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A schematic model for formation of "summit" and "valley" lava remnants due to tectonic uplift at constant basal level of erosion (a-c) and due to sudden lowering of the regional level of erosion, in this case, as a result of a lake drainage (d-f). In both cases, the final effect will be the same: older lavas situated at higher elevations, usually on top of the mountains, and younger lavas occupying river terraces. Dark and light gray colors are for older and younger lavas, respectively. Dotted area is for lacustrine sediments
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As known from inland sedimentary records, boreholes, and geophysical data, the initiation of the Baikal rift basins began as early as the Eocene. Dating of volcanic rocks on the rift shoulders indicates that volcanism started later, in the Early Miocene or probably in the Late Oligocene. Prominent tectonic uplift took place at about 20 Ma, but info...
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Context 1
... upwellings, referred to as upper mantle plumes, were the origin of high mountains; namely Hangai, Hentei, and Sayan ranges and uplands close to the Udokan and Vitim volcanic fields ( Fig. 1) ( Zorin et al., 2003). Thus, one may expect that rapid mountain growth should be followed by volcanic events. Schematically, this principle is shown in Fig. 6. Mountain uplift leads to fast erosion and formation of river valleys, which are filled by later lavas. It is worth mentioning that rapid river valley formation can result from the decrease of local level of erosion without any uplift, as for example in the case of paleolake drainage (Fig. 6). Such paleolakes existed in the Baikal rift ...
Context 2
... events. Schematically, this principle is shown in Fig. 6. Mountain uplift leads to fast erosion and formation of river valleys, which are filled by later lavas. It is worth mentioning that rapid river valley formation can result from the decrease of local level of erosion without any uplift, as for example in the case of paleolake drainage (Fig. 6). Such paleolakes existed in the Baikal rift system; for instance, Miocene lacustrine deposits are buried beneath lavas of the Vitim volcanic field (Rasskazov et al. 2000). Having this in mind, we focus only on those examples, where erosion could only result from tectonic uplift. Similar argumentation was used by Rasskazov et al. (1997) ...
Context 3
... Review Oriented to the Baikal and Hovsgol Lake Systems 43 Figure 7 represents a natural example of the concept schematically shown in Fig. 6. Late Oligocene-Early Miocene "summit" lavas in the western Hovsgol area occupy a level of 2,700 m, whereas Late Miocene "valley" lavas are located within the paleo- river valley at a lower level of 2,100 m. This means that about 600 m of uplift and erosion have happened between 21-24 and 7.8 mya. There is no strong constraint to ...
Citations
... This period, according to the data of thermochronological studies of the Mongolian Altai and Gobi Altai, started at 5 ± 3 Ma and is associated with the northward propagation of compression deformation from the India-Asia collision Vassallo et al., 2007). For the East Sayan, Khamar-Daban and Khangai mountains, the age of uplift is determined by a change in the morphology of dated basaltic lava, which changed from plateau-like to valley flows about 3-5 million years ago (Yarmolyuk, Kuzmin, 2006;Yarmolyuk et al., 2008;Ivanov and Demonterova, 2009;Jolivet et al., 2013). ...
... Within the SW segment of the Baikal Rift, the similar age has been proposed for the reactivation of the Tunka Fault, which controls the northern side of the Tunka Basin, starting from 5.8 − 3.5 Ma ago, as evidenced by (U-Th)/He-thermochronometry and morphometric analysis (Lunina et al., 2009;Chebotarev et al., 2021). The maximum age of the onset of subsidence of the Hovsgol Basin, estimated from the Ar/Ar dating of basalt lavas at the summit and at the foot of the Khardyl-Sardyk Ridge (in the footwall and hanging wall of the North Hovsgol Fault, respectively) is 7.8 Ma (Ivanov and Demonterova, 2009). The maximum thickness of Cenozoic deposits in the Hovsgol Basin is slightly more than 500 m (Kochetkov et al., 1993). ...
