Petrofyzika -Magnetické vlastnosti hornin Martin Chadima (František Hrouda a Marta Chlupáčová) AGICO, s.r.o., Brno (chadima^agico.cz) Geologický ústav AV ČR, v. v. i., Praha ADVANCED CEOSCIENCE INSTRUMENTS Institute of Geology of the CAS, v. v. i. Magnetic Field - magnet and/or coil fed by electrical current exerts force effect on magnetic particles in its vicinity Bar Magnet Solenoid lines of magnetic flux can be visualized by saw dust DIPOLE CHARACTER OF MAGNETISM ] ] I I I magnets remain dipoles even after cutting them into pieces Magnetický moment, magnetizace, magnetická susceptibilita q- i q+ m = ql m- magnetic moment q - magnetic charge /- distance Magnetization M = I m/v [A/m] Magnetic susceptibility k [106 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] Remanentní a indukovaná magnetizace •Stupeň namagnetování látky v magnetickém poli popisuje magnetizace •M = Mi + Mr [A/m] / \ indukovaná magnetizace remanentní magnetizace magnetická susceptibilita Mi = k H / Q = Mr / Mi Kónigsberger ratio DIAMAGNETISM Applied field No applied field nun HUH II IIIIII IIIIII Ml even number quartz, £ = -15.4 x 10~6 orthoclase, k = -13.7 x 10~6 calcite, = -13.1 x 106 opal, £=-12.9xl0-6 halite, it = -10.3 x 106 aragonite, k = -15.0 x 10~6 PARAMAGNETISM Applied field No applied field tttttt Itttlt tttttt tttttt t ocäca. number of electiirons olivine, k = 124 to 4270 x 10"6 pyroxene, k = 121 to 3700 x 10"6 hornblende, k = 750 to 1368 x 106 dolomite, k= 11.3 x 10"6 micas, k = 36 to 3040 x 10"6 garnets, k = 502 to 6780 x 10"6 FERROMAGNETISM sensu lato Ferrimagnetism, Antiferromagnetism, Ferromagnetism sensu stricto Magnetic Domains - regions with spontaneously oriented magnetic moments 60 f-im FERRIMAGNETISM 1 t»M»;t»t»t» t«t»M«t»t« r»t»t« t»t»t» t«t»t».t»M» Ferrimagnetlc Applied field t»t»t» No applied field Magnetite, k = 3 to 6 Titanomagnetite, k = 0.5 to 3.5 monoclinic Pyrrhotite, k = 0.2 to 0.7 ANTIFERROMAGNETISM nun tmu tmu tmu tmu tmu tmu tmu tmu tmu Antiferromagnetic tmu tmu Hematite, k = 0.001 to 0.2 hexagonal Pyrrhotite FERROMAGNETISM sensu stricto ttlttt Iftftt tttttt tttttt tttftt tttttt tttttt mm Ferromagnetic (s.s.) tttttt SS tttttt SS SS nun SS tum Metallic Iron Hysterezní smyčka 3 k r Msat - saturation magnetization, Hsat - saturating field M - remanent magnetization, Hcr - coercive force Hysterezní smyčka k - initial susceptibility Hc - coercive force Hcr - coercivity of remanence Initial susceptibility -počáteční susceptibilita Coercive force - koercitivní síla Důležité : susceptibilita se mění s polem, jen v počáteční oblasti je konstantní Diamagnetismus Paramagnetismus Feromagnetismus M M M k< 0 k>0 Indukovaná magnetizace působí proti směru vnějšího pole Indukovaná magnetizace ve směru vnějšího pole Složitější závislost mezi vnějším polem a indukovanou magnetizací Magnetická susceptibilita je relativně malá, záporná Magnetická susceptibilita je relativně malá, kladná Magnetická susceptibilita je relativně vysoká Bez vnějšího poleje indukovaná magnetizace rovna nule Bez vnějšího poleje indukovaná magnetizace rovna nule Bez vnějšího pole zůstává remanentní (zbytková) magnetizace křemen kalcit pyroxeny amfiboly olivín slídy železo magnetit hematit pyrhotin Magnetická susceptibilita > Magnetic susceptibility is the ability to acquire induced magnetization, i.e. ability to get magnetized k = Mi/H Laboratorní měření magnetické susceptibility Kappametr 101H Identification of magnetic minerals and phases Grain size assessment Paleotemperature estimation Concentration [%] 10rJ -í (ň ícr4 1CT3 (a) rocks basall gabbrti sedimentary rocks granity? sandstone sliĽik limestone LÍolt>tiiite — -5 0.1 g 0.01 60 (b) minerals igtieuus rocks c 0.0015 -í.