AN INSTABILITY GRAVITY MODEL FOR THE STRUCTURE AND STRESS-STRAIN STATE OF LITHOSPHERE IN THE BAIKAL RIFT
S.V. Gol'din, V.D. Suvorov, P.V. Makarov*, and Yu.P. Stefanov*
Institute of Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Institute of Physics of Strength and Materials Science, Siberian Branch of the RAS,
2/1 prosp. Akademichesky, 634021, Tomsk, Russia
Keywords: Lithosphere, seismic velocities, density, gravity instability, elastic-brittle-plastic strain, Baikal rift
Pages: 1079-1090
Abstract
The stress-strain state of undeformed but gravity-strained lithosphere is simulated in a 2D numerical model in the elastic-brittle-plastic approximation using combined seismic and density cross sections to depths of 80 km. The cross sections follow DSS profiles across the Baikal rift (Ust'-Uda-Khilok) and along the northeastern flank of the rift system (Ust'-Kut-Nizhneangarsk-Chara). Gravity instability is produced by a zone of anomalous mantle and the 10-12 km deep Baikal basin which have low elastic moduli and density.
We estimated the depth-dependent variations in shear strength and internal friction coefficient required for strain in the upper crust to fit the crustal density and velocity distributions and the observed Cenozoic shallow geological and tectonic structures. The greatest stress-strain contrasts are attributed to zones of most prominent density contrasts and show up in the horizontal stress component to 0.15 GPa. Relative strain in the crust and at the Moho reaches 10-15%. Gravity instability may have contributed significantly to lithospheric deformation and rift evolution.
|
