Komatiite

Cover......Page 1
Half-title......Page 3
Title......Page 5
Copyright......Page 6
Dedication......Page 7
Contents......Page 9
Preface......Page 13
Part I Background information - description of the field characteristics, mineralogy and geochemistry of komatiites......Page 17
1.1 The discovery and early investigations of komatiite......Page 19
1.2 More recent studies......Page 25
1.3 Nomenclature......Page 26
1.4 Komatiite lithofacies......Page 29
1.5 Conclusion......Page 31
2.2 Komatiites in the Barberton greenstone belt......Page 32
2.3 Komatiites in the Abitibi greenstone belt......Page 43
2.4 Ore-bearing komatiites at Kambalda......Page 49
2.5 Komatiitic basalts on Gilmour Island......Page 56
2.6 Karasjok-type Fe-Ti-rich komatiites and picrites in Fennoscandia......Page 58
2.7 Komatiites and picrites from Gorgona Island......Page 62
3.1 Introduction......Page 69
3.2 Types of komatiite flows......Page 71
3.3 Dimensions of komatiite flows......Page 73
3.4 Spinifex texture......Page 77
Chilled margins (A1)......Page 83
Spinifex (A2)......Page 85
The B1 layer......Page 88
Cumulate layer (B2-B4)......Page 91
Basal chill zones......Page 92
Other unusual spinifex-textured komatiites......Page 93
Harrisitic textures......Page 94
3.6 Komatiite flows without spinifex textures......Page 95
3.7 Flows with thin spinifex layers......Page 96
3.8 Thick dunitic units......Page 100
3.9 Pillowed komatiites......Page 103
3.10 Volcaniclastic komatiites......Page 104
Flow-top breccia of the Alexo komatiite flow......Page 105
Ultramafic pyroclastic komatiites at Sattasvaara, Finland......Page 107
3.11 Komatiitic basalts......Page 108
Textures......Page 109
3.12 Intrusive komatiites......Page 112
4.1 Introduction......Page 114
Morphological characteristics......Page 115
Chemical compositions......Page 119
Major elements and zonation......Page 120
Variations in olivine compositions within komatiite flows......Page 121
Ni contents......Page 123
Cr contents......Page 126
Ca contents......Page 127
Chromite......Page 128
Pyroxenes......Page 132
Megacrysts in spinifex lavas......Page 133
Interstitial grains......Page 137
Pyroxenes in gabbros and cumulate layers......Page 138
Other magmatic minerals......Page 139
Glass......Page 140
4.3 Secondary minerals......Page 143
4.4 Summary......Page 145
5.1 Introduction......Page 146
5.3 Mobile and immobile elements: the olivine control line criterion......Page 147
Immobile elements in Zvishavane komatiites......Page 151
Mobile elements in Zvishavane komatiites......Page 154
5.4 Mobility of Mg......Page 157
5.5 Other approaches used to demonstrate element mobility......Page 159
5.6 Other types of mobile element behaviour......Page 164
Major elements......Page 165
Al2O3/TiO2......Page 167
Incompatible elements......Page 170
Compatible trace elements......Page 172
5.8 Igneous chemistry of komatiitic basalts......Page 176
6.2 The Rb–Sr system......Page 183
6.3 The Sm–Nd system......Page 187
Early dating attempts......Page 188
Crustal contamination......Page 190
Post-eruption changes in Sm–Nd ratios......Page 193
Nd isotopic constraints on the composition of the mantle source......Page 194
Age dating......Page 198
Initial isotopic compositions......Page 200
Age determination......Page 201
Initial isotope compositions......Page 202
6.6 The Lu–Hf system......Page 204
6.7 Helium isotopes......Page 208
6.8 Stable isotopes......Page 210
6.9 Conclusions emerging from the isotopic compositions of komatiites......Page 216
7.2 Experiments at 1 atm pressure......Page 218
Mg–Fe partitioning between olivine and komatiitic liquid......Page 229
Ni partitioning between olivine and komatiitic liquids......Page 230
Other partitioning data......Page 231
7.4 Experiments at moderate pressures (1–4 GPa)......Page 233
7.5 High-pressure experiments on komatiites......Page 234
Densities of komatiite liquids at high pressures......Page 235
Phase relations at high pressures......Page 236
7.6 Trace-element partitioning at high pressures......Page 242
7.7 Dynamic cooling experiments......Page 243
7.8 Huppert and Sparks’ experiments......Page 245
7.9 Summary and implications for komatiite petrogenesis......Page 246
Part II Interpretation – the manner of emplacement, the origin and the tectonic setting of komatiites......Page 249
8.1 Introduction......Page 251
8.2 Temperature......Page 252
8.4 Viscosity......Page 254
8.5 Density......Page 257
