Earth and Planetary Science Letters 238 (2005) 156 – 171
www.elsevier.com/locate/epsl
Late Archean to Early Paleoproterozoic global tectonics,
environmental change and the rise of atmospheric oxygen
Mark E. Barley a,*, Andrey Bekker b,1, Bryan Krapež a,2
a
School of Earth and Geographical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia
b
Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington DC 20015, USA
Received 23 August 2004; received in revised form 14 June 2005; accepted 24 June 2005
Available online 24 August 2005
Editor: E. Boyle
Abstract
Analysis of the tectonostratigraphic records of Late Archean to Early Paleoproterozoic terranes indicates linkage between
global tectonics, changing sea levels and environmental conditions. A Late Archean tectonic cycle started at ~2.78 Ga
involving the breakup of a pre-existing continent (Vaalbara) and the most prodigious period of generation and preservation of
juvenile continental crust recorded in Earth history during a period of plume breakout (~2.72 to 2.65 Ga) accompanied by high
sea levels. During this period, cratons formed by accretion of granitoid–greenstone terranes at convergent margins started to
aggregate into larger continents (e.g. Kenorland). Lower sea levels between ~2.65 and 2.55 Ga were followed by a second
(~2.51 to 2.45 Ga) period of plume breakout resulting in a global peak in magmatism, high sea levels and deposition of banded
iron formations (BIF) on the trailing margins of the Pilbara and Kaapvaal cratons. Cratons in South Australia, Antarctica, India,
and China record convergent margin magmatism, orogeny and high-grade metamorphism between 2.56 and 2.42 Ga.
Continued aggregation of continental fragments (e.g. amalgamation of Indian cratons) may have formed the Earth’s first
supercontinent by ~2.4 Ga with a return to low sea levels and relative tectonic quiescence before the supercontinent started to
breakup from ~2.32 Ga.
Although oxygenic photosynthesis had evolved by 2.71 Ga, the irreversible rise of atmospheric O2 to N 10 5 PAL appears to
have occurred between 2.47 and 2.40 Ga following the second plume breakout and coinciding with a decline in BIF deposition
and the maximum extent of the supercontinent suggesting dynamic linkage between tectonics and both the sources and sinks of
oxygen. Periods of plume breakout (2.72 to 2.65 Ga and 2.51 to 2.45 Ga) would have limited ocean productivity and the rate of
photosynthesis and also enhanced the reduced conditions typical of the Archean biosphere, as well as the greenhouse gas
contents of the atmosphere necessary to maintain temperate conditions. This suggests that either an increase in the oxidation
state of volcanic gasses during the second plume breakout, or a decreased flux of reduced gasses following plume breakout,
coupled with the filling of crustal oxygen sinks and possibly also an increase in ocean productivity and the rate of
photosynthesis resulted in the global flux of reduced gasses falling below oxygen production leading to a rise of atmospheric
* Corresponding author. Tel.: +61 8 64887322; fax: +61 8 64881037.
E-mail addresses: [email protected] (M.E. Barley), [email protected] (A. Bekker), [email protected] (B. Krapež).
1
Tel.: +1 202 4787974; fax: +1 202 4788901.
2
Tel.: +61 8 64882771; fax: +61 8 64881037.
0012-821X/$ - see front matter D 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.epsl.2005.06.062
M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
157
O2 accompanied by loss of the CH4-rich greenhouse atmosphere resulting in the Earth’s first widespread glaciation. Detrital
pyrite and uraninite in 2.45 to 2.40 Ga sediments suggests that terrestrial surface environments were not yet extensively
oxidized. The oldest evidence of extensive oxidative weathering is associated with 2.32 to 2.22 Ga glacial deposits and breakup
of the supercontinent.
D 2005 Elsevier B.V. All rights reserved.
Keywords: Archean; Paleoproterozoic; global tectonics; environmental change; oxygen
1. Introduction
The Late Archean to Early Paleoproterozoic (2.8 to
2.2 Ga) is a key period in Earth history. It records one
of the most important episodes of growth and preservation of continental crust followed by the transition
from oxygen poor to oxygenated conditions in the
atmosphere and widespread glaciation. The recent
discovery of non-mass dependent fractionation
(NMDF) in sulfur isotopes has provided a new tool
for tracing changes in the oxygen content of the atmosphere and reduced the uncertainty regarding the timing of the initial rise in atmospheric oxygen [1–3].
Sulfur from Archean sedimentary sulfides and sulfates
has D33S values that range from 2.5 to + 8.1x
whereas sulfides and sulfates younger than ~2.32 Ga
have D33S signals b0.4x [3]. Preservation of large
NMDF signals in the Archean requires an anoxic
atmosphere; lack of NMDF in rocks younger than
2.32 Ga is thus consistent with significant quantities
of oxygen (N 10 5 PAL, present atmospheric levels) in
Earth’s atmosphere. The youngest well dated sedimentary sulphides with a NMDF signal N 0.4x are
hosted by 2.47 Ga banded iron formations (BIF) of
the Brockman Supersequence in the Pilbara Craton
[1,4]. The oldest sedimentary sulphides with a stratigraphically persistent NMDF signal that is b 0.4x
occur in shales of the Lower Huronian Supergroup
in the Superior Craton that directly underlie the first
Huronian glacial diamictite [5]. If, as we argue below,
the oldest glacial diamictites in the Superior and
Pilbara cratons can be correlated, it is most likely
that the transition from an anoxic atmosphere to an
atmosphere with oxygen N 10 5 PAL occurred
between 2.47 and 2.40 Ga.
