Cooperative Institute for Research in Environmental Sciences

The Viscosity of the Continents

Philip England

Department of Earth Sciences
University of Oxford

It can no longer be doubted that forces associated with density contrasts within the lithosphere(often referred to as 'Buoyancy Forces') drive the internal deformation of the continental lithosphere.However, the question is still completely open as to which portion, or portions, of the lithosphere give the continents their strength. There are three obvious layers that could contribute: the brittle, or seismogenic, upper crust, the primarily aseismic lower crust, and the lithospheric mantle. Relations between strain rates, determined from velocity fields measured over entire deforming zones, and buoyancy forces, estimated from crustal thicknesses and surface heights, suggest that the effective viscosity of continental lithosphere varies by less than a factor of one hundred, over a wide range of tectonic regimes.This narrow range of variation poses problems for models that attribute the strength of continental lithosphere entirely to an upper mantle, whose strength is limited by strongly temperature-dependent flow law. The view that the strength of the lithosphere resides entirely within the upper crust is equally incapable of accounting for the observations because -- though small -- the range of lithospheric strength is too great to be accounted for by variations in thickness of the brittle crust. The speaker may confine his remarks to the observations or may, if he feels adventurous, suggest a speculative interpretation of them.

About the Lecturer

B Sc Physics Bristol University 1972
PhD Geophysics Oxford University 1976
Post-doc Cambridge 1976-1980
Asst/Assoc Prof Harvard 1980-1986
Lecturer in Geophysics, Oxford University 1986-2000
Professor of Geology, Oxford University 2000-present

I am interested in most aspects of tectonics on scales from 10 kilometres to the size of the planet. In particular, I have worked on theoretical and observational aspects of the deformation of the continents, and on the analysis of geochronological and petrological data for revealing the processes of metamorphism and erosion.

I am currently working on the dynamics of the Aegean, New Zealand, and Asia, and on the question of why the Island Arc volcanoes are where they are.

More Information

http://comet.nerc.ac.uk/people.php?first=Philip&last=England

Philip England