1. Chapter 10:Planetary surfaces Volcanism and Tectonics

2. Dating craters Apollo missions returned rock samples from more than half a dozen locations on the Moon’s surface, both maria and highland. Radioactive dating of these samples provides ages which can then be compared with the number density of craters in each region. MissionLocationSample Age(y)#D>10#D>1 A17Mare Serenetatis basalt3.3-3.7x10 9 A17Nectaris highlands4.3x10 9 ≥100098000 A15Apennine, PreImbr highland4.3x10 9 A15Imbrium Basin, rim3.9x10 9 9540000 A14Fra Mauro, Imbrium basin3.9x10 9 130 A12Copernicus: ray+rim≤0.9x10 9 102000 A12Oceanus Procellarum basin3.3x10 9 202000 A11Mare Tranquilitatis3.7x10 9 5012000 The numbers in columns 4 and 5 are surface density for craters with diameters >10km (col.4) and >1km (col.5); the surface densities are in units of 10 -6 /km 2 so 2 means 2x10 -6.

3. Volcanoes Volcanism is the process by which material is brought from the interior of the planet to the surface

4. Volcanic structures Cinder cone Composite volcano: Mount Hood, Oregon Shield volcanoes: Mauna Loa, Hawaii, and Olympus Mons, Mars Lava plain

5. Volcanic craters CalderaDiatreme

6. Volcanoes in the Solar System

7. Mare Lava-covered plains Dark colour is due to basalt (igneous rock) Moon mare are exceptionally flat because magma was especially hot (1400-1600 K) and therefore fluid. Caloris Basin on MarsMare Crisium on the Moon

8. A simple volcano model Consider a magma chamber, at a depth z embedded in rock of density  R. Assume the hydrostatic pressure on this chamber is equal to the pressure exerted by the weight of the magma above it:  The magma has a lower density  M, and extends a height h above the ground. The pressure P at the depth of the magma chamber is So

9. Mauna Loa Calculate the depth of the magma chamber at Mauna Loa (17 km high). The magma has a density of 2770 kg/m 3 and the surrounding rock an average density of 3270 kg/m 3.

10. Outgassing Volcanoes release gas, as well as molten rock Can contribute significantly to the composition of the atmosphere.

11. Faults Thrust fault: compression Horsts and Grabens: stretching

12. Wrinkle ridge Wrinkle ridge Usually found in mare lava plains Arise from tectonic stresses associated with the cooling and contracting of the lava that flooded the maria

13. Rilles Sinuous rille: winding valley, resembling a channel cut by a river or lava flow Linear rille: straight-sided, like a graben

14. Tectonics

15. Plate tectonics Rodinia – the giant continent assembled from fragments ~1.2 Gyr ago began to break up ~750Myr ago eventually reassembled >200Myr ago “Pangaea” its breakup led to our continents today

16. model: bands of alternating colour also alternating magnetic polarity also crust age increases with distance from rift observations of Earth’s crust along mid- ocean ridge near Iceland support plate tectonic model

17. Mid-atlantic ridge

18. Tectonic activity on Mars The Acheron Fossae region on Mars, an area of intensive tectonic (continental ‘plate’) activity in the past. Shows how the rifting crosses the older impact crater with at least three alternating horsts and grabens.

19. Break

20. Atmospheric effects Saltation: wind can carry small particles, which bounce on surface and dislodge larger particles

21. Wind Erosion Some regions of Mars’ surface look strikingly like Earth deserts, due to wind erosion. Chryse Panitia, Mars Earth desert

22. Wind streaks As wind sweeps across the Martian plains, dust may be deposited on the leeward sides of craters

23. Dune Fields Sand dunes on Mars Sand dunes in Namiba

24. Geochemical cycles On planets with atmospheres, surface rock may be tranformed

25. Urey Reaction A geochemical link between rocks and the atmosphere On Earth, CO 2 from volcanic gases dissolved in rainwater and oceans Similarly, living organisms make calcium carbonate shells Subducted and reconverted to CO 2. This could not occur on Venus (no water), so atmosphere is rich in CO 2. This formed a weak carbonic acid, which can to form carbonate rocks.

26. Chemistry The hot atmosphere of Venus (750 K) drives unusual chemical reactions  Atmosphere reacts with rocks to produce volatile HCl, HF, sulfuric acid  Even mercury and lead may be produced Any water would have been used up in oxidizing iron minerals or hydrocarbons

27. Red Mars The red soil of Mars is due to the oxidation of iron atoms in minerals  Occurs in the intermittent presence of water  The same process that rusts (wet) iron on Earth