... Ermoskhin-Sardyk (Fig. 4c). There, a paleo-river valley is preserved, filled by a 260 m thick lava in the valley, and lava thickness up to 100 m at the shoulders of the valley (Ivanov & Demonterova, 2009). The thickness of other preserved lava outcrops does not exceed 100 m. ...
... K-Ar ages of 11-44 Ma were reported for lavas in our study region (Rasskazov, 1993), but new and more accurate K-Ar age determinations suggest a shorter interval between 15.1 ± 0.4 Ma and 17.3 ± 0.5 Ma (Ivanov & Demonterova, 2009) (Fig. 2c). We rely (Zorin et al., 1993) across the boundary of the Siberian Craton and the Tuva-Mongolian massif. ...
Continental rifting is usually viewed in terms of two contrasting models of active and passive extension. The origin of the Baikal Rift, adjacent to the southern part of the Siberian Craton, has been described by both models in the past. It is expected that basaltic magmatism in an active model scenario should be primarily sourced from a mantle plume or plume-fed asthenosphere, whereas melting of the lithospheric mantle is expected to be a predominant source for magmatism in the passive model. In this paper, we focus on the Miocene volcanic rocks sampled along two 60 km-long profiles that cross the boundary between the Neoproterozoic Tuva-Mongolian massif and the Archean-Paleoproterozoic Siberian Craton. Most of the samples studied are trachybasalts. In terms of trace element concentrations normalized to primitive mantle, the lavas mimic OIB-like patterns with troughs at Rb, Th–U, Pb, and Y, and peaks at Ba, Nb, Ta, K, and Sr. Moreover, similar trace-element patterns to the studied samples are also observed for Miocene and Quaternary lavas located in the southwestern of the Baikal Rift, and adjacent regions of non-rifted Mongolia. According to the ratio of CaO to MgO, and TiO2/Al2O3 to SiO2, the compositions of the studied lavas coincide with experimental melts derived from mafic lithologies. Trace element data of samples suggest that garnet was a residual phase during partial melting. The Sr-Nd isotopic characteristics of the studied lavas are 87Sr/86Sr 0.70427–0.70469 and 143Nd/144Nd 0.51267–0.51284. They are identical to the coeval Miocene lavas of neighbouring volcanic fields, but they differ from the Quaternary lavas that extend to lower 87Sr/86Sr (0.7038–0.7044) with near identical 143Nd/144Nd. Isotopes of Hf for studied samples show values εHf = 6.0–7.7, except for the two samples taken within the boundary between two lithospheric blocks with εHf 4.6 and 4.8. The δ18O of olivine from lava samples is everywhere higher than that of the asthenospheric mantle and ranges from 5.5 to 6.4‰. Variations of δ18O versus Mg#, 87Sr/86Sr and εHf in the studied samples do not correlate, but do unequivocally rule out crustal assimilation. The isotopic variations are consistent with recycling of mafic crustal lithologies at mantle depths. Lavas from the Tuva-Mongolian massif and the Siberian Craton differ in lead isotopes by lower values of 206Pb/204Pb (< 17.785) and higher values of Δ8/4Pb (61–75) for on-cratonic samples and the reverse relationship for off-cratonic lava (> 17.785 and 55–61) respectively. The equation for Δ8/4Pb=[208Pb/204Pb-(1.209*(206Pb/204Pb) +15.627)] *100 is from (Hart, 1984). The correlation of lead isotopes with the mafic recycled component, the sharp change of lead isotopic values at the cratonic boundary and decoupling of lead isotope ratios from other isotopic ratios lead us to suggest that the values of 206Pb/204Pb and Δ8/4Pb are associated with an ancient accessory mineral phase such as sulphide confined within the lithospheric mantle. The predominant role of the lithospheric sources in the formation of the Miocene volcanic rocks, indicate that the volcanism of the Baikal Rift was caused by a passive tectonic process, rather than active rifting.
