Journal of Conference Abstracts

Estimates of the Effective Elastic Thickness of the Continental Lithosphere from Bouguer and Free air Gravity Anomalies

Dan M^cKenzie (mckenzie@esc.cam.ac.uk)¹ & Derek Fairhead (jdf@getech.leeds.ac.uk)²

¹Institute of Theoretical Geophysics, Bullard Labs, Madingley Rd, Cambridge, CB3 0EZ, U.K.

²GETECH, Dept. of Earth Sciences, University of Leeds, Leeds, LS2 9JT, U.K.

In continental regions the Bouguer anomaly is commonly used to estimate the effective elastic thickness T_e, and gives thicknesses for shields as great as 130 km, where geotherms reach temperatures of 800-1000°C. However, detailed examination of the free air and Bouguer anomalies shows that values of T_e obtained in this way are upper bounds, rather than estimates, because most of the short wavelength topography has been removed by erosion, and what remains is incoherent with both the free air and Bouguer gravity anomalies. The present study uses free air gravity anomalies, and topography as a surface load whose geometry is known, to estimate T_e for North America, East Africa, Australia, the Indian peninsula and the former Soviet Union. No value exceeds 25 km, and all are smaller than the seismogenic thickness. There is therefore no evidence that the value of T_e for the continents is as great as that for the oceans, or that the continental lithosphere can support elastic stresses for geological times at temperatures above about 350°C.