[1] Apatite fission track analysis (AFTA) data are used to bring new light on the long-term and recent history of the Baikal rift region (Siberia). We describe the evolution of the topography along a NW-SE profile from the Siberian platform to the Barguzin range across the Baikal-southern Patom range and the northern termination of Lake Baikal. Our results show that the Baikal-Patom range started to form in the Early Carboniferous and was reactivated in Middle Jurassic-Lower Cretaceous times during the orogenic collapse of the Mongol-Okhotsk belt. Samples located in the Siberian platform recorded a continuous sedimentation up to the early Carboniferous but remain unaffected by later tectonic episodes. The Barguzin basin probably started to form as early as Late Cretaceous, suggesting a continuum of deformation between the postorogenic collapse and the opening of the Baikal Rift System (BRS). The initial driving mechanism for the opening of the BRS is thus independent from the India-Asia collision. AFTA show a late Miocene-early Pliocene increase in tectonic extension in the BRS that confirms previous thoughts and might reflect the first significant effect of the stress field generated by the India-Asia collision.Citation: Jolivet, M., T.

Current deformation in Pribaikalia, Western and Central Mongolia, and Tuva has been studied from measured horizontal GPS velocities and respective computed strain and rotation rates using 1994–2007 data of the Baikal–Mongolian GPS triangulation network. The GPS velocity field shows two main trends: an NE trend within Jonggaria, the Mongolian Altay, and the Great Lakes Valley and an SE trend in the Hangayn and eastern Gobi Altay mountains, and in the Transbaikalian block of the Amur plate. The velocity magnitudes and vectors are consistent with an SE motion of the Amur plate at a rate of ∼2 mm/year. The derived strain pattern includes domains of crustal contraction and extension recognized from the magnitudes of relative strains. Shortening predominates in the Gobi and Mongolian Altay and in the Khamar-Daban Range, where it is at ɛ2 = (19.2 ± 6.0)×10−9 yr−1 being directed northeastward. Extension domains exist in the Baikal rift and in the Busiyngol–West Hangayn area, where the crust is stretching along NW axes at ɛ1 = (22.2 ± 3.1) × 10–9 yr–1. The eastern Hangayn dome and the Gobi peneplain on its eastern border show low and unstable strain rates. In central and northern Mongolia (Orhon–Selenge basin), shortening and extension are at similar rates: ɛ2 = (15.4 ± 5.4)×10−9 yr−1 and ɛ1 = (18.1 ± 3.1)×10−9 yr−1. The strain pattern changes notably in the area of the Mogod earthquake of 1967. Most of rotation throughout Central Asia is clockwise at a low rate of about Ω = 6×10−9 deg·yr−1. High rates of clockwise rotation are observed in the Hangayn domain (18.1 ± 5.2)×10−9 deg·yr−1, in the Gobi Altay (10.4 ± 7.5)×10−9 deg·yr−1, and in the Orhon–Selenge domain (11.9 ± 5.2)×10−9 deg·yr−1. Counterclockwise rotation is restricted to several domains. One is in western Tuva and northwestern Great Lakes Valley of Mongolia (Ω = 3.7×10−9 deg·yr−1). Two more counterclockwise rotation regions occur on both flanks of the Baikal rift: along the craton edge and in basins of Transbaikalia on the rift eastern border, where rotation rates are as high as (13.0 ± 3.9)×10−9 deg·yr−1, while rotation within the Baikal basin does not exceed the measurement error. Another such domain extends from the eastern Hövsgöl area to the Hangayn northern foothills, with the counterclockwise rotation at a highest rate of (16.3 ± 2.8)×10−9 deg·yr−1.

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Today, one of the most topical questions in the recent geodynamics of eastern Asia is that concerning the existence of the Amurian Plate and its boundaries. An unambiguous answer is difficult to obtain because seismicity is relatively rare and weak and the plate boundaries are often geomorphologically unclear. One of the methods that can help is satellite geodesy. In the present study, the velocity field of recent horizontal crustal movements was obtained from five repeated GPS observations on the Amur–Zeya geodynamic test ground (Amur Region) in 2001–2007. On this basis, the parameters of the relative rotation of the Eurasian and Amurian plates were calculated. The coordinates of their rotation pole were found to be 122.285° E and 58.950° N, and the angular rotation velocity 0.095 deg/Myr. The resulting kinematic model describes the motion of the Eurasian and Amurian Plates as independent tectonic units. According to statistical analysis, this hypothesis is true at a confidence level of more than 99%. Also, calculations have shown that the eastern boundary of the Amurian Plate passes through a branch of the Tan-Lu fault system. The kinematic model for the Eurasian and Amurian Plates agrees well with data on the kinematics of active faults and the modern tectonic stress field at the plate boundary.

International audienc

Based on multiyear measurements of present-day motions in the central area of the Baikal rift system, new data on the kinematics of horizontal motions, relative horizontal deformation rates, and rotation velocities in the area of junction of the South Baikal, North Baikal, and Barguzin rift basins have been obtained. This area is an intricate structure with two transfer zones: Ol’khon–Svyatoi Nos and Ust’-Barguzin. It is shown that crustal blocks are moving southeastward, normally to the structures of transfer zones and at an acute angle to the Baikal Rift strike, which corresponds to the right-lateral strike-slip extensional faulting along the major structure. The average horizontal velocities increase from 3.0 mm yr–1 in the northern South Baikal basin to 6.5 mm yr–1 in the Barguzin basin. The elongation axes prevailing in the study region are mainly of NW–SE direction. The areas of intense deformations are confined to structures with high seismic activity in the South Baikal and, partly, Barguzin basins. This confirms the existence of a present-day zone of the Earth’s crust destruction in the Baikal rift system, which is the most likely source of strong earthquakes in the future. Two zones with rotations in opposite directions are recognized in the rotation velocity field. Clockwise rotation is typical of structures of N–NE strike (Maloe More basin, southern North Baikal basin, Barguzin Ridge rise). Counterclockwise rotation is determined for NE-striking structures (northern South Baikal basin, southern Barguzin basin). In general, the obtained data show an intricate pattern of present-day horizontal dislocations and deformations in the area of junction of NE- and N–NE-striking rift structures. This suggests left- and right-lateral strike-slip faults, respectively, within them.

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