Chapter 2* Does the Permo-Triassic geomagnetic dipole low exist?

191 Pages·2013·8.42 MB·English

by  Dunia Blanco

University of Alberta

Paleomagnetic studies of volcanic rocks in Siberia and sedimentary rocks
in Southern Alberta: From long-term geomagnetic field variations to age
determinations.

by

Dunia Blanco Acuña

A thesis submitted to the Faculty of Graduate Studies and Research
in partial fulfillment of the requirements for the degree of

Doctor of Philosophy
in
Geophysics

Department of Physics

©Dunia Blanco Acuña
Fall 2013
Edmonton, Alberta

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Abstract

Paleomagnetism is a fundamental tool to understand the ancient variations of
Earth’s magnetic field through time. Important applications to geochronology and
paleography come from interpreting the variations of the planetary magnetic
vector. This dissertation explores the different applications of paleomagnetism to
uncover important characteristics of the paleointensity magnetic field during the
Permo-Triassic boundary and the nature of the apparent polar wander path
(APWP) of Siberia, and to create geochronological frameworks for kimberlites in
the Siberian platform and for sediments at the Western Canada Sedimentary
Basin.

Detailed absolute paleointensity measurements from Permo-Triassic sills at the
Siberian platform are studied to determine the existence of a low dipole field,
which has been previously reported in the area. We found a mean virtual dipolar
moment value of 6.01 ± 1.45 × 1022 Am2 which is over 50% higher than the
results previously obtained by other authors.

Diamondiferous kimberlite pipes are exposed across the north-central part of the
Siberian platform. The age of the magmatic activity cannot be clearly determined
from isotopic age data – this is the reason why new paleomagnetic poles from
four kimberlite pipes are obtained to study their paleomagnetic age. On the basis
of a comparison with the Siberian APWP, we estimate the age of the kimberlite
magmatism. The acquired paleomagnetic ages span from the Early Silurian to the
Middle Late Jurassic.

Magnetostratigraphic analysis is used as a dating tool on three deep drilling cores
that penetrate Santonian-Campanian strata in southern Alberta, Canada. Chrons
34n and 33r are clearly identified from the studied sections - providing a high-
resolution age boundary that creates new age boundaries between adjacent
stratigraphic units. In addition, normal polarity zones are observed within C33r,
previously described as reverse polarity over its entire length.

Siberian APWP contains long unresolved segments; therefore, the nature of the
path depends largely on the curve fitting method used. A least square fitting
method computed through singular value decomposition is applied to create the
path. The method is compared to a smoothing cubic spline fitting and to the most
recent version of the Siberian APWP from the literature. For the Mesozoic Era
two possible scenarios are explored.
Acknowledgments

I would like to offer my special thanks to my supervisor Dr. Vadim A.
Kravchisnky. His constant support, constructive suggestions and patient guidance
were fundamental for the development of my Ph.D. I would also like to extend
my thanks to my supervisory committees Dr. Thomas Stachel, Dr. Frank
Hegmann, Dr. Mathieu Dumberry, Dr. Moritz Heimpel and Dr. William Harbert
for their carful and constructive review of my thesis.

Special thanks should be given to the Paleomagnetic group at the University of
Alberta: Ted Evans, Lei Wu and Taslima Anwar, as well to the laboratory
technicians: Luda P. Kuokhar, Len Tober and Lucas Duerkensen, for their support
during my studies. I would also like to thank Dr. Rui Zhang and Prof. Yue Leping
for allow me to contribute to their research and for giving me the opportunity to
visit their laboratories at the Northwestern University in Xi’an, China. In addition,
I would like to extend my gratitude to Andrew J. Mumpy for giving the
opportunity to participate in his research project, which resulted in the
magnetostratigraphy study presented in Chapter 4 of this contribution.

Thanks to the University of Alberta, Department of Physics for open me spaces to
grow as a scientist and as professional. I would like to give special thanks to
Sarah Derr and Dr. Sharon Morsink for their continuous help and support to
graduate students.

