1. Tectonic Settings of Archean Sedimentary Basins with possible
Implications for Plate Tectonics on the early Earth
Ken Eriksson
Subsidence in a sedimentary basin is a product of:
1) sediment loading, and 2) tectonics.
Is tectonic component related to plate tectonics?

2. Tectonic subsidence mechanisms and resultant sedimentary basins

3. Archean sedimentary associations
Bimodal volcanic + terrigenous conglomerate/sandstone: Rift?
Quartz arenite +/- carbonate: Intracratonic sag / passive margin?
Terrigenous conglomerate/sandstone:
Compressional foreland? and Collisional graben?
Calcalkaline volcanic + volcaniclastic conglom./sandstone: Forearc?
Sandstone, mudstone, BIF, mafic/ultramafic: Shelf to plume?

4. Modified from McKenzie, 1978)
(From McKenzie, 1978; Wernicke, 1985)
Pure Shear
Model
Simple Shear Model
Total Subsidence (S) =
Initial Rift-related Subsidence (Si)
+ Thermotectonic Subsidence (Sth)
(Pure Shear Model
Modified from McKenzie, 1978)

5. Widespread Thermal Subsidence represented by the Chuniespoort Group
( Ga)
– preserved in a structural basin
Initial Subsidence in isolated grabens and half grabens represented by the Ventersdorp Group (~2.7 Ga)

6. P – Pretoria C – Chuniespoort V – Ventersdorp
Based on Two Way Travel Times of Tinker et al. (2002)
1)Thickness of Venterdorp is
~4 km
2) Thickness of Chuniespoort is ~1.8 km
P – Pretoria
C – Chuniespoort
V – Ventersdorp
(from Tinker et al., 2002)

7. Sth (Chuniespoort) = 1.8km For crustal thickness:
Thicknesses 1 β =
S (∫s/v - ∫m)
tc (∫c - ∫m)
Si (Ventersdorp) = 4.0km
Sth (Chuniespoort) = 1.8km
S = 5.8km
For crustal thickness:
30km, β = 1.23
40 km, β = 1.17
(i.e. ~ 20% extension)
β = Amount of crustal extension
∫m = Mantle density (3.3g/cm3)
∫c = Crustal density (2.8g/cm3)
∫s/v = Average density of sediment/
volcanic fill (2.8g/cm3)
S = Total Subsidence
tc = Thickness Continental Crust
(from Bickle and Eriksson,1982)

8. The Witwatersrand and Pongola successions (3.0-2.8 Ga)
make up the “Greater Witwatersrand Basin” with
greater than 10 km of Total Subsidence
(based on Tankard et al., 1982)

9. Greater Witwatersrand Basin is interpreted as a
(From Nelson et al., 1995)
Greater Witwatersrand Basin
is interpreted as a
Retroarc Foreland Basin
passing southwards into a
passive margin -
comparable to modern South
America
Overall maximum
grain size
decreases
from northwest to
southeast
The two structural basins are
separated by a peripheral bulge
related to syndepositional
crustal loading

10. Auriferous conglomerates are anomalous Conglomerates overlie
low-angle unconformities
Pebbles and heavy minerals in
auriferous conglomerates (placers)
were concentrated by winnowing of
footwall
(Blenkinsop and Eriksson, 1995)
Unconformities are a product
of syndepositional warping/
folding in the basin
Evidence for syndepositional
warping?
(From Tweedie, 1986)

11. Other evidence for syndepositional warping/folding
(From Antrobus et al., 1986)
(From Antrobus and Whiteside, 1964)

12. Barberton Greenstone Belt
Fig Tree and Moodies Groups ( Ga)
are interpreted by Jackson, Eriksson and Harris (1986)
as foreland basin deposits associated with south-to-north
crustal shortening.
Others have interpreted the Moodies Group as rift deposits
(from Jackson, Eriksson and Harris, 1986)

13. Evidence for crustal shortening
Northern Barberton Greenstone Belt
Southern Barberton Greenstone Belt
Evidence for crustal shortening
Syndepositional folding and
thrust faulting
2. Intraformational unconformities
3. Recycling

14. Moodies conglomerates are dominated
by chert clasts and subordinate mafic
and felsic volcanic, granitic, jaspilitic
clasts + rare clasts of conglomerate
and botryoidal vein quartz
Clast types imply recycling of
Onverwacht and progressive
unroofing of granitic rocks
+ recycling of Fig Tree and
Moodies

15. Fig Tree sandstones (graywackes) are lithic and Moodies sandstones are
quartzose
This trend indicates recycling of
Onverwacht and progressive unroofing
of granitoids
Fig Tree

16. Moodies
Moodies
Moodies developed in shallow-water
alluvial and tidal environments – “Molasse”
Fig Tree developed in deeper water
environments – “Flysch”
Fig Tree

17. Pilbara Block, Western Australia Late-stage strike-slip faults
(From Krapez and Barley, 1988)
Pilbara Block,
Western Australia
From Krapez, 1984
Late-stage strike-slip faults
transect the Pilbara Block
Lalla Rookh Basin (~3.0 Ga)
is interpreted by Krapez as a
pull-apart basin

18. Evidence for marginal fault control
on basin development
Great thickness relative to basin size
Elongate shape of basin
Asymmetry of facies distribution
Vertical stacking of facies
Dominance of longitudinal infill

19. Superior Province is transected by late-stage, east-west trending
(From Mueller and Corcoran, 1998)
Superior Province is transected by
late-stage, east-west trending
strike-slip faults
Duparquet Basin is one of
a number of interpreted strike-slip
basin deposits in the Superior
Province with similar characteristics
to the Lalla Rookh Basin in the
Pilbara
(From Mueller and Corcoran , 1998)

20. CONCLUSION
On the modern Earth, sedimentary basins are a product of crustal thinning, thermal contraction, thrust loading and pull-apart related to mantle convection and plate tectonics.
Recognition of these basin types in the Archean record may similarly imply plume activity and relative plate motions.