Geodynamics of the Baikal rift zone and plate tectonics of Asia

L.P Zonenshain,L.A Savostin

doi:10.1016/0040-1951(81)90251-1

L.P Zonenshain, L.A Savostin

Open Access

https://doi.org/10.1016/0040-1951(81)90251-1

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Abstract

The Baikal rift zone stretches from the southern termination of Lake Baikal as far as 118°E, and includes the Baikal basin and the Barguzin, Upper Angara and Muysk grabens that form its easterly continuation. Coincident with the rift zone is a narrow seismic belt which extends further east along the Stanovoy range to the Okhotsk Sea. This belt can be considered as the boundary between the Eurasian and Amurian lithospheric plates. Earthquake focal-mechanism solutions that show a consistent orientation of extensional axes across the strike of the rift zone indicate the behaviour of the Eurasian and Amurian plates as rigid bodies. From 83 focal mechanism solutions, the pole of rotation of the Eurasian and Amurian plates was computed to lie at the point 56.95N 117.45E. The angular rate, estimated from the amount of Baikal opening, is about 1.10 −7 deg/year. The position of the pole at the eastern termination of the rift zone accounts for the dying-out of the rift zone and for the appearance east of the pole, of compressive structures in the Stanovoy range. To the southwest the Baikal rift zone is replaced by the mosaic of microplates in Central Asia that occupy the space between the Eurasian and Indian lithospheric plates. Prominent are the Mongolian, Dzungarian, Alashan, Tarim, Tibetan and Pamir microplates. Earthquakes in Central Asia are dispersed although higher concentrations of earthquakes associated with microplate boundaries are prominent. The tectonics of Central Asia are considered to be due to the interaction of rigid microplates, assuming that plastic deformations occur within the relatively wide zones along the microplate boundaries. By considering the strike-slip faults to define the trajectories of microplate motions, the parameters of relative movements of the microplates have been computed. The microplate mosaic of Central Asia is moving northeasterly, as a result of the collision and continued convergence of India and Eurasia. The mosaic acts as a wedge splitting off the Amurian plate from Eurasia causing it to rotate counterclockwise so opening the Baikal rift.

Highlights

Data on stress regimes and strain rates for intracontinental domains are of particular interest for understanding intraplate seismicity
The first conclusion inferred from the map is that the focal solutions of earthquakes in the southern Mongolia are rather homogeneous, whereas in the northern part they are widely variable
The results show that SHmax is turning from the W-E direction in the eastern Mongolia to NE-SW in the Gobi Altay and the central Mongolia, and to S-N in the western part of the region (Fig. 5)

Summary

Introduction

Data on stress regimes and strain rates for intracontinental domains are of particular interest for understanding intraplate seismicity. The eastern part of Mongolia, which is characterized by the moderate level of seismic activity and diffusive seismicity type, might be influenced by the Pacific subduction process [Barth, Wenzel, 2010; and others]. This part is assumed to belong to the Amurian block or plate, the existence of this plate is doubted by some researchers [De Mets et al, 1990; Calais et al, 2003; and others]. Local mantle anomalies, such as one under the Khangay dome, whose uplift is thought to be resulting from hot mantle upwelling [Windley, Allen, 1993; Priestley et al, 2006; and others] should not be excluded from consideration

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