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PLANETARY CRUSTS: THEIRCOMPOSITION, ORIGIN AND

EVOLUTIONSTUART ROSS TAYLOR

, Department of Earth and Marine SciencesAustralian National UniversityCanberra, Australia

. AND ' . . .. SCOTT M. McL ENN ANDepartment of GeosciencesState University of New York at Stony Brook,Stony Brook, NY, USA

C A M B R I D G EUNIVERSITY PRESS

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Contents

PrefaceAcknowledgmentsList of abbreviationsPrologue .

No tes and references ' The planets: their formation and differentiation1.1 Planetary formation .1.2 The solar nebu la and the giant planets '

1.2.1 The depletion ofthe volatile elements in the inner nebula1.3 Planetesim als and the accretion of the terrestrial planets1.4 The random nature of terrestrial planet formation

1.4.1 Meteorites and planetary com pos ition1.4.2 Uncompressed density and bulk planetary

compositions1.5 Types of crusts1-.6 Geochemical processe s during crust formation

1.6.1 Europium as a universal tracerSynopsisNotes and references

A primary crust: the highland crust of the Moon .2.1 The composition of the Mo on2.2 The lunar surface2.3 Structure of the crust ''-'

2.3.1 Tectonics2.3^2 Lunar stratigraphy'

2.4 Craters and multiring basins -2.4.1 A lunar cataclysm?2.5 Com position oft he lunar highland crust

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Contents2.5.1 Anorthosites .2.5.2 KREEP2.5.3 Th eM g-suite . . ' '2.5.4 Lunar highland terranes2.5.5 Th e Cayley Plains : a cautionary tale2.5.6 Tektites and the M oonS y n o p s i s . . . ' Notes and references

A secondary crust: the lunar maria3.1 The maria

3.1.1 M are basalt ages . 3.2 Com position ofth e mare basalts

3.2.1 The interior of the Mo on .3.3 Origin of the mare basalts . -

3.3.1 An impact origin?3.4 The magm a ocean

3.4.1 Th e depletion in europium 3.4.2 Depth1 of melting

3.5 Large-impact model for lunar originSynopsis ,No tes and references - " .Mercury '

4.1 The planet- 4.1.1 The com position and internal stru ctu reo f Mercury

4.2 Origin of M ercury4.3 Surface structure

4.311 The heavily cratered terrain4.3.2 The intercrater plains4.3.3 The Caloris Basin: a mercurian cataclysm?4.3.4 The smooth plains

4.4 The origin ofth e plains: a Cayley Plains analog?4.4.1 Lobate scarps

4.5 The crust of M ercury4.5.1 Primary and secondary crusts on Mercury?4.5.2 AtmosphereSynopsisNotes and referencesMars: early differentiation and planetary composition

5.1 The origin of M ars5.1.1 A volatile-rich and oxidized planet

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5.2

5.35.4

5.55.6

5.75.85.9

Mars6.1 .6.26.3

6.4

6.56.6

ContentsThe interior of Mars 5.2.1 Core ,5.2.2 Mantle.5.2.3 CrustMartian stratigraphyCratering record and the age ofthe martian surface5.4.1 Crustal dichotomy5.4.2 Quasi-circular depressions5.4.3 Tharsis and Valles MarinerisEarly plate tectonics?5.5.1 Crustal magnetization and plate tectonicsSamples from Mars5.6.1 M artian meteorites5.6.2 Shergottite crystallization agesEarly differentiation on Mars and magma oceansM ultiple reservoirs and the age ofth e earliest crustThe composition of Mars5.9.1 A cautionary noteSy no psi s . - Notes and references . - : crustal com position and evolutionSampling martian crustCrustal dimensions6.2.1 Hypsom etry _Igneous diversity in a basaltic crust6.3.1 SNC meteorites and crustal contam ination6.3.2 Hem ispheric dichotom y, Surface Types 1 and 2

and martian andesites6.3.3 Gusev plains and M eridiani Planum6.3.4 Alkaline volcanism and the Colum bia HillsThe sedimentary rock cycle on Mars6.4.1 Water, wind and ice6.4.2 Surficial processes6.4.3 ' Soils and dust6.4.4 Sedimentary rocks on Mars6.4.5 M eteoritic com ponentsBulk composition of the crust6.5.1 Com positional evolution of the martian surfaceHeat flow and crustal heat production6.6.1 Com positional variation with depth

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Contents .6.7 Crustal evolution on Mars ' ' 168

6.7.1 Tertiary crusts on M ars? 170Synopsis 171Notes and references 172Venus: a twin planet to Earth? 181

7.V The enigma of Venus 1817.2 Surface features of Venus 182

7.2.1 Plains , 1827.2.2 Channels ' , 1837.2.3 Volcanoes 1847.2.4 Coronae * 1857.2.5 Tesserae ' 1867.2.6 Ishtar Terra and Aphro dite Terra . . 186

