(ii)
East side.
The outcrop of the anticline is narrower on the East side. Such
narrowing occurs when an anticline has been moved down.
Xenoliths.
On its way up through the crust, granite magma has picked up
fragments of gneiss and carried them to higher levels.
(d) (i)
The galena is cut by the dolerite dyke so the dolerite is younger. The
granite cuts the dolerite so the granite is younger than the dolerite.
Thus, the granite was intruded after the galena had been formed so
the galena could not have been derived from the granite.
(e) (i)
Hornfels.
(ii) Accept any reasonable answer, for example:
 The limestone re-crystallises at a lower temperature than the
mudstone so shows the effects of metamorphism further away from
the granite.
 Limestone reacts with acidic fluids given off by the granite so shows
signs of alteration much further away from the granite.
6
A, C
7
Topographic profile.
8
L, D, J, K, F, B
Map Exercises – Answers
10
Map 9
(a) (i)
(ii)
Thrust fault.
It is a low-angle reverse fault which has carried older gneiss to lie
above younger conglomerate K and sandstone.
(b)
Two
(c) (i)
Ring dyke.
(ii)
(d) (i)
(ii)
(ii)
(e) (i)
(ii)
(ii)
It is vertical and its outcrop lies on part of the circumference of a
circle.
Tear fault.
It has displaced the outcrop of the anticline without changing the
width of the outcrop. This can happen only where there has been no
vertical movement.
Or
Dyke Q is vertical. Fault F4 has displaced the dyke. This means that
movement on F4 must have been sideways.
South-west side.
Younger conglomerate K on the South-west side is adjacent to older
gneiss on the North-east side. The conglomerate must have moved
down to be at the same level as the gneiss.
Or
The width of the outcrop of the anticline is less on the South-west
side. Such narrowing occurs when an anticline has been moved
down.
(f)
D, E
(g)
Topographic profile.
(h)
I, G, J, C, H, D.
Map Exercises – Answers
11
Map 10
(a) (i)
(ii)
South-eastern side.
Conglomerate K lies uncomformably on greywacke so the
conglomerate is younger. Greywacke on the North-west side of the
fault is adjacent to conglomerate on the South-east side of the fault
so the conglomerate must have been moved down to be at the same
level as the greywacke.
(iii) The vertical boundary of granite T has been displaced. A vertical
boundary can be displaced only by sideways movement.
(iv) North-west side has been moved to the South-west by 500m.
Or
(iv) South-east side has been moved to the North-east by 500m.
(b)
Isoclinal folding with the shale in the cores of repeated anticlines. The
axial planes of the folds dip to the West at 70º.
(c)
It is transgressive.
It is above conglomerate K on the South-west side of the anticline but
in the middle of conglomerate K on the North-east of the anticline. A
lava flow would not change levels in this manner.
(d)
The rocks between F1 and F2 have been moved down between a
pair of parallel normal faults. A rift valley is a feature of relief so for
this structure to be a rift valley it would require that it had been
preferentially eroded to a lower level or that it had been structurally
depressed.
(e)
B ,F
(f)
Topographic profile.
(g)
I, F, L, C, G, K
Map Exercises – Answers
12