Broken Hill - Sydney Tasman - Sea Transect: New South Wales, Eastern Australia

37 Pages·15.569 MB·English

GLOBAL GEOSCIENCE TRANSECT 5
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BROKEN HILL SYDNEY
TASMAN SEA TRANSECT
NEW SOUTH WALES,
EASTERN AUSTRALIA
@ American Geophysical Union
Publication No. 191 of the International Lithosphere Program
ISBN 0-87590-782-2
Copyright 1991 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 America.
American Geophysical Union
2000 Florida Avenue, N.W.
Washington, D.C. 20009
Preface
The Global Geoscience Transects Project (GGT) is surface-bound field geologist, can attest to the excite-
an ambitious international effort that draws together ment of working with geophysicists from around the
geoscientists in a variety of disciplines to produce the world to consider the nature and evolution of deeper
best possible portrayal of the composition and struc- parts of the crust and to attempt to integrate these data
ture of the Earth's crust. Since its inception in 1985, with surface features.
GGT has encouraged geoscientists in all countries of GGT compilation also plays a significant role in the
the world to compile cross sections of the Earth up to education of geoscientists. The problems being inves-
tigated are global and interdisciplinary in scope, and
a few thousands of kilometers in length and drawn to
international cooperation between geologists, geo-
the base of the crust using all available geological,
physicists, geochemists, and geodesists is required to
geophysical, and geochemical information. Transects
resolve them. Transects cannot be compiled without
are drawn to common scales and formats so that the
such interdisciplinary research.
Earth's crust in different parts of the world can be
The guidelines developed for the transects had to be
directly compared.
flexible enough to accommodate the variations in data
GGT was conceived by the Inter-Union Commis-
available in different parts of the world. Some areas
sion on the Lithosphere (ICL), a "child" of the
have very complete, freely available data bases; others
International Union of Geological Sciences and the
have at best only gravity or aeromagnetic maps as the
International Union of Geodesy and Geophysics
geophysical data base from which to construct crustal
(IUGG), at the IASPEI conference in Tokyo in August
cross sections.
1985. Project coordinators James W. H. Monger and
The first publications of the GGT Project, a transect
Hans-Jurgen Gotze organized a multidisciplinary, mul-
chart and accompanying booklet, are a joint activity of
tinational committee that coordinated the global proj-
ICL and AGU. The seven transects from China (2),
ect. Meeting at the IUGG XIX General Assembly in
South America (21, Australia (2), and Syria (I), were
Vancouver in August 1987, the committee developed
drafted and hand colored by the compilers. Transects
preliminary guidelines for transect compilations, fol-
combine the available data into interpretive sections
lowing suggestions from transect compilers. Proposals
drawn to the base of the Earth's crust. The product is
for transects were solicited from ICL national commit-
a large display-approximately 1 meter by 2 meters-
tees, government geoscience agencies, universities,
and scientists. A total of 140 proposals were received with the bottom line cross section as a vertical tectonic
from Africa (41), South America (30), China (18), map of the crust. The booklet includes an analysis of
USSR (12), USA (12), Europe (12), Australia and New the transect by the compilers and references to data
Zealand (1 I), India (3), and Southeast Asia (1). sources.
The GGT Project has generated a special intellectual The GGT Project is now embarking on a new
excitement among participants by encouraging geosci- direction that will make this wealth of data even more
entists to understand the evolution and physical be- useful to the scientific community. ICL and AGU plan
havior of the lithosphere by bridging the gap between to publish future transects in electronic format (dis-
surface geology and deeper geophysics. Monger, as a kettes, CD-ROM) that can be manipulated using small
"low-end" computers. A GGT Digitization Group was wide network of scientists cooperating on transects
established in 1988 to prepare guidelines for digitizing would be able to work interactively with these files,
transects; the guidelines and sample will be published adding data to them, analyzing, reconfiguring , and
by AGU. interpreting them.