Although the timing of the rise of atmospheric O2
is becoming better-established, its cause remains hotly
debated [6–10]. Cyanobacteria, the first oxygenic
photosynthesizers, have been identified from organic
biomarkers in sedimentary rocks as old as 2.71 Ga
[11], and may have been associated with much older
microfossils and stromatolites. Furthermore, the fact
that d 13C values of carbonates have remained near
0x throughout most of Earth history suggests that
organic carbon has been buried at a rate more-or-less
proportional to its production and input to the atmosphere [7]. If so, sinks for oxygen rather than its
source may have changed suggesting a geological
rather than biological control on the timing of the
rise in O2. Kasting et al. [12], Kump et al. [7], and
Holland [8] have argued that changing redox state of
volcanic gasses resulted in irreversible oxidation of
the atmosphere at some time between 2.5 and 2.2 Ga.
In contrast Catling et al. [6] and others have argued
that the oxidation state of volcanic gasses has
remained approximately constant and that higher
Archean atmospheric CH4 contents resulted in faster
escape of H2 to outer space. In this scenario, irreversible oxidation of the atmosphere would have
occurred when available crustal oxygen sinks were
satisfied such that the global flux of reduced gasses
fell below the photosynthetic rate of oxygen production [6,13]. Bjerrum and Canfield [9] have also
pointed out that adsorption of phosphorous onto iron
oxides deposited as BIF during the Late Archean and
Paleoproterozoic would have inhibited organic productivity reducing rates of photosynthesis and contributing to low concentrations of atmospheric oxygen.
Resolution of the cause of the rise in O2 requires a
much better understanding of the balance between
oxygen sources and sinks including the dynamic
role of those sinks and element cycles that are controlled by global tectonics (cf. [10]).
Links between Phanerozoic tectonics and environmental change are well documented, with greenhouse
conditions and high sea level accompanying periods
of enhanced global magmatism (plume breakout or
superplume events) during the breakup and aggrega-
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M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
lish correlation of key events and environmental indicators. The picture that emerges is of a Late Archean
to Early Paleoproterozoic tectonic cycle (including the
largest plume breakout event preserved in the rock
record), linked to changing relative sea levels culminating in formation of the Earth’s first supercontinent
by 2.4 Ga. Oxidation of the atmosphere and loss of
Late Archean greenhouse conditions resulting in the
Earth’s first widespread glaciations followed soon
after a second period of plume breakout coinciding
with a decline in BIF deposition during the final
stages of amalgamation of this supercontinent suggesting dynamic linkage between the source and
sinks of oxygen and global tectonics. Breakup of the
continent was accompanied by episodic glaciation and
oxidative weathering of the continental crust.
tion of supercontinents followed by periods of low
sea-level and episodic glaciation (Fig. 1). For plausible parameters computer modeling of mantle layering
and convection through geological time [14] predict
episodic mantle overturn and plume breakout during
the Archean (replacement of upper mantle by deeper
hotter mantle) with a major event at ~2.7 Ga possibly
involving orders of magnitude greater heat flux and
mafic magmatism than Phanerozoic plume breakout
events. Although it is widely accepted that plume
breakouts accompanied formation of a supercontinent
or supercontinents during the Late Archean to Early
Paleoproterozoic [15–20], links between global tectonics and environmental conditions during this period are not well understood. As a result, the transition
from the Late Archean to the Early Paleoproterozoic
is generally viewed as a secular change from a tectonic regime dominated by mantle plume activity to a
quiet period with little evidence of modern tectonic
processes.
We here review the tectonostratigraphic records of
several cratons using precise geochronology to estab-
2. Phanerozoic tectonics and environmental change
Although the Earth’s tectonic regime may have
changed since the Archean, links between Phanero-
Phanerozoic Tectonic Cycles
200
Relative Sea Level (m)
Pangea
Assembly
Breakup
Pannotia
PBE
Breakup
Pangea
PBE
100
PBE
Sea Level
0
*
*
G
600
NP
500
C
Ord
400
S
*
G
Dev
G
300
Age (Ma)
Carb
P
200
Tr
Jur
100
Cret
0
Cz
Fig. 1. Phanerozoic tectonic cycles and eustatic sea level relative to present sea level over the past 600 million years. PBE = plume breakout
event, G = glaciation.
M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
zoic tectonics and environmental change provide a
useful background for this analysis of the Archean
to Paleoproterozoic rock record. Global tectonics can
be viewed as the cyclic breakup, dispersal and assembly of supercontinents or the cyclic contraction and
expansion of the external ocean (currently the combined Pacific and Indian Oceans). Because the movement of fragments of continental crust is controlled by
the production and subduction of ocean crust at plate
margins, it is unlikely that each global tectonic cycle
involves the complete breakup and re-aggregation of a
supercontinent, rather that periods when continental
dispersal is the dominant tectonic process are followed by periods when continental assembly is dominant forming new supercontinents that include most,
but not necessarily all, continental fragments. The
rifting and breakup of continents forms internal or
Atlantic-type oceans which may either close or
become part of the external ocean as the next supercontinent forms with these tectonic events recorded by
the rock records of continental margins and orogens as
described by Murphy and Nance [21,22] and Krapez
[23]. Phanerozoic tectonic evolution can be described
in terms of one and a half ~360 Ma cycles of supercontinent breakup and aggregation [15,23–25]. During the Late Neoproterozoic (from ~590 Ma) and
Early Paleozoic, a supercontinent broke up. Continental plates later reassembled at the end of the Paleozoic
to form Triassic Pangea, which broke up during the
Mesozoic with continental separation closely linked to
mantle plume magmatism [26].
