TY - JOUR
T1 - Kinetics of intracrystalline olivine-ringwoodite transformation
AU - Kerschhofer, L.
AU - Rubie, D. C.
AU - Sharp, Thomas
AU - McConnell, J. D C
AU - Dupas-Bruzek, C.
N1 - Funding Information:
We thank C.B. Carter, P. Cordier, S.-I. Karato, J. Mosenfelder, J.-P. Poirier, M. Riedel and F. Seifert for helpful discussions, J. Mosenfelder and two anonymous reviewers for constructive criticisms, R. Miletich for orienting the olivine single crystals, and H. Küfner and H. Schulze for technical assistance. This work was supported by the Deutscher Akademischer Austauschdienst (A/95/09994), the EU “Training and Mobility of Researchers” programme (Contract No. ERBFMBICT960758), the EU “Human Capital and Mobility — Access to Large Scale Facilities” programme (Contract No. ERBCHGECT940053) and the Alexander von Humboldt Foundation.
Copyright:
Copyright 2006 Elsevier B.V., All rights reserved.
PY - 2000
Y1 - 2000
N2 - We studied the microstructural evolution and kinetics of intracrystalline olivine-ringwoodite transformation in order to evaluate the importance of this mechanism in subducting lithosphere. Intracrystalline transformation occurs within single crystals of San Carlos olivine (Fo90) at T ≥ 900°C and P ≥ 18 GPa and involves four stages: (1) Formation of (100)(α) stacking faults in olivine, (2) coherent nucleation of thin ringwoodite platelets on these stacking faults, (3) semi-coherent growth of the platelets and (4) incoherent nucleation of ringwoodite and/or wadsleyite grains at the platelet interfaces. Because rates of incoherent growth are about two orders of magnitude faster than rates of semi-coherent growth, the final stage is most important for bulk transformation. However, the ringwoodite platelets act as essential nucleation sites for intracrystalline incoherent transformation. The growth of ringwoodite platelets proceeds by the nucleation and migration of interface ledges (1.0-1.5 nm high) and is thermally activated with an activation energy of ~ 270 kJ mol-1. This is similar to the activation energy for incoherent growth, suggesting that both processes are controlled by Si-O bond breaking. The nucleation rate of platelets, as determined from the densities of platelets observed in transmission electron microscopy (TEM) sections, is also strongly temperature-dependent and has a similar activation energy. These results suggest that intracrystalline transformation is likely to be important in subducting lithosphere in addition to the grain boundary nucleation mechanism. The intracrystalline mechanism will reduce the depth interval over which the transformation occurs and may enhance rheological weakening by reducing the grain size of the reaction products. (C) 2000 Elsevier Science B.V. All rights reserved.
AB - We studied the microstructural evolution and kinetics of intracrystalline olivine-ringwoodite transformation in order to evaluate the importance of this mechanism in subducting lithosphere. Intracrystalline transformation occurs within single crystals of San Carlos olivine (Fo90) at T ≥ 900°C and P ≥ 18 GPa and involves four stages: (1) Formation of (100)(α) stacking faults in olivine, (2) coherent nucleation of thin ringwoodite platelets on these stacking faults, (3) semi-coherent growth of the platelets and (4) incoherent nucleation of ringwoodite and/or wadsleyite grains at the platelet interfaces. Because rates of incoherent growth are about two orders of magnitude faster than rates of semi-coherent growth, the final stage is most important for bulk transformation. However, the ringwoodite platelets act as essential nucleation sites for intracrystalline incoherent transformation. The growth of ringwoodite platelets proceeds by the nucleation and migration of interface ledges (1.0-1.5 nm high) and is thermally activated with an activation energy of ~ 270 kJ mol-1. This is similar to the activation energy for incoherent growth, suggesting that both processes are controlled by Si-O bond breaking. The nucleation rate of platelets, as determined from the densities of platelets observed in transmission electron microscopy (TEM) sections, is also strongly temperature-dependent and has a similar activation energy. These results suggest that intracrystalline transformation is likely to be important in subducting lithosphere in addition to the grain boundary nucleation mechanism. The intracrystalline mechanism will reduce the depth interval over which the transformation occurs and may enhance rheological weakening by reducing the grain size of the reaction products. (C) 2000 Elsevier Science B.V. All rights reserved.
KW - Nucleation
KW - Olivine
KW - Phase transformation kinetics
KW - Subduction
KW - Transmission electron microscopy
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U2 - 10.1016/S0031-9201(00)00160-6
DO - 10.1016/S0031-9201(00)00160-6
M3 - Article
AN - SCOPUS:0033810490
SN - 0031-9201
VL - 121
SP - 59
EP - 76
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
IS - 1-2
ER -