Geodynamics of the Eastern Pacific Region, Caribbean and Scotia Arcs

168 Pages·2000·4.35 MB·English

Geodynamics of the EasternP acific Region,
Caribbean and Scotia
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 of
the Eastern Pacific Region,
Caribbean and Scotia Arcs
Edited by Ram6n Cabr(cid:127), S.J.
Geodynamics Series
Volume 9
American Geophysical Union
Washington, D.C.
Geological Society of America
Boulder, Colorado
Final Report of Working Group 2, Geodynamics of the Eastern Pacific Region,
Caribbean and Scotia Arcs, coordinated by C. L. Drake 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
Main entry under title:
Geodynamics of the eastern Pacific region, Caribbean and Scotia arcs.
(Geodynamics series, ISSN 0277-6669; v. 9)
Bibliography: p.
1. Plate tectonics--Addresses, essays, lectures. 2. Geology--Latin
America--Addresses, essays, lectures.
I. Cabr(cid:127), Ram6n. II. Series.
QE511.4.G455 1983 551.1'36 83-3703
ISBN 0-87590-502-1
Copyright 1983 American Geophysical Union. Figures, tables and short excerpts
may be reprinted in scientific books and journals if the source is properly
cited; all other rights reserved.
Printed in the United States of
CONTENTS
FOREWORD
C.L. Drake and A.L. Hales
INTRODUCTION
R. Cabre, S.J.
GEODYNAMICS OF THE JUAN DE FUCA PLATE
R.P. Riddihough, M.W. Beck, R.L. Chase, E.E. Davis, R.D. Hyndman,
S.H. Johnson, and G.C. Rogers
BIBIOLOGRAPHY CONCERNING MEXICAN GEODYNAMICS 23
L. Del Castillo
SUMMARY AND BIBIOLOGRAPHY OF CARIBBEAN GEODYNAMIC INVESTIGATORS
J.F. Lewis, W. MacDonald, A.L. Smith, and J.D. Weaver
GEODYNAMICS OF CENTRAL AMERICA 33
G. Dengo
GEODYNAMIC RESEARCH IN COLOMBIA (1972-1979) 41
J. E. Ramirez, H. Duque-Caro, J.R. Goberna, and J.F. Toussaint
GEODYNAMICS OF ECUADOR 53
C.E. Acosta
BOLIVIAN GEOLOGICAL GEOTRAVERSE 65
S. Rivas
GEOPHYSICAL STUDIES IN CENTRAL ANDES 73
R. Cabre, S.J.
TECTONIC EVOLUTION OF PERUVIAN ANDES 77
J. Caldas V.
NAZCA PLATE AND ANDEAN FOREARC STUDIES 83
L.D. Kulm, J. Dymond, and K.F. Scheidegger
GEOPHYSICAL DATA AND THE NAZCA-SOUTH AMERICAN SUBJUCTION ZONE KINEMATICS: 95
PERU-NORTH CHILE SEGMENT
L. Ocola
KINEMATICS OF THE SOUTH AMERICAN SUBJUCTION ZONE FROM GLOBAL PLATE RECONSTRUCTIONS 113
R.H. Pilger, Jr.
GEODYNAMICS OF THE ARGENTINE ANDEAN ARC AND RELATED REGIONS 127
B.A.J. Baldis and J. Febrer
PROGRESS IN GEODYNAMICS IN THE SCOTIA ARC REGION
P.F. Barker and I.W.D. Dalziel
FOREWORD
After a decade of intense and productive WG 6 Geodynamics of the Alpine-Himalayan
scientific cooperation between geologists, Region, East
geophysicists and geochemistst he Interna- WG 7 Geodynamics of Plate Interiors
tional GeodynamicsP rogram formally ended on WG 8 Geodynamics of Seismically Inactive
July 31, 1980. The scientific accomplish- Margins
ments in more than seventy scientific reports WG 9 History and Interaction of Tectonic,
and in this series of Final Report volumes. Metamorphic and Magmatic Processes
The concept of the Geodynamics Program, as WG 10 Global Syntheses and
a natural successor to the Upper Mantle Pro- Plaeoreconstruction
ject, developed during 1970 and 1971. The These Working Groups held discussion
International Union of Geological Sciences meetings and sponsored symposia. The papers
(lUGS) and the International Union of Geodesy given at the symposiaw ere published in a
and Geophysics (IUGG) then sought support for series of Scientific Reports. The scientific
the new program from the International studies were all organized and financed at
Council of Scientific Unions (ICSU). As a the national level by the national committees
result the Inter-Union Commission on even when milti-national programs were
Geodynamics was established by ICSU to manage involved. It is to the national committees,
the International Geodynamics Program. and to those who participated in the studies
The governing body of the Inter-Union organized by those committees, that the
Commission on Geodynamics was a Bureau of success of the Program must be attributed.
seven members, three appointed by IUGG, three Financial support for the symposia and the
by lUGS and one jointly by the two Unions. meetings of the Commissionw as provided by
The President was appointed by ICSU and a subventions from IUGG, lUGS, UNESCOa nd ICSU.
