Download Cenozoic tectonic development of the Southwest Pacific

UNITED NATIONS ECONOMIC AND SOCIAL COMMISSION FOR
ASIA AND THE PACIFIC
COMMITTEE FOR CO-ORDINATION OF JOINT
PROSPECTING
FOR MINERAL RESOURCES IN SOUTH PACIFIC
OFFSHORE AREAS (CCOP/SOPAC)
TECHNICAL BULLETIN
No.6
CENOZOIC
TECTONIC DEVELOPMENT
OF THE
SOUTHWEST PACIFIC
by
LOREN w. KROENKE Hawaii
Institute of Geophysics Honolulu,
Hawaii
with a contribution
by
PETER RODDA
Mineral Resources Department, Suva, Fiji
All communications relating to this and other publications of
CCOP/SOPAC should be addressed to:
Technical Secretariat of
CCOP/SOPAC c/o Mineral Resources
Department, Private Bag, Suva, Fiji
This publication should be referred to as
U.N. ESCAP, CCOP/SOPAC Tech. Bull. 6
The designations employed and presentation of the material in this publication do not imply the
expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning
the legal status of any country or territory or of its authorities, or concerning the delimitation of the
frontiers of any country or territory.
Cataloguing in Publication
KROENKE, Loren W.
Cenozoic tectonic development of the
southwest Pacific I by Loren W. Kroenke
with a contribution by Peter Rodda. Suva: CCOP/SOPAC, 1984.
(Technical bulletin / United Nations
Economic and Social Commission for
Asia and the Pacific, Committee for Coordination of Joint Prospecting
for Mineral Resources in South Pacific
Offshore Areas, ISSN 0378-6447 : 6)
ISBN 0-477-06738-7
I. Kroenke, Loren W. II. Rodda, Peter
III. Series
UDC 551.24(265.7):551.77
The publication of this Technical Bulletin was made possible by the Australian Development
Assistance Bureau, who provided funds for printing.
Printed in New Zealand 1984
FOREWORD
The Cenozoic development of the Southwest Pacific is, in a very real sense, the continuing
development of the eastern margin of Gondwana, following its major dismemberment in the midCretaceous. In the Palaeocene, what had been the earlier eastern margin was now an oceanic
entity, most of it submerged. It consisted of what we know today as the Lord Howe Rise and the
Rennell-New Caledonia-Norfolk Ridge (the Inner Melanesian Arc system). By the early Miocene
an outer system of island arcs had developed (the Outer Melanesian Arcs) bordering the inner
system, bu' separated from it by a great marginal sea. Toward the Pliocene, convergence between
this expulding portion of the Indo-Australia Plate and the Pacific Plate had become increasingly
west-oriented; as the Indo-Australian/Pacific pole moved southward. This meant a
correspondingly increased strike-slip component of motion along the northern boundary (between
New Guinea and Tonga) and, this in turn, had brought about a glancing collision with that greater
submerged body, the Ontong Java Plateau. Subduction was initiated along the northern boundary.
The New Hebrides Arc swung away to the southwest, hinged on Santa Cruz, leaving the North
Fiji Basin in its wake; the great marginal sea was thus effectively split and greatly reduced in area.
As subduction flip progressed to the west, subduction plunge was to the north below the Solomon
Islands, and the Bismarck Archipelago was rent by great east-west strike-slip faults. Today,
maximum convergence occurs along the Tonga-Kermadec line, the South Fiji Basin is probably
expanding with outward migration of the Tonga-Kermadec Arc, the northern boundary is growing
as the Melanesian Borderlands and Ontong Java Plateau continue to move westwards.
This thumbnail sketch omits companion events in the New Guinea and New Zealand areas. As
a scenario, 20 years ago, it would have been not only incomprehensible to the interested reader
but nonsensical, smacking of the arcane and written in a cult-terminology. Today, the reasonably
informed geologist would read this scenario as a straightforward story of the continuing
interaction between the Indo-Australia, Pacific and Antarctic Plates over the last 70-odd million
years; the interaction would be explained in terms of the shifting poles of rotation of those plates.
Thirty years ago, even the geography, with its plethora of exotic names, would have seemed
quite as mysterious to nearly all readers. I know this from experience. In the early 1950s I had a
reply-paid telegram asking if I would join a University of Sydney expedition to the Solomon
Islands. I answered "Yes" and then went to an atlas to find out just where were the Solomons.
This first visit was followed by others, working in collaboration with Richard Stanton of the
University of New England, and John Grover, the founder of the Solomons Geological Survey.
Grover was an enthusiast with a global view. He delighted in welcoming George Woollard and his
crew, in their pioneer marine work in the Solomons region. One of the crew was Loren Kroenke
and one of the major results of that early work was Kroenke's delineation of that great submarine
enigma, the Ontong Java Plateau. Loren extended his interest beyond the Ontong Java. As UNDP
Marine Geologist for CCOP/SOPAC with headquarters in Suva, Fiji, he carried out original
research and organised a set of extremely fruitful seminar-workshops which are still in motion
today. He was the prime mover in accelerating multi-national research in the Southwest Pacific.
He had retained his position with Hawaii Institute of Geophysics and in this dual role he became a
kind of focus for earth science matters and materials to do with the Southwest Pacific. No other
person is in as favourable a position or is better qualified to attempt a summary of the Cenozoic
geotectonic history of this novel region.