This thesis as well as the completion of my studies would not have been possible
without the support of my family and friends. I wish to thanks my parents for
their continuous support in this path I have chosen to take. Without them I would
not be who I am.
Table of Contents

Chapter 1

Introduction

1.1 Geomagnetic Principles ............................................................................. 1
1.1.1 Magnetic Properties of Solids ............................................................... 2
1.1.2 Rock Magnetism ................................................................................... 5
1.2 Earth’s Ancient Magnetic Field ................................................................ 8
1.2.1 Paleomagnetic Principles ....................................................................... 8
1.2.2 Paleomagnetic Methods ......................................................................... 9
1.2.3 Paleointensity and Virtual Dipolar Moment .......................................... 13
1.3 Geochronogical Applications ..................................................................... 18
1.3.1 Geomagnetic Polarity Time Scale ......................................................... 19
1.3.2 Magnetostratigraphy .............................................................................. 20
1.3.3 Dating Using Apparent Polar Wander Paths ......................................... 21
1.4 Construction of Apparent Polar Wander Paths...................................... 22
1.5 Major Goals of the Thesis .......................................................................... 25

Chapter 2

Does the Permo-Triassic geomagnetic dipole low exist?

2.1 Introduction ................................................................................................. 34
2.2 Geological Settings ...................................................................................... 36
2.3 Methodology ................................................................................................ 38
2.3.1 Magnetic Mineralogy ............................................................................ 38
2.3.2 Directions .............................................................................................. 39
2.3.3 Absolute Paleointensity ........................................................................ 39
2.4 Results .......................................................................................................... 43
2.4.1 Thermomagnetic and Hysteresis Measurements ................................... 43
2.4.2 Directions ............................................................................................... 45
2.4.3 Absolute Paleointensity ......................................................................... 50
2.5 Discussion .................................................................................................... 52
2.6 Conclusions .................................................................................................. 55
Chapter 3

Paleomagnetic dating of Phanerozoic kimberlites in Siberia

3.1 Introduction ................................................................................................. 65
3.2 Geological Settings ...................................................................................... 65
3.3 Methods ....................................................................................................... 70
3.3.1 Laboratory Techniques .......................................................................... 70
3.3.2 Paleomagnetic Dating Techniques ........................................................ 71
3.4 Paleomagnetic Results ................................................................................ 72
3.4.1 Rock-Magnetic Properties of the Studied Kimberlites .......................... 71
3.4.2 Kimberlite from the Eastern Udachnaya Pipe ....................................... 75
3.4.3 Sediments Near the Eastern Udachnaya Kimberlite Pipe ...................... 78
3.4.4 Kimberlites from the Western Udachnaya Pipe .................................... 80
3.4.5 Sedimentary Rocks from the Baked Contact of the Western Udachnaya
Kimberlite Pipe ...................................................................................... 82
3.4.6 International Kimberlite Pipe ................................................................ 84
3.4.7 Obnazhennaya Kimberlite Pipe ............................................................. 86
3.5 Discussion .................................................................................................... 88
3.6 Conclusions .................................................................................................. 94

Chapter 4

Upper Cretaceous magnetostratigraphy in Western Canada:
Evidence for normal polarity zones in chron 33r and high
resolution age correlation between stratigraphic units

4.1 Introduction ............................................................................................... 102
4.2 Geological Background ............................................................................ 103
4.2.1 Regional Setting and Stratigraphic Units ............................................ 103
4.2.2 Studied Cores ....................................................................................... 107
4.2.3 Age Control ......................................................................................... 108
4.3 Methodology .............................................................................................. 110
4.4 Results ........................................................................................................ 112
4.4.1 Rock Magnetism Results ..................................................................... 112
4.4.2 Paleomagnetic Results ......................................................................... 113
4.4.3 Magnetostratigraphy ............................................................................ 117
4.5 Discussion .................................................................................................. 122
4.6 Conclusions ................................................................................................ 126
Chapter 5

Revised apparent polar wander path for Siberia during the
Phanerozoic: Application of a new fitting technique

5.1 Introduction ................................................................................................ 136
5.2 Methodology ............................................................................................... 137
5.2.1 Paleomagnetic Data Selection .............................................................. 137
5.2.2 Mathematical Approach ....................................................................... 144
5.3 Results ......................................................................................................... 149
5.3.1 European APWP ................................................................................... 149
5.3.2 APWP for the Siberia Platform ............................................................ 153
5.4 Conclusions and Future Work ................................................................. 158

Chapter 6

Conclusions .................................................................................... 165
List of Tables

Table 1.1. Summary of the remanent magnetizations observed in nature ...... 7

Table 1.2. Summary of the different check applied in thermal paleointensity
measurements .............................................................................. 16

Table 1.3. Statistical parameters to determine the goodness of the
paleointensity determination ........................................................ 17

Table 1.4. Summary of the different methods used in the calculation of APW
paths ……………………………………………………...…… 24