Secretary-General by the Bureau from among Information on the activities of the
its members. The scientific work of the Commission and its Working Groups is
Program was coordinated by the Commission, available in a series of 17 publications:
composedo f the Chairmen of the Working Geodynamics Reports, 1-8, edited by F.
Groups and the representatives of the Delany, published by BRGM; Geodynamics
national committees for the International Highlights, 1-4, edited by F. Oelany,
GeodynamicsP rogram. Both the Bureau and the published by BRGM;a nd Geodynamics
Commission met annually, often in association International, 13-17, edited by R. D.
with the Assembly of one of the Unions, or Russell. Geodynamics International was
one of the constituent Associations of the published by World Data Center A for Solid
Earth Geophysics, Boulder, Colorado 80308,
Unions.
Initially the Secretariat of the USA. Copies of these publications, which
Commission was in Paris with support from contain lists of the Scientific Reports, may
France through BRGM, and later in Vancouver be obtained from WDC A. In some cases only
with support from Canada through DEMRa nd microfiche copies are now available.
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 1Geodynamics 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 be
WG 3 Geodynamics of the Alpine-Himalayan solved. This volume from Working Group 2
Region, West was edited by RamonC abre(cid:127) S. J.
WG 4 Geodynamics of Continental and At the end of the Geodynamics Program it
Oceanic Rifts is clear that the kinematics of the major
WG 5 Properties and Processes of the plate movementsd uring the past 200 million
Earthøs Interior years is well understood, but there is
less understanding of the dynamics of the The framework for earth resources and the
processes which cause these movments. reduction of the hazards.
Perhaps the best measure of the success of
To all of those who have contributed their
the Program is the enthusiasm with which the
time so generously to the Geodynamics Program
Unions and national committees have joined in
we tender our thanks.
the establishment of a successor program to
be known as: C. L. Drake, President, ICG, 1971-1975
Dynamics and evolution of the lithosphere: A. L. Hales, President, ICG,
Geodynamics Series Geodynamics of the Eastern Pacific Region, Caribbean and Scotia Arcs Vol. 9
INTRODUCTION
Ramon Cabr(cid:127), S.J., Chairman of WG2,
Observatorio San Calixto, La Paz, Bolivia
Geodynamics in the Region of WG2 Collaboration among Researchers
Working Group No. 2, one of the four The research intensity applied to this range
'regional' Groups of the Geodynamics Project, of problems has varied considerably according
has been concerned with the Eastern Pacific and to the facilities and support available in each
Western Americas and with the Caribbean and country. In this respect, the interest and
Scotia Arcs. This has represented an generosity of the host of people and
exceptionally active and diverse area of study, institutions assisting in the research programs
diverse in the factors conditioning research, of less well endowed regions and remote areas
such as climates (ranging from the western deserves special mention.
United States to the poorest countries of In particular we would like to remember
Latin America) and the geodynamic conditions John D. Weaver who died as the Geodynamics
revealed in the interior of the earth. Project was approaching its end. He contributed
The region studied by WG2 included the with enthusiasm as Chairrotan of the Caribbean
western continental margin of North and Study Group and as volunteer translator for
South America or in plate tectonic terms, the parts of this volume written in Spanish.
region dominated by the interaction between the Unfortunately he died before he could complete
oceanic plates of the Pacific Ocean and the this work.
continental plates of the Americas. Here some We would also like to mention three
of the highest velocities of convergence on the Institutions whose contributions of interest and
globe have resulted in the formation of the encouragement were particularly important:
remarkable Cordilleran Arcs. Department of Terrestrial Magnetism of the
Deep seismic activity marks present Carnegie Institution of Washington, Pan American
subduction to a depth of at least 600 km Institute of Geography and History, The
beneath central South America and along about Scientific Program of the Organisation of
half the length of the continent. Activity to American States. These are only a few of many,
intermediate depths occurs in the remainder of we could continue with an almost endless list of
South America (except the extreme south) and in Universities and other Institutions. In many
Central America, the Caribbean and Scotia Arcs cases, such as the Scotia Arc, cooperation is
and closely traces the extent and dimensions of the 'conditio sine qua non' for research; in the
subduction in these regions. North America, work of WG2, co-operation has been consistently
except Alaska, is characterised by the absence evident.
of seismic activity below 70 km- in California
because there is no current subduction and in Constitution and Activity of WG2
the Pacific North-West, because the Juan de Fuca
plate is young and hot and becomes plastic at a The following membership of WG2 was initially
shallow depth. selected:
Although the varying size of the plates
studied by WG2, from the giant Pacific plate to Allen, C.R., Seismological Lab., California
the fragmented Juan de Fuca plate, has been Institute of Technology. Pasadena.
another diversifying factor, similarities have Barker, P.F., Dept. of Geophysics, Univ. of
begun to emerge. For example, the Caribbean and Birmingham. U.K.
