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Tian Shan is a vast and highly seismically active intracontinental mountain range. GPS measurements and field studies have shown that E-W and NW-SE trending thrusts and fault-related folds are distributed across central Tian Shan. However, few studies have determined the fault and fault-related-fold activity in the Bole Basin, the northernmost part of central Tian Shan. In this study, we focus on the Alashak Fold, which is situated along the southern margin of the Bole Basin. Using high-resolution uncrewed aerial vehicle-Digital Elevation Model data, field observations, and detailed mapping, we determined that the Alashak Fold is characterized by a trishear fault-propagation fold. Along the Alashak River, we identified five levels of fluvial surfaces, the T3 terrace was continuously preserved across the fold. Radiocarbon and surficial 10Be dating were used to determine the exposure age of the deformed T3 terrace. The folding characteristics of T3, trishear inversed modeling, and abandonment age indicate that the Alashak Fault has an uplift rate of 0.8 ± 0.3 mm/yr, a dip-slip rate of 4.2 ± 1.2 mm/yr, and a crustal shortening rate of 4.0 ± 1.2 mm/yr since the late Pleistocene, respectively. The Alashak and Latgan Faults intersect at a depth of 1.2 km, enclosing a wedge-shaped block. Our study emphasizes that tectonic activity along the southern margin of the Bole Basin has played a significant role in north-south shortening within central Tian Shan, as measured by geological measurements since the late Pleistocene. The Alashak Fault can potentially generate moderate–strong (Mw 5.0–7.0) earthquakes, while the Alashak and Latgan Faults can generate major (Mw 7.2) earthquakes. • Identification of rapid slip rate of 4.2 ± 1.2 mm/yr on a thrust-related fold in the central Tian Shan of China. • The Alashak Fault is a shallowly dipping thrust forming a fault-propagation fold. • The shallow Alashak Fault has the potential to generate strong earthquake (Mw 5.5 to 7.4) and surface rupture. • Significant shortening occurs within the southern margin of the Bole Basin. [ABSTRACT FROM AUTHOR]

The tenet of the Milankovitch theory is that Northern Hemisphere solar insolation, controlled by Earth's orbital is responsible for cyclic climate variations. Eccentricity in this context is responsible for cyclic variability of 100 ka and may drive periodicity in climate change during the middle and late Pleistocene. Although abundant evidence exists for 100 ka cyclic climatic fluctuations driving glacial-interglacial cycles, our knowledge about the record of cyclic climatic changes preserved in terrestrial landscapes remains limited, especially over multi-millennial (several glacial-interglacial) timescales. The intermontane Yanqi Basin in the southeastern Tian Shan, Central Asia, preserves at least seven generations of alluvial surfaces spanning multiple glacial cycles and yields insights into the record of climatic fluctuations that lead to aggradation and incision of river systems. We complement existing chronologic data with two new cosmogenic 10Be depth profiles and four surface exposure ages of alluvial surface abandonment in the south Tian Shan piedmont within the Yanqi Basin. New surface-exposure dating reveals the successive abandonment of these surfaces with a 100 ka cyclicity between 5.1 ± 0.9 and ~550 ka and indicates that there were multiple aggradation-incision cycles. The superimposed 100 ka cycles of aggradation-incision are best explained by eccentricity-driven climate change. Within these cycles, sediment is produced during glaciations by glacial and periglacial erosion. However, due to the dry and cold conditions of the glacial periods in central Asia, there is little discharge available to transport and evacuate the sediment from the valleys to the piedmont. Later, during the glacial to interglacial transition, higher precipitation and high discharge due to glacial melt water resulted in higher transport capacity of the river beyond a threshold to evacuate sediment. Subsequent rapid incision occurs after the upstream sediment reservoir is depleted and its timing corresponds to the glacial to interglacial transition period in our study area. Compared with the aggradation and incision of the northern piedmont of the Tian Shan governed by the Westerlies, the sedimentary systems of the South Tian Shan piedmont within the Yanqi Basin are mainly controlled by eccentricity-driven glacial-interglacial cycles. • 10Be chronology of alluvial surfaces of south Tian Shan was reconstructed since 600 ka. • The abandonment of alluvial surfaces occurs over 100-ka cycles. • Aggradation-and-incision cycles are best explained by eccentricity-driven climate change. • Incision correlates with global glacial-interglacial transition periods. [ABSTRACT FROM AUTHOR]

Deformed alluvial fans can indicate the subsurface fault-plane geometry of thrusts. Numerous seismic profiles have illustrated the subsurface fault-plane geometry of thrusts in the Tian Shan piedmonts. However, due to a lack of seismic profiles, the subsurface fault-plane geometry in the Tian Shan is not well-known. This paper focuses on a thrust-related anticline in the eastern Kusongmuxiek Fault (KF), the Latgan Anticline (LA), located in the southern margin of the Bole Basin, northern Tian Shan. Five alluvial fan surfaces, A1-A5 from young to old, are determined along the Dilike River. We used the alluvial fan surfaces and fault attitude to determinate the subsurface fault-plane geometry of the Latgan Fault. The geometric model reveals that the Latgan Fault can be divided into three segments: an upper ramp with a dip of 55°S, a central listric fault, and a lower ramp with a dip of 31°S. The abandonment age of the A4 surface based on its cosmogenic 10Be concentrations and use of a kinematic model of a listric fault fold reveal that the fault dip-slip rate is c. 0.5 mm/a, and the horizontal crustal shortening rate is c. 0.4 mm/a during the Pleistocene. The vertical incision rates of the Dilike River are 0.5–0.6 mm/a in the uplifted area and 0.2 mm/a in the non-uplifted area. This difference may be the result of tectonic uplift. Our field and remote sensing observations and the geometric characteristics of the eastern Keguqin Mountains piedmont thrusts indicate fault propagation into the basin via thick-skinned tectonics. The LA crustal shortening rate and previous studies indicate that the crustal shortening rates of the Bole, Borohoro, and Turfan Units are ~1.7–2.0 mm/a, >4.0 mm/a, and 3.2–4.4 mm/a, respectively. The lower shortening rate of the Bole Unit and higher shortening rates of the Borohoro and Turfan Units indicate that the Bole Unit is the lowest crustal shortening rate unit in the northern Tian Shan. • Study of fault-fold growth using dated alluvial fan surfaces (northern Tian Shan) • Uses remote sensing, field survey and 10Be cosmogenic exposure dating • Fan-fold morphology and fault attitude informs on sub-surface fault geometry • Reveals a listric fault fold with ~0.5 mm/a dip slip and ~ 0.4 mm/a horizontal shortening • Lowest rate thick-skinned fault propagation within the northern Tian Shan [ABSTRACT FROM AUTHOR]