Causes and mechanisms of remagnetisation in Palaeozoic sedimentary rocks [Elektronische Ressource] : a multidisciplinary approach / vorgelegt von Alexander Zwing

Zwing, Charles Wesley Alexander

Sujets

• Physik

Informations

• Publié par: ludwig-maximilians-universitat_munchen
• Publié le: 01 janvier 2003
• Nombre de lectures: 28
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

Causes and Mechanisms of
Remagnetisation in Palaeozoic
Sedimentary Rocks - a Multidisciplinary
Approach
Inaugural-Dissertation
zur Erlangung des Doktorgrades
an der Fakult¨ at fur¨ Geowissenschaften der
Ludwig-Maximilians-Universit¨ at Munchen¨
vorgelegt von
Alexander Zwing
4. Juli 2003i
1. Berichterstatter: Prof. Dr. V. Bachtadse
2. Bericht Prof. Dr. H.C. Soffel
Tag der mundlic¨ hen Prufung:¨ 13.11.2003Contents
List of Figures vi
List of Tables vii
Abbreviations viii
Preamble xi
Zusammenfassung 1
Summary 6
I Introduction 10
1 Remagnetisations: Occurrence and processes 11
1.1 Theremagnetisationphenomena..................... 1
1.2 Physicalmechanisms........................... 14
1.3 Chemicalproceses. 18
2 Scope of this study 23
3 Methods 26
3.1 Sampling.................................. 26
3.2 Magneticmethods . 27
3.3 Claygeochemistryandgeochronology.................. 28
3.4 Microscopy ................................ 31
3.5 Highgradientmagneticseparation.................... 31
3.6 Leachingexperiments........................... 34
iiCONTENTS iii
II Late Carboniferous Remagnetisation of Palaeozoic
Rocks in the NE Rhenish Massif, Germany 41
4 Geology and Sampling 42
4.1 Geological setting and palaeogeography . . . . . . . . . . . . . . . . . 42
4.2 Basinevolution.............................. 43
4.3 Deformationanddiagenesis....................... 4
4.4 Samplingareaandsampledescription.................. 45
5 Palaeomagnetism 49
5.1 Demagnetisationexperiments 49
5.2 Tectoniccorectionandfoldtests.................... 51
5.3 Interpretationofpalaeomagneticresults................. 5
6 Magnetomineralogy 59
6.1 IRM acquisition and demagnetisation . . . . . . . . . . . . . . . . . . 59
6.2 Lowtemperatureexperiments...................... 60
6.3 Hysteresismeasurements......................... 63
6.4 Viscosity and frequency dependence of susceptibility . . . . . . . . . . 64
6.5 Interpretationofrockmagneticresults................. 66
7 K-Ar dating and trace element geochemistry 69
7.1 Characterisationofclayfractions.................... 69
7.2 K-Ar dating of the < 0.2µm fractions.................. 73
7.3 Trace and REE geochemistry of the < 0.2µm fractions and leachates 80
7.4 Interpretation of K-Ar ages of < 0.2µm fractions and REE patterns
ofleachates................................ 84
8 Discussion and Conclusions 86
III Dating of remagnetisation events in the Barrandian,
Czech Republic and in the Holy Cross Mountains, Poland 90
9 Age of remagnetisation in the Barrandian 91
9.1 Geologyandsampling .......................... 91
9.2 Palaeomagnetism............................. 93
9.3 Magnetomineralogy10
9.4 K-Ardatingandtraceelementgeochemistry..............102
9.5 Discusionofresults ...........................106CONTENTS iv
10 Remagnetisations in the Holy Cross Mts. 108
10.1Geologyandsampling ..........................108
10.2Palaeomagnetism.............................10
10.3Magnetomineralogy16
10.4K-Ardatingandtraceelementgeochemistry..............118
10.5Discusionofresults ...........................121
IV Final conclusions and implications of this study 123
Bibliography 128
Acknowledgements 141
Appendices 143
A Samples 143
B Palaeomagnetic data 145
C Rock magnetic data 148
D X-ray diffraction data 150
E Geochemical data of clay fractions 152
F Geochemical data of leachates 156
Lebenslauf 159List of Figures
1.1 Global distribution of remagnetised Palaeozoic rocks . . . . . . . . . 12
1.2 Age of remagnetisation in Palaeozoic rocks . . . . . . . . . . . . . . . 13
1.3 Nomograms for magnetite and hematite . . . . . . . . . . . . . . . . 15
1.4 SEM micrographs of magnetite spheres and pseudoframboids . . . . . 19
2.1 Positionoftheworkingareas....................... 24
3.1 Highgradientmagneticseparationdevice................ 32
3.2 SEM micrograph of magnetic extracts from HGMS . . . . . . . . . . 33
3.3 Anhysteretic susceptibility and Fe O content of leachates . . . . . . 362 3
3.4 Leaching of Fe O andotheroxides................... 372 3
3.5 Ternary diagrams of cations K, Al, Si, and Ca, Fe, Mg in leachates . . 38
3.6 HREE depletion and REE content versus Th and P O ........ 392 5
4.1 Devonian to Permian palaeogeography . . . . . . . . . . . . . . . . . 43
4.2 Age of deformation in the Rhenish Massif and the Ardennes . . . . . 46
