WHAT ON EARTH HAPPENED
2.7 BILLION YEARS AGO?
Kent C. Condie
Dept. Earth and Environmental Science
New Mexico Tech
Socorro, NM 87801 USA
EXOGENIC
< 103 y
Atmosphere
Ocean
Biosphere
ENDOGENIC
107-108 y
PLANETARY CATASTROPHIES
2.7 Ga
Arc Systems
Large Igneous Provinces (LIPS)
Accretionary Orogens
3.0
2.5
2.0
1.5
AGE (Ga)
1.0
TECTONIC SETTINGS IN TIME
0.5
0
2.7 Ga
1.9 Ga
3.0
2.5
2.0
1.5
AGE (Ga)
1.0
0.5
JUVENILE CONTINENTAL CRUST AGE
DISTRIBUTION
0
2.7 Ga Zimbabwe
2.5 Ga Southern
India
4.0 Ga
Yellowknife
Canada
TTGs
DEFORMED GRANITOID ZIRCON AGES
WITH END ≥ +1
Relative probability
n = 1983
2700
1705
291
172
450
560
1655
1890
2115
807
2740
2555
1562
3785
3308
0
1000
2000
Age (Ma)
3000
4000
DEFORMED GRANITOID ZIRCON AGES
WITH END ≥ +1
Relative probability
2700
2695
2690
2710
2662
2650
2731
2740
2679
2700
Age (Ma)
2750
CATASTROPHIC
MANTLE PLUME EVENT
c=e-r
c = crustal preservation rate
e = crustal extraction rate
r = crustal recycling rate
s = sediment subduction
b = subduction erosion
d = lithosphere delamination
r=s+b+d
2.7 Ga Event
4
c=e-r
1.88-1.62 Ga Events
3
Preservation
Production
2
Recycling
4.0
2.0
3.0
Time (Ga)
1.0
0
Valley et al. 2005 CMP
2.7 Ga
Superior
2.7 Ga
Yilgarn
2.65 Ga
3.0
2.5
2.0
1.5
1.0
AGE (Ga)
OROGENIC GOLD DEPOSITS
0.5
0
2.7 Ga
Carajas
2.6 Ga
3.0
2.5
2.0
1.5
1.0
AGE (Ga)
IRON OXIDE COPPER-GOLD
(IOCG)
0.5
0
CHEMICAL INDEX OF ALTERATION (CIA)
50
60
70
80
Residual Clays
Amazon Muds
Average Shale
Glacial Clay
Average Upper
Continental Crust
CIA = [Al2O3/(Al2O3+CaO+Na2O+K2O)] x 100
Molecular values
includes silicate CaO only
Nesbitt and Young (1982)
90
100
Age (Ga)
Modern Stromatolites from Sharks
Bay, Western Australia
2.7-Ga
Stromatolites
From Eastern
Canada
Data from Hofmann 1998
1.9 Ga
Stromatolite occurrences
Per unit volume of
Juvenile crust
2.7 Ga
Age (Ga)
13C = {[(13C/12C)s/(13C/12C)st] - 1} x 103
0
Data from Pavlov et al 2001 Geol 29: 1003-1006
-10
-30
13
 Corg
-20
-40
-50
-60
1.2
1.6
2
2.4
2.8
Age (Ga)
3.2
3.6
4
Methanotrophs
CH4 + O2
CH2O + H2O
VOLCANIC
CH4, CO2
Oxidative Photosynthesis
CO2 + H2O
CH2O + O2
CH2O
CO2 + CH4
Methanogens
FRACTIONATION OF CARBON ISOTOPES IN ORGANICS
2
Fe-Mn
ppts
1
Ce/Ce*
BIF
0.5
0.1
0
0.5
1
1.5
2
2.5
Age (Ga)
3
3.5
4
After Kato et al. 2006
Eu Anomalies in BIF
5
4
Eu/Eu*
3
2
Modern
Hydrothermal
deposits
1
0.9
0.8
0.7
0.6
0.5
0
0.5
1
1.5
2
2.5
Age (Ga)
3
3.5
4
After Kato et al. 2006
0
2.7-Ga GLOBAL MANTLE PLUME EVENT
-10
CH4 + CO2
end
onset
Normal
Range
-30
13
 Corg
-20
-40
-50
-60
1.2
1.6
2
2.4
2.8
Age (Ga)
3.2
3.6
4
GLOBAL WARMING (CH4, CO2)
Increased intensity of chemical weathering
Negative 13C excursion in organic carbon
Enhanced CIA values in shales
Biodiversity/Biomass increase
Percent komatiite
Age (Ga)
KOMATIITES
AGE (Ga)
FLOOD BASALTS
Fortescue
2764-2756
Ma
PILBARA
Ventersdorp
2725-2710 Ma
KAAPVAAL
QuickTime™ and a
decompressor
are needed to see this pi cture.
