Transmission electron microscopy investigation of the defect microstructure of four natural orthopyroxenes |
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| Authors: | D L Kohlstedt J B Vander Sande |
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| Institution: | (1) Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, 02139 Cambridge, Massachusetts;(2) Department of Metallurgy and Materials Science, Massachusetts Institute of Technology, 02139 Cambridge, Massachusetts |
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| Abstract: | The defect structure of crustally deformed orthopyroxenes from a dunite, a peridotite, and a pyroxenite are characterized and their defect structures are compared with that of an orthopyroxene of a lherzolite from a volcanic xenolith. The microstructures contained isolated unit dislocations, isolated stacking faults, and Ca-rich, clinopyroxene lamellae. The isolated dislocations have Burgers vectors, b, which were predominantly 001]. The stacking faults have a displacement vector R =1/4001]. A lamellae consisted of a 1/4  wide Ca-rich region bounded by complex dislocation arrays. These lamellae are usually 100 or more in length and are nearly parallel to the (100) in the matrix. The dislocations in the boundary regions are spaced about 500 Å apart. The lherzolite orthopyroxenes were nearly free of isolated defects, in comparison to the other samples. Annealing at 1390° C for 1 hr produced no detectable recovery of the isolated defects in the orthopyroxene substructure. |
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