... This requires a detailed 87 Sr/ 86 Sr reference map. However, only sparse data are available for the isotopic compositions of Siberian water reservoirs such as Lake Baikal (Falkner et al., 1997;Chabaux et al., 2011;Scharlotta and Weber, 2014;Suhrhoff et al., 2022), Lake Hovsgol (Ivanov and Demonterova, 2009), and some Siberian rivers (Falkner et al., 1997;Chabaux et al., 2011;Scharlotta and Weber, 2014;Suhrhoff et al., 2022). ...
We provide an extended ⁸⁷Sr/⁸⁶Sr database for the water of Lake Baikal collected along the lake and within its bays at a depth range from the surface down to 1366 m, the major tributary rivers, lake animals, and atmospheric precipitation. The water of open Lake Baikal, the Little Sea (Maloe More) Strait, and large bays are characterized by a uniform ⁸⁷Sr/⁸⁶Sr = 0.7086266 ± 0.0000045 (n = 44, uncertainty at 95% confidence interval). Major volumetric contributors of water to the lake (the eastern rivers and precipitation) are only slightly different from the lake value in terms of ⁸⁷Sr/⁸⁶Sr. In the western rivers, ⁸⁷Sr/⁸⁶Sr is much higher, but due to their small incoming volume, their contribution is rapidly diluted by the water currents of the lake. The exception is water with high ⁸⁷Sr/⁸⁶Sr from isolated Mukhor Bay at the inland end of the Little Sea Strait and water above the underwater discharge of hydrothermal springs. Benthic and pelagic Lake Baikal animals have ⁸⁷Sr/⁸⁶Sr similar to the values of the open lake, supporting lake water homogenization. The modelled budget of Sr suggests that 86 ± 14% of input Sr is stored in the waters of Lake Baikal. In other words, according to the estimations some Sr (from 0 to 28%) may be precipitated at the lake bottom by chemical and biochemical processes.
... Compression related to the collision processes caused the uplift of the Altai-Sayan Range during the last 3-5 million years, as suggested by low-temperature thermochronology (De Grave et al., 2003Jolivet et al., 2007;Vassallo et al., 2007;Buslov et al., 2008). A change in lava flow morphology also indicates uplift in the area of East Sayan, Khamar-Daban and Khangai (Yarmolyuk and Kuzmin, 2006;Yarmolyuk et al., 2008;Ivanov and Demonterova, 2009). It was shown that about 3-5 Ma plateau-like basaltic lava was replaced by valley lava flows, indicating the onset of uplift and incision of the new drainage system. ...
Determining the fault displacement rates and the sequence of formation of intra-rift structures are essential aspects in the study of the evolution of intracontinental rifts. To better understand the development of the Tunka system of basins (Baikal Rift) and the influence of tectonics on landscape evolution, we conducted a morphometric analysis of the Tunka Fault and its transverse drainage network. We studied geomorphic parameters of 64 facets and 74 drainage basins within the Tunka mountain-front in the footwall of the Tunka Fault; these parameters include mountain front sinuosity, the ratio of facet height and width to base length, basin shape, hypsometric integral, asymmetry factor, and the valley width to height ratio. Our main objectives were to determine long-term throw rates for specific mountain front segments and estimate the timing of corresponding geomorphic structures, to characterize the geomorphological response of the transverse drainage systems to fault movements, and to understand the relationship between the morphometry and kinematics of different segments along the Tunka Fault. The analysis of the Tunka mountain front reveals evidence for strong tectonic control on its morphology. We found that the morphological features are strongly influenced by the Late Pleistocene – Holocene kinematic inversion along the eastern part of the Tunka Fault. The Late Pliocene–Quaternary throw rates estimated for specific geomorphic structures vary in the range of 0.8–1.0 mm year⁻¹, which is compatible overall with the long-term throw rates of other basins of the Baikal Rift. Based on these rates, we estimate the age of fault-controlled subsidence of the Tunka and Khoytogol basins and Nilovsky Spur to be between 3.5 and 1.5 Ma. We also show that geomorphological response of the transverse drainage varies along the Tunka Fault, indicating a close relationship between fault kinematics and landscape response.