A summary is most opportune just now. The Southwest Pacific canvas was becoming cluttered
and messy with isolated packets of data and it badly needed reorganisation. Loren Kroenke has
done this with skill and with energy. The result is this Bulletin. It is more than simply a
compilation of his own and other people's data; it contains brand-new information
and a number of new ideas. The Tertiary history of Papua New Guinea, for example, is
reinterpreted in an exciting, and challenging, way. The role of the Ontong Java Plateau is given
fresh and increased importance. Much if what is said has implications beyond merely the
Southwest Pacific region, large though that is. In our discussions, Loren and I have agreed that the
Southwest Pacific will prove to be an appropriate testing ground for refinement of plate tectonics
theory. The material in this Bulletin demonstrates this notion very well and supplies major
contributions in favour of subduction flipping, splitting of arcs, the importance of strikeslip
components in subduction, the effects of the style of subduction on the genesis of arc rocks, the
roles of allochthonous terrains and, even, the "oceanisation" of rifted cratonic slices. In addition to
its considerable theoretical significance it has strong economic implications, important to the
countries within the region. To name just the one example: for searchers after porphyry copper
deposits this Bulletin is mandatory reading. In writing this Bulletin, besides the manifest
contribution to the geology of the Southwest Pacific, Kroenke has done great service to its
developing countries.
Patrick J. Coleman University of
Western Australia Perth
PREFACE
Between mid-l 980 and mid-1981 the writer, working for the Committee for Co-Ordination of
Joint Prospecting for Mineral Resources in South Pacific Offshore Areas (CCOP/SOPAC), was
privileged to visit numerous South Pacific countries to compile as much information as possible
on the geological framework of the region. This information would provide the background for
future studies of the economic mineral potential in the region. The specific goal was to make a
systematic tectonic analysis of the Southwest Pacific and to describe structural elements, country
by country, in the context of geological evolution and tectonic development. Toward this end, area
reports were prepared on the regional geology and tectonics of CCOP/SOPAC member countries
situated along or near zones of convergence between the Indo-Australia and Pacific Plates. The
chapters that follow, which comprise the original reports and collectively constitute a synthesis of
Cenozoic tectonism in the Southwest Pacific, also form a companion text to charts of the
Bathymetry and Tectonic Elements of the Southwest Pacific (Charts 1 and 2 of the CCOP/SOPAC
Geophysical Atlas of the Southwest Pacific).
Preparation of the original reports was made possible by the co-operation and assistance of
CCOP/SOPAC member country representatives and officials, particularly at geological surveys in
Fiji, Papua New Guinea, Solomon Islands, Tonga, and Vanuatu, who provided access to
government technical reports and data on open file. In addition, the writer benefited from
stimulating discussions with colleagues at the Bureau of Mineral Resources, Australian National
University, University of Sydney, and University of Western Australia in Australia; Office de la
Recherche Scientifique et Technique Outre-Mer (ORSTOM) in New Caledonia; New Zealand
Oceanographic Institute (NZOI) in New Zealand; Hawaii Institute of Geophysics of the
University of Hawaii (HIG); and the Technical Secretariat Office in Suva, Fiji. In particular I
thank P.J. Coleman, H.L. Davies, P. Dunkley, J.V. Eade, D.A. Falvey, KB. Lewis, I. McDougall,
G.H. Packham, J. Recy, P. Rodda, and D. Woodhall for thought provoking sessions.
I deeply appreciate the efforts of N.F. Exon and D.L. Tiffin in critically reading early versions
of the manuscript and gratefully acknowledge P.J. Coleman and W.T. Coulbourn for critically
reviewing the final manuscript. For discerning· comments on various chapters I thankK
Anscombe,J.N. Carney, F. Coulson,J. Daniel,J.V. Eade,A.L. Jaques, R.W.Johnson, C. Jouannic,
H.R Katz, A. Macfarlane, J. Recy, J.M. Resig, P. Symonds, and B. Taylor. I am especially
indebted to T. Israel, M. Lee-Joe, and E. Morris for typing the numerous early versions of the
manuscript, and to E. Morris for typing the many "final" drafts. I deeply appreciate the editorial
advice and assistance provided by R Pujaletand D. Baysa. The efforts of R. Rhodes, M. Prins, J.
Holas-Simmons, and C. Yamauchi in the preparation and revision of illustrations are also
gratefully acknowledged, as are those of C. Meyers in photographing the art work. Finally, I
particularly thank RM. Thompson for the final copyediting of the manuscript and for liaison with
the printer.
Field work was funded by the United Nations Economic and Social Commission for Asia and
the Pacific (ESCAP) under Project RAS/79/074. Supplemental support for manuscript preparation
and graphics was provided by the University of Hawaii. This is contribution 1496 of the Hawaii
Institute of Geophysics.
Loren W. Kroenke University of
Hawaii at Manoa Honolulu
CONTENTS
Page
FOREWORD
iii
PREFACE
v
Chapter 1
Introduction
1
Chapter 2
New Caledonia: The Norfolk and Loyalty Ridges; The New Caledonia
and Loyalty Basins
15
Chapter 3
Papua New Guinea: A Montage of Island Arcs
29
Chapter 4
The Solomon Islands: San Cristobal to Bougainville and Buka
47
Chapter 5
Vanuatu and the Eastern Outer Solomon Islands: Formation of the
New Hebrides and Vitiaz Arcs and Development of the North Fiji
Basin
63
Chapter 6
Tonga: The Tonga Ridge and Trench; The Lau Ridge and Trough
77
Chapter 7
Fiji: A Fragmented Arc (by Peter Rodda and Loren W. Kroenke)
87
Chapter 8
A Southwest Pacific Regional Synthesis : Migration of the Indo-Australia/Pacific Plate Boundary During the Cenozoic Era
111