Cooperative Institute for Research in Environmental Sciences

Sierra Nevada

Lithospheric removal from beneath the Sierra Nevada

Support from NSF's Continental Dynamics Program pending

Collaborators (recent past and present)

• Chris Harig and Craig Jones, CIRES and Department of Geological Sciences, University of Colorado

We are participating in multidisciplinary study headed by Craig Jones that seeks constraints on the development of the Sierra Nevada as mountain belt, late Cenozoic volcanism and erosion of it, and the mantle structure beneath it as a test of the hypothesis that mantle lithosphere was removed from the Sierra Nevada since ~10 Ma. By exploiting the geologic history of the Sierra Nevada and scaling laws for Rayleigh-Taylor and Convective Instability of Mantle Lithosphere, we have tested laboratory-derived temperature-dependent flow laws of olivine, the main mineral of the mantle. Some consider olivine to be too strong to allow convective removal of mantle lithosphere, but the application of scaling laws for Rayleigh-Taylor Instability to laboratory measurements yield removal on a time scale consistent with that implied by geologic data from the Sierra Nevada [Molnar and Jones, 2004].

We are pursuing this with further study of for Rayleigh-Taylor Instability and tighter constraints on the geologic history of the Sierra Nevada.

Average values of B_eff(T,E) obtained by integrating laboratory based values of B over temperature from 1600 K (asthenosphere) to different values of temperature at the Moho. We show values obtained both by ignoring the high stress form of Evans and Goetze (1979) and by averaging it for three representative strain rates with values of B for power-law creep. Dashed lines surrounding the curve for a strain rate of 10-15 s^-1. show crude estimates of uncertainty of a factor of 2 in B_eff. Horizontal lines show the bounds on B_eff inferred for the Sierra Nevada, and vertical lines show the range of inferred temperatures at the Moho from heat flux and metamorphic geothermometry. This figure shows that the values predicted by laboratory measurements lie within those inferred for the Sierra Nevada, particularly if a high strain rate appropriate for rapid removal of Sierran lithosphere is considered.

References

Molnar, P., and C. H. Jones (2004), A test of laboratory based rheological parameters of olivine from an analysis of late Cenozoic convective removal of mantle lithosphere beneath the Sierra Nevada, California, USA, Geophys. J. Int., 156, 555-564.