8.6 Other thermal properties......Page 258
9.1 Introduction......Page 265
9.2 Nomenclature and terminology......Page 266
Komatiite lithofacies......Page 267
Komatiite flow facies......Page 269
Size and scale......Page 272
Emplacement of thick basalt flows: the inflation hypothesis......Page 274
Inflation in komatiite flows......Page 277
Alternatives to the inflation mechanism......Page 279
Did komatiites flow turbulently?......Page 281
Thermomechanical erosion beneath komatiite flows......Page 283
Timing of crust development......Page 286
Mechanism of growth of spinifex texture......Page 287
Crystallization and accumulation of polyhedral olivine......Page 290
Crystallization of adcumulates......Page 298
9.6 Models for the emplacement and solidification of komatiite flows......Page 299
Solidification of thin differentiated flow lobes......Page 300
Solidification of flow lobes without spinifex texture......Page 303
Origin of B1 zones......Page 304
Thick cumulate-rich flows......Page 306
9.7 What did komatiite volcanoes look like?......Page 310
Structure of komatiite flow fields......Page 311
The form of komatiite volcanoes......Page 314
9.8 Concluding comments......Page 316
10.1 Introduction......Page 317
10.2 General characteristics......Page 318
10.3 Type I deposits......Page 321
The host komatiite sequence......Page 322
The orebodies......Page 325
Origin of the ‘troughs’......Page 326
Geochemistry of the Kambalda komatiites......Page 327
Timing of ore formation and flow crystallization......Page 328
Example: Alexo (Ontario)......Page 329
Example: Black Swan (Western Australia)......Page 332
Example: Raglan (New Quebec)......Page 334
10.4 Type II deposits......Page 336
Example: Thompson (Manitoba)......Page 339
10.6 Compositions of komatiite-hosted sulfide ores......Page 342
Influence of the R factor......Page 343
Monosulfide solid solution fractionation......Page 344
The thermomechanical erosion model for Type I deposits......Page 345
Origin of Type II ores......Page 347
Province selection......Page 348
Unit selection......Page 349
11.1 Introduction......Page 350
The Jamestown ophiolite complex and intrusive komatiites: early papers by Brooks and Hart and by de Wit and coauthors......Page 351
Formulation of the hydrous komatiite modelpapers by Grove et al. and Parman et al. published between 1996 and 1999......Page 353
The Boston Creek komatiitic basalt......Page 357
Experimental studies advocating a hydrous deep mantle source of komatiite......Page 358
Responses to the hydrous komatiite model: papers by Nisbet et al., McDonough and Danushevsky, and Arndt et al.......Page 359
11.3 Extrusive Barberton komatiites: papers by J. Dann published in 2000 and 2001......Page 361
11.4 Elaboration of the subduction zone model: papers by Parman et al. and Grove and Parman published between 2001 and 2004......Page 362
11.5 Other papers discussing the hydrous komatiite model......Page 366
11.6 A critical evaluation of the hydrous komatiite model......Page 371
12.2 Methods used to estimate liquid compositions......Page 374
Chilled margins......Page 376
Combined use of olivine compositions and whole-rock analyses......Page 377
Alexo komatiite......Page 380
Three unusual high-Mg komatiites: Commondale, Weltevreden and Murphy Well......Page 382
Thick dunitic units......Page 383
Eruption temperatures......Page 384
13.1 Nature of the komatiite source......Page 385
13.2 What does it take to make an ultramafic magma?......Page 387
13.3 Conditions of melting......Page 390
13.4 The formation of various types of komatiite......Page 395
Barberton-type komatiite......Page 397
Munro-type komatiite......Page 399
Gorgona komatiites and picrites......Page 403
Commondale and Weltevreden komatiites......Page 404
Fe-rich Karasjok-type komatiites from Boston Creek and Lapland......Page 406
13.5 The formation of komatiitic and tholeiitic basalts......Page 408
13.6 Summary......Page 410
14.1 Introduction......Page 412
‘Mafic plains’......Page 413
Arcs and convergent margins......Page 420
Eruption in shallow water on continental basement......Page 422
14.2 The geodynamic setting of Archean greenstone belts......Page 427
14.3 A mantle plume does not know what it will meet at the surface......Page 429
14.4 Passage through the lithosphere......Page 431
14.5 The setting of komatiitic volcanism......Page 433
14.6 Conclusions......Page 435
References......Page 437
General Index......Page 481
Localities......Page 488