Variations in slip rates at the Million to Thousand-Year scale: A Case Study of the Huoerguosi Fold-and-Thrust Belt, Northern Tianshan, China

Whether or not the slip rate of intracontinental faults varies through time is of fundamental importance for the spatiotemporal distribution of strain, the strain release during earthquakes and the growth of fault-related topography; however, fault systems for which slip rate estimates over high-resolution scales ranging from millions to thousands of years are lacking (Hetzel et al., 2019). Here, we focused on the Huoerguosi fold-and-thrust belt, Northern Tianshan. Through field geological-geomorphological mapping, drone photography, differential GPS measurements, and analysis of petroleum seismic-reflection profiles, we studied the geometric and kinematic characteristics of the Huoerguosi anticline. It was found that the deep South Junggar Thrust (SJT) along the gypsum bearing Anjihaihe Formation (E_2-3a) detachment horizon, characterized by arcuate bending and faulting, controlled the growth of the Huoerguosi anticline, forming a wide and gentle active synclinal curve hinge zone in the southern limb of the anticline. All terraces near the active curve hinge zone exhibited folding deformation, resulting in broad, gentle fold scarps facing south. Through modeling and forward simulation of the growth strata and deformed terraces in the active curve hinge zone of the southern limb of the anticline, a geometric model for the growth strata and sporadically terraces was established, constraining the shortening of the SJT at different time periods. By using the optically stimulated luminescence dating method on fine sand fluvial sediments and granite cobbles, a chronological framework was established for these late Quaternary growth strata and deformed terraces. Combining previous Magnetochronological ages (Charreau et al., 2009) and cosmogenic nuclide ages (Puchol et al., 2017), the slip rates of the SJT at million-to-thousand-year scales were estimated. It was found that the slip rate of the SJT remains almost constant at the million-year scale and exhibits strong fluctuations at the tens of thousands to thousand-year scale, similar to the characteristics of normal faults at different time scales (Mouslopoulou et al., 2009). Comparing to climate records, it seems that there is a strong coupling relationship between the SJT deformation and climate change over the past 300 ka.

References

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