HR: 10:20h
AN: T22B-01 INVITED    [Abstracts]
TI: The Goldilocks problem of making cratons
AU: * Lee, C
EM: ctlee@rice.edu
AF: Rice University, 6100 Main St., MS 126, houston, tx 77005, United States
AU: Luffi, P
EM: pluffi@rice.edu
AF: Rice University, 6100 Main St., MS 126, houston, tx 77005, United States
AU: Hoink, T
EM: tobias.hoeink@rice.edu
AF: Rice University, 6100 Main St., MS 126, houston, tx 77005, United States
AU: Li, Z
EM: zxli@rice.edu
AF: Rice University, 6100 Main St., MS 126, houston, tx 77005, United States
AU: Lenardic, A
EM: ajns@rice.edu
AF: Rice University, 6100 Main St., MS 126, houston, tx 77005, United States
AB: Cratons form the cores of continents and were formed within a narrow window of time (2.5-3.2 Gy ago), the majority having remained stable ever since. Petrologic evidence suggests that the thick mantle roots underlying many cratons might have been built by lithospheric stacking, but paradoxically this requires that the building blocks of cratons are weak even though cratons must have been strong subsequent to formation. Here, we show that thickening is facilitated by thrusting of oceanic lithospheres along weak shear zones, generated in the serpentinized upper part of the oceanic lithosphere (crust + mantle) due to hydrothermal interaction with seawater. Heating of the shear zones by thermal diffusion eventually causes serpentine breakdown at 600 oC, shutting down the shear zone and culminating in craton formation. However, if shear zones are too thin, then heating is too fast and underthrusting does not occur. If they are too thick, heating is too slow and stacking is never given a chance. Shear zone thicknesses of ~18 km are found to be favorable for craton formation. Because the original depth of seawater-induced serpentinization into the lithosphere is limited by the isotherm for serpentine breakdown, the shear zone thickness should have increased with time as the Earth's heat flux decayed with time. Thus, the early Archean was too hot, the Phanerozoic too cold, and the late Archean just right for making cratons.
DE: 1020 Composition of the continental crust
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 8103 Continental cratons
DE: 8104 Continental margins: convergent
DE: 8139 Obduction tectonics
SC: Tectonophysics [T]
MN: 2007 Fall Meeting