This endeavor breaks new ground and goes a long Digitization of geoscience material will not only ease
way toward a goal of the ICL of closely linking the task of publishing transects and encourage the
exchange of data bases, it promises to allow quanti-
geological, geochemical, and geophysical data bases
tative comparisons of elements of different parts of the
and breaking down present barriers between different
Earth's crust. The use of digitized transect material is
Earth science disciplines. With the digitized transects,
the perfect training ground for the new breed: geosci-
geologists, for example, could manipulate gravity data
entists!
to test the validity of their structural models. A world-
James H. Monger
Geological Survey of Canada
100 West Pender Street
Vancouver V6B 1R8
Canada
Hans-Jurgen Gotze
Institut fiir Geologie, Geophysik und Geoinformatik
Freie Universitat Berlin
Malteserstrasse 47 100
D-1000 Berlin 45 Germany
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BROKEN HILL SYDNEY TASMAN SEA TRANSECT
Proterozoic to Cenozoic Crustal Development
of New South Wales, Eastern Australia
PRINCIPAL COMPILER
ERWINS CHEIBNER
COMPILER
C. McA. POWELL
AEROMAGNETIC DATA
Ross SPENCER
CONTRIBUTORS
A. AGOSTINI,H . BASDENM, . F. COFFINJ, . P. CULL,M . A. ETHERIDGED. . M. FINLAYSON,
R. A. GLEN,C .H ERBERT,P~.. L AINGJ, . MCINTYRES, . Y. ~'REILLYD, . J. POGSONI,. R. QURESHIR, . SPENCER,
B. P. J. STEVENSP,. A. SYMONDSE,. TYNE AND K. WAKE-DYSTER
EXPLANATOKY TEXT
ERWINS CHEIBNER
AEROMAGNETIC DATA
Ross SPENCER
New Soulh Wales Geological Survey, P.O. Box 536, St. Leonard, NSW 2065, Australia
BROKEN HILL-SYDNEY-TASMAN SEA TRANSECT EASTERN AUSTRALIA
SUMMARY in response to an active plate margin in the east
(Fig. 1).
This east-west orientated transect, together with the 2) To the east of it, across the so-called "Tasman
Eromanga-Brisbane Transect located 750 km to the Line", is the Neoproterozoic to Triassic
north (Finlayson, 1990), illustrates many typical orthotectonic Tasman Fold Belt System or
features of the Proterozoic-Phanerozoic development Tasmanides (Scheibner, 1987; Fig. 1).
of continental crust within the Tasman Fold Belt 3) The widespread Upper Carboniferous to
System or Tasmanides, which comprises most of Holocene platform cover (Fig. 2; Doutch and
eastern Australia. Eastern Australia was part of Nicholas, 1978; Plumb, 1979) consists of
Gondwanaland and evolved as the Ur-Pacific (earliest) sedimentary and igneous rocks, some of which
and Palaeo-Pacific active plate margin. The Broken are related to the rifting and the break-up of
Hill-Sydney-Tasman Sea Transect crosses, from west Gondwanaland.
to east, the widest outcropping part of the Tasmanides. 4) Late Mesozoic to Cenozoic passive margin
It shows, from west to east, the structure of the complexes occur along the eastern margin of
following five tectonic entities: Australia, (Fig. 2; Falvey and Mutter, 1981;
Colwell et al., 1989; Veevers, 1984) and in turn
1. Eastern part of the miogeoclinal foreland are flanked on the east by Late Cretaceous to
Adelaide Fold Belt, of Neoproterozoic to Paleogene and oceanic crust of the Tasman Sea
Cambrian age, in which basement is exposed in (Fig. 2; Hayes and Ringis, 1973).
an inlier, the Broken Hill Block of Palaeo- and
Mesoproterozoic age, with Early Paleozoic shear The Broken Hill-Sydney-Tasman Sea Transect was
zones and intrusions. selected principally to portray the tectonics of the
2. The orthotectonic Kanmantoo Fold Belt, of widest outcropping segment of the Tasmanides, and
Neoproterozoic to Early Palaeozoic age, in which updates and amplifies an earlier compilation made for
part of the basement forms an inlier, the older part the Geodynamics Project (cf. Rickard et al., 1983).
