Rock and Mineral Magnetism

ISBN-13: 9781468484700 / Angielski / Miękka / 2012 / 220 str.

W. O'Reilly

Opis

The past two decades have witnessed a revolution in the earth sciences. The quantitative, instrument-based measurements and physical models of. geophysics, together with advances in technology, have radically transformed the way in which the Earth, and especially its crust, is described. The study of the magnetism of the rocks of the Earth's crust has played a major part in this transformation. Rocks, or more specifically their constituent magnetic minerals, can be regarded as a measuring instrument provided by nature, which can be employed in the service of the earth sciences. Thus magnetic minerals are a recording magnetometer; a goniometer or protractor, recording the directions of flows, fields and forces; a clock; a recording thermometer; a position recorder; astrain gauge; an instrument for geo- logical surveying; a tracer in climatology and hydrology; a tool in petrology. No instrument is linear, or free from noise and systematic errors, and the performance of nature's instrument must be assessed and certified. This has been the task of the research worker in rock and mineral magnetism.

Spis treści

1 Introduction to the magnetism of rocks.- 1.1 Rocks as magnetic information stores.- 1.2 The recorded information.- 1.3 Rock and mineral magnetism.- 1.4 Magnetism—some preliminaries.- 2 Magnetic minerals in rocks.- 2.1 The magnetic mineral systems.- 2.1.1 The titanomagnetites.- 2.1.2 The titanomaghemites.- 2.1.3 Haematite and the haematite-ilmenite solid solution.- 2.1.4 The pyrrhotites.- 2.1.5 Other iron-bearing minerals.- 2.2 The magnetic mineralogy of igneous rocks.- 2.3 The magnetic mineralogy of sediments.- 2.4 The magnetic mineralogy of extra-terrestrial materials.- 2.5 Summary.- Selected bibliography.- 3 The atomic basis of magnetism.- 3.1 The electron spin; the transition elements.- 3.2 Exchange.- 3.3 Curie temperatures of spinel oxides.- 3.4 Magnetocrystalline anisotropy.- 3.4.1 Dipolar anisotropy.- 3.4.2 Single ion anisotropy.- 3.4.3 Anisotropic exchange.- 3.4.4 Magnetocrystalline anisotropy constants.- 3.5 Induced anisotropy.- 3.6 Categories of magnetic behaviour.- 3.6.1 Diamagnetism and paramagnetism.- 3.6.2 Antiferromagnetism.- 3.6.3 Ferrimagnetism and ferromagnetism.- 3.7 Summary.- Selected bibliography.- 4 The magnetization process.- 4.1 The demagnetizing field—shape anisotropy.- 4.2 Domains and domain walls.- 4.3 The magnetization process.- 4.3.1 The monodomain case.- 4.3.2 The multidomain case.- 4.3.3 The magnetization process near the monodomain/multidomain boundary.- 4.3.4 Alternating field demagnetization (‘fixed switching field’ model).- 4.3.5 Rotational hysteresis.- 4.3.6 Particle-particle interactions.- 4.4 The time-dependence of magnetization—equilibrium and thermal agitation.- 4.4.1 Equilibrium and disequilibrium.- 4.4.2 Approach to equilibrium.- 4.4.3 The time scale.- 4.4.4 Magnetic properties.- 4.4.5 Viscous magnetization.- 4.5 Summary.- Selected bibliography.- 5 Thermoremanent magnetization.- 5.1 The mechanism—definitions of blocking temperature.- 5.2 TRM models.- 5.2.1 Aligned monodomain grains.- 5.2.2 A random array of monodomain grains.- 5.2.3 Multidomain grains.- 5.2.4 TRM near the monodomain/multidomain boundary.- 5.3 Thermal demagnetization—partial TRM.- 5.4 Self-reversed TRM.- 5.5 Summary.- Selected bibliography.- 6 Other remanence-inducing mechanisms.- 6.1 Mechanisms in nature.- 6.1.1 Chemical remanent magnetization.- 6.1.2 Depositional remanent magnetization.- 6.1.3 Viscous remanent magnetization.- 6.1.4 Piezoremanent magnetization.- 6.2 Mechanisms in the laboratory.- 6.2.1 Anhysteretic remanent magnetization.- 6.2.2 Gyroremanent magnetization and rotational remanent magnetization.- 6.3 Summary.- Selected bibliography.- 7 Magnetic properties of titanomagnetites and titanomaghemites.- 7.1 The titanomagnetites.- 7.1.1 Intrinsic properties.- 7.1.2 The magnetization process in titanomagnetites.- 7.1.3 Weak field remanences in titanomagnetites.- 7.2 The titanomaghemites.- 7.2.1 Intrinsic properties.- 7.2.2 The magnetization process.- 7.2.3 The inversion of titanomaghemites.- 7.2.4 Weak field remanences.- 7.3 Multiphase products of the oxidation of titanomagnetite.- 7.3.1 Intrinsic properties.- 7.3.2 The magnetization process.- 7.3.3 Weak field remanence.- 7.4 Summary.- 8 Magnetic properties of other mineral systems.- 8.1 Haematite.- 8.1.1 Intrinsic properties.- 8.1.2 The magnetization process.- 8.1.3 Weak field remanence.- 8.2 The haematite-ilmenite solid solution.- 8.2.1 Intrinsic properties.- 8.2.2 The magnetization process.- 8.2.3 Weak field remanence.- 8.3 The pyrrhotites.- 8.3.1 Intrinsic properties.- 8.3.2 The magnetization process.- 8.3.3 Weak field remanence.- 8.4 Goethite.- 8.5 Iron.- 8.6 Alteration products of non-magnetic minerals.- 8.7 Summary.- 9 Applications of rock and mineral magnetism.- 9.1 Introduction.- 9.2 Physical models—the acquisition and removal of weak field remanences.- 9.2.1 Palaeomagnetism.- 9.2.2 Palaeointensity determinations.- 9.2.3 Geological applications—thermal histories.- 9.2.4 Magnetic granulometry.- 9.3 Determination of the composition, concentration and microstructure of the magnetic mineral fraction in a rock (or other material).- 9.3.1 Composition.- 9.3.2 Concentration.- 9.3.3 Microstructure.- 9.4 Connections in planetary physics—the magnetization of planetary crusts.- 9.5 Summary.