... first event occurred between 22 and 15 Ma (Rasskazov et al., 2000;Ivanov and Demonterova, 2009). This initial reactivation was followed, during most of the Neogene, by a new period of tectonic quiescence, erosion and emplacement of basaltic flows within early Miocene paleovalleys (Jolivet et al., 2013a). ...
... From late Miocene-early Pliocene, a second phase of active deformation and uplift established the main features of the present-day topography (Arzhannikova et al., 2011). This second period characterized by the rapid growth of some of the ranges began between 8.7 Ma (Rasskazov et al., 2000) and about 5 Ma (Ivanov and Demonterova, 2009). (U-Th)/He analysis on the Tunka range showed that its fast exhumation falls within the interval 10-5 Ma with a considerable increase in exhumation rate after 5.8 Ma (Lunina et al., 2009). ...
The formation of the Baikal rift system basins is controlled by active faults separating each basin from the adjacent horsts. The kinematics of these faults is mainly explored through investigation of complex sequences of the fault-intersecting river terraces that record both tectonic and climatic events. This study focuses on the northern margin of the major Tunka basin that develops south-west of Lake Baikal. The development of the basin is controlled by the segmented Tunka fault. We performed a detailed mapping of the Kyngarga river terraces, the best preserved terraces staircase in Baikal rift system, at their intersection with the Tunka fault. In order to decipher the chronology of seismic events and the slip rates along that segment of the fault, key terraces were dated using in situ produced cosmogenic ¹⁰Be. We demonstrate that the formation of the terrace staircase occurred entirely during MIS1–MIS2. The obtained data allowed us to estimate the rate of incision at different stages of the terrace staircase formation and the relationship between the vertical and horizontal slip rates along this sub-latitudinal segment of the Tunka fault making respectively 0.8 and 1.12 mm yr− 1 over the past ~ 12.5 ka. Analysis of the paleoseismology and paleoclimate data together with terrace dating provided the possibility to estimate the influence of tectonic and climatic factors on the terrace formation. Our proposed model of the Kyngarga river terrace development shows that the incisions into terraces T3 and T6 were induced by the abrupt climatic warming episodes GI-1 and GI-2, respectively, whereas terraces T5, T4 and T2 were abandoned due to the vertical tectonic displacement along the Tunka fault caused by coseismic ruptures.
... Prior to the sedimentation rate change at the seismic boundary B9, terrigenous sediments were deposited with a sedimentation rate two times higher than the sedimentation rate above this boundary. After the uplift of Academician Ridge, the influx of sediments decreased, which is recorded by the lower rate of sedimenta-tion above seismic reflector B9. Ivanov and Demonterova (2009), following an idea in Logatchev and Zorin (1987), explained that this change in sedimentation rate could have been caused by a forceful tectonic event at 4.5 Ma which led to the rapid growth of Academician Ridge between the central and northern Baikal basins. ...
Lake Baikal sedimentary records in general and magnetostratigraphy in particular have already enormously contributed in the global context to evaluate environmental and climatic changes in the deep continental setting. The Baikal Drilling Project (BDP) has become a world leader in pioneering recovery of extremely long (several hundred meters) lacustrine sediment sequences from deep water. This has made it possible, for the first time, to obtain a continental archive with the same chronostratigraphic integrity as marine records to address critical questions of the last eight million years. It explains why the amount of publications on Lake Baikal sedimentary and magnetic records can be compared to the number of papers for the Oceanic Drilling Program.
