Magnetostratigraphy of syntectonic growth strata and implications for the late Cenozoic deformation in the Baicheng Depression, Southern Tian Shan

Neogene Paleomagnetic Study of the Western Baicheng Depression: Implications for the Intensified Deformation of Tian Shan Since the Latest Miocene

“…The field observations and magnetostratigraphy of syntectonic deposits on the northern limb of the northern Kalayuergun anticline allow us to constrain the basal age of growth strata at ~5.3 Ma (Figure ), indicating that the growth of the northern Kalayuergun anticline initiated at ~5.3 Ma, which is close to the initial age of growth strata in the Kuchetawu (~6.5 Ma; Sun et al, ), Kelasu (~5.3 Ma; Zhang et al, ) and Yaken (~5.5 Ma; Hubert‐Ferrari et al, ) sections in the southern Tian Shan forelands and the age of ~6 Ma in the forelands of the northern Tian Shan (Lu et al, ; Sun et al, ). These results suggest that a prominent crustal shortening episode initiated since the latest Miocene in the forelands of the Tian Shan Range.…”

“…In addition, the sedimentation rates can be underestimated as the sampled strata just contain the lowest part of the Kuqa formation. However, the sedimentation rate in the Kangcun formation is much higher than that of the Kelasu section (~47 m/Myr; Zhang et al, , ), which can be attributed to the shorter distance of the studied section to the Cenozoic depocenter of the depression. Generally, the variations of sedimentation rates in different parts of the depression are roughly comparable to the coeval sedimentary thickness (Wang et al, ).…”

“…Considering the several episodes of deformation observed in different parts of Tian Shan, the tectonic event since ~5.3 Ma should be an important part during the basinward propagation of deformation. It is worth emphasizing that this episode of deformation must be an intensified one, as nearly synchronous deformation evidenced by syntectonic deposits have been observed on the first and second rows of fold‐and‐thrust belts in the Baicheng Depression (Sun et al, ; Zhang et al, ) and in the northern Tian Shan forelands (Lu et al, , ; Sun & Zhang, ).…”

“…In a recent apatite fission track study of the SW Tian Shan (Bande et al, ), researchers proposed an onset of exhumation at ~25 Ma, which was followed by a final strong late Miocene rapid cooling event. The chronology of syntectonic sediments constrained the initiation of deformation to ~7–5 Ma (Lu et al, ; Sun et al, ; Sun & Zhang, ; Zhang et al, ). The extrapolation of shortening rates suggested that the initial growth of Tian Shan occurred at ~10 Ma, which may be related to the tectonic uplift of Tibet (Abdrakhmatov et al, ).…”

“…The younger basal ages of the growth strata on the middle and southern Kalayuergun anticlines suggest the later basinward propagation of deformation. Additionally, this deformation must have continued to present which can be evidenced by the records of growth strata (Sun et al, ; Sun & Zhang, ; Zhang et al, ), the migration of Quaternary folding (Fu et al, ), and the current crustal shortening rates across the long range revealed by GPS observations (Abdrakhmatov et al, ; Wang et al, ; Yang et al, ).…”