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S339 Tutorial 4 2011K - Trial exam question answers
Q1 Identify which five of the following statements are true:
A. The facing direction of a fold defines the
relative ages of the folded beds.
True. Fig. 5.3
B. Folds that are downward-facing indicate
that at least two deformation events have
occurred.
True. Fig. 5.5. p.79
C. Fold vergence can be used to establish
movement directions in shear zones.
True. p.68
D. Cleavage vergence in folded beds can be
used to identify way-up structures.
Untrue
E. Mylonites within shear zones are
strongly foliated with reduced grain size
as a result of brittle deformation.
First part is true, but mylonites are the
product of ductile - not brittle - deformation.
Untrue
F. Buckle folds are associated with planar
and linear tectonic fabrics.
True. p.59
G. A duplex structure is associated with
thrust imbrication.
True. Sections 2.2.1 and 2.7
H. Normal and reverse faults can be
distinguished using slickensides
observed on the fault plane.
Untrue. p.62
I. The terms antiform or synform can only
be applied if the younging direction of
the folded beds is known.
Untrue. The statement would be true of
anticline and syncline, but antiform and
synform are based on closing direction, not
facing. Box 3.1
Your answer should consist of only 5 letters = A, B, C, F, G.
Q2 (a) Discuss the relationship between plate convergence and uplift of narrow mountain
belts by considering:
(i) how crustal shortening is achieved in the Himalayas.
Block 4 sections 7.5 and 7.6.
(ii) how this varies along the Himalayan chain.
Major structures (STDS, MCT, MBT, MFT) can be traced for 2000 km along the centeal
Himalaya (Fig. 7.5, 7.19. Convergence is often oblique (Figs. 7.45, 7.46). Western Himalaya
is often different on account of Kohistan.
(iii) what is the cause of Himalayan uplift?
Crustal thickening resulting from stacking of thrust sheets, and homogeneousd thickening of
the lithosphere generally. Also an isostatic response to unloading owing to STDS.
(iv) the relationship between uplift rate and local structures in the western Himalayas.
Relates to Block 4 section to 7.6.3 and Activity 4.7.4.
S339 Tutorial 4 2011K - Trial exam question answers
(b) Discuss the relationship between plate convergence and uplift of wide plateaux by
considering possible causes for rapid uplift of the Tibetan plateau millions of years after plate
collision.
Convergence has led to considerable thickening of the crust and mantle lithosphere beneath
Tibet may have led to convective thinning of the lithosphere root, removing dense mantle
lithosphere some time after collision, and leading to rapid isostatic uplift.