Although the present distribution of mantle plumes
appears independent of plate-scale mantle flow, periods of constant magnetic field polarity lasting up to 40
Ma and enhanced global magmatism during the Ordovician (~500–460 Ma), Permo–Carboniferous (~300–
260 Ma), and Cretaceous (120–80 Ma) are interpreted
to represent elevated mantle plume activity (Fig. 1),
referred to as plume breakout or superplume events
[20,27,28]. While numerous large igneous provinces
provide strong evidence for periods of plume breakout
during the Cretaceous and Late Archean to Proterozoic [20,29], evidence for the Paleozoic events is
more ambiguous. Worsley et al. [30] and Nance et
al. [15] have proposed models linking sea-level, biogeochemical cycles and climate changes to supercontinent cyclity since the Archean, whereas Krapez [23],
Barley et al. [29], and Condie [20,31] described the
159
combined effects of plume breakout events and global
tectonics.
Because a range of tectonic processes are occurring
in different places on the Earth at any one time, links
between global tectonics and environmental conditions are complex with changes reflecting the effects
of those processes which have a dominant input at a
particular time. Aggregation of fragments of continental crust to form a supercontinent tends to favor global
low sea levels and cooler climates [32,33]. This is
because rapid uplift and exposure along sutures during
the assembly of continental fragments will result in
enhanced erosion and chemical weathering which
together with biological productivity draw CO2
down from the atmosphere. This combined with
increasing albedo (linked to land–water ratio) can
lead to large continental ice sheets. However, tectonic
stasis during the maximum extent of a supercontinent
will depress both physical erosion and chemical
weathering allowing atmospheric CO2 levels to rise
and resulting in warmer climates. Breakup of the
supercontinent, with uplift during the early stages of
rifting, will initially favor erosion and weathering
thereby drawing down atmospheric CO2 and resulting
in cool climates. Enhanced volcanism during breakup
will result in new hydrothermally active spreading
ridges and subduction zone magmatism, elevating
sea levels, and promoting anoxia in the deep ocean.
Elevated CO2 levels, due to mantle degassing, promote warmer climates and increased weathering rates
with increased deposition of carbonate, both as sediment on continental margins and by submarine hydrothermal alteration. Expansion of anoxic water onto
continental shelves and into intracontinental basins
increases burial of organic carbon. The environmental
effects of plume breakout (high sea level, ocean
anoxia, elevated CO2, increased carbonate and
organic carbon burial, warm climates) will enhance
the effects of continental breakup (possibly to the
extent of nullifying the effects of initial uplift and
weathering of rifting continental margins), and may
also either nullify or moderate the environmental
effects of supercontinent formation.
The Neoproterozoic saw the growth of a supercontinent, episodic global glaciation and a rise in
atmospheric oxygen to levels comparable to present
atmospheric abundances [34]. This was followed by
continental breakup and dispersal during the Cam-
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brian and Ordovician, with volcanism and sedimentation in marginal basin environments and thick successions of sulfide-rich black shales (Fig. 1). The
Ordovician saw one of the global peaks in production
of volcanogenic massive sulfide deposits, episodic
ironstone deposition, a peak in ophiolite obduction
(closure of marginal basins and terrane accretion),
convergent margin magmatism, the largest explosive
volcanic eruption preserved in the Phanerozoic rock
record, and high sea level during plume breakout
[28,35–38]. This was followed by sea level drop
and Late Ordovician–Silurian glaciation [33], with
sea levels reaching a minimum during the Silurian.
As more continental fragments assembled during the
late Paleozoic to form Pangea, ~50% of the world’s
coal reserves were deposited during the Permo–Carboniferous plume breakout accompanied by high sealevels, episodic marine anoxia, excursions in C and Sr
sea-water isotopic signatures [20,28] and elevated
atmospheric oxygen levels. Although northern hemisphere climates were warm at this time the southern
continent Gondwanaland experienced Permian glaciation [32] with sea-level reaching a minimum at the
Permo–Triassic boundary.
The breakup of Pangea was initiated by lithospheric extension and coincident plume magmatism
during the Triassic and Jurassic with the development
of extensive marginal basins [26]. Plume breakout
during the Cretaceous saw the closure of many of
these basins due to terrane accretion, a peak in convergent margin magmatism, high sea level, oceanic
anoxia, extensive deposition of black shales (including ~60% of world’s oil reserves), and episodic
deposition of ironstones [20,27]. This also coincided
with high concentrations of atmospheric CO2, elevated global temperatures and extensive deposition
of marine carbonates. Following the separation of
Australia and Antarctica and India–Eurasia collision,
global climates have become cooler with late Cenozoic ice ages [32,33].
3. Archean to Paleoproterozoic tectonics — 2.8 to
2.41 Ga
In the absence of reliable paleomagnetic constraints, the geological records of Late Archean to
Paleoproterozoic continental margins (Figs. 2 and 3)
provide the best record of the breakup and assembly
of ancient continents and supercontinents [23], and
the abundance of large igneous provinces including
komatiites and coeval accelerated growth of juvenile
continental crust provide evidence for periods of
plume breakout [20,29,31].
