LONG-WAVELENGTH GRAVITY-ANOMALIES AND THE DEEP THERMAL STRUCTURE OF THE BAIKAL RIFT

The analysis of the gravity field over the Baikal rift area has been carried out in order: (1) to detect the amount of the deep hot material, and (2) to constrain the flexural rigidity of the lithosphere. We removed a few first harmonics of the global field and the gravity effects due to the crust from the observed field and found a residual anomaly which is aligned with the rift. This residual, which we attribute to the mantle, shows a minimum of about 15 mgal in amplitude and 900 km in width, which is superimposed over a wider minimum with smaller amplitude. A model involving a simple stretching of the lithosphere with diffusion of heat predicts right order of magnitude for both the amplitude and the wavelength of the “900‐km” anomaly. Our results confirm that the stretching factor is of the order of 1.2 to 1.5. Interpretation of the coherence function computed between gravity and topography shows that the lithosphere in the area has a significant equivalent elastic thickness of about 30 km (i.e. flexural rigidity about 2.3 1023N.m). Copyright 1990 by the American Geophysical Union.