Exhumation of basement‐cored uplifts: Example of the Kyrgyz Range quantified with apatite fission track thermochronology

Abstract

[1] The Kyrgyz Range, the northernmost portion of the Kyrgyzstan Tien Shan, displays topographic evidence for lateral propagation of surface uplift and exhumation. The highest, most deeply dissected segment lies in the center of the range. To the east, topography and relief decrease, and preserved remnants of a Cretaceous regional erosion surface imply minimal amounts of bedrock exhumation. The timing of exhumation of range segments defines the lateral propagation rate of the range-bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology. New multicompositional apatite fission track (AFT) data from three transects from the eastern Kyrgyz Range, combined with published AFT data, demonstrate that the range has propagated over 110 km eastward over the last $7-11 Myr. On the basis of the thermal and topographic evolutionary history, we present a model for a time-varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift. Easily eroded, Cenozoic sedimentary rocks overlying resistant basement control early, rapid exhumation and exhibit slow surface uplift rates. As increasing amounts of resistant basement are exposed, exhumation rates decrease while surface uplift rates are sustained or increase, thereby growing topography. As the range becomes high enough to cause ice accumulation and to develop steep river valleys, fluvial and glacial erosion becomes more powerful, and exhumation rates once again increase. Independently determined range-normal shortening rates also varied over time, suggesting a feedback between erosional efficiency and shortening rate.

Cenozoic tectono-geomorphological growth of the SW Chinese Tian Shan: Insight from AFT and detrital zircon U–Pb data

“…Similar reheating event observed in samples TK-09 and TK-10 was also reported from AFT thermal modelling of the sample 99WT-3, 7 km south of the Maidan fault (Sobel et al, 2006a), and in the Kyrgyz Range to the north and in the Aksu to the east Sobel et al, 2006b;Zhang et al, 2009). Finally, both models thus show an intense exhumation phase during the late Cenozoic (ca.…”

“…Oligocene-Miocene cooling ages corresponding to the onset of main deformation phase, which formed the modern Tian Shan, were detected along most of the sub-ranges except the southern flank of the Kyrgyz Range (Sobel et al, 2006a(Sobel et al, , 2006bDe Grave et al, 2007, 2010Zhang et al, 2009;Glorie et al, 2010Glorie et al, , 2011Chang et al, 2012;Macaulay et al, 2013Macaulay et al, , 2014Bande et al, 2014Bande et al, , 2015. AFT thermal modelling revealed a late Cenozoic reheating event along the Kyrgyz Range, Atbashi Range and Kokshaal Range, which might reflect sediment loading in this region or local tectonic burying in these regions (Sobel et al, 2006a(Sobel et al, , 2006b).…”

“…AFT thermal modelling revealed a late Cenozoic reheating event along the Kyrgyz Range, Atbashi Range and Kokshaal Range, which might reflect sediment loading in this region or local tectonic burying in these regions (Sobel et al, 2006a(Sobel et al, , 2006b). An intensive exhumation event occurred during the late Miocene to Pliocene (10 -3 Ma) was found along the Atbashi Range, the northern flank of Kyrgyz Range and the central Kyrgyz Tian Shan (Bullen et al, 2001;Sobel et al, 2006b;Glorie et al, 2011;Macaulay et al, 2014). …”

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

“…For the northern Kazakh Tien Shan, De Grave et al (2013) reported Late Cretaceous and Neogene AFT ages for the Trans-Ili Range, and Late Jurassic-Early Cretaceous ages for the Zhetyzol Range. In the northern Kyrgyz Tien Shan, Early Cretaceous AFT ages are characteristic for the central Kungey Range, while many Early to Late Cretaceous AFT ages were obtained for the Terskey Range (De Grave et al, 2013;Macaulay et al, 2014;Sobel et al, 2006). Furthermore, in and around the Chinese part of the Ili Basin, Cretaceous AFT ages are reported by Jolivet et al (2010) and north of Lake Balkhash (in the Sayak ore field) Late Cretaceous AFT ages are reported by Chen et al (2012).…”

“…Glorie et al, 2011b), the building of the modern Tien Shan is generally believed to have started in the Oligocene-early Miocene, and exhumation was widespread from the Miocene onwards (e.g. Bullen et al, 2001Bullen et al, , 2003Buslov et al, 2008;De Grave et al, 2013;Jolivet et al, 2010;Macaulay et al, 2013Macaulay et al, , 2014Sobel and Dumitru, 1997;Sobel et al, 2006;Yu et al, 2014). For example, Bullen et al (2001) reported AFT ages between 20 and 10 Ma for the Kyrgyz Range, in the northern Kyrgyz Tien Shan.…”