Direction and intensity of Earth's magnetic field at the Permo-Triassic boundary [Elektronische Ressource] : a geomagnetic reversal recorded by the Siberian Trap Basalts, Russia / vorgelegt von Christoph Heunemann

Heunemann, Christoph

Sujets

• Physik

Informations

• Publié par: ludwig-maximilians-universitat_munchen
• Publié le: 01 janvier 2003
• Nombre de lectures: 8
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

Direction and intensity of Earth’s magnetic
field at the Permo-Triassic boundary: A
geomagnetic reversal recorded by the
Siberian Trap Basalts, Russia
Inaugural-Dissertation
zur Erlangung des Doktorgrades
der Fakult¨ at fur¨ Geowissenschaften der
Ludwig-Maximilians-Universit¨ at Munchen¨
vorgelegt von
Christoph Heunemann
4. August 20031. Berichterstatter: Prof. Dr. H. C. Soffel
2. Bericht Prof. Dr. V. Bachtadse
Tag der mundlic¨ hen Prufung:¨ 12.11.2003Contents
List of Figures 3
List of Tables 5
Glossary 6
Preamble 8
Zusammenfassung 9
Abstract 13
1 Introduction 17
1.1 TheEarth’smagneticfield........................... 17
1.2 Polaritytransitions............................... 19
1.2.1 Palaeomagnetic records of reversals . . . . . . . . . . . . . . . . . . 19
1.2.2 Modelsofgeomagneticreversals.................... 20
1.3 TheMesozoicdipolelow. 22
1.4 Scientificaims.................................. 24
2 The Siberian Trap Basalts 25
2.1 GeologicalSeting................................ 25
2.2 Age and duration of the Siberian Trap volcanism . . . . . . . . . . . . . . 27
2.3 OriginoftheSiberianTrapBasalts...................... 28
3 Palaeomagnetic Results 30
3.1 Sampling..................................... 30
3.2 NRMdemagnetisation............................. 32
3.3 PalaeomagneticRecord............................. 41
3.4 Foldandreversaltest.............................. 47
3.5 PalaeosecularVariation 50
3.6 Magnetostratigraphiccorelation ....................... 52
1CONTENTS 2
4 Rockmagnetic Studies 56
4.1 Microscopy: Evidence for high-temperature oxidation . . . . . . . . . . . . 56
4.2 Rockmagneticparameters........................... 58
4.3 Continuous thermal demagnetisation of the NRM . . . . . . . . . . . . . . 61
4.4 Summary .................................... 63
5 Palaeointensity determinations 67
5.1 Sampleselection................................. 67
5.2 Methods..................................... 67
5.3 Reliability criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.4 InterpretationoftheArai-plots........................ 73
5.5 Results...................................... 74
6 Discussion: Features of the record 83
6.1 TransitionalVGPpath............................. 83
6.2 Phase 1: Stability of the transitional cluster . . . . . . . . . . . . . . . . . 87
6.3 Phase2:Independentorreversal-related?................... 8
6.4 Phase3:Stablenormalpolarity........................ 89
6.5 Asymmetryoftheintensityacrosthereversal................ 91
6.6 Angularsecularvariationandintensity.................... 91
6.7 Durationoftherecord............................. 92
7 Conclusions 95
Bibliography 98
Acknowledgments 112
Appendix 114
A Compilation of the VDM between 56 and 280 Ma 114
Curriculum Vitae 116List of Figures
1.1 ThevariationoftheVDMduringtheMesozoic ............... 23
2.1 Geological outline of north-western and central Siberia . . . . . . . . . . . 26
2.2 Compilation of published ages of the Siberian Traps . . . . . . . . . . . . . 29
3.1 Simplified geological map of the Noril’sk area . . . . . . . . . . . . . . . . 32
3.2 Stratigraphyofthesampledsections ..................... 33
3.3 OutcropoftheIvakinskysuite......................... 34
3.4 Welpreservedsurfaceofaflow........................ 34
3.5 Geological map of the Abagalakh/Icon river valley . . . . . . . . . . . . . . 35
3.6 Zijderveld plots of representative samples of reversed polarity . . . . . . . . 36
3.7 Zijderveld plots oftative carrying transitional directions . 36
3.8 DecayoftheNRMduringthermaldemagnetisation............. 37
3.9 Zijderveldplotsofnormaldirections...................... 37
3.10 Inclination and declination record of the Listvjanka and Abagalakh section 43
3.11 Plot of all directions in stereographic projection . . . . . . . . . . . . . . . 44
3.12 Compilation of palaeomagnetic poles obtained from the Siberian Traps . . 46
3.13 Movement of the VGPs during the emplacement of the flows . . . . . . . . 48
3.14Resultoftheinternalfoldtest......................... 50
3.15 Magnetostratigraphic correlation of borehole and in situ data . . . . . . . . 53
3.16 Correlation between the STB and the global P/T magnetostratigraphic scale 54
4.1 Light-microscopical and SEM observations . . . . . . . . . . . . . . . . . . 64
4.2 Representative M (T)-curves ......................... 65
S