The Pilbara and Kaapvaal cratons (Figs. 2 and 3)
functioned as stable continental lithosphere at 2.8 Ga
and may have been part of the continent Vaalbara [14].
In the Pilbara, bimodal tholeiitic volcanic rocks and
associated clastic sedimentary rocks of the Nullagine
Supersequence were deposited in continental graben
between 2.77 and 2.73 Ga [39,40]. These are overlain
by the Mt Jope Supersequence, a large igneous province comprising tholeiitic to mildly alkaline flood
basalt, with local komatiitic basalts and interlayered
stromatolitic carbonates deposited in an intracontinental rift basin between 2.73 and 2.715 Ga [40]. In the
northern Pilbara, lava flows were subaerial, whereas in
the south submarine pillowed flows are typical. The
overlying Jeerinah Formation deposited after 2.71 Ga
records a marine transgression. This unit contains
N 200 m of sulfidic black shales, and is intruded by a
suite of dolerite sills. The distribution of volcanic and
sedimentary facies is consistent with successful rifting
of the now southern margin of the craton. In the eastern
Pilbara, the Jeerinah Formation is overlain by the
shallow-water stromatolitic ~2.63 Ga Carawine Dolomite [41]. In the western and central Pilbara, there is
apparently an unconformity at the base of the ~2.63 Ga
Roy Hill Shale of the Jeerinah Formation that coincides with the transition from rifting to passive margin
sedimentation [41] indicating breakup of a continent
and formation of an internal ocean.
The Kaapvaal Craton records a similar history with
2.72 to 2.64 Ga continental komatiitic basalts, tholeiitic basalts and sedimentary rocks of the Ventersdorp
large igneous province overlain by transgressive black
shales and carbonates of the ~2.64 Ga Schmidtsdrif
Subgroup of the Griqualand West Basin and Buffalo
Springs/Wolkberg and Black Reef Quartzite of the
Transvaal Basin [42]. The 2.78 to 2.60 Ga histories
of the Pilbara and Kaapvaal cratons provide clear
evidence for a Late Archean period of continental
breakup enhanced by mantle plume magmatism.
In contrast, granitoid–greenstone terranes worldwide record the formation of new continental crust
at convergent margins between 2.8 and 2.6 Ga. The
M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
161
Fig. 2. Comparison of the tectonic histories of representative Late Archean rifted and convergent margins during the Late Archean to
Paleoproterozoic.
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M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
eastern Yilgarn Craton in Western Australia and the
Abitibi Belt in the Canadian Superior Province (Figs.
2 and 3) are Earth’s largest and most intensely mineralized Late Archean greenstone belts. Both terranes
have tectonic histories that are tightly constrained by
high-precision geochronology. The evolution of the
Superior Province involved multiple komatiite, tholeiite and calk-alkaline volcanic assemblages from
~2.78 Ga [43]. Submarine magmatism culminated
with the eruption of extensive suites of mantle
plume derived komatiites at 2.72 to 2.70 Ga. Extensive hydrothermal activity, produced volcanic massive
sulfide mineralization and BIF deposition in anoxic
arc-related basins. Arc and plume magmatism were
followed by orogenic deformation, granitoid emplacement (by 2.68 Ga), stabilization of continental lithosphere and collision with the other cratons to form the
Kenorland continent [16,18].
In the eastern Yilgarn Craton, early ~2.78 to 2.72
Ga arc and back-arc basin associations were followed
by coeval 2.72 to 2.70 Ga deep-marine mantle-plume
derived tholeiite–komatiite and tholeiite–calc-alkaline
arc associations [29]. The period 2.70 to 2.66 Ga saw
episodic deep-water volcaniclastic sedimentation
(with black shales and layered mafic–ultramafic
sills) in the Kalgoorlie Terrane and regional emplacement of granitoids. This was followed by terrane
accretion, orogeny and stabilization of continental
lithosphere between 2.65 and 2.62 Ga. Most other
Late Archean greenstone terranes show similar histories that parallel those recorded by marginal basins
to the Pacific (such as the Rocas Verdes Basin) during
the Mesozoic breakup of Pangea [29]. The postulated
period of plume breakout between 2.72 and 2.66 Ga
[29,31] is recorded by elevated magmatism and high
sea levels on all Late Archean cratons.
Fig. 3. A. Schematic diagrams (not to scale) illustrating changing environmental conditions and the tectonic evolution of the Pilbara Craton as a
type example of the rock record of the margin to an internal ocean during a full Late Archean to Paleoproterozoic global tectonic cycle. B.
Schematic diagrams (not to scale) illustrating changing environmental conditions and the tectonic evolution of representative convergent
margins during the Late Archean to Paleoproterozoic global tectonic cycle.
M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
163
Fig. 3 (continued).
