I. General Setting -- the Baikal rift opens in Siberia between the large Eurasian craton to the NW and several smaller plates to the SE

...the entire rift system is 2000 km in length while Lake Baikal (which occupies the central portion of the rift) is 600 km long, 50 km wide, and 1634 m deep

...the Primorsky-Baikalsky rift shoulder runs along the NW side of Lake Baikal with elevation ranging from 1000-2500m Baikal, Photo 189

II. Time frame of the initiation and propagation of the Baikal rift

A. Oligocene - Early Pliocene -- Baikal area is dominated by compressional and strike-slip faulting

B. Late Pliocene - Quaternary -- active rifting stage where rifting begins in the south and propagates to the NE

1. rifting follows faults that were already present between the Precambrian basement rock of the Eurasian craton and the Saya-Baikal fold-and-thrust belts to the SE

2. major change from transpressional to transtensional faulting, the geometry of which causes the formation of so called rhombochasms, the rhombehedral basins which characterize the modern day rift

3.volcanism reaches a peak between 14 and 8 Ma at NE and SW tips of the rift

4. rate of subsidence and of sediment accumulation increases in all 3 lake basins

III. Structural framework

A. rift is composed of 3 separate sub-basins formed by asymmetrical fault-bounded depressions

B. there is E-W strike-slip movement along a fault system with NE-SW principle compressive stresses and NW-SE extension

C. unlike other continent rifts such as the East African Rift Basin because it is isolated in the center of the continent, unconnected with an oceanic spreading margin

D. shallow focus earthquakes line up roughly according to fault lines...Map of Seismic Lines, Lake Baik

E. tectonic subsidence within the basins

IV. Stratigraphic units

A. the deposits in the rift have been separated into 3 stratigraphic units, the deposition of which represents change in the tectonic setting

... the 3 units combined range from 3.5 to 7.5 km in thickness within Lake Baikal

1. Proto-rift sediments (Oligocene - early Pliocene)

a. fine grained sediments with coal beds... indicative of a low energy environment (ie. shallow lake or swamp)

2. Middle rift sediments (early Pliocene - Quaternary)

a. deep water deposits represent a major gap in depositional style...coarse sand, silt, argillite

3. Modern rift sediments (Quaternary)

a. fluvial, glacial, and deltaic sediments

B. major sediment sources in the modern are the deltas from the Barguzin and Selenga river systems to the East...these sediment piles separate the 3 lake basins

V. Current theories on the causes of rifting

A. Classic continental rifting scenario

1. rifting occurs due to convection in the upper mantle... diapiric upwelling (Logtchev, N.A., 1987)

a.) doming of lithosphere over hot asthenospheric upwelling

b.) teleseismic tests done by Saolong Gao in 1994 proved the existence of asthenospheric upwarping under the central part of the Baikal rift... NW-SE mantle flow influences spreading in the highly elastic overlying lithosphere

B. Rifting is occurring as a secondary effect of the collision between India and Eurasia (Tapponier 1979)

1. rifting is a means of compensating for the compressive tectonics at the destructive margin to the south

a.) Baikal does not have the graben structure of other rift basins

b.) there is a relatively smooth transition of stresses acting on the lithosphere from the thrust faults and crustal thickening in South Asia, to strike slip faulting in Southern Mongolia, to fissuring and normal faulting in Northern Mongolia near the site of rifting

c.) domed lithosphere occurred prior to the onset of rifting

d.) rifting did not involve the disruption of a long standing craton, but rather occurred in a gap that already existed between two plates

Bibliography

Delvaux, D. et al.. 1997. Paleostress reconstructions and geodynamics of the Baikal region, Central Asia, Part 2. Cenozoic rifting. Tectonophysics. v.282. p.1-38

Hutchinson, D.R., Golmshtok, A.J.. 1992. Depositional and tectonic framework of the rift basins of Lake Baikal from multichannel seismic data. Geology. v.20. p.589-592

Logtchev, N.A., and Zorin, Y.A.. 1987. Evidence and causes of the two stage evolution of the Baikal rift. Tectonophysics. v.143. p.31-41

Mats, V.D.. 1993. The structure and development of the Baikal rift depression. Earth-Science Reviews. v.34. p.81-118

Moore, T.C. et al. 1997. Sedimentation and subsidence patterns in the central and north basins of Lake Baikal from seismic stratigraphy. GSA Bulletin. v.109. p.746-766

Tapponier, P. and Molnar, P.. 1979. Active faulting and Cenozoic tectonics of the Tien Shan, Mongolia, and Baikal regions. Journal of Geophysical Research. v.84. p.3425-3459