Redefining Rodinia
Redefining Rodinia
Redefining Rodinia
10
INSIDE
October 1999
GSA TODAY
A Publication of the Geological Society of America
ABSTRACT
BALTICA
SWEAT
TR
AN
C
SS
AN
G
W.
DIN
OT
IA
AV
M
IA
KETILIDEAN
AN
RI
O
AD
R
B
LA
LAURENTIA
AUSWUS
ARUN
TA
MI
MUSG
RAVE
I
PA
VA
YA
AUSTRALIA
BH
MA
TZ
ZA
LL
VI
AL
1.3
1.5
Ga
EN
GR
Nd MODEL AGE
1.0 - 1.3 Ga
1.3 - 1.5 Ga
1.6 - 1.8 Ga
1.8 - 2.0 Ga
2.0 - 2.3 Ga
> 2.5 Ga
Massive Sulfides
Rift Margins
OA
CA
ANTARCTICA
XA
1000 Km
Thrust Faults
CRUSTAL AGE
Figure 1. AUSWUS reconstruction for 1.7 to 0.8 Ga, modified from Brookfield (1993). The Tasman line
forms the eastern edge of Proterozoic Australia (Myers et al., 1996); the 87Sr/86Sr = 0.706 line marks the
west edge of Proterozoic Laurentia. Continents were rotated to this configuration about an Euler pole
located at 51.46N 106.70E, rotation angle 114.33. Both continents appear in equal-area projection in
North American coordinates. The position of Australia in the SWEAT reconstruction is shown for comparison (from Moores, 1991). Crustal age provinces inferred from Nd data. Massive sulfide deposits of Broken Hill (BH) are to similar deposits in Jerome (J) in central Arizona and Mount Isa (MI) is across from the
Carlin area of Nevada.
INTRODUCTION
Many recent papers have concluded
that a supercontinent called Rodinia
existed in the Neoproterozoic between 1.0
and 0.8 Ga. There is speculation that the
breakup of Rodinia may have been related
to dramatic changes in Earth systems such
as diversification of life, multiple lowlatitude glaciations, fluctuating ocean
GSA TODAY
October
1999
Vol. 9, No. 10
SUBSCRIPTIONS
IN THIS ISSUE
Refining Rodinia: Geologic Evidence
for the AustraliaWestern U.S.
connection in the Proterozoic . . . . . .
Memorial Preprints . . . . . . . . . . . . . . . . . . . . .
In Memoriam . . . . . . . . . . . . . . . . . . . . . . . . . .
SAGE Remarks: Redesigning the Geological Map for the Public Audience . . . . .
Dialogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Washington ReportDefining a National
Environmental Framework Continues . . .
Penrose Conference ReportMidCretaceous to Recent Plate Boundary
Processes in the Southwest Pacific . . . . . .
Geochemist, Petrologist Named
Honorary Fellows . . . . . . . . . . . . . . . . . . . . . .
GSA Penrose Medal, Day Medal,
and Honorary Fellows. . . . . . . . . . . . . . . . . . .
GSA on the Web . . . . . . . . . . . . . . . . . . . . . . .
Young Scientist Award . . . . . . . . . . . . . . . . .
Call for Nominations
National Awards for 2002 . . . . . . . . . . . . . .
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SWEAT MODEL
The most influential continental reconstruction for the late Precambrian has
been the SWEAT hypothesis (Moores,
1991; Hoffman, 1991; and Dalziel, 1991).
In this model, the western U.S. is matched
to Antarctica, western Canada to Australia,
and the truncated 1.0 Ga Grenville orogen
in Texas to East Antarctica.
AUSWUS MODEL: AN
ALTERNATIVE RECONSTRUCTION
Proposed modifications of the SWEAT
reconstruction have placed Australia farther south relative to North America. Ross
et al. (1992) suggested that 1580 1600 Ma
detrital zircons in the Belt Supergroup
were derived from the Gawler Range volcanic rocks of South Australia and indicate
that Australia was well south of the original SWEAT position (Fig. 1). Similarly,
Borg and DePaolo (1994) speculated that
the Ross et al. (1992) reconstruction might
explain Nd isotopic provinces in Antarctica, if terranes had been translated southward as allochthonous strike-slip blocks.
However, neither these provenance nor
Nd province studies provide unique piercing points.
Brookfield (1993) placed Australia
adjacent to the western United States by
matching inferred rift-transform segments
of Proterozoic rift margins. Using a modified version of the Brookfield (1993)
reconstruction (Fig. 1), we propose that
Australia was adjacent to the southwestern
U.S. during much of the Proterozoic. To
test this hypothesis, we have rotated
BALTICA
1.4
1.51.3
1.46
1.3
1.46
1.25
1.27
BELT LAURENTIA
1.47 - 1.35
ROPER
GP.