The formation of Kenorland [16,18] and possible
collision of the Zimbabwe and Kaapvaal cratons at
~2.6 Ga [44] provides evidence that Late Archean
cratons started to aggregate into larger continents at
that time. Importantly granitoid–greenstone terranes
and high-grade gneiss belts in the Gawler Craton,
Antarctica, India, and China [45–48] provide evidence
for a second cycle of convergent margin tectonics and
collision of cratons between 2.6 and ~2.42 Ga. The
Gawler Craton (Figs 2 and 3) contains 2.56 to 2.5 Ga
ultramafic to felsic volcanic rocks (including ~2.51
Ga plume-derived komatiites), metasedimentary
rocks, and granitoids with compositions that are typical of Archean granitoid–greenstone terranes interpreted to have formed at convergent continental
margins [49]. These were deformed, intruded by granitoids and metamorphosed to high-grade (up to granulite facies) during the 2.48 to 2.42 Ga Sleafordian
orogenic cycle, that also affected equivalent rocks in
east Antarctica [46]. Central India and possibly eastern North China have similar histories from ~2.6 Ga
culminating with orogeny and high-grade granulite
facies metamorphism between ~2.5 and 2.42 Ga
[47,48] corresponding to the aggregation and stabilization of Indian cratons within a larger continent.
Anticlockwise P–T-time paths in granulites are characteristic of thickened and magmatically heated crust
in continental margin magmatic arcs such as the Cretaceous granulites of Fiordland in SW New Zealand
[50].
The Pilbara and Kaapvaal are the only cratons with
relatively complete and well-dated 2.6 to 2.4 Ga
supracrustal rock records (Figs. 2 and 3). Flexural
reactivation of the southern Pilbara margin from
~2.59 Ga, following deposition of platform carbonates, black shales and banded iron formations on a
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M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
passive margin (Carawine Dolomite, Roy Hill Shale,
Marra Mamba Iron Formation, making up the Marra
Mamba Supersequence), led to deposition of a deepwater carbonate ramp and then a condensed sequence
of black shales (respectively Paraburdoo and Bee
Gorge Supersequences in the Wittenoom Dolomite).
These are overlain by repeated cycles of deep-water
shale, carbonate and banded iron formation of the
2.50–2.45 Ga Brockman Supersequence, with maximum BIF deposition between 2.47–2.45 Ga coincident with emplacement of a bimodal large igneous
province [41,51,52]. The Brockman Supersequence is
the youngest well-dated unit that contains sulfides
with D33S values N0.4x [1, 4], indicating that atmospheric oxygen levels were still low at this time. The
Boolgeeda Iron Formation at the top of the Brockman
Supersequence is overlain by the upwards-shallowing
Turee Creek Supersequence comprising basin-plain
(including resedimented glacial diamictites of the
Meteorite Bore Member), carbonate-platform and fluviodeltaic facies, deposited in a foreland basin [25],
indicating collision with another continental fragment,
lower relative sea levels and a colder climate. Our
ongoing work indicates that the youngest relatively
abundant, distinct population of detrital zircons in
quartzites in the upper part of the Turee Creek
Group (overlying the Meteorite Bore Member) is
2420 F 10 Ma, consistent with deposition of the
group between 2.45 and 2.40 Ga.
The Kaapvaal succession comprises 2.6–2.5 Ga
upward-deepening carbonates overlain by BIF, including shallow-water reduced facies [53], and an uppermost predominantly clastic sedimentary succession
recording conversion to compressional tectonics
[54]. Zircons in tuff layers in the BIF indicate that
volcanism and BIF deposition are the same age as in
the Pilbara [55]. The 2.59–2.40 Ga tectonic histories
of the Pilbara and Kaapvaal cratons are interpreted to
reflect the conversion from trailing passive margins of
an internal ocean to convergent continental margins of
a Tethyan-style external ocean [23].
Barley et al. [51] and Kump et al. [7] suggest that
the period 2.5–2.45 Ga is a global plume breakout
event recorded by mafic magmatism on several continents as well as high sea-levels and BIF deposition.
Large igneous provinces between 2.5–2.45 Ga also
occur in the Superior, Wyoming and Fennoscandian
Cratons. In the Superior Craton, the Matachewan and
Hearst Dykes are dated at 2.47 and 2.45 Ga coeval
with bimodal volcanism at the base of the Huronian
Supergroup [56]. Continental extension and mafic
large igneous provinces are also dated at 2.5 to 2.44
Ga in Fennoscandia [57]. These igneous provinces are
generally viewed as incipient rifting of the Kenorland
continent [18], but the global picture with magmatism
coeval with BIF deposition on the continental margins
to the Pilbara and Kaapvaal, and with granitoid–
greenstone terranes and high-grade gneiss belts in
other cratons followed by low sea level and global
tectonic quiescence, is consistent with the ~2.5 to 2.45
Ga event representing plume breakout during the
advanced stages of supercontinent assembly with limited production of new continental crust, similar to the
Permo–Carboniferous event. The best age constraint
on the final stages of Late Archean continental assembly is the 2.42 Ga end to the Sleafordian orogenic
cycle [46] that coincides with foreland basin sedimentation in the Pilbara and Kaapvaal cratons and the start
of a period with little evidence of orogeny (tectonic
quiescence).
Thus, the growing database of high precision geochronology from most Archean cratons reinforces the
interpretation of Blake and Barley [39] that the
Hamersley Province (Mount Bruce Supergroup) of
the Pilbara Craton is the rock record of a Late Archean
to Paleoproterozoic 2.78 to 2.40 Ga global tectonic
cycle involving continental breakup and the possible
formation of a supercontinent. Plume breakout during
the breakup phase of this cycle resulted in enhanced
submarine and convergent margin magmatism corresponding to one of the most prodigious periods of
continental crust formation in Earth history
[20,29,31]. These continental fragments appear to
have amalgamated to form Earth’s first supercontinent
by ~2.40 Ga.