of the Wonominta Block (Mesoproterozoic to Within eastern Australia, the Tasmanides comprise
Neoproterozoic Wonominta beds sensu stricto). five orthotectonic fold belts which become
Upper Cambrian to Lower Ordovician molassic progressively younger from west to east: Kanmantoo,
overlap sequences post-date terrane accretion. Thomson, Lachlan, Hodgkinson-Broken River and
Younger overlap sequences fill the Bancannia New England (Fig. 3). Of these, the Kanmantoo and
Trough (Middle Devonian to Lower Lachlan fold belts occur within the transect corridor,
Carboniferous). with minor elements of the New England Fold Belt
3. The orthotectonic Lachlan Fold Belt is a possibly concealed in the present continental shelf and
composite orogenic belt of Lower-Middle slope region. These structural elements differ in the
Palaeozoic age. timing of their stages of tectonic evolution from (1)
4. The Sydney Basin, of Late Carboniferous to the pre-cratonic stage (active plate margin) featuring
Triassic age, overlies the Lachlan Fold Belt, but is turbiditic sedimentation, widespread orogenic igneous
the foredeep to the New England Fold Belt to the rocks and scarce ophiolites and greenstones, through
east. The latter belt is not exposed along the (2) the transitional tectonic stage with molassic
transect corridor, but may occur in subsided sediments, bi-modal volcanics and post-kinematic
blocks along the present continental margin. intrusives, to (3) the final cratonic (neocratonic) stage,
5. Lower Cretaceous to Holocene passive margin which is characterized by platformal sedimentation
complexes and adjacent Tasman Sea oceanic (Scheibner, 1976, 1987). The transitional tectonic
crust of Late Cretaceous to Paleogene age. basins in stage (2) are usually referred to as "foreland,
downwarp and successor basins" in the classical North
The tectogenesis of eastern Australia is complex, American tectonic literature.
but a general eastward progressive growth of Tectonosh-atigraphic interpretations indicate that
continental crust can be discerned. This was achieved the fold belts developed within an active plate margin
in part by successive accretion of suspect setting by interaction of Ur-Pacific and Palaeo-Pacific
tectonostratigraphic terranes. plates with the Australian plate, which then was part
of eastern Gondwanaland.
INTRODUCTION The youngest fold belt, the New England Fold Belt
in the east, is separated at the surface from the older
Eastern Australia comprises the following distinct fold belts by the Sydney-Bowen Basin, a rift-initiated
structural elements: molassic foredeep. A minor part of New England
1) The composite, Palaeoproterozoic to Mesopro- Fold Belt appears to be concealed in the continental
terozoic Craton (cf. Plumb and James, 1986; shelf region of the transect.
Cowie and Bassett, 1989; Plumb, 1979; Rutland, In the Tasmanides, as in most other orogenic belts
1982) in the west, with associated Neoproterozoic developed at active plate margins, it is suspected that
to Middle Palaeozoic platformal basins and allochthonous tectonostratigraphic terranes are present
miogeoclinal to intracratonic paratectonic fold (Scheibner, 1985; Leitch and Scheibner, 1987). The
belts (Rutland, 1976) which probably developed probability of the presence of terranes increases with
GLOBAL GEOSCIENCE TRANSECT 5
Figure 1. Schematic structural map of eastern Australia. Modified from Scheibner
(1987).
BROKEN HILL-SYDNEY-TASMAN SEA TRANSECT EASTERN AUSTRALIA
I
GLOBAL GEOSCIENCE TRANSECT 5
Figure 3. Schematic structural map of
eastern Australia. Modified from
Scheibner (1987).
BROKEN HILL-SYDNEY-TASMAN SEA TRANSECT EASTERN AUSTRALIA 5
the distance away from the old craton. Most workers Surveys on land used helicopters for transport and
agree that exotic terranes occur in the New England barometers to determine heights (Frazer, 1973).