The unique continuity of the Lake Baikal deep drilled cores — short piston cores and deep drilled cores — of 1993, 1996, and 1998 enables one to reconstruct reliably the geomagnetic polarity chrons and a number of the shorter geomagnetic events. Data from three very long cores allows a comparison to the geomagnetic polarity time scale (GPTS) and detailed records of geomagnetic events in the last 8.4 Ma. A refined age model, supported by ¹⁰Be dates, provides constraints for the short geomagnetic events. Some geomagnetic events are correlated with geomagnetic excursions already discussed in the literature; others are identified for the first time and may need future confirmation.
... The BRZ has been studied by many research teams of the former Soviet Union, Russia and of other countries with foci made to its geological history (e.g., Logatchev, 1983;Logatchev et al., 1996;Zonenshain et al., 1990), tectonic structure (e.g., Delvaux et al., 1995;Jolivet et al., 2009Jolivet et al., , 2013Ufimtsev et al., 2009), deep seismic structure (Zhao et al., 2006;Koulakov, 2011;Zhu, 2014), GPS-geodesy (Ashurkov et al., 2011), and magmatism (Rasskazov, 1993;Yarmolyuk and Ivanov, 2000;Rasskazov et al., 2003;Yarmolyuk et al., 2005;Ivanov and Demonterova, 2009;Ivanov et al., 2015). However, its origin remains debatable, in particular, in terms of its Meso-Cenozoic history. ...
... 3) The Miocene Baikal rift volcanism formed the majority of basaltic fields of the BRZ (Fig. 1B). The Early Miocene volcanism was manifested in the southwestern BRZ as shown by numerous K-Ar and Ar-Ar age estimates ranging from 22 to 15 Ma (Rasskazov, 1993;Ashchepkov et al., 2003;Rasskazov et al., 2000Rasskazov et al., , 2003Yarmolyuk et al., 2003;Ivanov and Demonterova, 2009;Tsypukova et al., 2014). The main fields of the Early Miocene volcanism are Tunka and Hovsgol. ...
... The initiation of the deep lake could be linked to accelerated tectonics at the Miocene/Pliocene boundary. The initiation of the Hovsgol Basin was probably also related to that event because the "valley" basalts were incised into a plateau of "top" basalts at ca. 8-7 Ma (Ivanov and Demonterova, 2009). The tectono-stratigraphic record from Hovsgol sediments suggests their 6-5.5 Ma age (Fedotov, 2007). ...
In this paper we present a review of sedimentological, geomorphological, lithological, geochronological and geophysical data from major, minor and satellite basins of the Baikal Rift Zone (BRZ) and discuss various aspects of its evolution. Previously, the most detailed sedimentological data have been obtained from the basins of the central BRZ, e.g., Baikal, Tunka and Barguzin, and have been used by many scientists worldwide. We add new information about the peripheral part and make an attempt to provide a more comprehensive view on BRZ sedimentation stages and environments and their relations to local and regional tectonic events. A huge body of sedimentological data was obtained many years ago by Soviet geologists and therefore is hardly accessible for an international reader. We pay tribute to their efforts to the extent as the format of a journal paper permits. We discuss structural and facial features of BRZ sedimentary sequences for the better understanding of their sedimentation environments. In addition, we review tectono-sedimentation stages, neotectonic features and volcanism of the region. Finally, we consider the key questions of the BRZ evolution from the sedimentological point of view, in particular, correlation of Mesozoic and Cenozoic basins, bilateral growth of the Baikal rift, Miocene sedimentation environment and events at the Miocene/Pliocene boundary, Pliocene and Pleistocene tectonic deformations and sedimentation rates. The data from deep boreholes and surface occurrences of pre-Quaternary sediments, the distribution of the Pleistocene sediments, and the data from the Baikal and Hovsgol lakes sediments showed that 1) BRZ basins do not fit the Mesozoic extensional structures and therefore hardly inherited them; 2) the Miocene stage of sedimentation was characterized by low topography and weak tectonic processes; 3) the rifting mode shifted from slow to fast at ca. 7–5 Ma; 4) the late Pleistocene high sedimentation rates reflect the fast subsidence of basin bottoms.
