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
ENDOGENIC
107-108 y
< 103 y
PLANETARY CATASTROPHIES
Atmosphere
Ocean
Biosphere
00.51.01.52.02.53.0AGE (Ga)
Accretionary Orogens
Large Igneous Provinces (LIPS)
Arc Systems
2.7 Ga
TECTONIC SETTINGS IN TIME
00.51.01.52.02.53.0AGE (Ga)
2.7 Ga
1.9 Ga
JUVENILE CONTINENTAL CRUST AGE
DISTRIBUTION
TTGs
2.5 Ga Southern
India
2.7 Ga Zimbabwe
4.0 Ga
Yellowknife
Canada
DEFORMED GRANITOID ZIRCON AGES
WITH END +1
DEFORMED GRANITOID ZIRCON AGES
WITH END +1
CATASTROPHIC
MANTLE PLUME EVENT
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
c = e - r
01.02.03.04.0
Time (Ga)
2
3
4
Production
Recycling
Preservation
2.7 Ga Event
1.88-1.62 Ga Events
c = e - r
Valley et al. 2005 CMP
00.51.01.52.02.53.0
AGE (Ga)
2.7 Ga
Superior
2.7 Ga
OROGENIC GOLD DEPOSITS
Yilgarn
2.65 Ga
00.51.01.52.02.53.0
AGE (Ga)
2.7 Ga
Carajas
2.6 Ga
IRON OXIDE COPPER-GOLD
(IOCG)
CHEMICAL INDEX OF ALTERATION (CIA)
50 60 70 80 90 100
Residual ClaysAmazon 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)
Age (Ga)
CIA
Mean
Modern Stromatolites from Sharks
Bay, Western Australia
2.7-Ga
Stromatolites
From Eastern
Canada
Stromatolite occurrencesPer unit volume of
Juvenile crust
1.9 Ga
2.7 Ga
Age (Ga)
Data from Hofmann 1998
-60
-50
-40
-30
-20
-10
0
1.2 1.6 2 2.4 2.8 3.2 3.6 4
13C
org
Age (Ga)
Data from Pavlov et al 2001 Geol 29: 1003-1006
13C = {[(13C/12C)s/(13C/12C)st] - 1} x 103
CH4 + O2 CH2O + H2O
VOLCANIC
CH4, CO2
CO2 + H2O CH2O + O2
CH2O CO2 + CH4
Methanogens
Methanotrophs
Oxidative Photosynthesis
FRACTIONATION OF CARBON ISOTOPES IN ORGANICS
0.1
1
0 0.5 1 1.5 2 2.5 3 3.5 4
0.5
2
Ce/
Ce*
Age (Ga)
BIF
Fe-Mn
ppts
After Kato et al. 2006
0.5
0.6
0.7
0.8
0.91
2
3
4
5
0 0.5 1 1.5 2 2.5 3 3.5 4
Eu
/Eu
*
Age (Ga)
Eu Anomalies in BIF
ModernHydrothermal
deposits
After Kato et al. 2006
-60
-50
-40
-30
-20
-10
0
1.2 1.6 2 2.4 2.8 3.2 3.6 4
13C
org
Age (Ga)
2.7-Ga GLOBAL MANTLE PLUME EVENT
onsetend
CH4 + CO2
Normal
Range
GLOBAL WARMING (CH4, CO2)
Increased intensity of chemical weathering
Negative 13C excursion in organic carbon
Enhanced CIA values in shales
Biodiversity/Biomass increase
Age (Ga)
Perc
ent
kom
ati
ite
KOMATIITES
�3.1
3.0
2.9
2.8
2.7
2.6
2.5
2.4
PILBARA KAAPVAAL
Ventersdorp
2725-2710 MaFortescue
2764-2756
MaAG
E (
Ga)
FLOOD BASALTS
0
10
20
30
40
50
60
70
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4
Archean cratonsProterozoic cratons
TRD
(Ga)
TRD
Re Model ages Mantle Xenoliths
187 Re 187 Os
4
6
8
10
12
14
5 10 15 20 25
PRIMARY MAGMA COMPOSITIONS
FeO
(T
) (%
)
MgO (%)
Mantle Plumes
Primary Magmas Calculated forArchean Cratonic Mantle
MORB and Arcs
After Herzberg (2004)
"Log-jam Tectonics"Stacked slices of hydrated oceanic
crust, plateaus, arcs
partial meltingof hydrated roots
DOWNWELLING
TTG
"Plume-head Underplating"
Older crustFlood Basalts
partial meltingin plume head
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 Mackenzie Swarm 1267 Ma
Northern Canada
Amerilyk Dykes 2.9 Ga SW
Greenland
Age (Ma)
LIP EVENTS
JUVENILE CRUST
EVENTS
BANDED IRON
FORMATION
Transvaal Group
South Africa
2.5 Ga
Lake Superior Region
USA-Canada
2.0 Ga
Superior
Yilgarn
Banded Fe
Formation
India, S Africa,
Brazil, Ukraine
LIP
Events
Age (Ma)
Hamersley
N China
CONTROLS ON BIF DEPOSITION
BIF
Submarine Volcanism
Marginal Basins
Upwelling Photosynthesis
Fe+2
OxygenSea Level R
ise
BIF
Submarine Volcanism
Marginal Basins
Upwelling Photosynthesis
Fe+2
Oxygen
Sea Level R
ise
POTENTIAL TRIGGERS FOR 2.5-Ga BIF
EVENT: Fe+2, CO2, Sea level rise
1. Supercontinent breakup
2. Global mantle plume event
1. Juvenile Crust Events
2. LIP Events
TWO TYPES OF MANTLE
PLUME 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
1. SLAB AVALANCHE (Condie, 1998)
2. CORE RESONANCE (Greff-Lefftz & Legros, 1999)
3. ASTEROID IMPACT (Abbott & Isley, 2002)
POSSIBLE TRIGGERS FOR
CATASTROPHIC MANTLE PLUME EVENTS
AN UPDATE OF THE CONTINUING SAGA
DURING THE LATE ARCHEAN
• High resolution U/Pb zircon ages suggest the existenceof a global tectonic/thermal event at 2.7 (perhapsmultiple events over < 50 My).
• This resulted in rapid growth of continental crust andmantle lithosphere. This may have been caused bycatastrophic collapse of slabs through the 660-kmseismic discontinuity initiating a global mantle plumeevent. Alternatively, this may reflect the onset ofglobal plate tectonics.
• Plume-derived CH4 (± CO2) may be responsible forglobal warming and increased 13 C fractionation inorganics at 2.7 Ga.
• A “shielding” type mantle plume event at 2.5 Ga maybe responsible for deposition of enormous amounts ofBIF at this time.
Proterozoic Prokaryotic microfossils. Methanotrophs?
-4
-2
0
2
4
6
8
10
0 1000 2000 3000 4000
Epsilo
n N
d (
T)
Age (Ma)
DM
CHUR
ENd Evolution of Depleted Mantle
After Bennett 2003
2.7-Ga Event