^x iir1 -1.4 x ]»■ 1 1 0.0065 1.5 10" 10" 10" ](1 4 10" qujrtz cakite pyrite hematite pyrrlmtite magnetite 0.1 0,01 o Temperature ferromagnetism <£■ -5> paramagnetism Pi matrix mineral r~\ magnetite ^/ grain magnetization direction Oxidy železa (a titanu) Rutile Fe304 Susceptibility Variation with Mineral Composition Fig. 2 Magnetic susceptibility of minerals. Adapted from Hrouda & Kahan (J 991), Nagata {1961), Jackson et al (J 998). a - mineral contributions to rock susceptibility, note that 100% of mafic silicates contribute less than 1% of magnetite b - susceptibility variation with chemical composition in orthopyroxene c - susceptibility variation with chemical composition in synthetic titanomagnetiie (symbols in different colours denote different experiments producing grains of different sizes) Curiova teplota ferromagnetických minerálů 580°C 675°C Paramagnetic minerals Kbulk [E-6] 400 300 200 100 0 biotite Hyperbolic course according to the Curie Law k= CI T C- proportionality constant T- absolute temperature .....i........ .....i........ .....i........ -200 100 0 100 200 300 400 T\T] Ktot [E-6] 3000 MAGNETIT 2000 1000 -200 Magnetite Verwey transition 7"v ~ - 150 °C Transition from cubic to ortho-rhombic symmetry, decrease in susceptibility Ktot [E-6] 500 400 300 200 - 100 - 0 0 Ml 6 - coarse-grained magnetite i i i i i i i i i i i i li i i i i i i i i i i i i i i i i i i i i i i li 100 200 300 400 500 feOO 700TpC] Curie temperature Tc ~ 585 °C Transition from ferrimagnetic to paramagnetic state, rapid decrease of susceptibility iFeTi205 Ferropseudobrookite lFeTi03, llmenite IFe TiO 3 2 Ulvospine iFe2Ti05 . Pseudobrookite Variation of characteristic temperatures with chemical composition in titanomagnetites FeO t-H O £ 0.20 0.00 IFe O 3 3 4 Magnetite Hematite 50 100 150 200 250 300 Temperature (K) (Moskowitz et al. 1998, EPSL) 5001 600 o 400 =. CD r—t- CD TJ CD 200 S CD O -200 1.0 Composition, x Fe2TiQj (after N agáta 1961) KbulW [E-3] 30 20 10 0 -200 0 Morin transition rm~-20 °c Hematite 200 Hopkinson peak .................i...................i...................i...................11111.............. 400 600/ 700 T pCl Curie temperature 71 - 695 °C Fe2Ti05 Pseudobrookite Variation of characteristic temperatures with chemical composition in titanohematites 0.0 0.2 0.4 0.6 0.8 1.0 Fe203 Composition, x FeTi03 (after Nagata 1961) Pyrrhotite Monoclinic pyrrhotite Ktot [E-6] Ferrimagnetic pyrrhotite 400 T[*C] Curie temperature Tc = 325 °C Ktot [E-6] 400 300 200 - 100 Mixture of monoclinic and hexagonal pyrrhotite P29 - ferrimagnetic and antiferromagnetic pyrrhotite Lambda peak 100 200 300 400 T[*C] Tc antiferromagnetic Tc ferrimagnetic Geologické aplikace magnetické susceptibility • Geological Mapping of Magnetically Different Rocks • Delineation of Metamorphic Zones • Discrimination of l-type and S-type Granites • Indication of Alteration Processes • Tracing Metasomatic Changes • Interpretation of Magnetometric Anomalies • Application to Volcanology • Susceptibility in Economic Geology l\0 llfAiiknHl.*] // /v*X a F H ***** C 1 2 J < S»r íraríůCfulfife i—■—■—■—■—i £ 50 n u (D I] IT aj 0 □ ^-ICOfiT □tJ1ů!5nT -50 la -100 rtT CDi5lo 50 nT I_j -ZS 1o -50 nT I_15010 100 nT I_] 0 (o -25 nT I_1100 to 200 nT IZZIsOOloMOnT 10: 10' 10; 10: & 50 c OJ (D C 10! 