187 Re
T
RD
187 Os
Re Model ages Mantle Xenoliths
70
60
Archean cratons
Proterozoic cratons
50
40
30
20
10
0
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4
T (Ga)
RD
PRIMARY MAGMA COMPOSITIONS
14
Primary Magmas Calculated for
Archean Cratonic Mantle
FeO (T) (%)
12
Mantle
Plumes
10
8
MORB and Arcs
6
After Herzberg (2004)
4
5
10
15
MgO (%)
20
25
"Log-jam Tectonics"
"Plume-head Underplating"
Stacked slices of hydrated oceanic
crust, plateaus, arcs
Flood Basalts
TTG
Older crust
partial melting
in plume head
partial melting
of hydrated roots
DOWNWELLING
Superior and Zimbabwe Provinces
Kaapvaal and Pilbara Provinces
2.7 Ga Tectonic Scenarios
CATASTROPHIC MANTLE
PLUME EVENT
•
•
•
•
•
•
Juvenile continental crust
Supercontinent
Mineral Deposits
Thick lithosphere (plume restite)
Global warming
Increase in biologic activity
LARGE IGNEOUS PROVINCES
YOUNG LIPS
Flood basalts in Iceland with
Columnar Joints
Karoo Basalts at
Victoria Falls
Zimbabwe
GIANT DYKE SWARMS
Amerilyk Dykes 2.9 Ga SW
Greenland
Mackenzie Swarm 1267 Ma
Northern Canada
2445
2215
2040
LIP EVENTS
2410
2505
2110
2712
2735
2903
2574
2000
2200
2400
2600
2800
3000
JUVENILE CRUST
EVENTS
Relative probability
2700
2100
2000
2200
2400
2600
(Ma)
Age Age
(Ma)
2800
3000
BANDED IRON
FORMATION
Transvaal Group
South Africa
2.5 Ga
Lake Superior Region
USA-Canada
2.0 Ga
SEA LEVEL AND
UPWELLING
High Sea Level
BIF Deposition
Upwelling
Low Sea Level
Relative probability
2440
LIP
Events
2410
2215
2505
2712
2040 2110
2735
2574
2000
2200
2400
2600
2903
2750
2800
3000
Age (Ma)
Hamersley
N China
Banded Fe
Formation
India, S Africa,
Brazil, Ukraine
Superior
Yilgarn
CONTROLS ON BIF DEPOSITION
Submarine Volcanism
Fe+2
Upwelling
Photosynthesis
BIF
Oxygen
Marginal Basins
Submarine Volcanism
Fe+2
Upwelling
BIF
Photosynthesis
Oxygen
Marginal Basins
POTENTIAL TRIGGERS FOR 2.5-Ga BIF
EVENT: Fe+2, CO2, Sea level rise
1. Supercontinent breakup
2. Global mantle plume event
TWO TYPES OF MANTLE
PLUME EVENTS ?
1. Juvenile Crust Events
2. LIP Events
OR
The onset of the first episode of global plate tectonics
(Juvenile Crust Event)
And a global mantle plume event
(LIP Events)
1. JUVENILE CRUST EVENTS (Catastrophic Mantle Event)
2. LIP EVENTS
(Large Plate Shielding)
Growth Continents
Global warming
Biologic expansion
Thick lithosphere
Mineral deposits
BIF
Giant dyke swarms
Flood basalts
POSSIBLE TRIGGERS FOR
CATASTROPHIC MANTLE PLUME EVENTS
1.
SLAB AVALANCHE
2. CORE RESONANCE
(Condie, 1998)
(Greff-Lefftz & Legros, 1999)
3. ASTEROID IMPACT
(Abbott & Isley, 2002)
AN UPDATE OF THE CONTINUING SAGA
DURING THE LATE ARCHEAN
• High resolution U/Pb zircon ages suggest the existence
of a global tectonic/thermal event at 2.7 (perhaps
multiple events over < 50 My).
• This resulted in rapid growth of continental crust and
mantle lithosphere. This may have been caused by
catastrophic collapse of slabs through the 660-km
seismic discontinuity initiating a global mantle plume
event. Alternatively, this may reflect the onset of
global plate tectonics.
• Plume-derived CH4 (± CO2) may be responsible for
global warming and increased  C fractionation in
organics at 2.7 Ga.
• A “shielding” type mantle plume event at 2.5 Ga may
be responsible for deposition of enormous amounts of
BIF at this time.
Proterozoic Prokaryotic microfossils. Methanotrophs?
ENd Evolution of Depleted Mantle
10
After Bennett 2003
Epsilon Nd (T)
8
DM
6
4
2
0
CHUR
-2
-4
0
1000
2000
3000
Age (Ma)
4000
2.7-Ga Event