Transmission electron microscopy investigation of the defect microstructure of four natural orthopyroxenes

D. L. Kohlstedt, J. B. Vander Sande

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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 =1/4[001]. A lamellae consisted of a 1/4 μ wide Ca-rich region bounded by complex dislocation arrays. These lamellae are usually 100 μ 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.

Original languageEnglish (US)
Pages (from-to)169-180
Number of pages12
JournalContributions to Mineralogy and Petrology
Volume42
Issue number2
DOIs
StatePublished - Jun 1 1973

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