7.3 Impact craters and the age o fth e surface 1867.4 Heat production and rates of volcanism 190

7.4.1 A one-plate planet ' 1917.5 Crustal com position - 192

7.5.1 .Pancak e dom es: rhyolites on Venus? . 1947.5.2 The differentiation of Venus 196

7.6 The geological history of Venus ' . ' 1977.6.1 Water on Venus 199Synopsis > 201No tes and references . 202

The oceanic crust of the Earth 2078.1 The sea floor and plate tectonics . 2078.2 Structure of th e oceanic crust - 2088.3 M id-ocean ridges - 2098.3.1 Formation processes at mid-ocean '

ridges ' ' . 2 1 18.4 Mid-ocean ridge basalts (MO RB) 211

8.4.1 Interaction with seawater , : ' 2158.5 Oceanic island basalts (OIB) 2168.6 Com position of the oceanic crust 2178.7 Mantle structure . . 2 1 8

8.7.1 M antle plumes 2208.8 Compositiotfof the Earth . - ' . 2228.8.1 Core 2238.8.2 M antle . ' ' . . 2 2 3Synopsis _ , ~ 226No tes and references 227

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Contents

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The Hadean crust ofthe Earth ' .9.1 The Hadean crust and mantle9.2 A terrestrial magm a ocean9.3 . The early crust : ' .. .9.3.1 The bom bardm ent record9.4 The early continental crustal myth9^5 Isotop ic constraints: 142Nd and 17 6Lu

9.5.1 M antle keels in the Hadean?9.6 A model for the Hadean

SynopsisNotes and references ' .

The Archean crust of the Earth10.1 Th e Archean -10.1.1 The earliest Archean rocks10.1.2 Akilia island, southwest Greenland

10.2 The Archean.upper crust10.2.1 Archean high-grade terrains

10.3 The Archean bulk crust10.3.1 The Archean oceanic crust10.3.2 Heat flow in the Archean

10.4 The formation of the TTG suite10.4.1 Adak ites and the TTG suite10.4.2 The evidence from sanukitoids

10.5 Plate tectonics in the Archean?10.5.1 The subcrustal lithosphere and man tle

keels10.6 M eteorite impacts in the ArcheanSynopsis

Notes and references1The Post-Archean continental crust11.1 The Archean-P roterozo ic transition11.2 Changes in crustal composition during the

Archean-Proterozoic transition11.3 The Post-Archean upper crust

-11.3.1 Paradoxes: niobium and lead11.4 The lower crust (Post-Archean)11.4.1 Anorthosites ^ .Synopsis Appendices

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xii ContentsArea, thickness and densiiy of the present continental crust 290Ag e ofthe continental crust - - " 291Sedimentary rocks as crustal samples , . 2 9 2

Notes and references - . . . . 29312 Composition and evolution of the continental crust . 30112.1 Heat flow constraints 302

12.2 Com position ofth e bulk crust . 30412.3 The andesite model 305

12.3.1 Delamination and its problems 30612.3.2 The formation of andesites 30712.3.3 Granites and granites .309

12.4 . Alternatives: basaltic com positions 31112.5 Alternatives : felsic compositions " 31212.6 Crustal grow th and its episodic nature 313

" 12.6.1 The freeboard constraint 31312.6.2 Recycling ... 31412.6.3 Continental break-up and assembly 315Synopsis '. . .' ' 316Notes and references 317

\ 1 3 Crusts on minor bodies 32513.1 Minor bodies in the Solar System 32513.2 Observational problem s 327

13.2.1 Nanophase iron . . 3 2 813.2.2 Eros and Itokawa 329

13.3 Vesta, a differentiated asteroid 33013.3.1 Evolution of Vesta 33113.3.2 Eucrites and the Moon 332

13.4 The Galilean satellites . 33213.5 The extraordinary crust of Io 33313:5.1 Volcanic activity 33313.5.2 M ountains - . - . 3 3 513.5.3 Nature ofth e crust 335

13.6 The thick icy crust of Europa 33713.7 Two crusts on Ganym ede 33813.8 Calh'sto, an ancient crust 339.13.9 Sand dunes on Titan 34013.10 Nitrogen ice on Triton . 343

Synopsis . ' 344Notes and references . 345

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Contents - xiii14 Reflections: the elusive patterns of planetary crusts .352

14 1 Too many variables . - . 35214.1.1 Sampling 357

14.2 Earth -like planets elsewhere? 35814 3 plan etary evolution and plate tectonics , 361N ote s and references 362

Indexes 364