Magnetic Field – magnet and/or coil fed by electrical current exerts force effect on magnetic particles in its vicinity lines of magnetic flux can be visualized by saw dust MAGNETIC PROPERTIES OF ROCKS Bar Magnet Solenoid l magnets remain dipoles even after cutting them into pieces DIPOLE CHARACTER OF MAGNETISM m = ql m – magnetic moment q - magnetic charge l - distance Magnetization M = Σ m/v [A/m] Magnetic susceptibility k [10-6 SI] Magnetization induced by field M = k H Magnetization of rocks M = kH + NRM M – magnetization, v - specimen volume k – magnetic susceptibility, H – intensity of magnetic field NRM – natural remanent magnetization [A/m] Magnetic Moment, Magnetization, Magnetic Susceptibility MAGNETIC DIPOLE OF A COIL Dipole Field of the Earth Magnetic anomalies on ocean rift Shift of anomalies on transform fault. Black belts indicate basalts with normal NRM polarity, white ones indicate basalts with reverse polarity. quartz, k = -15.4 x 10-6 opal, k = -12.9 x 10-6 orthoclase, k = -13.7 x 10-6 halite, k = -10.3 x 10-6 calcite, k = -13.1 x 10-6 aragonite, k = -15.0 x 10-6 DIAMAGNETISM olivine, k = 124 to 4270 x 10-6 dolomite, k = 11.3 x 10-6 pyroxene, k = 121 to 3700 x 10-6 micas, k = 36 to 3040 x 10-6 hornblende, k = 750 to 1368 x 10-6 garnets, k = 502 to 6780 x 10-6 PARAMAGNETISM Ferrimagnetism, Antiferromagnetism, Ferromagnetism sensu stricto Magnetic Domains – regions with spontaneously oriented magnetic moments FERROMAGNETISM sensu lato Doménová stavba feromagnetika Doménová stavba bez vlivu vnějšího magnetického pole Nulový magnetický moment Změna magnetizace na hranici domén Magnetizace feromagnetika H – magnetické pole (přesněji intenzita magnetického pole) J – magnetizace Js – sytná magnetizace Jr – remanentní magnetizace Hc – koercitivní síla Hcr – koercitivita remanentní magnetizace Hysterézní smyčka : Msat – saturation magnetization, Hsat – saturating field Mrm – remanent magnetization, Hcr – coercive force HYSTERESIS LOOP in Ferromagnetic sensu lato Materials Magnetite, k = 3 to 6 Titanomagnetite, k = 0.5 to 3.5 monoclinic Pyrrhotite, k = 0.2 to 0.7 FERRIMAGNETISM Hematite, k = 0.001 to 0.2 hexagonal Pyrrhotite ANTIFERROMAGNETISM Metallic Iron FERROMAGNETISM sensu stricto Parazitický feromagnetismus antiferomagnetika feromagnetismus ferimagnetismus antiferomagneti- smus čistý Antiferomagnetismus s parazitickým feromagnetismem Demagnetizační faktor N Je definován rovnicí : kext = kint/[1 + Nkint] Kext se liší od kint u silně magnetických látek, z minerálů např. u magnetitu a maghemitu. Výsledná magnetizace závisí na tvaru zrna (b,c) a jeho orientaci v magnetickém poli. Demagnetizační faktor je příčinou tzv. tvarové magnetické anizotropie. TERNARY DIAGRAM FOR IRON-TITANIUM OXIDES 3 α - haematite γ - maghemite Hyperbolic course according to the Curie Law, k = C/T C – proportionality constant, T – absolute temperature Temperature Variation of Susceptibility in Paramagnetics Morin Transition Curie Temperature Hopkinson Peak Temperature Variation of Susceptibility in Hematite Curie Temperature Tc = 585oC Temperature Variation of Susceptibility in Magnetite Curie Temperature Tc = 585oC Temperature Variation of Susceptibility in Magnetite Verwey Transition Tc = 325oC Temperature Variation of Susceptibility in Monoclinic Pyrrhotite Lambda Peak Tc antiferro Tc ferri Temperature Variation of Susceptibility in mixture of monoclinic and hexagonal pyrrhotite AMPHIBOLITE (Hornblende + Magnetite) orthopyroxene Susceptibility Variation with Mineral Composition magnetite – ulvospinel series Variation of Curie Temperature with Mineral Composition 22 Susceptibility Variation with Composition in Titanomagnetites ilmenite – hematite series Variation of Curie Temperature with Mineral Composition Magnetic Susceptibility of Minerals Oxidace Fe-Ti minerálů V průběhu geologického vývoje dochází ke změnám PT podmínek vzhledem k těm, ve kterých se původně horniny vytvářely. U