EVOLUTION OF THE GALAPAGOS RISE AND THE BAUER MICROPLATE: IMPLICATIONS FOR THE NAZCA PLATE A Dissertation by JENNIFER CATHERINE MCGUIRE WRIGHT Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY December 2004 Major Subject: Geophysics EVOLUTION OF THE GALAPAGOS RISE AND THE BAUER MICROPLATE: IMPLICATIONS FOR THE NAZCA PLATE A Dissertation by JENNIFER CATHERINE MCGUIRE WRIGHT Submitted to Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved as to style and content by: ___________________________ ___________________________ Thomas W.C. Hilde Mark E. Everett (Chair of Committee) (Member) ___________________________ ___________________________ David Sparks William W. Sager (Member) (Member) ___________________________ ___________________________ William R. Bryant Richard L. Carlson (Member) (Head of Department) December 2004 Major Subject: Geophysics iii ABSTRACT Evolution of the Galapagos Rise and the Bauer Microplate: Implications for the Nazca Plate. (December 2004) Jennifer Catherine McGuire Wright, B.S., State University of New York at Stony Brook Chair of Advisory Committee: Dr. Thomas W.C. Hilde Analysis of the satellite altimetry based predicted bathymetry, magnetic anomalies, and earthquake seismic data relating to the geophysical structure on the Nazca plate indicates that the Galapagos Rise system served as the transitional spreading system between Pacific-Farallon spreading and the current East Pacific Rise (EPR) system. First order age/depth relationships for this area indicate that the Galapagos Rise, the most prominent extinct spreading system within the Nazca plate, accommodated most of the Pacific-Nazca plate separation from ~23 million years ago (Ma) to ~8 Ma. After this time, spreading was dominantly along the EPR, with probable ultra slow spreading along the Galapagos Rise continuing until very recent times (0-5 Ma). Magnetic lineations and depth trends across the Bauer Basin suggest that it was captured between the failing Galapagos Rise and the currently active EPR. Anomalously shallow ridge crests along the Galapagos Rise indicate that magmatic activity may have occurred iv until very recent time (0-5 Ma). Tightly curved (concave southward) fracture zones offsetting Galapagos Rise ridge segments indicate a pole of rotation at the present day position of ~22.5°S and ~99.5°W. The curvature of the fracture zones and the fan-shaped spreading pattern of seafloor structures produced at the Galapagos Rise indicate that the Galapagos Rise initiated parallel to the Mendaña fracture zone. Consistent with the rotation of the Nazca plate after the fragmentation of the Farallon plate, the Galapagos Rise rotated counter- clockwise during its active phase. The Galapagos Rise initiated in the vicinity of Gallego fracture zones and propagated southward. Failure of the Galapagos Rise occurred as spreading jumped westward in stages to the East Pacific Rise. v DEDICATION This work is dedicated to my family, for their constant encouragement and belief in my success, and to my son, whose smile inspires me. vi ACKNOWLEDGMENTS I would like to sincerely thank Dr. Thomas Hilde for his support and guidance during my pursuit of my graduate degree. I greatly appreciate his contributions to my research and my professional development. In addition, I would like to thank Dr. Mark Everett for his continual assistance and interest in my development as a scientist. I have benefited from their enthusiasm, advice, and support in my research pursuits. Thanks are also due to Drs. David Sparks and William Sager, who provided a great deal of help in the form of critical review, and Dr. Gary Acton for his contribution and support in the operation of the magnetic anomaly modeling program. Most important of all, I would like to thank my family for their unending support in all phases of my professional career and personal life. Most especially my parents, John Edward McGuire Sr. and Catherine Dolores McGuire, and my brother, John Edward McGuire, Jr., always show their confidence in my abilities and faith in my success. My husband, Granville Clay Wright, Jr., believes in me and supports me in more ways than I can count. My son, Granville Clay Wright IV, inspires me to always strive for the better. Without the love of my family, this work would not have been possible. vii TABLE OF CONTENTS Page ABSTRACT ............................................................................................ iii DEDICATION ......................................................................................... v ACKNOWLEDGMENTS ......................................................................... vi TABLE OF CONTENTS.......................................................................... vii LIST OF TABLES ................................................................................... ix LIST OF FIGURES ................................................................................. x INTRODUCTION .................................................................................... 1 GEOLOGIC SETTING ............................................................................ 9 The Nazca Plate .......................................................................... 9 Previous Galapagos Rise Reconstructions.................................. 13 DATA AND METHODS........................................................................... 22 NGDC Ship track Bathymetry and Magnetic Anomaly Data......... 23 Predicted Bathymetry................................................................... 33 Seafloor Fabric............................................................................. 36 Earthquakes................................................................................. 42 Euler Poles................................................................................... 46 Reconstructions ........................................................................... 49 ANALYSIS ............................................................................................. 52 Age/Depth Relationships ............................................................. 52 Bathymetry and Seafloor Structure .............................................. 55 Seafloor Fabric............................................................................. 70 Magnetic Anomalies..................................................................... 73 Reconstructions ........................................................................... 82 The 23 Million Years Reconstruction ........................................... 83 The 19.5 Million Years Reconstruction ........................................ 91 The 14.7 Million Years Reconstruction ........................................ 94 The 9.5 Million Years Reconstruction .......................................... 95 The 5.9 Million Years Reconstruction .......................................... 96 viii Page The Present Day ......................................................................... 97 DISCUSSION ........................................................................................ 99 CONCLUSIONS .................................................................................... 106 REFERENCES ...................................................................................... 110 VITA ....................................................................................................... 117 ix LIST OF TABLES Table Page 1 Identification numbers and source institutions of bathymetric and magnetic for ship track data obtained from the NGDC and used in this study....................................................................... 25 2 List of parameters used to calculate synthetic magnetic anomaly profile.......................................................................... 32 3 List of parameters used in the tectonic reconstruction program..................................................................................... 51 x LIST OF FIGURES Figure Page 1 Location map of study area illustrating locations of significant morpho-tectonic features........................................................... 2 2 Predicted bathymetry [Smith and Sandwell, 1997] map illustrating depth variation within the study area........................ 4 3 Magnetic anomaly lineations in the study area adapted from Herron [1972]. ................................................................... 11 4 Reconstruction of the Galapagos Rise system adapted from Mammerickx et al. [1980]. ......................................................... 16 5 Reconstruction of the Galapagos Rise system adapted from Lonsdale [1989]......................................................................... 18 6 Reconstruction of the Galapagos Rise system adapted from Goff and Cochran [1996]. .......................................................... 19 7 Map illustrating coverage of ship track bathymetry and magnetic anomaly data in the study area.................................. 24 8 Synthetic model of the total field magnetic reversal sequence.. 31 9 Comparison of ship track bathymetry locations from the R/V Yaquina cruise (1971) obtained from the NGDC plotted verses the same locations from the Smith and Sandwell (1997) predicted bathymetry grid.......................................................... 35 10 Comparison of independent ship track bathymetry and predicted bathymetry extracted