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Titolo:
Experimental constraints on the depth of olivine metastability in subducting lithosphere
Autore:
Mosenfelder, JL; Marton, FC; Ross, CR; Kerschhofer, L; Rubie, DC;
Indirizzi:
Univ Bayreuth, Bayer Geoinst, D-95440 Bayreuth, Germany Univ Bayreuth Bayreuth Germany D-95440 eoinst, D-95440 Bayreuth, Germany Carnegie Inst Washington, Geophys Lab, Washington, DC 20015 USA Carnegie Inst Washington Washington DC USA 20015 Washington, DC 20015 USA Carnegie Inst Washington, Ctr High Pressure Res, Washington, DC 20015 USA Carnegie Inst Washington Washington DC USA 20015 Washington, DC 20015 USA St Jude Childrens Hosp, Dept Biol Struct, Memphis, TN 38105 USA St Jude Childrens Hosp Memphis TN USA 38105 Struct, Memphis, TN 38105 USA Siemens Business Serv GMBH & Co OHG, D-81739 Munich, Germany Siemens Business Serv GMBH & Co OHG Munich Germany D-81739 nich, Germany
Titolo Testata:
PHYSICS OF THE EARTH AND PLANETARY INTERIORS
fascicolo: 1-4, volume: 127, anno: 2001,
pagine: 165 - 180
SICI:
0031-9201(200112)127:1-4<165:ECOTDO>2.0.ZU;2-0
Fonte:
ISI
Lingua:
ENG
Soggetto:
ALPHA-BETA TRANSFORMATION; SAN-CARLOS-OLIVINE; DEEP-FOCUS EARTHQUAKES; SPINEL TRANSFORMATION; PHASE-TRANSFORMATIONS; ZONE CONDITIONS; SEISMIC DISCONTINUITIES; OCEANIC LITHOSPHERE; ELASTIC STRAIN; KINETICS;
Keywords:
olivine; wadsleyite; ringwoodite; kinetics; subduction; deep earthquakes;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
65
Recensione:
Indirizzi per estratti:
Indirizzo: Mosenfelder, JL CALTECH, Dept Geol & Planetary Sci, M-C 170-25, Pasadena, CA 91125 USA CALTECH M-C 170-25 Pasadena CA USA 91125 ena, CA 91125 USA
Citazione:
J.L. Mosenfelder et al., "Experimental constraints on the depth of olivine metastability in subducting lithosphere", PHYS E PLAN, 127(1-4), 2001, pp. 165-180

Abstract

The hypothesis that metastable olivine persists in some subducting slabs into the transition zone has wide implications for mantle dynamics and rheology. In order to evaluate this possibility we derive new thermo-kinetic subduction zone models to predict the extent of olivine metastability within the stability fields of its high-pressure polymorphs, wadsleyite and ringwoodite. Our updated models improve on previous work by incorporating experimental kinetic data on realistic mantle compositions ((Mg, Fe)(2)SiO4) ratherthan analogue systems. Furthermore, latent heat due to the transformation is fed back into both the kinetics and the thermal model. We also consider the effects of transformation stress on growth kinetics and the possibilityof an intracrystalline transformation mechanism, previously thought to be important only at high shear stresses. Our models predict significantly smaller wedges of metastable olivine than previous work. In the case of Tonga,for example, where high values of lithospheric age (100-140 million years)and convergence rate (similar to 14 cm per year) are most favorable for metastability, models considering only grain boundary nucleation and interface-controlled growth predict olivine metastability to similar to 600km depth, in contrast to similar to 660km predicted previously by Kirby et al. [Rev. Geophys. 34 (1996) 261]. When intracrystalline transformation is considered, the depth of metastability is further reduced by as much as 100km, due to the large increase in the density of nucleation sites. Inhibition of growth by transformation stress can increase the depth interval over which thetransformation takes place, but is unlikely to be a dominant factor, especially if the intracrystalline mechanism operates. These results indicate that the existence of metastable olivine at depths corresponding to those of the deepest earthquakes (similar to 680 km) requires subduction of old lithosphere (> 100 million years) and a high vertical subduction velocity (greater than or similar to 15 cm per year). Such conditions currently may only be achieved in the very northern part of the Tonga subduction zone, yet earthquakes occur at depths down to 680 km in other subduction zones in which lithospheric age and/or subduction velocity are relatively low (e.g. Indonesia and the Marianas). Therefore, mechanisms other than transformational faulting in metastable olivine must operate to cause the deepest earthquakes. (C) 2001 Elsevier Science B.V. All rights reserved.

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Documento generato il 26/09/20 alle ore 02:00:51