Continental and Oceanic Rifts

316 Pages·6.755 MB·English

Continental and
Oceanic
Geodynamics Series
Inter-Union Commission on Geodynamics
Editorial Board
A. L. Hales, Chairman
R. D. Russell, Secretary
O. L. Anderson
F. M. Delany
C. L. Drake
J. Sutton
American Geophysical Union/Geological Society of America
Editorial Board
Kees Dejong
C. L. Drake
D. H. Eckhardt
E. Irving
W. I. Rose
Rob Van der Voo
The Final Reports of the International Geodynamics Program sponsored
by the Inter-Union Commission on
Geodynamics
Geodynamic Series
The Final Reportso f the International Geodynamics Program sponsored by the
Inter-Union Commission on Geodynamics
Dynamics of Plate Interiors
A. W. Bally, P.L . Bender, T.R . McGetchin, and R.I . Walcott (Editors)
2 Paleoreconstruction of the Continents
M.W. McEIhinny and D.A. Valencio (Editors)
3 Zagros ßH indu Kush' Himalaya Geodynamic Evolution
H. K. Gupta and F. M. Delany (Editors)
4 Anelasticity in the Earth
F.D . Stacey, M. S. Patterson,a nd A. Nicholas (Editors)
5 Evolution of the Earth
R.J. O'Connell and W. S. Fyfe (Editors)
6 Dynamics of Passive Margins
R.A . Scrutton [Editor]
7 Alpine-Mediterranean Geodynamics
H. Berckhemer and K. Hs(]
Continental
and
Oceanic Rifts
Edited by G. P(cid:127)lmason
Geodynamics Series
Volume 8
American Geophysical Union
Washington, D.C.
Geological Society of America
Boulder, Colorado
Final Report of Working Group 4, Continental and Oceanic
Rifts, coordinated by G. Palmason on behalf of the Bureau
of Inter-Union Commission on Geodynamics
American Geophysical Union, 2000 Florida Avenue, N .W.
Washington, D.C. 20009
Geological Society of America, 3300 Penrose Place, P.O. Box 9140
Boulder, Colorado 80301
Library of Congress Cataloging in Publication Data
Inter-Union Commission on Geodynamics. Working Group 4.
Continental and oceanic rifts.
(Geodynamics series; v. 8)
Includes bibliographies.
1. Rifts (Geology)--Addresses, essays, lectures.
I. Palmason, Gudmunder. II. Title. III. Series.
QE606 .I57 1982 551 .8 '7 82-3991
ISBN 0-87590-504-8 AACR2
Copyright 1982 by the American Geophysical Union,
2000 Florida Avenue, N .W., Washington, D.C. 20009
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First Printing: 1982
Second Printing: 1985
Printed in the United States of
CONTENTS
Foreword
A. L. Hales and C. L. Drake
Preface
G. P(cid:127)lmason
History of Rift Studies
C. L. Drake and R. W. Girdler
Recent Ground Deformation in Continental and Oceanic Rift Zones 17
E. Tryggvason
The Role of Shear in Rifting 31
R. Freund
The Seismicity of the East African Rift Systema nd ComparisonW ith Other 41
Continental Rifts
J. D. Fairhead and G. W. Stuart
Seismicity of Oceanic Rifts 63
R. C. Lilwall
Seismic Structure of the Lithosphere in Rift Zones 81
K. Fuchs
Gravity Anomalies Over Oceanic Rifts 99
A. B. Watts
Heat Flow in Rift Zones 107
P. Morgan
Physical Aspects of Hydrothermal Systems 123
V. Stefdnsson and S. Bj(cid:127)rnsson
Magma Chambers in Rifts 147
A. R. Sanford and P. Einarsson
Magnetotelluric and Geomagnetic Deep-Sounding Studies in Rifts and Adjacent 169
Areas: Constraints on Physical Processes in the Crust and Upper Mantle
J. F. Hermance
Physical Aspects of Magmatism in Continental Rifts 193
L. A. J. Williams
Chemical Aspects of Rift Magmatism 223
F. Barberi, R. Santacroce and J. Varet
Metallogenesis in Relation to Rifting 259
F. Sawkins
Terrestrial Energy Currents and Transfer in Iceland 271
G. Bodvarsson
Mass Displacement and Geothermics Within the Upper Mantle of the Rhinegraben 283
Rift System: A Model to Interpret Data From Gravimetry and Seismology
D. Werner, H.-G. Kahle, J. Ansorge and St. Mueller
Musings on Continental Rifts
P. Mohr
FOREWORD
After a decade of intense and productive Region, East
scientific cooperation between geologists, WG 7 Geodynamics of Plate Interiors
geophysicists and geochemists the Inter- WG 8 Geodynamics of Seismically Inactive
national Geodynamics Program formally Margins
ended on July 31, 1980. The scientific WG 9 History and Interaction of Tectonic,
accomplishments of the program are Metamorphic and Magmatic Processes
represented in more than seventy scientific WG 10 Global Syntheses and Paleorecon-
reports and in this series of Final Report struction
volumes. These Working Groups held discussion meetings
The concept of the Geodynamics Program, as and sponsored symposia. The papers given at
a natural successor to the Upper Mantle the symposia were published in a series of
Project, developed during 1970 and 1971. Scientific Reports. The scientific studies
The International Union of Geological were all organized and financed at the national
Sciences (IUGS) and the International Union level by national committees even when multi-
of Geodesy and Geophysics (IUGG) then sought national programs were involved. It is to the
support for the new program from the Inter- national committees, and to those who partici-
national Council of Scientific Unions (ICSU). pated in the studies organized by those
As a result the Inter-Union Commission on committees, that the success of the Program
Geodynamics was established by ICSU to manage must be attributed.
