(a) Does the chemical composition of lunar and Martian basalts (Table 3.1) follow the pattern of element-portioning behaviour expected during the partial melting of peridotite? What does this indicate regarding the source of basaltic magmas on these two bodies? (to determine the behaviour of the different elements, compare the patterns of element enrichment and depletion shown in the completed peridotite and oceanic basalt spider grams in the answer to Question 2.3 b.)

Table 3.1

(b) Which of the analyses listed in Table 3.1 are most like peridotite mantle (i.e. most

‘primitive’) and which have the most MORB-like composition? Briefly account for these differences.

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Table 3.1 Compositions of rocks from the Earth's mantle and other important basalt types. Oceanic Deccan Primitive basalt basalt (CFBPa) (experimental) basalt 44.2 48.8 3.7 2.5 13.7 14.8 0.2 6.2 10.6 2.4 0.30 0.02 Weight % Peridotite oxide (mantle) SiO TiO AlO3 FeO3 MnO MgO CaO NaO KO CrO3 Totals 45.4 0.2 4.3 8.2 0.1 38.2 3.4 0.3 0.03 0.43 100.6 12.1 12.1 0.2 13.1 10.1 3.6 1.30 0.1 100.5 (MORB) 48.2 1.4 15.4 10.8 0.2 9.6 11.1 3.4 0.07 0.05 100.2 99.5 Komatiite (ancient terrestrial lava) 45.2 0.2 3.7 12.2 0.2 32.2 5.3 0.4 0.10 0.22 99.7 Lunar mare basalt 42.7 2.6 7.7 23.6 0.3 14.6 8.1 0.2 0.10 0.25 100.2 Martian basaltb 50.1 0.9 6.7 20.8 0.5 9.4 10.0 1.3 0.20 0.20 100.1