4. Paleoproterozoic tectonics — 2.40 to ~2.2 Ga
Widespread continental erosion and the scarcity of
easily datable supracrustal rocks, are consistent with
the existence of a 2.4 Ga high-standing supercontinent, but hamper interpretation of Earth history in the
critical period between 2.40 and 2.2 Ga. Most cratons
preserve evidence of intracontinental extension and
episodic mafic magmatism from ~2.4 to 2.2 Ga,
M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
with continental, rift and passive margin environments
variably preserved in the Kaapvaal, Superior, Hearne,
Rae, Wyoming and Fennoscandian cratons. In the
Pilbara, an ~380 Ma hiatus separates the Turee
Creek Supersequence from oxidized clastic sedimentary rocks, basalts and carbonates of the Lower Wyloo
Group that were deposited at ~2.03 Ga [58].
The Kaapvaal Craton (Fig. 2) has an important and
poorly dated succession of continental volcanic and
sedimentary rocks deposited between 2.4 and 2.0 Ga
[59]. In the Transvaal Basin, the Lower Pretoria
Group unconformably overlying N 2.40 Ga BIFs, carbonates and clastic sedimentary rocks comprises the
Rooithoogte–Duitschland and Timeball Hill formations was deposited in a continental basin open to
an ocean to the southwest. The Rooithoogte Formation comprises a lower glacial diamictite, overlain by
basalt, sandstones and black shales containing the
oldest well-dated syngenetic pyrite (2.32 Ga by ReOs isochron [60]) with D33S values less than 0.4x
indicating that atmospheric oxygen was N10 5 PAL
[3]. The correlative Duitschland Formation also contains glacial diamictites overlain by cap carbonates
with negative carbon isotope values, sandstones marking a prominent sequence boundary, and overlying
carbonates with carbon isotope values as high as
+ 10x [59]. Sandstones overlying the Lower Timeball
Hill shales contain extensive shallow-water deposits
of hematite oolites and pisolites indicating oxygenated
conditions. These are in turn overlain by younger
diamictites, the oldest partially oxidized lateritic
weathering profile [61] developed on continental
lavas of the Hekpoort Formation. This succession is
generally correlated with altered submarine lavas of
the ~2.22 Ga Ongeluk andesite that overlie the Makganyene diamictites [62,63] and are conformably
overlain by BIF and manganese deposits of the Hotazel Formation and the Mooidrai dolomite indicating
rifting and flooding of the continental margin. In both
the Kaapvaal and Pilbara cratons economically important BIF-hosted hematite deposits formed between 2.2
and 2.0 Ga [58,62,64].
In the Superior Craton a major hiatus separates the
greenstone and granite–gneiss terrane from the overlying Huronian Supergroup (Fig. 2). The Huronian
Supergroup comprises four tectonostratigraphic cycles
[19]. The oldest contains 2.48 to 2.45 Ga bimodal
volcanic rocks (coeval with the Matachewan and
165
Hearst Dyke swarms) overlain by continental sedimentary rocks that are in turn overlain by three cycles
that begin with glaciogene sedimentary rocks and pass
upwards into basinal mudrocks and carbonates and
then to fluvial or shallow-marine sandstones deposited
under more temperate conditions. Successions below
and above the first glacial diamictite (the Ramsay
Lake Formation) contain detrital uraninite and pyrite,
although shales immediately underlying and overlying
the Ramsay Lake Formation contain the oldest sedimentary sulfides with D33S values b0.4x suggesting
that levels of atmospheric oxygen were N10 5 PAL at
this time [5]. Carbonates of the Espanola Formation
sitting on the second glacial diamictite (the Bruce
Formation) have negative carbon isotope values and
are likely correlative with carbonates of the Duitschland Formation in South Africa [59,65]. The third
Huronian glacial diamictite occurs in the lower part
of the Gowganda Formation, the lowermost unit of the
upper Huronian. The upper part of the Gowganda
Formation contains redbeds, with an oxidized paleosol developed below the overlying Lorrain Formation
[66]. The upper Huronian is interpreted as comprising
the transition from a rifted to passive continental
margin [19]. The mafic Nipissing sills dated at
2217 F 1.6 Ma provide the minimum age for deposition [67]. Thin carbonates in the upper Huronian
Supergroup, above the Gowganda Formation diamictite have highly positive carbon isotope values similar
to those found worldwide in carbonates with ages
between N 2.22 and 2.1 Ga [65,68]. The Wyoming
and Fennoscandian cratons also contain a similar
record of continental sedimentation, rifting, glaciation, carbon isotope excursions and subsequent
breakup [65,69,70].
Bekker et al. [59] have suggested that it is possible
to correlate early Paleoproterozoic successions based
on glacial deposits and carbonate chemostratigraphy
inferring that the second and third Huronian diamictites are equivalent to diamictites at the base of the
Rooithoogte–Duitschland Formation and top of the
Timeball Hill Formation, respectively. If so the oldest
Huronian diamictite and the N2.40 Ga Turee Creek
diamictite may also be equivalents, as both occur in
conformable successions above 2.45 Ga volcanic
rocks, with the first widespread glaciation following
relatively soon (perhaps within 10 to 40 million
years) after the 2.5–2.45 Ga plume breakout event.
