The structure of the Earth

SOLUTION AT My Australian Academy

Study the recorded lecture then enter key essential mineralogy in text boxes provided Teaching week 3Polar 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 Z900 18 890 41 850 42850 22 850 43 810 37812 24 790 34 708 31703 28 700 31 660 30690 30 612 33 590 32620 32 567 29 563 32560 30 490 36 460 35425 24 421 41 359 34390 23 362 37 299 36365 21 290 32 270 33295 31 270 34 195 40272 33 230 36 179 38220 35 183 42 167 44180 40 110 43 90 39110 26 87 39 67 4090 23 67 34 64 4060 32 60 33 60 41
Teaching week 3Polar wandering
Teaching week 4Seafloor 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 followingRate 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
Find the polar reversal that occurred 2 million years ago on survey line A and determine how far the reversal is from the ridge in km
Determine half-rate velocity c) given the calculated rate of spreading, would you expect seafloor spreading to be accomplished primarily by magmatic or amagmatic extension and why ?3) Determine the horizontal distance between the ridge in survey line A and B.4) Describe the likely nature of the geological structure between survey lines A and B, using appropriate terminology5) What differences in seafloor basement bathymetry between Survey lines A and B would you expect to occur in support your interpretation, and why ?6) Suggest why Survey D crosses the ridge twice, (note the ship only measures polarity directly beneath the ship, i.e. the lines drawn extend further than the ship can actually see. KmSurvey line A km Survey line B km Survey line C km Survey line D0 Normal 800 Reversed 1600 Reversed 1200 Normal60 Reversed 920 Normal 1640 Normal 1240 Reversed80 Normal 1000 Reversed 1720 Reversed 1360 Normal220 Reversed 1040 Normal 1760 Normal 1400 Reversed300 Normal 1100 Reversed 1820 Reversed 1420 Normal380 Reversed 1200 Normal 1920 Normal 1600 RIDGE580 Normal 1240 Reversed 1960 Reversed 1780 Reversed780 Reversed 1360 Normal 2080 Normal 1800 Normal800 Normal 1420 Reversed 2140 Reversed 1840 Reversed860 Reversed 1440 Normal 2160 Normal 2080 Normal920 Normal 1600 RIDGE 2300 RIDGE 2120 Reversed1080 Reversed 1780 Reversed 2480 Reversed 2140 Normal1100 Normal 1800 Normal 2500 Normal 2320 RIDGE1240 Reversed 1860 Reversed 2560 Reversed 2500 Reversed1320 Normal 1960 Normal 2680 Normal 2520 Normal1400 Reversed 2020 Reversed 2720 Reversed 2540 Reversed1460 Normal 2120 Normal 2820 Normal 2680 Normal1640 Reversed 2180 Reversed 2900 Reversed 2720 Reversed1680 Normal 2220 Normal 2940 Normal 2820 Normal1760 Reversed 2300 Reversed 3020 Reversed 2900 Reversed1860 Normal 2380 Normal 3120 Normal 2920 Normal1900 Reversed 2400 END OF LINE 3180 Reversed 3020 Reversed2020 Normal 3200 Normal 3100 Normal2060 Reversed 3280 Reversed 3140 Reversed2100 Normal 3380 Normal 3160 Normal2280 RIDGE 3460 END OF LINE 3240 END OF LINE2460 Reversed2500 Normal2540 Reversed2660 Normal2700 Reversed2800 Normal2860 Reversed2900 Normal2980 Reversed3080 Normal3100 END OF LINE
Teaching week 4Seafloor spreading Teaching week 5 Oceanic lithosphere

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Sediment thickness

Drill Site number537 0.5m538 214m539 404m540 610m541 800m542 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 zonesFocus depth distance from trench Focus depth distance from trench37 40 62 6445 53 102 8050 12 200 15062 23 170 10038 18 137 8041 9 163 12041 36 400 21063 50 330 20097 74 270 18068 74 223 16062 64 380 210102 80 330 190200 150 530 290170 100 557 300137 80 540 286163 120 610 307400 210 650 323330 200 490 260270 180 507 268223 160 630 301380 210330 190530 290557 300540 286610 307650 323490 260507 268630 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 subductionc) Comment on the likely nature of the stress regime in the overriding plated) 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 settingsThe 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

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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 99.48Sample 2 60.34 0.73 18.49 4.32 5.58 2.09 0.08 1.76 5.01 0.17 0.73 99.30Sample 3 70.84 0.35 14.27 3.73 2.49 0.63 0.08 3.45 3.53 0.08 0.29 99.74Sample 4 75.82 0.09 13.07 2.66 0.28 0.25 0.04 3.72 3.95 0.01 0.10 99.99Sample 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
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