4.3 Continuous thermal demagnetisation . . . . . . . . . . . . . . . . . . . . . 65
4.4 Self-reversal identified by continuous thermal demagnetisation . . . . . . . 66
5.1 Representative NRM-TRM plots for quality class A and B results . . . . . 69
5.2 Rejectedpalaeointensityresults........................ 71
5.3 NRM-TRMplotsfordifferentstratigraphiclevels.............. 72
5.4 Palaeointensities and VDMs across the studied sections . . . . . . . . . . . 75
3LIST OF FIGURES 4
6.1 MovementoftheVGPsacrossthestudiedsections ............. 85
6.2 VGPscorectedforplatemotion........................ 86
6.3 Comparison of VDM distribution for different time intervals . . . . . . . . 90List of Tables
3.1 Volcanic suites sampled in the Noril’sk area . . . . . . . . . . . . . . . . . 31
3.2 Mean characteristic directions of the Listvjanka and Abagalakh section . . 38
3.3 Mean c d of the Talnakh section . . . . . . . . . . . . 41
3.4 Mean directions and poles of the observed directional groups . . . . . . . . 42
3.5 Selected poles for the STB and the Siberian platform around the P/T
boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.6 Results of the palaeosecular variation estimates . . . . . . . . . . . . . . . 51
4.1 Resultsoftherockmagneticinvestigations.................. 59
5.1 Resultsofthepalaeointensityexperiments.................. 76
A.1 Compilation of the VDM between 56 and 280 Ma . . . . . . . . . . . . . . 114
5Glossary
Abbreviations
APWP.....................................................apparentpolarwanderpath
BSE ............................................................backscatteredelectron
ChRM ..........................................characteristicremanentmagnetisation
CMB ............................................................core-mantleboundary
EDXanalyses .........................................energydispersiveX-rayanalyses
LIP .............................................................largeigneousprovince
MD ......................................................................multidomain
MDL ..............................................................Mesozoicdipolelow
NRM .................................................naturalremanentmagnetisation
PSV ............................................................palaeosecularvariation
P/T ....................................................................Permo-Triassic
pTRM ..........................................partialthermoremanentmagnetisation
PSDpseudosingledomain
SEM .....................................................scanningelectronmicroscope
SBG ..........................................................submarinebasalticglass
SD ......................................................................singledomain
SP .................................................................superparamagnetic
STB .............................................................SiberianTrapBasalts
TRM ..................................................thermoremanentmagnetisation
TCRM .......................................thermochemicalremanentmagnetisation
VFTB ..............................................VariableFieldTranslationBalance
VDM .virtualdipolemoment
VGP .........................................................virtualgeomagneticpole
Symbols and constants
◦α /A [ ] ......radius of the 95% confidence circle of a palaeomagnetic direction/pole
95 95
◦ ◦d /d [ / ] ..................95%confidencelimitsofthelatitude/longitudeofaVGP
m p
k ...................precisionparameterforthedispersionofpalaeomagneticdirections
6GLOSSARY 7
◦T [ C] .............................................................Curie-temperature
C
◦T [ C]...........................................................blockingtemperature
b
◦T [ C]........................................................unblockingtemperature
ub
T ..................................................................roomtemperature
0
H [T] .coerciveforce
c
H [T] ...........................................................remanencecoercivity
cr
2
AmM [ ] .............................................specificsaturationmagnetisation
s
kg
2
AmM [ ] ................................................specificsaturationremanence
rs
kgPreamble
Parts of this thesis are based on, or directly taken from papers to be published in
scientific journals. Below, these papers are listed in order of their appearance in the text:
Heunemann, C., Kr´asa, D., Gurevitch, E.L., Soffel, H.C. and Bachtadse, V. Direc-
tions and intensities of the Earth’s magnetic field during a reversal: results form the
Permo-Triassic Siberian Trap Basalts, Russia, Earth Planet. Sci. Lett. (in press)
Gurevitch, E.L., Heunemann, C., Rad’ko, V., Westphal, M., Bachtadse, V., Pozzi, J.
P. and Feinberg, H., Palaeomagnetism and magnetostr