GEOLOGY 2 THEMATIC UNIT 5 GEOLOGY OF THE LITHOSPHERE. A.M. THURSDAY, 31 January (1 hour)

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1 WELSH JOINT EDUCATION COMMITTEE General Certificate of Education Advanced Level Advanced Supplementary CYD-BWYLLGOR ADDYSG CYMRU Tystysgrif Addysg Gyffredinol Safon Uwch Uwch Atodol GEOLOGY 2 THEMATIC UNIT 5 GEOLOGY OF THE LITHOSPHERE A.M. THURSDAY, 31 January 2002 (1 hour) Centre Number Candidate s Name (in full) Candidate s Examination Number Answer both questions in Section A (25 marks) and one question in Section B (25 marks). JLD*(0016/9)

2 2 Examiner SECTION A Answer all questions in the spaces provided. This section should take approximately half an hour to complete. 1. Figure 1a is a generalized block diagram across an active orogenic belt. Figure 1a (a) On Figure 1a, draw two arrows in the boxes provided to show the present day relative movement of the continental and oceanic lithosphere. [1] (b) With reference to the sequence of rocks marked (M) on Figure 1a, (i) state the name given to such a sequence, [1] (ii) suggest one structure within the basalt lavas which would indicate that they had erupted under water, [1]

3 3 Examiner (iii) account for the presence of rock sequence (M) within the orogenic belt. [3] (c) Explain the decrease in age of magma plutons from west to east. [2] (d) Figure 1b is a detailed section of the accretionary prism on the margin of the ocean trench seen in Figure 1a. Figure 1b (i) On Figure 1b, number the sediment wedges which are older than sediment wedge 5 (shaded), in the order that they were formed, (1 being the oldest). [1] (ii) Describe the mechanism by which an accretionary prism forms, commenting on the nature of the boundaries between the sediment wedges. [3] [Total 12] Turn over.

4 4 Examiner 2. Figure 2a is a section through the upper lithosphere showing the paths taken by two sets of P waves (P 1 and P 2 ) from a shallow focus earthquake. P 1 waves travel in the crust directly to the recording station while P 2 waves reach the recording station via the mantle. The graph shows the arrival times of all P waves at increasing distances from the earthquake focus. Figure 2a (a) (i) Mark in and label on Figure 2a the path that a reflected P wave would take from the earthquake focus to recording station 2. [1] (ii) Explain the path and behaviour of P 2 waves as they cross the Moho discontinuity. [3]

5 5 Examiner (b) With reference to the graph in Figure 2a state in the box below which set of waves (P 1 or P 2 ) will be first to arrive at distances of 100 km and 400 km from the earthquake focus. Explain your answer. [3] Distance from the earthquake focus P wave set to arrive first (P 1 or P 2 ) 100km 400km Explanation (c) An estimate of the thickness of the crust in Figure 2a can be calculated from this seismological data using the following formula: Where t = x = t = x v -v v + v 2 1 thickness of the crust distance from the earthquake at which both sets of P waves (P 1 and P 2 ) arrive together v 1 = average velocity of P 1 waves via the crust (6 km s -1 ) v 2 = average velocity of P 2 waves via the mantle (8 km s -1 ) (i) Using the graph, state the distance (x) from the earthquake at which both sets of P waves (P 1 and P 2 ) arrive together. [1] Distance (x)... km (ii) Using the formula, calculate the thickness of the crust (t). Show your working in the space below. [2] Thickness of the crust (t)... km Turn over.

6 6 Examiner (d) Figure 2b is a schematic section of part of the lithosphere. With reference to all the data available (given and calculated) and your own knowledge, suggest which one of the locations (A-D) in Figure 2b, would most likely be underlain by the type of crust identified in Figure 2a. Give a reasoned explanation for your choice of location. [3] Location... Explanation [Total 13]

7 7 SECTION B Answer one question from this section. Write your answer in the remaining pages of this booklet. 3. With reference to specific examples, describe and explain the J Tuzo-Wilson cycle of ocean growth and destruction. [25] 4. (a) Explain what is meant by a magnetic anomaly and account for their presence in ocean basins. (b) Giving examples, describe how it is possible to calculate the direction and rate at which an ocean basin is widening. [25] 5. With reference to plate boundaries, explain the formation of the following types of fault: (i) normal; (ii) thrust; (iii) transform. [25] Turn over.

8 8 Examiner

9 9 Examiner Turn over.

10 10 Examiner

11 11 Examiner