... One explanation involves outflow via the Palaeo-Manzurka towards the Lena, and suggests that the level of Lake Baikal was higher in the geological past (Kononov and Mats 1986;Mats 1993;Mats et al. 2002). An alternative interpretation is that the Primorsky Range was lower, and the absolute water level of Lake Baikal stayed similar to its present-day level (Colman 1998;Ivanov and Demonterova 2009). The sedimentary deposits of the Palaeo-Manzurka are typically horizontally layered with boulders and pebbles at their lower parts and mainly sandy upper parts of the cross-sections ( Figure 5), similar to those accumulated by megafloods (Carling 2013). ...
Lake Baikal, the largest freshwater reservoir on Earth (~600 × 30 km in size and up to 1.6 km in depth), has more than 300 contributing rivers but only one N-trending outflow – River Angara. In the Pliocene or Pleistocene, another N-trending outflow operated through the Palaeo-Manzurka to Lena. Provenance analysis using U–Pb dating of detrital zircons from the Palaeo-Manzurka sediments demonstrates that the dominant source of the zircons was the lake deposits, while the contribution of zircons from local bedrocks was limited to about 8% only. Looking for an explanation of this, we propose a hypothesis that formation of the Palaeo-Manzurka sediments took place in association with a catastrophic mega-landslide (~15 × 3 km) into the lake and the resulting mega-tsunami flooding.
... M.M. Arakelyants †, V.A. Lebedev, V.V. Ivanenko, M.I. Karpenko Chernyshev et al. (2006) 1970-2014 (N300) Saltykovskii et al. (1984), Kononova et al. (1988), Yarmolyuk et al. (2001Yarmolyuk et al. ( , 2003aYarmolyuk et al. ( , 2003bYarmolyuk et al. ( , 2007aYarmolyuk et al. ( , 2007b, Stupak et al. (2008Stupak et al. ( , 2012, Ivanov and Demonterova (2009), this work. Institute of Geochemistry AS USSR, Irkutsk, USSR V.N. ...
... The overall history of volcanism and sedimentation of the rift stage is much better known and understood than earlier stages. Thus the following few sections will significantly overlap with previously published reviews (Mats, 1993;Rasskazov, 1993;Rasskazov, 1994;Rasskazov et al., 2000;Logachev, 2003;Yarmolyuk et al., 2003b;Yarmolyuk and Kuz'min, 2004;Ivanov and Demonterova, 2009) in both the data and interpretation. We contribute some new K-Ar and 40 Ar/ 39 Ar ages, which help to better understand the volcanism and rifting. ...
... The Baikal rift continued to grow in the Early Miocene, especially as the North-Baikal Basin extended eastwards (Fig. 16) (Logachev, 1993(Logachev, , 2003. Early Miocene volcanism was widespread in the southwestern part of the Baikal rift (Fig. 16), where numerous K-Ar ages have been determined (Rasskazov, 1993;Ashchepkov et al., 2003;Rasskazov et al., 2003b;Yarmolyuk et al., 2003b;Ivanov and Demonterova, 2009) and 40 Ar/ 39 Ar ages also obtained (Rasskazov et al., 2000(Rasskazov et al., , 2003bTsypukova et al., 2014). The oldest 40 Ar/ 39 Ar age of 21.86 ± 0.05 Ma was obtained for a lava unit from the Hamar-Daban range in the Dzhida river area (Fig. 16) (Rasskazov et al., 2003b). ...
