Building the Northern Tien Shan: Integrated Thermal, Structural, and Topographic Constraints

Abstract

A B S T R A C TPaired apatite fission track and U-Th/He dates provide the first Late Cenozoic cooling ages for the northern Tien Shan. These data clearly argue for pulsed deformation since the Late Miocene, with early (10-11 Ma) and late (0-3 Ma) intervals of rapid exhumation separated by an extended interval of much slower rates. By integrating these bedrock cooling rates with shortening estimates derived from a balanced section, detrital cooling ages, and geomorphological estimates of conditions before deformation, we reconstruct a four-stage history of range growth and exhumation. Following ∼100 m.yr. of tectonic quiescence, abruptly accelerated rock uplift, exhumation, and cooling in the Kyrgyz Range commenced at ∼11 Ma with rates exceeding ∼1 km/m.yr. During the subsequent 7 m.yr., deformation and cooling rates decreased three-to sixfold before accelerating by comparable amounts during the past 3 m.yr. Since mid-Miocene times, the surface elevation of the Kyrgyz Range has increased ∼2 km, consistent with the reconstructed magnitude of crustal shortening (∼11 km) and thickening (∼12 km) across the range. The highly pulsed deformation rates indicate that the locus of deformation probably shifted repeatedly within the Tien Shan from the Miocene to present. Even at their most rapid, Cenozoic shortening rates in the Kyrgyz Range were equivalent to only 10%-20% of the modern geodetic convergence rate across the entire Tien Shan. This requires several ranges within the Tien Shan to have deformed simultaneously since the Middle Miocene, a situation analogous to the distributed shortening seen today.

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

“…7), but some caution is needed to interpret this slow cooling phase because it often takes place at temperatures just outside the PAZ where the sensitivity of the model decreases. However, such a slow cooling period is also recognized in the thermochronological data from the northern Kyrgyz Tien Shan (Bullen et al, 2001(Bullen et al, , 2003De Grave et al, 2013;Glorie et al, 2010;Macaulay et al, 2013Macaulay et al, , 2014 and southern Altai (De Grave and Van den haute, 2002;De Grave et al, 2008;Yuan et al, 2006).…”

“…the Altai-Sayan; Glorie and De Grave, in press). Following these Mesozoic reactivation episodes, the study area became tectonically more stable and evidence exists that a mature peneplain developed during the Late Cretaceous-early Paleogene Bullen et al, 2001Bullen et al, , 2003De Grave et al, 2013;Delvaux et al, 2013;Glorie et al, 2010;Macaulay et al, 2014). 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 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.…”

Paleo-erosion rates in Central Asia since 9Ma: A transient increase at the onset of Quaternary glaciations?

“…The Tianshan is a 2500-km-long tectonically active mountain range that dominates Central Asia with an average altitude of 2500 m and summits reaching up to 7000 m. While its geology consists of mainly island arc rocks linked to a long-lived Paleozoic history of subduction/collision (Burtman, 1975;Charvet et al, 2007;Gao et al, 1998;Lin et al, 2008;Wang et al, 2008;Windley et al, 1990), the present high topography attests to a more recent and intense deformation. This later owes its origin to the Cenozoic reactivation of the range during the Oligocene to early Miocene (>16 Ma) (Avouac et al, 1993;Bullen et al, 2003;Bullen et al, 2001;Charreau et al, 2009a;Charreau et al, 2005;Charreau et al, 2006;Dumitru et al, 2001;Sobel et al, 2006;Sobel and Dumitru, 1997;Windley et al, 1990;Yin et al, 1998), under the influence of the ongoing India-Asia collision. The Tianshan range indeed plays a major role in the IndiaAsia collision since it presently accomodates up to 40% of the total convergence between those two continents (Abdrakhmatov et al, 1996;Reigber et al, 2001).…”

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

“…Hendrix et al 1994;Sobel & Dumitru 1997;Sobel et al 2006a;Heermance et al 2008;Amidon & Hynek 2010;Wei et al 2013;Bande et al 2015a) and again in the Late Miocene (e.g. Bullen et al 2003;Heermance et al 2008;Macaulay et al 2014) can be linked to the evolution of the Pamir (Bande et al 2015b).…”