166
M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
The first and second glacials are further constrained
by the ~2.32 Ga age of the Rooithoogte Formation
[60], with a minimum age for the third provided by
the 2.22 Ga age of the Ongeluk lavas [63] and
Nipissing sills [67] Although there is not yet sufficient precise geochronology to allow chronostratigraphic correlation of 2.4 to 2.2 Ga tectonic events
between cratons, the picture that emerges is one of
widespread continental erosion (low relative sea
level) and sedimentation in intracontinental basins
followed by rifting, flooding of continental margins
and breakup of the supercontinent, with some rifted
continental margins formed by ~2.32 Ga.
5. Global tectonics environmental change and the
rise of atmospheric oxygen
This review suggests that although containing the
rock record of the largest episode of plume breakout
recorded in Earth history, the tectonostratigraphic
records of Late Archean and Early Paleoproterozoic
terranes record a global tectonic cycle involving continental breakup followed by growth and aggregation
of continental fragments to form large continents or a
supercontinent that was broadly similar in style, duration and relative timing to Phanerozoic tectonic cycles.
Were relative sea level, climate and conditions in the
atmosphere and hydrosphere also linked to tectonics?
Late Archean (Figs. 2 and 3) continental breakup
started at ~2.78 Ga with stable, high-standing (low
relative sea level) continental crust in the Pilbara and
Kaapvaal Cratons (possible Vaalbra continent). Subsequent intracontinental extension, sedimentation,
volcanism and rifting were succeeded by flooding of
continental margins and deposition of sulphidic black
shales during a 2.71 to 2.65 Ga period of plume
breakout. These passive margins to an Atlantic-type
internal ocean saw a return to lower relative sea levels
by 2.59 Ga. Coeval 2.78 to 2.6 Ga granitoid–greenstone terranes record growth and stabilization of juvenile continental crust via the opening and closure of
marine basins (including BIF deposition), terrane
accretion and magmatism at convergent continental
margins of the external ocean. The period of plume
breakout between 2.72 and 2.65 was the most prodigious episode of juvenile continental crust formation
preserved in Earth history [20,29,31] consistent with
computer models which predict that this event
involved orders of magnitude greater heat flux and
mafic magmatism than Phanerozoic plume breakout
events [12]. Granitoid–greenstone and granite–gneiss
terranes started to amalgamate to form stable cratons
and continents from ~2.65 Ga (e.g. Kenorland). However, shallow-marine carbonate sedimentation after
2.6 Ga was followed by deposition of black shales
and BIF on the trailing continental margins of the
Pilbara and Kaapvaal cratons coincident with plume
breakout from ~2.50 to 2.45 Ga. The following return
to lower relative sea levels and orogenic sedimentation after 2.45 Ga reflects possible terrane collision
and conversion to the margin of an external ocean.
Importantly, granitoid–greenstone terranes, and gneiss
belts in Australia, Antarctica, India and North China
record histories of convergent margin tectonics, magmatism, orogeny and high-grade metamorphism
between 2.6 and ~2.42 Ga culminating in the amalgamation of cratons into a larger continent or supercontinent (e.g. amalgamation and stabilization of
Indian cratons, [47]).
Archean continental sediments contain detrital pyrite, uraninite and siderite [71,72]. Highly carbonaceous shales from this period are also not enriched in
redox sensitive elements [73], early diagenetic pyrite
has d 34 S compositions consistent with low seawater
sulfate concentrations [74], and sedimentary sulfide
NMDF signals N0.4 per mil D33S [1,2,4]. All these
features are consistent with an anoxic atmosphere and
hydrosphere, although oxygenic photosynthesis dates
from at least 2.71 Ga [11] and may be older. In this
regard it is noteworthy that black shales from the
period 2.72–2.65 Ga have some of the most negative
d 13C isotopic compositions of kerogen and total
organic carbon recorded, most likely reflecting
methane production and recycling by methanogens
and methanotrophs [75,76].
If the Turee Creek and oldest Huronian glaciation
represent the Earth’s oldest widespread glaciation, the
rise of atmospheric O2 to N 10 5 PAL occurred at some
time between 2.47 and 2.40 Ga, following a period of
plume breakout and coinciding with assembly of the
Earth’s first supercontinent. If oxygenic photosynthesizers had evolved by 2.71 Ga, why did reducing
conditions persist for more than 250 million years?
The most likely explanation for this is that atmospheric
O2 levels were not able to rise until photosynthetic
M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
oxygen production was able to satisfy the available
global oxygen sinks. The magnitude of the oxygen
sinks (reduced volcanic gasses, plus new ocean and
continental crust and BIF) produced during the 2.71 to
2.66 Ga plume breakout, compared to younger plume
breakout events, would have delayed oxidation of the
oceans and atmosphere, favoring anerobic biogenic
production of CH4 (e.g. [76]), enhanced atmospheric
CO2 and CH4 levels, and the greenhouse conditions
necessary to maintain temperate conditions. The
increased hydrothermal flux of iron and deposition
of iron oxides as BIF during plume breakout would
have also limited phosphorous abundance and inhibited ocean organic productivity and rates of photosynthesis contributing to low concentrations of
atmospheric oxygen [9,10]. Reduced conditions with
atmospheric O2 b10 5 PAL continued during the 2.51
to 2.45 Ga plume breakout event.