In this review we focus on the volcanism, that occurred in Transbaikalia, Siberia after the closure of the Mongolia-Okhotsk Ocean. The closure happened in the Early Jurassic. After that time, lithosphere in Transbaikalia went through two phases of rifting; in the Early Cretaceous and again in the Late Cretaceous until present. The latter rifting event is known as the Baikal rifting. We consider the chronology of the volcanism and basin formation in the Baikal rift and show that there has been a complex relationship between the two. Extension initiated in the central part of the rift system; this area is now occupied by Lake Baikal. Sedimentary basins initially developed by deepening and widening of the central part of the rift system and then by bilateral propagation of basin formation outwards. Volcanism was generally offset from the axial rift. Considering along axis distribution of volcanism, it initiated in the central part of the system and propagated bilaterally to the modern rift ends. We argue that tectonic stress controlled localization of the eruptive centres. Extension and shearing probably caused melting at mantle depth, suggestive of the passive model of volcanism. However, when considering the Baikal rift and adjacent non-rifted regions of Mongolia in a wider context of tectonics and volcanism of Central and East Asia, it is not possible to rule out that the volcanism may be associated with mantle transition zone diapirs; thus the active model of volcanism may also apply. The diapirs are located by regional isostatic gravity anomalies and considered as upwelling parts of the upper mantle convective cell controlled by the Pacific subduction and slab stagnation in the mantle transition zone. We do not see any geochemical, geophysical and geochronological evidence for involvement of deeper mantle to explain volcanism in either Baikal rift, non-rifted regions of Mongolia or anywhere else within Central and East Asia.
... The uplifting of East Sayan had an arch-block character and was accompanied by the renewal of ancient faults, formation of intermountain basins, and effusion of basaltic lavas. Two-stage orogeny in East Sayan was repeatedly pointed out (Ivanov and Demonterova, 2009;Rasskazov et al., 2000;Strelkov and Vdovin, 1969;Vdovin, 1976). In the earlier publications (Strelkov and Vdovin, 1969;Vdovin, 1976), it was stated that the first stage in the Cenozoic orogeny began in the Oligocene. ...
... From then on, active orogeny entered its second stage, which has lasted throughout the Quaternary and given rise to the main features of recent topography. In later geochronological studies of volcanic and sedimentary rocks (Ivanov and Demonterova, 2009;Rasskazov et al., 2000), absolute dating was used to reconstruct the main orogenic stages in East Sayan. According to these data, the first stage of extensive uplifting falls on 22-15 Ma. ...
... It was accompanied by slight erosional dissection with subsequent effusion of basaltic lavas, which shielded the Early Miocene paleotopography. The second stage, characterized by the rapid uplifting of individual mountain ranges, began at 8.7 (Rasskazov et al., 2000) or ca. 5 Ma (Ivanov and Demonterova, 2009). It was associated with the transformation of the drainage network, deformations of the peneplanation surface, and volcanic eruptions. ...
The history of the peneplain in East Sayan was studied using apatite fission-track analysis (AFTA). This method is suitable for determining the formation time of the erosional surface and estimating its denudation rate. The largest known relic of the peneplanation surface in this area is the Oka Plateau, separated from the Kropotkin Ridge by the Oka–Zhombolok fault. The AFTA shows that the peneplain on the Oka Plateau formed in the Late Jurassic–Early Cretaceous. This peneplain is much younger than the erosional surfaces that persist today in the Tien Shan, Gobi Altai, and Mongolian Altai (Early Jurassic). However, it is older than the peneplain on the Chulyshman Plateau, Altai (Late Cretaceous), suggesting asynchronous formation of the ancient peneplain in Central Asia. The similar exhumation histories of samples from the Oka Plateau and Kropotkin Ridge indicate that these morphotectonic structures developed from Jurassic to late Miocene as a single block, which underwent continuous slow denudation at an average rate of 0.0175 mm/yr. Active tectonic processes in the Late Miocene caused the destruction of the peneplanation surface and its partial uplifting to different altitudes. The rate of Pliocene–Quaternary vertical movements along the Oka–Zhombolok fault is roughly estimated at 0.046–0.080 mm/yr, which is several times higher than the denudation rate in this area. During the Pliocene–Quaternary, the Oka Plateau has not undergone any significant morphologic changes owing to its intermediate position between the summit plain and datum surface of East Sayan and to its partial shielding by basaltic lavas.
