Stopping Plate Tectonics
Paul G. Silver
Carnegie Institution of Washington, DTM
Mark Behn
Woods Hole Oceanographic Institution
Intermittent Plate Tectonics on Earth:
I. Demonstrating Plausibility
• Assumption: Plate tectonics has never stopped.
 This assumption has rarely been challenged.
 There is, however, little compelling evidence to support it.
• Explore alternative: Plate tectonics (i.e., subduction) is intermittent.
 Significant hiatus possible during collisional phase of Wilson
Cycle due to “trench lock”.
 Length of hiatus depends on timing of subduction re-initiation.
 Implications of plate tectonic hiatus:
• A significant increase in sublithospheric mantle temperature
while in stagnant-lid mode.
• Implies temporal variations in mantle temperature tied to
Wilson Cycle.
Example: When the Pacific Closes
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Today
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100 my in future
• At current rates, Pacific closes in about 350 my.
• At this time all subduction stops, plate tectonics ceases.
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200 my in future
300 my in future
Critical Issue: Subduction Death and Birth
• Continent-continent collisions produce trench lock.
• Commonly assumed plate tectonic conservation law: Conservation of
Subduction-Zone Length. Subduction will spontaneously initiate
elsewhere to maintain plate tectonics.
• Plate tectonics is continuous in time only if subduction initiates
elsewhere during or before the onset of trench lock. Otherwise plate
tectonics stops.
• Question: When and where does (does not) subduction initiation
occur? Look at recent record.
• Intra-oceanic in Pacific.
• Not in Atlantic (neither at passive margin nor intra-oceanic).
• Not in response to response to recent episodes of trench lock.
Subduction Birth and
Death (Cont.)
• Cases of subduction initiation
in the last 80 my: TongaKermadec, Izu-BoninMarianas, Aleutians.
 All are in Pacific
 All are intra-oceanic.
• No subduction initiation in the
Atlantic (200my).
• No subduction initiation related
to either the India-Eurasian or
Africa-Eurasian trench lock.
(Gurnis et al., 2004)
Consequences of a Hiatus in Plate
Tectonics
• A long lag between the stoppage and initiation of subduction has
important geodynamic implications.
• Based on present-day examples, plate tectonics could stop for 10’s to
100’s of millions of years.
• This represents a transition from plate tectonics to stagnant-lid
tectonics: much less efficient in removing heat from mantle.
• Consequence: a significant increase in mantle temperature of up to
several hundred degrees.
Plate Tectonics
(Reese et al., 1998)
Stagnant Lid
Switching Between Plate Tectonics, Stagnant Lid
• Assume heat flow q solely a function of potential temperature q=q(T)
(large planet approximation).
• Two modes: Plate Tectonics, Stagnant lid.
• Trench lock leads to switch to stagnant lid.
• Trench lock produced by continent-continent collision, governed by
Wilson Cycle.
(After Sleep, 2000)
How Much, How Fast Does the Earth
Heat Up in Stagnant Lid Mode?
• T /t  A/C where,
 A = radioactive heat generation rate
 C = mantle heat capacity.
• Assume that in stagnant lid regime, heat
generation rate is much greater than
conductive heat loss.
• Then T /t is ~10oK/100my today and up
to 100oK/100my in the early Earth.

Time(109 yrs)
(Solomatov and Moresi, 1996)
Stopping Plate Tectonics
• Plate tectonics may shut down during supercontinent assembly
(trench lock).
• There will be a hiatus in plate tectonics if subduction initiation is
delayed.
• Such a hiatus constitutes stagnant lid convection and may be
accompanied by significant increase in sublithospheric mantle
temperature (tied to Wilson Cycle).
• Alternative: There is a subduction conservation law.
• Outstanding issues:
 Looking in geologic record.
 Highlights importance of understanding subduction initiation.