Table 2.1. Late Permian – Early Triassic basalt mean directions of the high
temperature primary stable component of NRM for the Eastern
Siberian traps (Aikhal (66.17°N, 111.33° E), Sytikanskaya
(66.11°N, 111.80°E), Yubileinaya (66.0°N,111.7°E) kimberlite
mine pit areas) and northwestern Noril’sk sill intrusion (69.21°N,
88.03°E). N is the number of directions for specimens or sites
accepted for calculation; D (I) is the declination (inclination) of
the NRM in geographic (g) or stratigraphic (s) system of
coordinates; k, α - precision parameter and half angle radius of
95
the 95% probability confidence cone ….………………………. 49

Table 2.2. Statistical parameters of the paleointensity results. Site:
Nomenclature for each of the studied sites. Class: Category for
each of the samples as defined in the text. ΔT: Temperature range
of the linear segment. Prot: paleointensity protocol applied: ZI,
Coe protocol; IZ, Atkin protocol. B : Applied laboratory
lab
magnetic field. N: Number of successive data points used for
paleointensity calculations. β: measure of linearity (Selkin and
Tauxe, 2000). f, is the fraction of the NRM, as
defined by Coe et al. (1978) and Prévot et al. (1985). MAD:
maximum angular deviation ...................................................... 53
Table 2.3. Paleointensity results. Site: Nomenclature for each of the studied
sites. B±σ : paleointensity result with its associated standard
b
deviation. VDM±σ : Virtual dipolar moment and its associated
VDM
standard deviation ...................................................................... 54

Table 3.1. Site mean paleomagnetic directions for the high temperature
components for the Eastern Udachnaya pipe (66.9°N, 112.5°E);
the Western Udachnaya pipe (66.9°N, 112.5°E); and the host
sediments and sediments from the baked contact
zone …………………………………………………................. 77

Table 3.2. Paleomagnetic high temperature components mean directions for
the International Pipe (62.4°N, 113.7°E) and the Obnazhennaya
Pipe (70.5°N, 120.5°E) ............................................................... 86

Table 3.3. Paleomagnetic poles and estimated ages for the studied pipes. Lat
(Long): Latitude (Longitude) of the sampling sites of
paleomagnetic pole. dp/dm: semi-axes of the oval of 95%
confidence of the paleomagnetic pole; A : radius of the
95
95% confidence circle ................................................................. 91

Table 5.1. Selected paleomagnetic poles for Siberian platform and their
reliability. Selected paleomagnetic poles for Siberian platform.
Formation – Geological formation name were sample was
acquired, B(N) – number of sites (poles) included in the statistics,
Mean Age – age in Ma. Q – classification factor due to Van der
Voo (1993) (7 is the best score) Pole Lat (Long) – Paleomagnetic
pole latitude (longitude), dp/dm – semi-axes of the confidence
cone of the paleomagnetic pole, Site Lat (Long) – sampling site
coordinates. Ref – Reference..……………………………....... 141
List of Figures

Figure 1.1. The geomagnetic field can be described by total magnitude (H),
declination (D) and inclination (I) ............................................................... 1

Figure 1.2. Present magnetic field of the Earth .................................................. 2

Figure 1.3. Magnetization (M) versus applied field (H) for a diamagnetic
material......................................................................................................... 3

Figure 1.4. Magnetization (M) versus applied field (H) for a paramagnetic
material ........................................................................................................ 4

Figure 1.5. a) M versus H plot for a ferromagnetic material. M represents the
s
magnetization of saturation. b) Categories for spin alignment. AFM:
antiferromagnetism. Modified from Dunlop and Özdemir (2007) ………. 5

Figure 1.6. a. Single domain spherical particle. Surface charges are shown by the
plus and minus signs. b. Multidomain spherical particle. Region separating
the domains are known as domain walls. Modified from Butler
(1992)……………………………………………………………………... 6

Figure 1.7. Magnetic flux lines produced by a geomagnetic axial dipole ........... 8

Figure 1.8. Principles of spherical geometry are applied to determine the
geomagnetic pole position P from magnetic field directions measured at S.
S is the site location and has latitude λ and a longitude φ and D and I as
s s
magnetic field mean directions.; M is the geomagnetic dipole that creates
the observed magnetic field directions; P is the magnetic pole position at λ
p
and φ ; p is the magnetic colatitude; N is the geographic north pole; β is the
p
difference in longitude between the P and S. Modified from Tauxe
(2002)…………………………………………………………………….. 11