1.43
BIRRINDUDU
1.56
AUSWUS
1.1
1.47
1.
1.44
1.1
1.451.35
1.44
1.1
BANGEMALL
GAWLER
1.45 - 1.3
1.59
1.42
1.37
AUSTRALIA
EASTERN
G -R 1.47
SOUTHERN
G - R 1.37
Shortening
Direction
Faults and Shear Zones
Dikes
1.1
Sedimentary Basins
Volcanics & Juvenile Crust
Granite & Anorthosite
ANTARCTICA
1000 Km
Pre-1.6 Ga Crust
1.6 - 1.3 Ga
BALTICA
1.2
1.16
SWEAT
1.3
1.3
1.3
1.25
1.25
1.27
1.27
AUSWUS
1.1
1.1
AUSTRALIA
1.1 E
MU
R
SE
SGR
1.1
D.V. 1.1
OA
XA
CA
GAWLER
BA
AL
UNKAR
AV
1.25
APACHE 1.1
Mafic Volcanics,
Anorthosite, Granite
Sedimentary Basins
Grenville Orogen
HI
se
O
nt
R
GE
Pr
Normal Faults
LL
BU
Mafic Dikes
GR
EN
VI
LL
E
NY
-FR
A
YENEENA
1.14
LAURENTIA
VICTORIA
1.2
Pre-1.3 Ga Crust
1000 Km
ax
ANTARCTICA
ac
a
1.3 - 1.0 Ga
BALTICA
0.9
SWEAT
Grenville Tectonism
FRANKLIN
.78
1.3
1.25
1.27
LAURENTIA
.58
AUSWUS
WYOMING
.78
Centralian
Super Basin
1.1
Mafic Dikes
1.1
A
C
1.1
DV
Oa
xa
ca
Gairdner
.83
Adelaidian
Normal Faults
and Transforms
OK
.55
AL
A-
Mo
So jave
no
ra
a
ac
ax
tO
en
es
Pr
ANTARCTICA
Chuar
Tex
a
0K
Neoproterozoic Basins
Pre-1.0 Ga Crust
1000 Km
900 - 600 Ma
4
equivalents; Ross, 1991). New paleomagnetic data from the Mundine Well dikes of
Australia (Wingate and Giddings, 1999)
also suggest that rifting between the western United States and Australia began
before 755 Ma.
PALEOMAGNETIC CONSTRAINTS
Paleomagnetic data provide another
way to test the competing Proterozoic
plate reconstructions. However, the scarce
Proterozoic data set with precise ages and
demonstrably primary magnetizations
does not unequivocally validate either the
SWEAT or the AUSWUS reconstruction.
Paleoproterozoic (2.51.6 Ga) data are
sparse for North America. Nevertheless,
using a reconstruction intermediate
between SWEAT and AUSWUS (Ross et al.,
1992), Idnurm and Giddings (1995) noted
a broad agreement between the Australian
and North American APW paths over the
entire interval 1.70.7 Ga. This conclusion
must be viewed with caution because of
the overall lack of well-dated primary paleomagnetic poles between 1.7 and 1.5 Ga
and 0.9 and 0.7 Ga, especially for
Laurentia.
A comparison of Mesoproterozoic
poles from Australia and North America
qualitatively favors the AUSWUS model.
With some uncertainties, the APW path
Refining Rodinia continued on p. 6
Figure 3. Orthogonal global projections centered on 30N, 180E showing comparison of the paleomagnetic poles from Australia with those from North
America for the AUSWUS and SWEAT reconstructions. In each projection, Australia and the Australian paleomagnetic poles are rotated into present-day North
American coordinates using Euler poles discussed in Table A (see footnote 1). The thick pink lines show the overall track of the ca. 1.45 to 1.1 Ga apparent
polar wander path for North America. Solid circles and thin lines denote Paleomagnetic poles for North America and their 95% confidence limits; red squares
and red heavy lines denote Australian poles and 95% confidence limits. Blue lettering gives age limits for segments of the North American path; black lettering
gives Australian poles and ages. Pole locations for the 1.25 to 1.08 Ma part of the North American apparent polar wander path are tabulated in Harlan et al.
(1994); sources for the ca. 1450 Ma poles are from Harlan and Geissman (1998). The 780 Ma North American poles are from Park et al. (1995), as slightly
modified by Harlan et al. (1997). The 723 Ma North American pole is from the Global Paleomagnetic Online Database. Sources and rotated coordinates for the
Australian poles are in Table A (see footnote 1).