4.3 GeologicalmapoftheNERhenishMassif ............... 47
4.4 SamplinglocationsintheNERhenishMasif ............. 48
5.1 Thermal demagnetisation behaviour in orthogonal projection . . . . . 50
5.2 Structural correction of folds with inclined fold axes . . . . . . . . . . 52
5.3 Foldtestresults.............................. 53
5.4 Site mean directions in stereographic projection . . . . . . . . . . . . 54
5.5 Anisotropy of magnetic susceptibility . . . . . . . . . . . . . . . . . . 55
5.6 Palaeolatitudinal drift history of the NE Rhenish Massif . . . . . . . 56
6.1 IRM acquisition and thermal demagnetisation of a triaxial IRM . . . 60
6.2 Lowtemperaturebehaviour....................... 62
6.3 Characteristichysteresisloops...................... 63
6.4 Hysteresis ratios M /M and H /H .................. 64rs s cr c
6.5 Magnetic viscosity of clastic and carbonate rocks . . . . . . . . . . . 65
6.6 M /M and the intensity decay across the Verwey transition . . . . . 66rs s
vLIST OF FIGURES vi
7.1 Scanningandtransmisionelectronmicrographs............ 71
7.2 Typical XRD patterns for clastic and carbonate rocks . . . . . . . . . 72
7.3 Illite crystallinity of < 0.2µm and 0.2− 2µm fractions......... 73
7.4 K-Ar ages of clay fractions from four pilot samples . . . . . . . . . . . 74
7.5 K-Ar ages and illite crystallinity . . . . . . . . . . . . . . . . . . . . . 75
7.6 K-Ar isochrons for isotopic data from < 0.2µm fractions . . . . . . . 77
7.7 Apparent K-Ar ages of < 0.2µm fractions................ 80
7.8 REE patterns of untreated < 0.2µm fractions ............. 81
7.9 CorelationofREEandFeintheleachates 82
7.10REEpatternsofdithioniteleachates .................. 83
7.11 Correlation of MREE-enrichment with Ba, Fe O and CaO + P O .842 3 2 5
8.1 Diagenetic and deformation history of the NE Rhenish Massif . . . . 87
9.1 GeologicalmapoftheBarrandian.................... 92
9.2 Thermaldemagnetisationbehaviour................... 94
9.3 Poles of bedding planes in stereographic projection . . . . . . . . . . 96
9.4 Foldtestsresults............................. 97
9.5 Site mean directions in stereographic projection . . . . . . . . . . . . 98
9.6 Palaeolatitudinal drift history of the Barrandian . . . . . . . . . . . . 100
9.7 Characteristichysteresiscurves.....................101
9.8 Hysteresis ratios M /M and H /H ..................102rs s cr c
9.9 SEMimagesofFe-oxides.........................103
9.10 K-Ar isochron and apparent ages of < 0.2µm fractions . . . . . . . . 105
9.11 REE patterns of untreated < 0.2µm fractions and Fe-oxide leachates 106
10.1 Geological map of the Holy Cross Mountains . . . . . . . . . . . . . . 109
10.2Thermaldemagnetisationbehaviour...................11
10.3Foldtestresults..............................13
10.4 Palaeopole positions with respect to the APWP for Baltica . . . . . . 115
10.5Characteristichysteresiscurves.....................16
10.6SEMimagesofFe-oxides.........................17
10.7 Illite crystallinity of < 0.2µm and 0.2− 2µm fractions . . . . . . . . . 119
10.8 K-Ar isochron and apparent ages of < 0.2µm . . . . . . . . 120
10.9 REE patterns of untreated < 0.2µm fractions and Fe-oxide leachates 122List of Tables
5.1 UnitmeandirectionsfromtheNERhenishMassif........... 54
9.1 UnitmeandirectionsfromtheBarandian............... 9
10.1 Unit mean directions from the Holy Cross Mts. . . . . . . . . . . . . 112
A.1 Sampling locations in the Barrandian and Holy Cross Mountains . . . 143
A.2SamplinglocationsintheNERhenishMasif .............14
B.1 Site mean directions (Barrandian and Holy Cross Mountains) . . . . 146
B.2Sitemeandirections(RhenishMasif) .................147
C.1Rockmagneticresults(RhenishMassif) ................149
D.1 Illite crystallinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
D.2XRDpeaksandmineralogy.......................151
E.1 Major element data of < 0.2µm clayfractions.............152
E.2K-Ardataofclayfractions........................153
E.3 Trace element data of < 0.2µm clayfractions..............154
E.4 Rare earth element data of < 0.2µm clayfractions...........15
F.1Majorelementdataofleachates.....................156
F.2Traceelementdataofleachates157
F.3Rareearthelementdataofleachates..................158
viiAbbreviations
40 36 40 36( Ar/ Ar) initial Ar/ Ar ratioini
α radius of cone of 95% confidence95
AF alternating field
AS Attendorn syncline
AMS anisotropy of magnetic susceptibility
APWP apparent polar wander path
ARM anhysteretic remanent magnetisation
BSE backscattered electrons
CAI conodont alteration index
CGS Centre de Ge´ochimie de la Surface, Strasbourg
CNSC Cretaceous normal geomagnetic superchron
CRM crystallisation remanent magnetisati