Fold Belt, but their presence in the other fold belts While the prevailing spacing of gravity stations is
remains contentious (Fig. 4). Individual fold belts can about 10-12 km, there are local surveys with spacing
be regarded as "super-terranes" characterized by ranging from 1-11 km.
different times of terrane accretion (Fig. 5). Most marine observations were gathered during a
From west to east (Fig. 6), the Broken Hill- reconnaissance survey of the Australian continental
Sydney-Tasman Sea Transect traverses (1) the eastern margins in 1970-73 when about 185,000 km of
edge of the Neoproterozoic to Cambrian miogeoclinal systematic traversing were completed (Compagnie
foreland Adelaide Fold Belt, (2) the orthotectonic Generale de Geophysique, 1975). Line spacing varied
Neoproterozoic to Early Palaeozoic Kanmantoo Fold from 30 to 50 km and gravity values used are based on
Belt, (3) the Early to Middle Palaeozoic Lachlan Fold preliminary hourly values representing an average
Belts, (4) the Late Palaeozoic to Triassic Sydney spacing of about 15 km along each traverse.
Basin, (5) probably concealed Late Devonian to Remaining on landoff shore data were obtained by
Carboniferous strata of the New England Fold Belt, BMR, State mines departments, exploration
(6) the Late Mesozoic to Cenozoic passive continental companies, tertiary institutions and the United States
margin, and terminates (7) in the Late Cretaceous to Navy.
Paleogene oceanic crust of the Tasman Sea.
Reduction of observations: Compilation and
SOURCES OF DATA AND BACKGROUND production of the 1976 1:5,000,000 Gravity Map of
INFORMATION Australia is described by Anfiloff et al. (1976).
Anomalies on this map are based on the Potsdam
The Broken Hill-Sydney-Tasman Sea Transect datum for observed gravity values, and the 1930
succeeds the earlier "Geodynamics" profile No. 4 International Gravity Formula. Values of observed
through the Tasmanides (Scheibner et al., in Rickard gravity are relative to May 1965 isogal values at
et al., 1983). It presents a working hypothesis of stations of the Australian National Gravity Network,
crustal evolution, based on synthesis of mainly which consists of a series of east-west isogal traverses
geological, gravity and aeromagnetic data, and between airports of nearly equal gravity, joined by
supported by only a limited amount of deep seismic three north-south traverses. This network of some 200
reflection data (Drummond et al., in prep.). It is base stations spaced at about 300 km was established
derived from the work of earth scientists at over Australia and Papua New Guinea during
universities, in the exploration industry, and in Federal 1964-1967.
and State Public Service research organizations. The observed gravity values at sea have been
reduced to free-air anomalies (FAA) in milligals,
Geological Maps according to the formula:
+
Sources of data are standard geologic maps at FAA = go - g, + 7.5 Ve cos (1)
1:250,000 (Fig. 7) and special maps at 1:500,000 and
1: 1,000,000 scale. Detailed maps at 1:25,000 scale where go is the observed gravity, g, the normal values
+,
are available for the Broken Hill region and 1:100,000 of gravity depending on latitude and obtained from
scale maps for the Cobar region and Sydney Basin. the 1930 International Gravity Formula:
All these maps have been published by the New South
Wales Geological Survey, NSW Department of
Minerals and Energy. A revised tectonic map at
1:1,000,000 scale has recently been produced
(Scheibner, unpubl.) for the Tectonic Map of the and Ve is the eastward component of the ship's speed
Tasman Fold Belt System which will be published by in knots used to calculate the Eotvos correction.
the Bureau of Mineral Resources (BMR) in For land stations the simple Bouguer anomaly (BA)
co-operation with State Geological Surveys and has been used:
universities. Explanatory Notes to this map contain
up-dated information.
Gravity Data where h is the altitude in metres and p is taken as 2.67
t/m3. No terrain corrections have been applied for the
The whole region is covered by the Bureau of published map, but on the transect corrections were
Mineral Resources (BMR; 1976) Gravity Map of computed by Qureshi (1984) over the Blue
Australia at a scale of 1:5,000,000 showing Bouguer Mountains.
gravity anomalies on land (calculated at a Bouguer
density of 2.67), and free air anomalies at sea. Accuracy of anomalies: The general precision within
each helicopter land gravity survey is better than 0.3
Sources of data: For about 85 percent of the mGal for observed gravity differences, better than 5 m
contoured area data were acquired on contract basis. altitude, and within about 0.1 minutes of arc for