vulkanitů, intruzív a výše metamorfovaných hornin dochází při jejich ochlazování a výstupu k povrchu k tzv. oxidaci Fe-Ti minerálů, a to jak titanomagnetitů, tak ilmenohematitů a hemoilmenitů. Oxidace se projevuje lamelováním původních zrn, tj. vznikem lamel bohatších na Ti a lamel naopak chudých na Ti. Proces končí lamelami ilmenit-magnetitovými nebo ilmenit-hematitovými. Oxidace ferimagnetických minerálů v horninách Hemoilmenit s magnetitem z lokality Orlík u Humpolce (foto V. Procházka) Tenké lamely hemoilmenitu (šedé) v hematitu (světlý), magnetit je černý. Bulk susceptibility and magnetite content Závislost susceptibility na velikosti zrna Iron-rich spherule Magnetic spherule from the topsoil from Jaworzno power Station (Poland) Bacterial magnetites TEM images of different shapes of bacterial magnetites in a core from the Tasman Sea, 4520 m water depth Different species produce different shapes of magnetosome particles Susceptibility and HM polution Correlation of magnetic susceptibility with lead and zinc contents in a soil pit near Jaworzno power station (Poland) Susceptibility profile, China Susceptibility profile at Xifeng, China, compared with oxygen isotope profile The sequence of soils (S) and Loess (L) Age in kYr, mass susceptibility in 10-8 m3kg GEOLOGICALAPPLICATIONS OF MAGNETIC SUSCEPTIBILITY Geological Mapping of Magnetically Different Rocks Delineation of Metamorphic Zones Discrimination of I-type and S-type Granites Indication of Alteration Processes Tracing Metasomatic Changes Interpretation of Magnetometric Anomalies Application to Volcanology Susceptibility in Economic Geology Čistá - Jesenice Pluton Granite Classifications (after Clarke, 1992) Granite Tectonic Setting (I and S Types) (after Beckinsale & Mitchell, 1981) Magnetite and Ilmenite Series Granites Magnetic Susceptibility in Granites Magnetic susceptibility of granites is extremely variable, ranging from 10-6 [SI] to 10-1 and displaying a bimodal distribution. Weakly Magnetic Granites (Dortman) Paramagnetic Granites (Bouchez) Magnetic Granites (Dortman) Ferromagnetic Granites (Bouchez) Brno Massif 1 - Eastern Zone 2 - Metabasite Z. 3 - Western Zone Eastern Zone magnetic Western Zone weakly magnetic Magnetic Susceptibility in Various Rocks Magnetic Susceptibility in Metamorphic Rocks ? Susceptibilita anomálních ortometamorfitů stoupá zpravidla až do amfibolitové facie. V ČM mají granulity, i ty tmavé, jen zvýšenou susceptibilitu. ČM 01 01 – bazika od extruze k prehnit –pumpellyitové facii Magnetic Susceptibility in Serpentinized and Carbonatized Ultrabasic Rocks Magnetic Susceptibility in Altered (propylitized) Andesites Magnetic Susceptibility in Rocks that Underwent Alkaline Metasomatism Magnetic Susceptibility and Magnetometry Magnetic Susceptibility in Lava Flows 1 Magnetic Susceptibility in Lava Flows 2 Sulphide Deposits Magnetic Susceptibility in Environs of Sulphide Deposits PALEOMAGNETISM Magnetic field of the Earth - coaxial dipóle Record in remanent magnetization (RM). Volcanics – cooling under Curie temperature (rock becomes ferromagnetic). Sediments – during deposition RM may preserve since its origin to present. Methods exist how to find whether the RM is fossil and stable. Magnetic Field of the Earth Variations of Magnetic Field Presentation of Palaeomagnetic Data fix pole, plate movement fix plate, apparent pole path Construction of Palaeopole Apparent Polar Wandering Paths for Individual Continents Key evidence of the continental drift. Fold Tests of Palaeomagnetic Stability Conglomerate Test of Palaeomagnetic Stability Thermal and AF Demagnetization CONTINENTAL DRIFT Reconstruction of continents about Atlantics Bullard (1965) Fit of continental margins in depth of 500 fathoms (927 m) Plate Movements after Breakdown of Gondwana Laurasia and Gondwana. Atlantic Opening. Drifting of India Magnetic Stratigraphy Palaeomagnetism of Ore Deposits Krusne hory Ore Deposits