Convergence of the Pamir and the South Tian Shan in the late Cenozoic: Insights from provenance analysis in the Wuheshalu section at the convergence area

Abstract

In response to collision and convergence between India and Asia during the Cenozoic, convergence took place between the Pamir and South Tian Shan. Here we present new detrital zircon U-Pb ages coupled with conglomerate clast counting and sedimentary data from the late Cenozoic Wuheshalu section in the convergence zone, to shed light on the convergence process of the Pamir and South Tian Shan. Large Triassic zircon U-Pb age populations in all seven samples suggest that Triassic igneous rocks from the North Pamir were the major source area for the late Cenozoic Wuheshalu section. In the Miocene, large populations of the North Pamir component supports rapid exhumation in the North Pamir and suggest that topography already existed there since the early Miocene. Exhumation of the South Tian Shan was relatively less important in the Miocene and its detritus could only reach a limited area in the foreland area. Gradually increasing sediment loading and convergence of the Pamir and South Tian Shan caused rapid subsidence in the convergence area. Since ca. 6–5.3 Ma, the combination of a major North Pamir component and a minor South Tian Shan component at the Wuheshalu section is consistent with active deformation of the South Tian Shan and the North Pamir. During deposition of the upper Atushi Formation, a larger proportion of North Pamir–derived sediments was deposited in the Wuheshalu section, maybe because faulting and northward propagation of the North Pamir caused northward displacement of the depocenter to north of the Wuheshalu section.

Cenozoic Tectono‐Geomorphologic Evolution of the Pamir‐Tian Shan Convergence Zone: Evidence From Detrital Zircon U‐Pb Provenance Analyses

“…During the Eocene‐middle Miocene, sediments in the eastern foreland of the Pamir (Aertashi and Oytage sections) contain Triassic, Paleozoic and Proterozoic detrital zircon grains, accompanied by small clusters of Cenozoic zircon grains (Figures 7 and 8) (Bershaw et al., 2012; Blayney et al., 2016; Sun et al., 2016). Coeval sediments in the northeastern foreland of the Pamir (Tierekesazi and Wuheshalu sections) show a dominance of Triassic zircon grains and similar Paleozoic and Precambrian detrital zircon U‐Pb age distribution patterns with that of the sediments in the eastern foreland of the Pamir (Figures 7 and 8) (Chen et al., 2019 and this study). Overall, despite the appearance of a few Cenozoic zircon grains, the patterns in detrital zircon U‐Pb age distributions indicate that the sediments in the eastern and northeastern foreland of the Pamir were primarily sourced from the Northern Pamir during the Eocene‐middle Miocene period.…”

“…Sediment eroded from the SW Tian Shan started to fill in the northern Pamir-Tian Shan convergence zone. Consistent with east directed paleocurrent observations, Pliocene sediments thicken eastward from the Urugqat and Tierekesazi sections in the eastern Pamir-Tian Shan corridor to the Boguzi section in the northwestern Tarim basin (Chen et al, 2002(Chen et al, , 2015(Chen et al, , 2019Heermance et al, 2007;Thompson et al, 2015;Wei et al, 2013). In this period, the Pamir-Tian Shan convergence zone might have been squeezed into a narrow corridor, which had limited space to accommodate the sediments eroded from adjacent orogens (Figure 9c).…”

“…Overall, despite the appearance of a few Cenozoic zircon grains, the patterns in detrital zircon U-Pb age distributions indicate that the sediments in the eastern and northeastern foreland of the Pamir were primarily sourced from the Northern Pamir during the Eocene-middle Miocene period. This observation suggests that the paleo rivers sourcing these areas were primarily restricted to the Northern Pamir (e.g., Blayney et al, 2016;Chen et al, 2019;this study). The large abundance of Triassic zircon grains of the sediments in the Tierekesazi and Wuheshalu sections is in good agreement with the spatial distribution of the Karakul-Mazar magmatic belt (Figures 1 and 8) (Imrecke et al, 2019;Li, Robinson, Gadoev, et al, 2020).…”

“…Detrital zircon U‐Pb analyses have been carried out in Cretaceous‐Quaternary sediments from a series of sections surrounding the Pamir, including the Dashtijumb, Peshtova, West Algurkan, Tierekesazi, Wuheshalu, Oytage and Aertashi sections (Figure 7) (Bershaw et al., 2012; Blayney et al., 2016; Chapman et al., 2019; Chen et al., 2019; Sun et al., 2016; Wang et al., 2019; Yang et al., 2018 and this study). E‐W extension along the Kongar Shan fault system since 14–7 Ma may have blocked the basinward transport of the sediments from the hinterland of the Pamir to the Tarim basin.…”

“…However, large portions of Northern Pamir derived Paleozoic and Neoproterozoic detrital zircon grains in latest Cretaceous-Miocene sediments in the northwestern and western foreland basins of the Pamir (Peshtova, West Algurkan and Peshtova and West Algurkan sections Dashtijumb sections) shows that positive topography was still preserved in the western Northern Pamir since the latest Cretaceous (<76 Ma) (Figure 8) (Chapman et al, 2019;Li, Robinson, Gadoev, et al, 2020;Wang et al, 2019). In addition, deposition of thick (Bershaw et al, 2012;Chapman et al, 2019;Chen et al, 2019;Sun et al, 2016;Wang et al, 2019;Yang et al, 2018;this study). The locations of these cross sections are shown in Figure 7.…”