WHEN DID PLATE TECTONICS BEGIN ON PLANET EARTH• The onset of plate tectonics is not an event, but an evolving process that began locally by about 3 Ga. • Plate tectonics, in some
Post on 05-Jun-2020
1 Views
Preview:
Transcript
WHEN DID PLATETECTONICS BEGIN ON
PLANET EARTH ?
Kent C. CondieDepartment of Earth and Environmental Science
New Mexico TechSocorro, NM 87801 USA
3000
2800
2600
2400
220001.02.03.04.0
Time (Ga)
1018
1017
1016
1015Temperature
Viscosity
MANTLE EVOLUTION
POSSIBLE PLATE TECTONIC RETURNS
1. Asymmetric Subduction 2. Symmetric Subduction
3. Plate Sinking
Distance (km)
Figure Courtesy of Steve Holbrook
New Continental Crust is formed in arcs
such as the Aleutian Arc
Pillow basalts
Andesites
Breccia
Felsic volcanics
Graywackes
Boninites
Melange
ISLAND
ARCS
Pillow basalts
Andesites
Breccia
Felsic volcanics
Graywackes
Boninites
Melange
ISLAND
ARCS
Pillow basalts
Andesites
Breccia
Felsic volcanics
Graywackes
Boninites
Melange
ISLAND
ARCS
Pillow basalts
Andesites
Breccia
Felsic volcanics
Graywackes
Boninites
Melange
ISLAND
ARCS
Pillow basalts
Andesites
Breccia
Felsic volcanics
Graywackes
Boninites
Melange
ISLAND
ARCS
Pillow basalts
Andesites
Breccia
Felsic volcanics
Graywackes
Boninites
Melange
ISLAND
ARCS
Pillow basalts
Andesites
Breccia
Felsic volcanics
Graywackes
Boninites
Melange
ISLAND
ARCS
3.4
2.7Foreland Basins
Passive Margins
3.1Arcs
2.7
Continental Rifts3.0
1.0 2.0 03.0Ga
Accretionary Prisms
3.0 Ga 1.0 2.0 0
3.0 Ga 1.0 2.0 0
2.7Foreland Basins
DEVELOPMENT OF PASSIVE MARGINS
3.0 Ga 1.0 2.0 0
Passive Margins2.7
3.0 Ga 1.0 2.0 0
Continental Rifts3.0
3.0 Ga 1.0 2.0 0
3.4Metallic Mineral Deposits
Accretionary Prisms3.1
Arcs
2.7Foreland Basins
Passive Margins2.7
Continental Rifts3.0
3.0 Ga 1.0 2.0 0
3.4Metallic Mineral Deposits
3.3
Paired Metamorphic Belts
3.0 Ga 1.0 2.0 0
Subduction zones are coldSubduction zones are cold
Backarcs are hotBackarcs are hot
3.0 Ga 1.0 2.0 0
Large Transcurrent Faults
3.2
3.0 Ga 1.0 2.0 0
Accretionary Orogens
3.7
3.0 Ga 1.0 2.0 0
Collisional Orogens
2.2
PALEOMAGNETISM ALLOWS THE
RECONSTRUCTION OF SUPERCONTINENTS
SUCH AS GONDWANA SOME 600 Million years
ago
3.0 Ga 1.0 2.0 0
Paleomagnetism3.0
10
100
0 10 20 30
Zr/Nb
Nb/Th
DEP
NMORB
DM
EN
ARC
UC
EM2
HIMU
EM1
OIB
REC
PM
3.0 Ga 1.0 2.0 0
3.1Igneous Geochemistry
Arc type
> 3 Ga 1.0 Ga2.5 Ga
Non-Arc
type
SEISMIC REFLECTION PROFILE EASTERN CANADA
Magnetotelluric data illustrate Magnetotelluric data illustrate
lithospheric mantle structure: frozen slabs?lithospheric mantle structure: frozen slabs?
2.7 Deep Seated Geophysics
3.0 Ga 1.0 2.0 0
3.3
Paired Metamorphic Belts
Collisional Orogens
2.2
3.0 Ga 1.0 2.0 0
3.1Igneous Geochemistry
Large Transcurrent Faults
3.2Accretionary Orogens
3.7
Paleomagnetism3.0
2.7 Deep Seated Geophysics
• Pi; Pillow Basalts from
the Troodos
Ophiolite , CyprusText
Blueschist with garnet from the Alps
courtesy of Jane Selverstone
Ultra-high pressure eclogite (garnet, omphacite, coesite)
courtesy of Mike Brown
38
3939
40
SUMMARY OF PLATE TECTONIC INDICATORS
3.4 -3.1 Ga
First
Appearances
2.7-2.0 Ga
Widespread
Distribution
Symmetric Subduction
Steep Subduction
Plate Stacking
Delamination
> 4.5 Ga ?
3.0 - 2.0 Ga
4.5 - 3.0 Ga
eclogite
sinkers
43
Stagnant
Lid
Episodic
Subduction
Modern
Subduction
I II III
After O’Neill et al 2007
SUMMARY
• The onset of plate tectonics is not an
event, but an evolving process that
began locally by about 3 Ga.
• Plate tectonics, in some form, probably
existed on planet Earth from the
magma ocean stage onwards.
• Modern subduction became
widespread beginning about 2.7 Ga.
AND HIGHER LIFE FORMS REQUIRE
CONTINENTS
and
CONTINENTS REQUIRE PLATE
TECTONICS
IS THERE A RELATIONSHIP
BETWEEN LIFE AND PLATE
TECTONICS?
Life requires water and nutrients
But water and nutrients are
available on planets without plate
tectonics
The Oldest Fossils occur
In the Marble Bar Chert in
Western Australia at 3.45 Ga
Modern hydrothermal vent
on the seafloor
HOW CONTINENTS GROW
JUVENILE
CONTINENTAL
CRUST
2.5 Ga Southern
India
2.7 Ga Zimbabwe
4.0 Ga
Yellowknife
Canada
top related