(Farallon) plates since 30 million years ago

106 Pages·2015·5.37 MB·English

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Graduate Theses and Dissertations Graduate School
7-18-2003
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Douglas T. Wilder
University of South Florida
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SScchhoollaarr CCoommmmoonnss CCiittaattiioonn
Wilder, Douglas T., "Relative Motion History of the Pacific-Nazca (Farallon) Plates since 30 Million Years
Ago" (2003). Graduate Theses and Dissertations.
https://scholarcommons.usf.edu/etd/1506
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RELATIVE MOTION HISTORY OF THE PACIFIC-NAZCA (FARALLON) PLATES
SINCE 30 MILLION YEARS AGO

by

DOUGLAS T. WILDER

A thesis submitted in partial fulfillment
of the requirements for the degree of
Master of Science
College of Marine Science
University of South Florida

Co-Major Professor: David F. Naar, Ph.D.
Co-Major Professor: Sarah F. Tebbens, Ph.D.
Sarah E. Kruse, Ph.D.

Date of Approval:
July 18, 2003

Keywords: marine geology and geophysics, tectonics, seafloor spreading,
magnetic anomaly

© Copyright 2003, Douglas T. Wilder
Dedication
Humbly, to Yvonne and Maeve who endured for me.
Acknowledgments

This work would not have been possible without the guidance, patience,
dedication, support and enthusiasm provided throughout every phase of this research by
my advisor Dr. David F. Naar. I am extremely grateful to him for providing me the
opportunity to conduct this research and complete my degree. Special thanks also to Dr.
Sarah F. Tebbens, my co-major professor, who provided invaluable assistance during the
course of this study beginning with initial data acquisition from Lamont-Doherty and
including revision of programs used for finite and stage pole calculations. Thanks also to
Dr. Sarah E. Kruse, my third committee member, who was extremely helpful at several
points during completion of this work and helped immensely in tightening up the text for
the final draft.
There are many others who provided help or otherwise offered support that
contributed to the successful completion of this work. Ruoying He provided
programming expertise in the early stages of the work. Doug Myhre committed a great
deal of time rewriting the MagBath program in Java and was always there to troubleshoot
a myriad of computing problems. Dr. Mark Hafen was instrumental in getting me
acquainted with the labs and procedures of the department (now college). William Self
offered sight-unseen mathematical assistance from somewhere in cyberspace. Special
thanks also to the following for comments and scientific assistance: Dr. Steve Cande, Dr.
Yasushi Harada, Dr. Paul Wessel, Dr. Tanya Atwater, Dr. David Sandwell, Dr. Ben
Horner-Johnson, Dr. Walter H. F. Smith, Dr. R. Dietmar Müller, Dr. Robert Detenbeck,
and Dr. Dawn Wright. The National Science Foundation provided funds that allowed
this work to occur.
Crucial administrative support that made graduation possible was provided by
Barb Daugherty, Nadina Piehl and Flo Cole. Janet R. Giles, of the graduate school office,
provided cheerful help with finalizing and submitting this document for graduation. Dr.
Ted VanVleet was especially helpful as the graduate coordinator for the college and
provided special attention for me on several occasions. As my employer for much of the
time I worked on this thesis, Henry Norris exhibited encouragement and flexibility that
allowed me to pursue this work. My co-worker, Jim Burd, provided invaluable
encouragement and prodding near the completion of this work. Finally, this work was
greatly facilitated by the moral support of Michelle McIntyre, my comrade in arms, who
lent encouraging words and an open ear along the way.
Table of Contents

List of Tables iii

List of Figures iv

Abstract vi

Chapter 1 Introduction 1

Chapter 2 Methods 7
Data 7
Anomaly Identification 7
Finite and Stage Poles 9
Reconstruction 14

Chapter 3 Results 16
Magnetic Anomaly Identifications 16
Spreading Rates 16
Asymmetrical Spreading 25
Anomaly Juxtapositions 26
Finite Poles 27
Stage Poles 29
Tectonic Reconstructions 30
Chron 10y 30
Chron 7y 37
Chron 6c 37
Chron 5d 37
Chron 5b 38
Chron 5aa 38
Chron 5o 39
Chron 4a 39
Chron 3a 39
Present 40

Chapter 4 Discussion 41

Chapter 5 Conclusions 47

References 49
i
Appendices 53
Appendix A: Data File Information 54
Appendix B: 2D Magnetic Modeling 58

ii
List of Tables

Table 1. Calculated finite poles for PAC-NAZ. 13

Table 2. Covariance matrices for finite poles calculated in this study. 14

Table 3. Stage poles calculated from finite poles. 14

iii
List of Figures

Figure 1. General tectonic setting of southeast Pacific. 3

Figure 2. Cruises used in 2D magnetic modeling. 8

Figure 3. Synthetic magnetic anomaly model and magnetic timescale
of Cande and Kent (1995) used in this study. 10

Figure 4. Magnetic profiles for cruises CATO4c (A) and EEL29d (B). 11

Figure 5. Magnetic data used in this study. 12

Figure 6. Interpreted magnetic isochrons. 17

Figure 7a. Grey-shade predicted bathymetry, magnetic data,
interpreted tectonic lineations (blue lines) and volcanics
(red hachures) with anomaly picks used to calculate finite
poles for panel A. 18

Figure 7b. Detail of data for panel B. 19
Figure 7c. Detail of data for panel C. 20

Figure 7d. Detail of data for panel D. 21

Figure 7e. Detail of data for panel E. 22

Figure 7f. Detail of data for panel F. 23

Figure 8. Full-spreading rates calculated along estimated flowlines
for Pacific-Nazca spreading. 24

Figure 9. Spreading asymmetry calculated from spreading rates
(Figures 8). 25

Figure 10. Finite pole comparisons. 28

Figure 11. Stage poles for Pacific-Nazca relative motion. 29

iv
Figure 12. Full spreading rate vectors compared to interpreted tectonic
features and predicted bathymetry. 31

Figure 13. Tectonic reconstruction for chrons 10y (grey) (A) and
7y (olive) (B). 32

Figure 14. Tectonic reconstruction for chrons 6c (lt. red) (A) and
5d (red) (B). 33

Figure 15. Tectonic reconstruction for chrons 5b (orange) (A) and
5aa (lavender) (B). 34

Figure 16. Tectonic reconstruction for chrons 5o (purple) (A) and
4a (green) (B). 35

Figure 17. Tectonic reconstruction for chrons 3a (lt. blue) (A) and
5d (lt. purple) (B). 36

v