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