CONCLUSIONS
We view the southern margin of Laurentia as a long-lived (1.81.0 Ga)
Cordilleran-type convergent margin
involving several orogenic events or tectonic pulses. This interpretation links a
sequence of southward-younging belts
along the evolving margin and leads to
looking for their continuations outside
present-day Laurentia. The approach of
using the integrated tectonic evolution of
an orogenic system for Precambrian plate
reconstructions is a powerful test of the
supercontinent concept. We note similar
1.80.8 Ga rocks and tectonic histories in
Australia, southern Laurentia, and Baltica.
In evaluating these three key segments of
the global supercontinent puzzle, we argue
that the AUSWUS model provides a better
explanation for the geologic and paleomagnetic data than does the SWEAT
reconstruction. In view of the uncertainty
1
Acknowledgments
Critical reviews by Paul Hoffman, Ian
Dalziel, and Eldridge Moores helped us
improve the manuscript. We also thank
Michael Wingate and Gerry Ross for helpful reviews and discussions.
References Cited
hll, Karl-Inge, and Connelly, Jim, 1998, Intermittent
1.531.13 Ga magmatism in western Baltica; age constraints and correlations within a postulated supercontinent: Precambrian Research, v. 92, p. 120.
hll, Karl-Inge, and Gower, C. F., 1997, The Gothian and
Labradorian orogens: Variations in accretionary tectonism
along a late Paleoproterozoic Laurentia-Baltic margin:
GFF, v. 119, p. 181191.
Aleinikoff, J. N., Evans, K., Fanning, C. M., Obradovich,
J. D., Ruppel, E. T., Zieg, J. A., and Steinmetz, J. C., 1997,
Shrimp U-Pb ages of felsic igneous rocks, Belt Supergroup,
western Montana: Geological Society of America Abstracts
with Programs, v. 28, no. 7, p. A-376.
Anderson, T. H., and Silver, L. T., 1979, The role of the
Mojave-Sonora megashear in the tectonic evolution of
northern Sonora, in Anderson, T. H. and RoldanQuintana, J., eds., Geology of northern Sonora (Geological Society of America Fieldtrip Guidebook 27): Pittsburgh, Pennsylvania, University of Pittsburgh, p. 5968.
Bennett, V. C., and DePaolo, D. J., 1987, Proterozoic
crustal history of the western United States as determined
by neodymium isotopic mapping: Geological Society of
America Bulletin, v. 99, p. 674685.
Blewett, R. S., Black, L. P., Sun, S. S., Knutson, J., Hutton,
L. J., and Bain, J. H. C., 1998, U-Pb zircon and Sm-Nd
geochronology of the Mesoproterozoic of North Queensland: Implications for a Rodinian connection with the
Belt Supergroup of North America: Precambrian Research,
v. 89, p. 101127.
Bond, G. C., Nickeson, P. A., and Kominz, M. A., 1984,
Breakup of a supercontinent between 625 and 555 Ma:
New evidence and implications for continental histories:
Earth and Planetary Science Letters, v. 70, p. 325345.
Borg, S. G., and DePaolo, D. J., 1994, Laurentia, Australia,
and Antarctica as a Late Proterozoic supercontinent: Constraints from isotopic mapping: Geology, v. 22, p.
307310.
Broookfield, M. E., 1993, Neoproterozoic LaurentiaAustralia fit: Geology, v. 21, p. 683686.
Camacho, A., Simons, B., and Schmidt, P. W., 1991, Geological and palaeomagnetic significance of the Kulgera
Dyke swarm, Musgrave Block, NT, Australia: Geophysical
Journal International, v. 107, p. 3745.
Clarke, G. L., Sun, S. S., and White, R. W., 1995,
Grenville-age belts and associated older terranes in Australia and Antarctica: AGSO Journal of Geology, v. 16, p.
2539.
Collins, W. J., and Shaw, R. D., 1995, Geochronological
constraints on orogenic events in the Arunta Inlier: A
review: Precambrian Research, v. 71, p. 315346.
Dalziel, I. W. D., 1991, Pacific margins of Laurentia and
East AntarcticaAustralia as a conjugate rift pair: Evidence
and implications for an Eocambrian supercontinent:
Geology, v. 19, p. 598601.
Dalziel, I. W. D., 1997, Overview: Neoproteorozic-Paleozoic geography and tectonics: Review, hypothesis, environmental speculations: Geological Society of America
Bulletin, v. 109, p. 1642.
Davidson, A., 1995, A review of the Grenville orogen in
its North American type area: Journal of Australian Geology and Geophysics, v. 16, p. 324.
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