A broad array of new provenance and stable isotope data are presented from two magnetostratigraphically dated sections in the south‐eastern Issyk Kul basin of the Central Kyrgyz Tien Shan. The results presented here are discussed and interpreted for two plausible magnetostratigraphic age models. A combination of zircon U‐Pb provenance, paleocurrent and conglomerate clast count analyses is used to determine sediment provenance. This analysis reveals that the first coarse‐grained, syn‐tectonic sediments (Dzhety Oguz formation) were sourced from the nearby Terskey Range, supporting previous thermochronology‐based estimates of a ca. 25–20 Ma onset of deformation in the range. Climate variations are inferred using carbonate stable isotope (δ18O and δ13C) data from 53 samples collected in the two sections and are compared with the oxygen isotope compositions of modern water from 128 samples. Two key features are identified in the stable isotope data set derived from the sediments: (1) isotope values, in particular δ13C, decrease between ca. 26.0 and 23.6 or 25.6 and 21.0 Ma, and (2) the scatter of δ18O values increased significantly after ca. 22.6 or 16.9 Ma. The first feature is interpreted to reflect progressively wetter conditions. Because this feature slightly post‐dates the onset of deformation in the Terskey Range, we suggest that it has been caused by orographically enhanced precipitation, implying that surface uplift accompanied late Cenozoic deformation and rock uplift in the Terskey Range. The increased scatter could reflect variable moisture source or availability caused by global climate change following the onset of Miocene glaciations at ca. 22.6 Ma, or enhanced evaporation during the Mid‐Miocene climatic optimum at ca. 17–15 Ma.

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Researchers of the border regions of Xinjiang and the Central Asian countries are actively discussing two alternative models for the relationships between the main structural units of the Tianshan mountains. Most researchers believe that the Kyrgyz Middle Tianshan wedges out to the east along the Atbashi-Inylchek-Nalati marginal fault. According to the second hypothesis, the structures of the Middle Tianshan continue within the range Nalati where they are described as Chinese Central Tianshan. Comparing the characteristics of the Paleozoic and Proterozoic sedimentary, volcanogenic, intrusive, and metamorphic formations of these regions leads us to the conclusion that the structural units of the Kyrgyz Middle and most of the Northern Tianshan, including the superimposed Middle-Late Paleozoic troughs, are not continued into China, but are successively cut along the echelon system of conjugated strike-slip faults, united by us into the Frontal Tianshan Dextral Strike-slip (FTDS). And only the northern segment of the Issyk-Kul massif can be considered as an analogue of the Chinese Central Tianshan, displaced along the FTDS to the northwest for a distance of at least 80 km. Therefore, adjacent geological complexes are eroded along the FTDS like the oblique boundaries of convergent lithospheric plates are tectonic eroded.