ISSN 2538-1016; 30 NEW ZEALAND DEPARTMENT OF' SCIENTIFIC AND_ INDUSTRIALI RESEARCH BULLETIN 170 GEOLOGY AND ·GEOMAGNETISM OF THE BOUNTY REGION EAST OF THE SOUTH ·ISLAND, N�W ZEALAND ( ( by DALE C. KRAUSE .. New Zealand Oceanographic Institute Memoir No. 30 1966 GEOLOGY AND GEOMAGNETISM OF THE BOUNTY REGION EAST OF THE SOUTH ISLAND, NEW ZEALAND This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ tr - ,1. __ l ,,, . � Photo, E. J. Thorn/Pt' MV Taranui in Wellington Harbour. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ NEW ZEALAND DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH BULLETIN 170 GEOLOGY AND GEOMAGNETISM OF THE BOUNTY REGION EAST OF THE SOUTH ISLAND, NEW ZEALAND by DALE C. KRAUSE New Zealand Oceanographic Institute Memoir No. 30 Price: 1 s. 6d. (S1.75) 1966 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ This publication should be referred to as: N.Z. Dep. sci. industr. Res. Bull. 170 CROWN COPYRIGHT R. E. OWEN', GOVER. "'.!ENT PRINTER, WELLINGTON, NEW ZEALAND-1966 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ CONTENTS Paa• FOREWORD 7 ABSTRACT 9 INTRODUCTION 9 BATHYMETRY - SOURCES OF INFORMATION 11 ' '. REGIONAL DESCRIPTION 11 Hikurangi Trench 11 North Chatham Slope 12 . Chatham Ri�e 16 Urry Bank 16 Bounty Trough 16 · · Channels of the Bounty Trough 16 · Bounty Islands 17 Tasman Sea (West Coast) 17 INTERPRETATION OF THE BATHYMETRY 18 Implications of the Channels 18 Interpretation of Lower Platform of Bounty Trough 18 Geologic Structure 19 Geologic History 20 EARTHQUAKES 20 GEOMAGNETIC RESULTS 23 INTERPRETATION OF GEOMAGNETIC DATA 26 REGIONAL GEOMAGNETIC PATTERN 27 ORIGIN OF THE BOUNTY TROUGH 27 ACKNOWLEDGMENTS .. 30 REFERENCES 31 INDEX .. 32 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ FIGURES Page Frontispiece: M.V. Taranui. 1. Locations of bathymetric profiles across Bounty Trough region 12 2. Bathymetric profiles across region 13 3. Profile of MernooBank 13 4. Profile of a Veryan Channel .. 14 5. Profile across submarine canyons east of the Otago Peninsula 14 6. Profile across canyons of the Canterbury Bight .. 14 7. Profile across North Channel 15 8. Profile across North Channel 15 9. Profile across the northern part of eastern end of the Bounty Trough 15 10. Bathymetric and magnetic profiles of RV Verna 17 11. Structural interpretation of the Bounty Trough .. 19 12. Distribution of earthquake epicentres .. 21 13. Distribution of earthquake energy 22 14. Magnetic profiles of the Bounty Trough 23 15. Alternative magnetic contours of the central Bounty Trough 24 16. Theoretical anomaly of a dyke and the recorded magnetic anomaly 25 17. Magnetic and bathymetric profiles showing spatial correlation 26 18. Regional magnetic pattern around southern New Zealand 28 CHARTS (in pocket) N.Z. Oceanographic Institute Chart 1: 1,000,000 Oceanic Series, Bathymetry, Bounty Sheet, 1963. Bounty Trough, Magnetic Field, Total Intensity and Anomalies. N.Z. Oceanographic Institute Chart, Miscellaneous Series No. 8. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ FOREWORD Over the past few years there has been a notable increase in the amount of mag­ netic data from measurements of the earth's field in the New Zealand region. Much of this has arisen from work carried out by Geophysics Division, D.S.I.R., com­ prising individual traverses in the near-shore region fromships operating with towed magnetometers. The study reported represents the first occasion on which a close survey of a re­ latively extensive oceanic area in the vicinity of New Zealand has been carried out using this technique. The results, as well as throwing light on the near-surface physi­ cal properties of the earth's crust in this region, give an indication of the results likely to be expected from extensions of this technique to other areas around our coasts. In this memoir Dr Krause has considered the correlations between the magnetic data and the sea-floor morphology and structure in an area that is of fundamental interest in problems of New Zealand structural geology. The manuscript for this memoir has been prepared for publication by Mrs P. M. Cullen. J. W. BRODIE, Director, New Zealand Oceanographic Institute, Wellington. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ GEOLOGY AND GEOMAGNETISM OF THE BOUNTY REGION, EAST OF THE SOUTH ISLAND, NEW ZEALAND ABSTRACT THE ocean floor east of South Island, New Zealand, is a sub-continental region of predominantly east-west trend dominated by the Chatham Rise on the north and the Bounty Trough, which lies between the rise and the Campbell Plateau to the south. At least three banks exist on the rise. A system of submarine channels arises at the head of the Bounty Trough mainly as submarine canyons in the continental shelf and slope of south-east South Island. These channels coalesce to form a single channel that runs the length of the trough. At least three moderate-sized submarine canyons occur offthe west coast of South Island. A geanticline trending north constricts the trough and is marked by the Mernoo Bank on the rise. The distribution pattern of earthquake epicentres shows northerly and easterly trends superimposed on the regional north-easterly structural trend of New Zealand for the north and north-west part of the area where information is available. A magnetometer survey of part of the Bounty Trough revealed three features: (I) an intense, long arcuate magnetic anomaly with associated anomalies in the western part of the trough, (2) a low but persistent negative anomaly trending east in the eastern part of the trough, associated with local, intense anomalies and (3) wide­ spread, low, ill-defined anomalies. The arcuate anomaly can be caused by a deep-seated highly magnetic in­ trusion piercing the lower levels of the crust. East-trending faults can be associated with this intrusion. The eastern anomaly can be caused by basement faulting with some local intrusions. The widespread, ill defined anomalies were too small to be adequately defined by the survey. Magnetic profiles around New Zealand reveal several geomagnetic provinces in the sea floor: the Bounty Trough; the deep ocean floor characterised by large broad anomalies; the Macquarie Ridge characterised by intense, highly variable anomalies; the Campbell Plateau with numerous anomalies ranging from very large and extensive to intense but local; and lastly, the following with no or very local anomalies - Chatham Rise, the sea floor immediately flanking most of South Island and some of the Campbell Plateau, and Lord Howe Rise. The last two regions are probably areas of very thick sediments. The areas with widespread anoma­ lies may be composed of relatively shallow, structurally complex crystalline basement rocks and of igneous intrusions. Large changes in depth in the Bounty Region have occurred, probably mostly in Mesozoic time. The Chatham Rise and the Bounty Islands were uplifted near or above sea level, leaving the Bounty Trough as a relatively depressed region. Late Cenozoic movements have continued the trend. The ages of most of the faults, folds, and intrusions are unknown, but probably many formed in the earlier deformation and were reactivated in late Cenozoic time. Althoughthe channels and certain other bathymetric features indicate recent geological changes and deformation, the area is thought to have been stable (relative to continental New Zealand) through most of Tertiary time. INTRODUCTION From 23 January to 7 February 1962, a bathy­ geomagnetic surveys of the sea floor off New metric-geomagnetic survey was made of the Zealand. Joint investigations had been agreed Bounty Trough (bathymetric chart in pocket) on upon and thus the stage was set to undertake the the New Zealand Oceanographic InstituteTaranui. cruise, study when the author joined the New Zealand Magnet I aboard the chartered vessel MV Oceanographic Institute for a year under a post­ The cruise was undertaken by the New Zealand doctoral fellowship of the U.S. National Science Oceanographic Institute and the Geophysical Foundation in 1961. Survey of the New Zealand Department of Scien­ The objectives of the cruise were threefold: tific and IndustrialD. Research.N. Scientific M. personnel 1. To survey a major geological feature using consisted of: C.N.Z. Krause, Ridgway, and the proton magnetometer. A. Langford of R. B.Oceanographic Institute; 2. To obtain soundings over this relatively un­ X L. Roberts and Williams of Geophysical known area. Survey. 3. To test the existence of a possible east The cruise grew out of discussions regarding the trending, geological structure in the south importance and necessity of undertaking detailed Pacific (Menard, 1958). 9 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ The time and facilities available dictated the The first published geomagnetic data of '-e scope of the investigation.