International audienceThe Ili-Balkhash Basin in southeastern Kazakhstan is located at the junction of the actively deforming mountain ranges of western Junggar and the Tien Shan, and is therefore part of the southwestern Central Asian Orogenic Belt. The basement of the Ili-Balkhash area consists of an assemblage of mainly Precambrian microcontinental fragments, magmatic arcs and accretionary complexes. Eight magmatic basement samples (granitoids and tuffs) from the Ili-Balkhash area were dated with zircon U-Pb LA-ICP-MS and yield Carboniferous to late Permian (~ 350-260 Ma) crystallization ages. These ages are interpreted as reflecting the transition from subduction to (post-) collisional magmatism, related to the closure of the Junggar-Balkhash Ocean during the Carboniferous – early Permian and hence, to the final late Paleozoic accretion history of the ancestral Central Asian Orogenic Belt. Apatite fission track (AFT) dating of 14 basement samples (gneiss, granitoids and volcanic tuffs) mainly provides Cretaceous cooling ages. Thermal history modeling based on the AFT data reveals that several intracontinental tectonic reactivation episodes affected the studied basement during the late Mesozoic and Cenozoic. Late Mesozoic reactivation and associated basement exhumation is interpreted as distant effects of the Cimmerian collisions at the southern Eurasian margin and possibly of the Mongol-Okhotsk Orogeny in SE Siberia during the Jurassic – Cretaceous. Following tectonic stability during the Palaeogene, inherited basement structures were reactivated during the Neogene (constrained by Miocene AFT ages of ~ 17–10 Ma). This late Cenozoic reactivation is interpreted as the far-field response of the India-Eurasia collision and reflects the onset of modern mountain building and denudation in southeast Kazakhstan, which seems to be at least partially controlled by the inherited basement architecture

The Central Asian Orogen was reactivated in the Cenozoic, which gave rise to mountain systems and sedimentary basins, strike-slip and thrust faults, ramps, and rift basins under the far-field effect of the India–Eurasia collision. Pre-Cenozoic structures, as well as the superposed Cenozoic deformation, are traceable in the gravity pattern. Analysis and correlation of stratigraphic, tectonic, geomorphological, and geophysical (resistivity and gravity) data from Gorny Altai and tectonic modeling on the basis of apatite fission-track thermochronology show that vertical motions have been the most active for the past 5 Ma. The uplift and subsidence produced, respectively, the Chulyshman and Ukok Plateaus with high mountains around and the the Kurai–Chuya basin between them. Gravity data suggest the existence of Late Carboniferous, Jurassic, and Cretaceous rocks found in tectonic wedges around the basin at the base of its sedimentary fill.

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In this study, we present zircon U/Pb, plagioclase and K-feldspar 40Ar/39Ar and apatite fission track (AFT) data along the South Tannuol Fault Zone (STFZ). Integrating geochronology and multi-method thermochronology places constraints on the formation and subsequent reactivation of the STFZ. Cambrian (~510 Ma) zircon U/Pb ages obtained for felsic volcanic rocks date the final stage of STFZ basement formation. Ordovician (~460–450 Ma) zircon U/Pb ages were obtained for felsic rocks along the structure, dating their emplacement and marking post-formational local magmatic activity along the STFZ. 40Ar/39Ar stepwise heating plateau-ages (~410–400 Ma, ~365 and ~340 Ma) reveal Early Devonian and Late Devonian–Mississippian intrusion and/or post-magmatic cooling episodes of mafic rocks in the basement. Permian (~290 Ma) zircon U/Pb age of mafic rocks documents for the first time Permian magmatism in the study area creating prerequisites for revising the spread of Permian large igneous provinces of Central Asia. The AFT dating and Thermal history modeling based on the AFT data reveals two intracontinental tectonic reactivation episodes of the STFZ: (1) a period of Cretaceous–Eocene (~100–40 Ma) reactivation and (2) the late Neogene (from ~10 Ma onwards) impulse after a period of tectonic stability during the Eocene–Miocene (~40–10 Ma).

