Tectonic history of the Kyrgyz South Tien Shan (Atbashi‐Inylchek) suture zone: The role of inherited structures during deformation‐propagation

Abstract

Multimethod chronology was applied on intrusives bordering the Kyrgyz South Tien Shan suture (STSs) to decipher the timing of (1) formation and amalgamation of the suturing units and (2) intracontinental deformation that built the bordering mountain ranges. Zircon U/Pb data indicate similarities between the Tien Shan and Tarim Precambrian crust. Caledonian (∼440–410 Ma) and Hercynian (∼310–280 Ma) zircon U/Pb ages were found at the edge of the STSs, related to subduction and closure of the Turkestan Ocean and the formation of the suture itself. Permian‐Triassic (∼280–210 Ma) titanite fission track and zircon (U‐Th)/He data record the first signs of exhumation when the STSs evolved into a shear zone and the adjacent Tarim basin started to subside. Low‐temperature thermochronological (apatite fission track, zircon and apatite (U‐Th)/He) analyses reveal three distinct cooling phases, becoming younger toward the STSs center: (1) Jurassic‐Cretaceous cooling ages provide evidence that a Mesozoic South Tien Shan orogen formed as a response to the Cimmerian orogeny; (2) Early Paleogene (∼60–45 Ma) data indicate a renewed pulse of STSs reactivation during the Early Cenozoic; (3) Neogene ages constrain the onset of the modern Tien Shan mountain building to the Late Oligocene (∼30–25 Ma), which intensified during the Miocene (∼10–8 Ma) and Pliocene (∼3–2 Ma). The Cenozoic signals may reflect renewed responses to collisions at the southern Eurasian border (i.e., the Kohistan‐Dras and India‐Eurasia collisions). This progressive rejuvenation of the STSs demonstrates that deformation has not migrated steadily into the forelands, but was focused on pre‐existing basement structures.

Late-Paleozoic emplacement and Meso-Cenozoic reactivation of the southern Kazakhstan granitoid basement

“…Since the early Eocene, major structures in the southern CAOB were reactivated, which is likely a response to the continuous closure of the Tethys Ocean and associated accretions of island-arcs or continental slivers of 'Greater India' to the southern Eurasian margin (e.g. Glorie and De Grave, in press;Glorie et al, 2011b). From the late Oligocene-Miocene onwards, the southern CAOB was once more subjected to deformation, this time induced by the India-Eurasia collision.…”

“…Traditionally, the western Tien Shan (post-Soviet states) is divided into three tectonic units: the North Tien Shan (NTS), Middle Tien Shan (MTS) and South Tien Shan (STS) units (e.g. Biske et al, 2013;De Grave et al, 2012Glorie et al, 2010Glorie et al, , 2011bSeltmann et al, 2011) (Fig. 2).…”

“…the Kyrgyz Tien Shan (e.g. Bullen et al, 2001;De Grave et al, 2011a, 2012Glorie et al, 2010Glorie et al, , 2011bKonopelko et al, 2007;Macaulay et al, 2014), the Chinese Junggar (e.g. Hendrix et al, 1992;Shen et al, 2012;Zhou et al, 2008) and the southern Altai (e.g.…”

Geological evolution of Central Asian Basins and the western Tien Shan Range

“…Hendrix et al 1992;Sobel & Dumitru 1997;Allen et al 2001;Dumitru et al 2001;Glorie et al 2011). Indeed, the role of Palaeozoic structures and sutures is particularly important during later Cenozoic deformation.…”

“…It is separated from the North Tien Shan by the Terskey Suture (suture of the Terskey Early Palaeozoic ocean; e.g. Burtman 2010; Glorie et al 2011). The Middle Tien Shan wedges out eastwards near the border of Kyrgyzstan with China; further east, it has no recognized equivalent (Xiao et al 2013).…”