Scotia Arcs were apparently produced by the same Cabr(cid:127), T., Observatorio San Calixto. La Paz,
process but are at different stages. They offer Bolivia. Chairman.
weak resistance to the eastward push of Pacific Casaverde, M., Instituto Geofisico del Per(cid:127).
ocean plates resulting in arc displacement and Lima, Per(cid:127).
basin formation. Chase, R.L., Dept. of Geology, Univ. of
Copyright American Geophysical Union
Geodynamics Series Geodynamics of the Eastern Pacific Region, Caribbean and Scotia Arcs Vol. 9
British Columbia. Vancouver, Canada. Co-Chairman of the WG2 edited a "Boletfn de
Dengo, G., ICAITI. Guatemala. Geodinjmica" in Spanish, the language spoken in
Fiedler, G., Inst. Seismo16gico, Observ. the part of the region where communication was
Cagigal. Caracas, Venezuela. most difficult. It was financed by Venezuelan
Gabrielse, H., Dept. of Energy, Mines and institutions. Two issues were published.
Resources. Vancouver, Canada.
GonzRles-FerrJ(cid:127), 0., Depto. Geologia, Univ. de Study Groups
Chile. Santiago, Chile.
Because it became clear that a single
Linares, E., Depto. Ciencias Geo16gicas, Univ.
coordinating group acting over so large a region
de Buenos Aires. Argentina.
would be practically impossible, zone study
Lomnitz, C., Inst. de Geoffsica, UNAM. M(cid:127)xico.
groups were organized. This had the added
Ramirez, J.E. , Inst. Geof%sico de los Andes
advantage of involving a larger number of
Colombianos. BogotR, Colombia.
geo s cien tis ts:
Ritsema, A.R., Koninlijk Nederlands Meteoro-
logisch Instituut. De Bilt, Netherlands.
Study Group Chairman
Tomblin, J., Seismic Research Unit, Univ. of
the W. Indies. St. Augustine, Trinidad. Juan de Fuca Plate Riddihough (initially, Chase)
Van Andel, Tj. R., Dept. of Oceanography, Cocos Plate Del Castillo
Oregon State Univ. Corvallis, Oregon. Caribbean Weaver (initially, Dengo)
Weaver, J., Dept. of Geology, Univ. of Nazca Plate Kulm (initially, Lomnitz)
Puerto Rico. Mayaguez, Puerto Rico. Scotia Arc Gonz(cid:127)les-FerrJn
Argentina Comm. on Baldis
Several changes were later made in WG2 Andean Geodynamics
membership at different times and for different
reasons: Allen, Chase, Fiedler, Linares, The results of the Study Groups have been
Lomnitz, Ritsema and Van Andel left the WG2; in uneven. This is not to say that zones assigned
their place the following researchers entered to less active Groups were neglected, but that
the Group: in practice much research effort was often
Baldis, B.A., Museo Argention de Ciencias coordinated under National Geodynamic Committees
(for instance in the United States). This
Naturales. Buenos Aires, Argentina.
Beets, D.J., Geological Institute. Amsterdam, explains, at least partially, why the present
Netherlands. volume presents geodynamic research and results
Bellizzia, A., Servicio Geoldgico Nacional, in a varied manner. The different studies are
Minis terio de Minas y Emergfa(cid:127) Caracas, presented in geographical order (both Study
Venezuela. Co-Chairman. Group and National Reports). [Note that the
Del Castillo, L., Instituto de Geof%sica. UNAM. responsibility for the individual reports in
M(cid:127)xico. this volume rests entirely with the listed
Dorman, L.R.M., Scripps Inst. of Oceanography. authors. ]
La Jolla, California. Summary Comments
,
Kulm, L.V., Dept. of Oceanography, Oregon State
Univ. Corvallis, Oregon. Although advances in geodynamics have been
Riddihough, R.P., Pacific Geoscience Centre. important, possibly the most significant result
Sidney, B.C., Canada. of the Geodynamics Project in the region has
Shimamura, H., Dept. of Geophysics, Hokkaido been the increase in communication between
Univ. Saporo, Japan. geoscientists. There is still, however,
considerable room for improvement. In the
WG2 was faced, among other difficulties, with subject of our research, a number of major
a considerable communications problem. geodynamic problems remain. Some of these
Distances and lack of funding on the one hand problems existed before the Project began,
and overlapping commitments on the other, others have appeared as a consequence of new
challenged mail, meeting and press communication. discoveries. Clearly there is ample
Meetings were held in: Lima (August 22-24, opportunity and need for a continuing effort, an
1973); Vancouver (August 19-20, 1975); Acapulco effort that could possibly be coordinated
(June 14-15, 1976); Curacao (July 22-23, 1977); through a similar project.