Results of apatite fission track dating have been summarized and correlated with stratigraphic, geoelectrical, tectonic, and geomorphological data. The average regional rate of rock denudation in southeastern Gorny Altai is reflected in three thermotectonic events: (1) Late Cretaceous–Early Paleogene tectonic activity with a denudation rate of ~200 m/Myr, related to the distant impact of the Mongol–Okhotsk orogeny; (2) Middle Paleogene–Early Neogene stabilization with peneplanation; and (3) Neogene–Quaternary “stepwise” tectonic activity with a denudation rate of ≤270 m/Myr, related to the distant impact of the Indo-Eurasian collision. We present results of study of the evolution of regional tectonic processes and topography over the last 100 Myr by analysis of digital and shaded elevation models and apatite fission track dating.

The Kolyvan–Tomsk folded zone (KTFZ) represents part of the Central Asian Orogenic Belt (CAOB). The KTFZ is mainly composed of detrital Late Palaeozoic sedimentary deposits, with minor intrusions. Detrital zircon geochronology on the Upper Devonian to Lower Permian sedimentary sequences of the KTFZ and the associated Gorlovo foreland basin yields four age peaks, reflecting the magmatic events in the source terranes. These events consist of (a) a minor Neoproterozoic peak (0.9–0.7 Ga), (b) a significant Early Palaeozoic peak (550–460 Ma), with a maximum at 500 Ma, and two well‐defined Late Palaeozoic peaks during (c) the Middle–Late Devonian (385–360 Ma) and (d) the Carboniferous–Early Permian (360–280 Ma), with a maximum at 320 Ma. Older zircons (>1 Ga) are quite rare in the sampled sedimentary sequences. Slightly negative εNd values and associated relatively young Nd model ages were obtained (εNd(T) = −0.78, T (DM) ~1.1 Ga for Upper Devonian sandstones, εNd(T) = −1.1, T (DM) ~1.1 Ga for Lower Permian sandstones), suggesting only minor contribution of ancient continental crust to the main sedimentary units of the KTFZ. All intrusive and volcaniclastic rocks on the contrary are characterized by high positive εNd(T) values in the range of 3.78–6.86 and a Late Precambrian model age (T (DM) = 581–916 Ma), which corroborates its juvenile nature and an important depleted mantle component in their source. The oldest unit of the KTFZ, the Bugotak volcanic complex formed at the Givetian–Early Frasnian transition, at about 380 Ma. Upper Devonian detrital deposits of the KTFZ were formed in the Early Palaeozoic accretion belt of the Siberian continent and specifically in a passive continental margin environment. Deposits of the Gorlovo foreland basin, adjoining the KTFZ, were accumulated as a result of erosion of the Carboniferous–Early Permian volcanic rocks, which are now buried under the Meso–Cenozoic sedimentary cover of the West Siberian Basin. The magmatic events, recorded in the KTFZ zircon data, correspond to the most significant magmatic stages that affected the western part of the CAOB as a whole.

—Middle Mesozoic and Cenozoic tectonic events on the periphery of the West Siberian Plain and in the flanking mountains of the northwestern Altai–Sayan province produced highland topography over a part of southeastern West Siberia. The activity stages were separated by a long lull from Late Cretaceous through middle Paleogene, when the Mesozoic mountains were denuded to the base level corresponding to the level of the West Siberian epicontinental sea. The sea of that time was connected to the World Ocean, and its level fell in several successive events. The periods of stable sea level are marked by surfaces at 200, 250, and 300 m above sea level (in the present reference of elevations) and correlate with global sea level changes according to Haq and Vail. The stability surfaces were revealed during geomorphological surveys in the Salair Range and in the Bugotak–Sokur upland. Their elevations have not changed since the origin in the studied part of the Bugotak–Sokur area, but the SW tilting Salair block delineated by thrust faults in the north and in the east has been uplifted at 0.1 mm/year. In the course of neotectonic activity, the line of mountain growth shifted notably to the southeast, leaving behind the Fore-Altai plain and the Bugotak–Sokur upland, which were occupied by high mountains in the Jurassic. The lack of post-Mesozoic molasse in the Kuznetsk Basin and in the Chulym plain indicates that the present Kuznetsk Alatau and Salair Ranges are considerably lower than their middle Mesozoic precursors.