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THIS PAPER IS NOT TO BE REMOVED FROM THE EXAMINATION HALLS

UNIVERSITY OF LONDON PGM151 (GGL 5151) 

MSc and Postgraduate Diploma

PETROLEUM GEOSCIENCE

Tectonics and Lithosphere Dynamics

Thursday 7 June 2012 : 2.30 – 4.30 pm

Candidates should answer THREE questions. Each answer should take about40 minutes.

Candidates are allowed to bring into the examination hall calculators, rulers,set squares, protractors and compasses.

Use a SEPARATE answer book for each question.

© University of London 2012

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1. This is a question about continental extension and extended continentalmargins.

(a) Draw a cross section of a magma-rich (or volcanic) extended continentalmargin. Include a vertical and horizontal scale and label important features.

(45%)

(b) Describe how magma is produced at margins like this. (15%)

(c) With reference to features on your cross section, describe two separatemechanisms that may have accommodated plate divergence at a magma-rich margin. (25%)

(d) How might the products of these mechanisms be of importance topetroleum systems in magma-rich margins? (15%)

2. This is a question about subsidence in extensional basins

(a) Draw a graph with labelled axes to show the increasing depth of asedimentary basin that formed by pure-shear extension of the lithospherefrom 100 to 90 million years ago. Show the depths where the oil and gaswindows might be. (40%)

(b) Sketch the pattern of sediment packages in the basin today, includinglabels to name the various packages according to subsidence mechanisms.(25%)

(c) Graphs like the one in part (a) can be produced by subsidence analysis ofa basin’s fill. Decompaction forms part of this kind of analysis. Using a graphshowing porosity, describe why decompaction is necessary. (25%)

(d) Name two further corrections that are necessary in completing asubsidence analysis. (10%)

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3. This is a question about heat in the lithosphere

(a) Draw a sketch showing typical surface heat flow ranges for the following:i. an active mid-ocean ridge;

ii. an active rift basin;iii. an extended continental margin;iv. a foreland basin;v. a craton; andvi. an area of oceanic crust that is 200 million years old. (40%)

(b) Fission track analysis can give details about a rock’s tectonic history.Sketch a graph with two curves that compare the distribution of fission tracklengths in two apatite grains:

- one grain is from rocks that were buried during a 10 million year long

rifting event at 110 Ma but have since then been near the surface,- the other grain is from rocks that were not buried in the rift but havesince experienced 80 million years of steady burial during thermalsubsidence of a continental margin. (30%)

(c) Both grains come from potential source rocks in the same region. The firstsource rock is dated to 330 Ma, and also shows some very high vitrinitereflectance values. The second is dated to 80 Ma, but there are no vitrinitereflectance data from it. Comment on the possible maturation histories of thetwo source rocks. (30%)

4. This is a question about continental convergent plate boundaries.

(a) Draw THREE labelled sketch maps and/or cross sections of the followingparts of the Alpine-Himalayan collision zone:

i. the Dasht e Lut desert in eastern Iran;ii. the Zagros mountains;iii. the area including the country of Turkey.

In each case, explain how plate convergence is being accommodated in theupper crust. 60% 

(b) Describe two possible ways in which the convergence might beaccommodated deeper down, in the mantle lithosphere. 20% 

(c) In the case of the Zagros, describe ways in which the regional response toconvergence has influenced the petroleum system there. (20%) 

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5. This is a question about the strength of the lithosphere.

(a) Draw TWO simple strength envelopes (graphs of yield strength vs. depth)i. one for the oceanic lithosphere, and

ii. one for the continental lithosphere. (40%) Explain the shapes of the different parts of the graphs in terms of how failureprocesses might evolve with changing temperature and pressure. (10%) 

(b) Using your graphs, show at what depths we might expect the largestearthquakes to occur, and explain why. (20%) 

(c) A strong lithosphere can transmit stress over long distances. Suggestways in which this might be of interest to petroleum exploration or production.(30%) 

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