HR: 1340h
AN: U43B-0835    [Abstracts]
TI: Episodic Precambrian subduction
AU: * ONeill, C
EM: cjoneill@rice.edu
AF: Rice University, MS-126, Dept. Earth Science, 6100 Main St Houston, Houston, TX 77005 United States
AU: Lenardic, A
EM: adrian@geophysics.rice.edu
AF: Rice University, MS-126, Dept. Earth Science, 6100 Main St Houston, Houston, TX 77005 United States
AU: Moresi, L
EM: louis.moresi@sci.monash.edu.au
AF: Monash University, School of Mathematical Sciences, Melbroune, VIC 3800 Australia
AU: Torsvik, T
EM: trond.torsvik@ngu.no
AF: Geological Survey of Norway, Centre for Geodynamics Geological Survey of Norway Leiv Eirikssons vei 39, Tronheim, - 7491 Norway
AU: Lee, C A
EM: ctlee@rice.edu
AF: Rice University, MS-126, Dept. Earth Science, 6100 Main St Houston, Houston, TX 77005 United States
AB: The question of whether or not plate-tectonics operated in the early Precambrian has been hotly contested. Our primary source of information on Precambrian tectonics - the continental crust - shows marked peaks in preserved crust at discrete times. These peaks have been attributed to massive crustal growth during mantle avalanche events, where accumulating subducted slabs periodically penetrate the 670km discontinuity, initiating vigorous plume formation and, subsequently, large amounts of surface volcanism. Here we present paleomagnetic evidence for periods of rapid plate motions coinciding with the observed peaks in crustal age distribution. We have also run a large suite of numerical simulation that show that for hotter mantle conditions in the Precambrian Earth, steady-state plate tectonics breaks down, and subduction becomes extremely episodic. Episodic subduction explains the synchronous increase in plate velocities and massive crustal growth by arc-accretion, and the association of massive orogenesis with these periods. Subducting slabs would initiate plume formation at the CMB, resulting in surface volcanism and crustal remelting ~100Myr after the initial crustal formation events - consistent with late-stage intracrustal melting observed on many cratons, and providing an explanation for the combined plume/subduction signatures observed in many juvenile terranes.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8125 Evolution of the Earth (0325)
SC: Union [U]
MN: Fall Meeting 2005