Field-based constraints on finite strain and rheology of the lithospheric mantle, Twin Sisters, Washington | Academic Article individual record

We present direct finite strain and rheological estimates of naturally deformed mantle materials using field observations in the Twin Sisters ultramafi c body of Washington State. Folded and elongated (boudinaged or ductilely thinned) orthopyroxenite dikes within the host dunite provide strain markers that allow us to characterize the finite strain over an ~15,000 m 2 area. Using dynamic instability analysis on the folded orthopyroxenite dikes, orthopyroxene is calculated to have ~25 times the effective viscosity of olivine-rich host rocks (based on a power-law exponent of 3.0 for this dislocation creep process). Detailed mapping also indicates that inclusion of up to 15% orthopyroxene in the olivinerich host rocks does not affect their viscosity, constraining the rheological behavior of two-phase, mantle material. 2010 Geological Society of America.

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Tikoff, B., Larson, C. E., Newman, J., & Little, T
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