The Kump et al. model [7] for irreversible oxidation
of the atmosphere due to an increase in the oxidation
state of volcanic gasses between the two plume breakout events accompanied by filling of crustal O2 sinks is
the only model that specifically predicts rapid initial
oxidation of the atmosphere (sufficient to reduce the
sulfur NMDF signal) during or before the 2.51 to 2.45
Ga plume breakout. The main objection raised to this
hypothesis is that the abundances of redox sensitive
trace elements indicate little difference between the
redox state of the sources of Archean and modern
Mg-rich mafic magmas [77]. However, most preserved
Archean Mg-rich volcanic rocks are thought to have
formed in either mantle-plume or subduction-related
environments [29,43,78] and therefore may reflect
subducted oceanic crust and not be representative of
the oxidation state of magmas derived from the upper
mantle at Late Archean oceanic spreading centres.
Thus changing oxidation states of volcanic gasses
[7,8,12] remains a possible explanation for the initial
rise of atmospheric oxygen. If global deposition of
BIFs declined at the end of the 2.51 to 2.45 Ga
plume breakout [51,79] ocean productivity and the
rate of photosynthesis may also have increased at
this time contributing to rising O2 levels [9,10].
If rapid loss of hydrogen to space from a CH4-rich
atmosphere coupled with filling of the main global
sinks for oxygen as argued by Catling et al. and
Kasting [6,13] provides the explanation for the rise
of oxygen, Early Paleoproterozoic tectonics may pro-
167
vide favorable conditions for this change (Fig. 4). The
major flux of reduced gasses, hydrothermal alteration
and serpentinization of oceanic crust, and oxidation of
ferrous iron to form extensive BIFs would have been
major global O2 sinks during 2.51–2.45 Ga plume
breakout. High-grade metamorphism during 2.5 to
2.42 Ga continental assembly may also have been
an important oxygen sink producing a significant
flux of reduced gasses, although coeval weathering
of uplifted orogens would draw down atmospheric
CO2. Thus the decreased flux of reduced gasses
after 2.45 Ga coupled with a possible increase in
ocean productivity and the filling of oxygen sinks
produced during plume breakout and continental
assembly may have resulted in the global flux of
reduced gasses falling below that of photosynthetic
oxygen production leading to a rise in atmospheric O2
to N 10 5 PAL which was accompanied by loss of the
CH4-rich greenhouse atmosphere resulting in the
Earth’s first widespread glaciation. The persistence
of detrital pyrite and uraninite in 2.45 to 2.40 Ga
sediments suggests that deep weathering oxidative
weathering of continental crust in terrestrial environments had not yet occurred.
A plausible climatic scenario is rapid reduction of
atmospheric CH4 levels due to rising atmospheric O2
following 2.51 to 2.45 Ga plume breakout during
supercontinent assembly accompanied by draw
down of CO2 resulting in the first widespread glaciation (Meteorite Bore Member of the Turee Creek
Group, Ramsay Lake Formation of the Huronian
Supergroup). This was possibly followed by a period
of rising atmospheric CO2 from ongoing mafic volcanism, and inhibited weathering during tectonic
quiescence with a return to milder climates. Atmospheric O2, CH4 and CO2 levels may have fluctuated
between glacial and interglacial periods [65,80]. Deep
weathering during the initial stages of rifting and
breakup reduced atmospheric CO2 and resulted in
further glaciations at ~2.32 Ga. with a positive carbon
isotope excursion between the second and third suggesting increased organic carbon burial and a further
rise in atmospheric oxygen [59] coinciding with the
oldest evidence of extensive oxidative surface weathering. If the oxidation state of volcanic gasses has not
changed significantly since the Archean, lower magnitude post-Archean plume breakout events (compared to the 2.72 to 2.65 Ga event) clearly have not
168
M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
Fig. 4. Schematic diagrams (not to scale) illustrating the links between tectonics and changing global environmental conditions between 2.5 and
2.22 Ga.
M.E. Barley et al. / Earth and Planetary Science Letters 238 (2005) 156–171
produced sufficient volumes of reduced gasses and
crustal oxygen sinks to reverse oxidation of the atmosphere, although widespread deposition of BIF during
a major period of increased growth of juvenile continental crust and plume breakout between 2.0 and 1.8
Ga [20,79] suggests a return to anoxic conditions in
the ocean at that time [10].
Although there remains uncertainty over its exact
timing and cause, this analysis indicates that irreversible oxidation of the atmosphere most likely occurred
during or soon after the 2.51 to 2.45 Ga plume breakout coinciding with a decline in BIF deposition and
maximum assembly of the Earth’s first supercontinent.
Systematic S and Fe isotope studies linked to geochronology of diagenetic sulfides and phosphates in
the upper Brockman and Turee Creek supersequences
and Lower Huronian Supergroup, and the geochronology of low temperature alteration in Late Archean
sedimentary basins have the potential to unambiguously resolve the timing of specific events related to
the rise of atmospheric oxygen. It is clear that better
chronostratigraphic resolution of the geological and
geochemical records will ultimately resolve the true
complexity of coevolving Earth systems during the
Late Archean and Early Paleoproterozoic and may
ultimately allow a quantitative view of the dynamic
interplay between the source and sinks for oxygen.
Acknowledgements
We acknowledge support from the Australian
Research Council, the Minerals and Energy Research
Institute of Western Australia, NASA Astrobiology
and the Carnegie Institution of Washington. Lee
Kump is thanked for prompting this exploration of
dynamic links between Archean–Paleoproterozoic
global tectonics and environmental conditions, for
reading early drafts of the manuscript and discussion
and comments that significantly improved them. We
appreciate helpful reviews by David Evans, Jim Kasting and an anonymous reviewer.
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