10"* H Čistá g ran od i o rile l^l Tis granite i i Proterozoic □ Young volcanics □ Permo-Carbonifenous 101 k [SI] 101 k [SI] Fig. 12 Geological scheme (a) by Orlov (1933), map ofmagnetic AT anomalies (b), and recent geological scheme (c) of the eastern part of the Čistá ■ Jesenice massif. Adapted from Chlupáčová et at. {1975) and Šalanský (1995). Magnetite and llmenite Series Granites Fig. 3 Bimodal distribution of susceptibility in granitic rocks of the former U.S.S.R (a), inferred distributions of magnetite-series/ibnenite-sehes rocks (b) and S- and I-types granitoids (c) in eastern Asia. Adapted from Dortman (J984} and Pitcher (J982). Geologická prospekce N [%] 40 30 20 10 0 •bimodální rozdelení magnetické susceptibility (granity bývalého SSSR) slabě magnetické (paramagnetické) granity S typ nositel magnetizace hlavně biotit (amfibol) silně magnetické (feromagnetické) granity Intruzivní -1 typ nositel magnetizace hlavně magnetit 0 1 3 7 15 30 60 103 [SI] Brno Massif Eastern ^ soJ Susceptibility, k a) Fig. 14 Susceptibility changes during serpentinization and carbonatization of ultrabasic rocks (a) and susceptibility histogram of ultramqftc rocks from the locality of Bory, Western Moravia, Czech Republic (b). Adapted from Dortman (1984) and Urouda et al (2008). Magnetic Susceptibility in Altered (propylitized) Andesites io-2- 103- 10 Massive an desíte Magnetic Susceptibility in Lava Flows Fig, 6 Geological scheme of the Velký Roudný volcano (a) and the depth variation in magnetic susceptibility in several boreholes drilled through the Chřihský les lava ßowatthe locality of Slezská Harta (by Adapted from Koloßkovd (1976) and MUllerová & Müller (1972). Studium změn klimatu v geologické minulosti Země paleosol silty paleosol Fig, 22 Magnetic susceptibility profile at Xifeng, China, compared with the oxygen isotope profile at ODP677. The sequence of soil (S) and loess layers (L) at Xifeng is indicated on the right. Adapted from Evans & Heller (2003). Paleomagnetismus •vnější jádro tavenina železa •více než 7 krát objem Měsíce •na povrchu Země by tvořilo vrstvu vyšší než 300 km Země jako velký magnet AGICO rotační magnetometr kryogenní magnetometr Teplotní remanentní magnetizace lávová tavenina 1.0 -| 0.8- 0.6- r;w o.4 - 0.2- 0.0 •T> Tc •krystaly rostou •nejsou magnetické 0 100 200 300 400 500 600 700 Temperature(°C) •T< Tc •magnetické momenty se fixují ve sméru „easy axis" proporcionálně k orientaci krystalu Detritickä remanentni magnetizace Turbulent Water Still water or laminar flow sediment/water interface bioturbation consolidation "lock-in depth" compaction Chemická remanentní magnetizace Červené půdní horizonty, Nemagnetická matrix Růst hematitu s přednostní Ch i j i Formát ion, Siwaliks, orientací od rážej ící magnetické Pákistán pole Studium chovaní magnetického pole Země v geologické minulosti Magnetic Reversal Age in Millions Rocks become magnetized in Time-Scale " of years O r- o CO O C) I I I I II I II I I II I II I II I HIHI III III I I I b 01 ro o 'JD co M ľ- ■:r: —JO Ul n in n 111 i in i mi ii mi in i nil ni i i mini mi ii nim ii ii i m m ii m n mi ii mi min m 1 1 1 ■ 1 II 1 5 > * Normal polarity Intermediate polarity Reversed polarity > — ZS n < = ^ T " f - _ (j) o o> (ľ) ;:■ cz ZS o Q) 3 C 3 5 3 co í cr 'sj o í/1 si st CL Epoch P bint- 8 M a L tú ü_ Singa ci TSIi Í2 Zandán Meisinian Tcrtfiian ■it SerrawallisnE Landnlan Eurdhjslisn I Aquitanien iľhattian Rupelian Priakriian Bartfiian Lutetian VprsBJan Tharetiar Salandlan i34 ■35 ■35 Dan Ian , «7 ! 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