Oceanic Basalts

I Structure.- 1 Introduction and the ophiolite model.- 1.1 Historical perspectives.- 1.2 Oceanic lithospheric processes.- 1.3 Concluding statements.- 2 Surveying and sampling the ocean floor.- 2.1 Introduction.- 2.2 Surveying the ocean floor.- 2.3 Acoustic systems.- 2.3.1 Multibeam swath bathymetric systems.- 2.3.2 Signal amplitude measurements: side-scan sonar.- 2.4 Deep-sea photography.- 2.5 Geological information from bathymetric mapping: Chile TripLe Junction region.- 2.6 Selecting sampling targets.- 2.7 Sampling methods.- 2.7.1 Dredging.- 2.7.2 Coring.- 2.7.3 Drilling.- 2.7.4 Submersible sampling.- 2.8 Concluding statements.- 3 Structure of the oceanic crust from geophysical measurements.- 3.1 Introduction.- 3.2 Ocean basins.- 3.3 Normal oceanic crust.- 3.4 Spreading centres.- 3.5 Fracture zone structure.- 3.6 Oceanic islands and swells.- 3.7 Concluding statements.- 4 Structure of the oceanic crust as deduced from ophiolites.- 4.1 Introduction.- 4.2 Alpine-type peridotites: variants and nomenclature.- 4.3 Seismic comparisons between oceanic crust and mantle.- 4.4 Implications for magmatic processes occurring at oceanic ridges.- 4.5 Implications for metamorphic processes occurring in the oceanic crust.- 4.6 Concluding statements.- II Processes.- 5 Mineralogy and crystallization of oceanic basalts.- 5.1 Introduction.- 5.2 Quench textures: the consequences of supercooling.- 5.3 Primary mineralogical controls on fractionation pathways of abyssal tholeiites.- 5.3.1 General course of fractionation in abyssal tholeiites: influence of magma chamber mixing.- 5.3.2 Advanced differentiation.- 5.3.3 Role of oxygen fugacity and oxide minerals.- 5.3.4 Apatite and sulphides.- 5.4 Liquid immiscibility and the significance of melt densities.- 5.5 Mantle-crust environments controlling oxygen fugacity.- 5.6 Alkalic magmatic lineages on seamounts.- 5.7 Concluding statements.- 6 Experimental phase petrology of mid-ocean ridge basalts.- 6.1 Introduction.- 6.2 Experimental studies at 1 atm.- 6.2.1 Experimental techniques.- 6.2.2 Results from experimental studies of basalts at 1 atm.- 6.2.3 Poorly known aspects of low pressure crystallization.- 6.2.4 Extreme differentiation of MORBs at low pressure.- 6.3 Experimental studies at high pressure.- 6.3.1 Experimental techniques.- 6.3.2 Results from experimental studies at high pressure.- 6.3.3 Poorly known aspects of high pressure equilibria relevant to MORBs.- 6.4 Concluding statements.- 7 Magmatic processes in oceanic ridge and intraplate settings.- 7.1 Introduction.- 7.2 Compositional diversity of oceanic magmas.- 7.2.1 Mid-ocean ridge basalt.- 7.2.2 Oceanic island basalt.- 7.3 Phase equilibrium and fluid dynamic constraints.- 7.3.1 Phase equilibria.- 7.3.2 Fluid dynamics.- 7.4 Melt generation: active versus passive.- 7.4.1 Passive melting at ’normal’ ridge systems.- 7.4.2 OIB shields: rising mantle jets versus shear melting.- 7.5 Melt transport and storage in the oceanic lithosphere.- 7.5.1 Fractionation mechanisms.- 7.5.2 Mid-ocean ridge fractionation models.- 7.5.3 Intraplate fractionation models.- 7.6 Concluding statements.- 8 Metamorphic and hydrothermal processes: basalt-seawater interactions.- 8.1 Introduction.- 8.1.1 Importance of seawater-rock interactions.- 8.1.2 Controls of seawater-rock interactions.- 8.1.3 Effects of seawater-rock interactions.- 8.2 Low temperature alteration.- 8.2.1 Dredged basalts.- 8.2.2 Drilled basalts.- 8.3 High temperature reactions.- 8.3.1 Dredged basalts.- 8.3.2 Experimental evidence.- 8.3.3 Ophiolite evidence.- 8.3.4 Drilled basalts.- 8.4 Concluding statements.- III Environments.- 9 Oceanic islands and seamounts.- 9.1 Introduction.- 9.2 Hypotheses of intraplate volcanism.- 9.2.1 Mantle plume model.- 9.2.2 Propagating fracture model.- 9.3 Seamount distribution and morphology.- 9.4 Internal structure and composition.- 9.5 Basalt types.- 9.6 Geochemical features.- 9.6.1 Incompatible element abundances.- 9.6.2 Rare earth elements.- 9.6.3 Highly incompatible el...