the International Geodynamics Program. Financial support for the symposia and the
The governing body of the Inter-Union meetings of the Commission was provided
Commission on Geodynamics was a Bureau of by subventions from IUGG, lUGS, UNESCO and
seven members, three appointed by IUGG, ICSU.
three by IUGS and one jointly by the two Information on the activities of the
Unions. The President was appointed by ICSU Commission and its Working Groups is available
and a Secretary-General by the Bureau from in a series of 17 publications:
among its members. The scientific work of Geodynamics Reports, 1-8, edited by F.
the Program was coordinated by the Commission, Delany, published by BRGM; Geodynamics
composed of the Chairmen of the Working Groups Highlights, 1-4, edited by F. Delany,
and the representatives of the national published by BRGM; and Geodynamics Inter-
con(cid:127)nittees for the International Geodynamics national, 13-17, edited by R. D. Russell.
Program. Both the Bureau and the Commission Geodynamics International was published
met annually, often in association with the by World Data Center A for Solid Earth
Assembly of one of the Unions, or one of the Geophysics, Boulder, Colorado 80308, USA.
constituent Associations of the Unions. Copies of these publications, which contain
Initially the Secretariat of the Commission lists of the Scientific Reports, may be
was in Paris with support from France through obtained from WDC A. In some cases only
BRGM, and later in Vancouver with support microfiche copies are now available.
from Canada through DEMR and NRC. This volume is one of a series of Final
The scientific work of the Program was Reports summarizing the work of the
coordinated by ten Working Groups. Commission. The Final Report volumes,
WG 1 Geodynamics of the Western Pacific- organized by the Working Groups,
Indonesian Region represent in part a statement of what
WG 2 Geodynamics of the Eastern Pacific has been accomplished during the Program and
Region, Caribbean and Scotia Arcs in part an analysis of problems still to
WG 3 Geodynamics of the Alpine-Himalayan be solved. This volume from Working Group 4
Region, West (Chairman, J. Sutton) was edited by G.
WG 4 Geodynamics of Continental and P(cid:127)imason.
Oceanic Rifts At the end of the Geodynamics Program it
WG 5 Properties and Processes of the is clear that the kinematics of the major
Earth's Interior plate movements during the past 200 million
WG 6 Geodynamics of the Alpine-Himalayan years is well understood, but there is
less understanding of the dynamics of the Dynamics and evolution of the litho-
processes which cause these movements. sphere: The framework for earth resources
Perhaps the best measure of the success and the reduction of the hazards.
of the Program is the enthusiasm with To all of those who have contributed
which the Unions and national committees their time so generously to the Geodynamics
have joined in the establishment of a Program we tender our thanks.
successor program to be known as:
C. L. Drake, President ICG, 1971-1975
A. L. Hales, President ICG, 1975-1980
Members of Working Group 4:
G. PRimason P. Gouin
F. Aumento J.H. Illies
R.J. Bridwell D.E. Karig
R.W. Decker N. Logatchev
A. Dimitriev P.A. Mohr
L.V. Dmitriev D. Peck
N.A. Florensov I.A. Ramberg
J. Francheteau L. Rykunov
J.G. Francis R. Schlich
T. Francis G.E. Sigvaldason
I.G. Gass M. Talwani
R.W. Girdler L.A.J.
PREFACE
During the past decade of the International Geo- from the early work in East Africa at the end of
dynamics Program many publications dealing with the 19th century to the present time, when the
specific rift areas of the Earth's surface have main features of the World Rift System have been
appeared. Most of them followed symposia that recognized. Subsequent papers deal with various
were held in the respective rift zones. Among physical aspects of rifts, including ground defor-
the rifts thus treated are the Rhinegraben, Afar, mation, seismicity, gravity and heat flow. One
Iceland, the Baikal rift, the Oslo paleorift, the paper deals with hydrothermal systems, which seem
Rio Grande rift and the Dead Sea rift. Further- to be as integral a part of active rift systems
more, publications dealing with studies of the as e.g. volcanism and seismicity. Magmatism is
ocean floor have discussed many oceanic rift the subject of three papers, and metallogenesis in
areas. relation to rifting is discussed in one paper.
In view of the recent growth of publications Two papers deal with certain aspects of the Ice-
dealing with specific rift areas, the Working land rift zone and the Rhinegraben system. Final-
Group 4 (Continental and Oceanic Rifts) decided ly, one paper gives some thoughts on unsolved
at its meeting in Santa Fe, New Mexico, in 1978, problems of the continental rifts.
that this volume should emphasize comparative It is hoped that this collection of papers will
studies on topical subjects rather than focus on prove a valuable source of information for rift
geographical areas. It is hoped that this will studies during the decade of the International
prove to be a useful approach to reviewing the Lithosphere Program.
present state of knowledge of the rift zones of
the Earth.
The papers in this volume deal with many aspects
of rift systems that have received attention in Gudmundur PRimason
recent years. An introductory paper gives a much Chairman, ICG Working Group 4, Geodynamics of
needed overview of the history of rift studies Continental and Oceanic