Study the recorded lecture then enter key essential mineralogy in text boxes provided
Teaching week 3
Polar wandering
The table below shows age and paleo-latitude for continental lithosphere (cratons) [X], [Y] and [Z]. Craton [Z] is located to the present day west of your map area. The age data (taken from a variety of sedimentary and igneous rocks) is generally considered accurate +/-3 Ma. The paleo-latitude estimates are reported accurate +/- 1.5°.
a) Plot the apparent polar wandering curves for the three cratons on a single excel graph.
b) State the time duration(s) (if any) when you consider there is circumstantial evidence for a potential supercontinent (i.e. all three cratons joined).
c) Outline the key assumptions that you have made in reaching this interpretation.
d) What evidence would you seek to confirm your interpretation(s).
age (Ma) Craton X age (Ma) Craton Y age (Ma) Craton Z
900 18 890 41 850 42
850 22 850 43 810 37
812 24 790 34 708 31
703 28 700 31 660 30
690 30 612 33 590 32
620 32 567 29 563 32
560 30 490 36 460 35
425 24 421 41 359 34
390 23 362 37 299 36
365 21 290 32 270 33
295 31 270 34 195 40
272 33 230 36 179 38
220 35 183 42 167 44
180 40 110 43 90 39
110 26 87 39 67 40
90 23 67 34 64 40
60 32 60 33 60 41
Teaching week 3
Polar wandering
Teaching week 4
Seafloor spreading
Overleaf You are provided with magnetic data from the Southern Oceans, taken across the plate boundary between two hypothetical plates. Before starting the questions you will note the following
Rate of Spreading = distance the sea floor moved / length of time or R = d/t Generally expressed as cm/yr. 1 km = 1000m. Half-rate (velocity) of sea floor spreading = (distance / time = velocity in cm/year), total rate (velocity) of sea floor spreading = (2 X half-rate = total spreading rate)
Study the map of the area provided and the associated table for the four transects made by the ship and marked on the map. Note that the ship only actually records the anomaly pattern directly beneath its path of travel. Also ignore the boreholes (marked with numbered crosses) at this stage
Teaching week 4
Seafloor spreading
Teaching week 5 Oceanic lithosphere
Sediment thickness
Drill Site number
537 0.5m
538 214m
539 404m
540 610m
541 800m
542 220m
Plot the Borehole data from sites 537,538,539,540,541 on a graph showing sediment thickness (to top of basement) against distance from ridge axis. Now plot Site 542 as a separate point.
b) Explain why the sediment thickness increases from Sites 537 to 540, and why 537 & 542 are so different, despite the close proximity.
c) The uppermost sediments from Sites 537,538 and 542 are rich in calcareous sediments of planktonic origin. In contrast the upper most sediment from Sites 539, 540 and 541 show no such enrichment in calcareous material. Given that calcareous plankton is prevalent within the upper ocean waters throughout the study area account for their absence at some sites and not others and give the underlying tectonic causative factor.
Teaching week 5 Oceanic lithosphere
Teaching week 6: Hydrothermal seawater circulation in oceanic lithosphere
Teaching week 7: Subduction zones
Focus depth distance from trench Focus depth distance from trench
37 40 62 64
45 53 102 80
50 12 200 150
62 23 170 100
38 18 137 80
41 9 163 120
41 36 400 210
63 50 330 200
97 74 270 180
68 74 223 160
62 64 380 210
102 80 330 190
200 150 530 290
170 100 557 300
137 80 540 286
163 120 610 307
400 210 650 323
330 200 490 260
270 180 507 268
223 160 630 301
380 210
330 190
530 290
557 300
540 286
610 307
650 323
490 260
507 268
630 301
The table above shows the focus depths of earthquake plotted against distance from the trench (heading east).
a) Plot the data and outline any potential seismic gaps in the data set and state the significance (if any)
b) Characterise the angle of subduction
c) Comment on the likely nature of the stress regime in the overriding plate
d) Why does earthquake activity appear to terminate at ca 650km depth ? and, what (if any) internal boundary within the mantle would you expect to encounter around this depth ?
Teaching week 7: Subduction zones
Teaching week 8: Melting mechanisms in subduction settings
The table below gives wt% oxides analyses for five igneous rock samples, from this table calculate the normalised FeOtotal, total alkalis (K2O+Na2O) and MgO content of each rock in the box below the table and then mark their positions directly on the AFM diagram
SiO2 TiO2 Al2O3 FeO CaO MgO MnO K2O Na2O P2O5 LOI Total
Sample 1 57.15 1.30 17.55 6.02 6.20 3.00 0.07 2.35 4.90 0.61 0.33 99.48
Sample 2 60.34 0.73 18.49 4.32 5.58 2.09 0.08 1.76 5.01 0.17 0.73 99.30
Sample 3 70.84 0.35 14.27 3.73 2.49 0.63 0.08 3.45 3.53 0.08 0.29 99.74
Sample 4 75.82 0.09 13.07 2.66 0.28 0.25 0.04 3.72 3.95 0.01 0.10 99.99
Sample 5 78.03 0.05 12.37 1.23 0.47 0.12 0.00 4.49 3.62 0.00 0.52 100.89
In the box below indicate if the rocks are consistent with a tholeiitic or calc-alkaline trend, then suggest rock type names for each sample.
Week 9: Orogenesis
In the box below explain what possible bearing these two simple cartoon diagrams have in relation to the evolution of the Himalayas.
Week 10: Passive margins
In terms of what you understand of volcanic and non-volcanic passive margin case studies list the short comings of this diagram in the text box below
Sample Solution