Mathematics – Logic
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995e%26psl.129...85d&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 129, no. 1-4, p.85-102
Mathematics
Logic
188
Continental Drift, Lithosphere, Magma, Ocean Bottom, Slabs, Subduction (Geology), Tectonics, Basalt, Buoyancy, Collisions, Planetary Evolution
Scientific paper
We present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision (slab breakoff), allowing an explanation of syn-to post-collisional magmatism and metamorphism. Continental collisions are preceded by subduction of dense oceanic lithosphere, and followed by attempted subduction of buoyant continental lithosphere. This situation of opposing buoyancy forces leads to extensional deformation in the subducted slab. A narrow rifting mode of deformation will result if there is strain localization. Slab breakoff results. We have assessed the plausibility of this process by quantitatively evaluating an upper bound for the strength of the lithosphere, and have compared it with the change in buoyancy force during continental subduction. Whether breakoff will occur, and the depth at which it will occur, is a strong function of temperature and hence the subduction velocity. As a result of the rifting during breakoff, the asthenosphere upwells into the narrow rift, and following breakoff it impinges on the mechanical lithosphere of the overriding plate. The resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere, producing basaltic magmatism that leads to granitic magmatism in the crust. Breakoff removes the force at the downdip side of the continental crust, while the enhanced heating leads to a reduction of the strength of the underlying crust. Both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface, leading to the rapid exhumation of eclogite facies continental curst. The cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen. We tested the variety of predicted expressions of slab breakoff in the geological record of the Alps, the Aegean Islands, and the Dabie Shan.
Davies John H.
von Blanckenburg Friedhelm
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