OSL dating of offset streams across the Altyn Tagh Fault: Channel deflection, loess deposition and implication for the slip rate

- Loess in fault-deflected streams was used to trace past slips of Altyn Tagh Fault.
- A conceptual model is proposed for the relationship between loess and fault.
- Average slip rate is 11 ± 2mm/year since 7 ka estimated from 16 OSL ages.

Two deflected streams flowing across the Altyn Tagh Fault (ATF) were investigated at the Aksay segment, NW China. Due to strike of the ATF, stream channels are deflected and elongated by adding new sections along the fault line. After subsequent water erosion and fluvial refreshment, banks of these deflected streams are overlain by aeolian loess. Geomorphological features suggest that stream deflections along the fault were developed as a result of faulting activities and displacements were progressively accumulated from multiple faulting cycles. Each faulting cycle is composed of faulting event triggered elongation of channels, creation of stream banks or risers and subsequent aeolian loess deposition on the banks. A model is proposed to illustrate the relationship between fault movement and loess deposition, which is supported by OSL dating of the loess on the offset stream channels. Our results demonstrated that: (1) loess deposits along deflected streams can be used to trace fault slip history, given specific geomorphic assumptions discussed in the text; and (2) based on stream channel offsets and loess ages, the Holocene slip rate of the ATF is estimated to be 11 ± 2 mm/year along the Aksay segment.