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The Puzyrev-Krylov model was substantially developed by Grachev in his study
of continental rifting dynamics (Grachev, 1996). Grachev stresses the asymmetry of
the Baikal Rift, which manifests itself in a rise of the low-velocity asthenosphere
on the transition from platform to folded zone (Fig. 12.29b). The formation of the
anomalous mantle, with its subvertical stem and subhorizontal apophysis, is inter-
preted in terms of a mantle diapir, that is, as intrusion of magma into the continental
lithosphere, typical of the prerifting regime.
2. The asthenospheric-upwarp concept. This alternative concept, conceived by
Zorin and his colleagues, is based on gravimetry, deep seismic soundings, and tele-
seismic observations (Zorin, 1971; Gao et al., 1994). In developing this concept,
they passed through several versions. The earliest version of the model is illus-
trated in Fig. 12.30a. Here, the rift zone mantle includes a vast, compact region
of lower density, reaching and even crossing the Moho. It is considered to be an
Fig. 12.30
Asthenospheric-
upwarp model of the Baikal
rift zone; (
a
) early version,
after Zorin (1971), (
b
)-
recent version, after Gao
et al. (1994); 1 - sediments,
2 - The Earth's crust,
3-basicandultrabasic
intrusion, 4 - normal mantle,
5 - anomalous mantle,
6-density,g/sm
3
,
7 - numerator-velocity of
P
-wave, km/s, denominator-
density, g/sm
3