Bogot(cid:127) (March 28-30, 1979).
Acknowledgements. Final revision of this
To stimulate communication between the WG2 introduction by Robin Riddihough is
members and with the geoscience community, the acknowledged and appreciated.
4 CABRE
Copyright American Geophysical Union
Geodynamics Series Geodynamics of the Eastern Pacific Region, Caribbean and Scotia Arcs Vol. 9
GEODYNAMICS OF THE JUAN DE FUCA PLATE
R.P. Riddihough1 , M.E. Beck2 , R.L. Chase(cid:127), E.E. Davis1 ,
R.D. Hyndma1n, S.H. Johnson(cid:127) and G.C. Rogers1
Abstract. The Juan de Fuca plate in the N.E. Pacific Ocean by Raff and Mason (1961) (Figure 1)
Pacific Ocean, although small by global provided a critical piece of evidence which led
standards, is very complex. Over the last 10 m. to the development of sea floor spreading
years, the Juan de Fuca ridge at which it has theory and plate tectonics. Key papers by
been generated, has slowed its spreading rate Wilson (1965), Vine and Wilson (1965) and Tobin
(from 8 cm/yr to below 6 cm/yr), has become and Sykes (1968) followed by the work of Atwater
segmented and has rotated clockwise. This (1970) established that the Juan de Fuca ridge
process has been associated with fragmentation was a spreading ridge and that between the ridge
into a series of sub-plates, each with its own and the North American continent lay a separate
recent history. Oblique convergence with the plate which was probably subducting along the
margin of North America at 2-4 cm/yr is a continental margin.
consequence of plate geometry and is supported By the beginning of the Geodynamics Project
by deformation of the sediments of the the main features of the area had been estab-
continental slope and the burial of sea-floor lished (Dehlinger et al., 1971); however it was
magnetic anomalies. Low heat flow, recent widely recognized that the area was extremely
movements and the regional gravity field of complex and that many of the accepted criteria
western British Columbia and the NW United States of the simple plate tectonic model were missing
provide some characteristic features of a or unrecognizable. Despite Atwater's exposition
subduction zone, as does the calc-alkaline vol- of the implications of plate tectonic modelling
canic chain of the Mt. Garibaldi - Cascades for the North-east Pacific, the climate of
system. Although the lack of a deep Benioff zone scientific opinion was not whole-heartedly in
is explicable as a function of the slow favour of its application to the region. In
subduction of a young plate, the absence of any our opinion, one of the main achievements of the
seismicity specifically associated with under- work done during the period of the Geodynamics
thrusting remains unexplained. Amongst the Project has been to gain wide acceptance for the
other features which are now well established existence of the Juan de Fuca plate and to
but not yet understood in geodynamic terms are develop a realization that the apparent
regional north-south compression in the adjacent contradictions of its geodynamics are not so
land areas, the rotations of blocks within the much proof that plate tectonics does not work in
arc-trench gap, and the origin and influence of this region but examples of the detailed
the large seamount province immediately west of complexity of plate tectonics in action.
the ridge system.
The Ridge
Introduction
The Juan de Fuca ridge system consists of a
The Juan de Fuca plate has occupied a unique number of different segments (Figs. 2 and 3).
place in the development of recent geodynamics From south to north, these are the Gorda ridge,
studies in that the magnetic surveys in the NE the Juan de Fuca ridge, the Explorer ridge and
the Dellwood knolls. The main segments are
connected by right-lateral transform faults
1pacific Geoscience Centre, Earth Physics Branch, which shift the ridge north of the transform to
Dept. Energy, Mines and Resources, Box 6000, the west. The transforms were initiated at
Sidney, B.C., Canada, V8L 4B2 progressively later times from south to north:
2GeologyD ept., Western WashingtonU niv., Mendocino fracture zone (70 m.y.), Blanco
Bellingham, Washington 98225 fracture zone (15 m.y.), Sovanco fracture zone
3GeologyD ept., Univ. of British Columbia, (8 m.y.) and the Revere-Dellwood fracture zone
Vancouver, B.C., Canada (1-2 m.y.). Rates of motion across these
4School of Oceanography,O regon State Univ., transforms are at present of the order of
Corvallis, Oregon 97331 5 cm/yr but in detail the individual sections
Copyright American Geophysical Union