Partitioning of intermontane basins by thrust‐related folding, Tien Shan, Kyrgyzstan

Abstract

Well‐preserved, actively deforming folds in the Tien Shan of Kyrgyzstan provide a natural laboratory for the study of the evolution of thrust‐related folds. The uplifted limbs of these folds comprise weakly indurated Cenozoic strata that mantle well‐lithified Palaeozoic bedrock. Their contact is a regionally extensive unconformity that provides a persistent and readily traceable marker horizon. Based on the deformation of this marker, preserved fold geometries support simple geometric models for along‐strike gradients in fold amplitude and displacement along the underlying faults, linkage among multiple structures, transfer of displacement among folds and evolution of the folds as geomorphic entities. Subsequent to initial uplift and warping of the unconformity surface, steeply dipping reverse faults cut the forelimbs of many of these folds. Wind gaps, water gaps, recent faulting and progressive stripping of the more readily eroded Cenozoic strata indicate the ongoing lateral propagation and vertical growth of fault‐related folds. The defeat of formerly antecedent rivers coincides in several places with marked increases in erosional resistance where their incising channels first encountered Palaeozoic bedrock. Persistent dip angles on the backlimbs of folds indicate strikingly uniform geometries of the underlying faults as they propagate both laterally and vertically through the crust. Deformation switches irregularly forward and backward in both time and space among multiple active faults and folds with no systematic pattern to the migration of deformation. This distributed deformation appears characteristic of the entire Kyrgyz Tien Shan.

Irregular earthquake cycle along the southern Tianshan front, Aksu area, China

“…The Tianshan extends laterally over $2000 km with active thrusting occurring on both sides and within the belt [Avouac et al, 1993;Burbank et al, 1999;Burchfiel et al, 1999;Thompson et al, 2002]. Along the central southern Tianshan, deformation has propagated into the Tarim basin except in the Aksu reentrant (Figure 1a), where a drastic change in stratigraphy occurs.…”

Seismic Hazard in Tien Shan: Basement Structure Control Over the Deformation Induced by Indo-Eurasia Collision

“…This latter study also suggest that the recent outspoken uplift of the Tien Shan could be the result of a marked increase in horizontal compressive forces following the abrupt rise of the Tibetan Plateau, as proposed by England and Houseman (1989). Apatite fission-track thermochronology, structural modelling and magnetostratigraphy in the Kyrgyz Range (and adjoining ranges) and the Chu Basin in the northern Kyrgyz Tien Shan further showed that a first strong phase of rock uplift and deformation affected the northern Tien Shan 10-11 Ma ago, and a second accelerated phase occurred 5-3 Ma ago [Burbank et al 1999;Bullen et al, 2001;De Grave et al, 2004;Sobel et al, 2006]. The latter acceleration is also expressed in the stratigraphy by a marked change in sedimentary environment in the Late Pliocene-Early Pleistocene: thick sequences of coarse conglomerates, sedimentary gaps and tectonic unconformities are observed [Cobbold et al, 1994;Abdrakhmatov et al, 2001].…”

“…However in most cases, it is safe to say that cooling initiated, seemingly in a somewhat poly-phased fashion, during the last 10 to 15 Ma. These cooling curves in the models might thus represent the timing of the denudation of the modern Tien Shan orogenic edifice and can be corroborated by several lines of independent geological evidence from such fields as sedimentology [Cobbold et al, 1994;Métivier & Gaudemer, 1997;Dill et al, 2007], magneto-stratigraphy [Sun et al, 2004;Charreau et al, 2005;Huang et al, 2006;Ji et al, 2008], geomorphology and structure [Tibaldi et al, 1997;Yin et al, 1998;Burbank et al, 1999;Abdrakhmatov et al, 2001;Thompson et al, 2002;Buslov et al, 2003;Fu et al, 2003;Hubert-Ferrari et al, 2007;Oskin & Burbank, 2007], geophysics [Trapeznikov et al, 1997;Bielinski et al, 2003;Rybin et al, 2004;, geodesy [Abdrakhmatov et al, 1996;Reigber et al, 2001;Vinnik et al, 2004;Tychkov et al, 2008], and other geochronological studies [Sobel & Dumitru, 1997;Bullen et al, 2001;Sobel et al, 2006;De Grave et al, 2007a;Heermance et al, 2007]. We should caution the reader that this Late Cenozoic feature is mainly obtained by modelling the AFT data [Laslett et al, 1987;Ketcham et al, 2000].…”

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

“…The close association of the Fergana Basin with the Talas -Fergana Fault resulted in the development of a basin morphology that differs from that of other Cenozoic-age intramontane basins within the Tien Shan typically bounded by north-or southverging faults (e.g. Cobbold et al 1996;Burbank et al 1999;Macaulay et al 2014). The Fergana Basin is located due north of the Pamir, suggesting a possible tectonic link between indentation of the latter and basin evolution.…”

“…The Jurassic -Cretaceous was characterized by a general planation of the previously formed relief (e.g. Makarov 1977;Chediya 1986;Burbank et al 1999;Allen et al 2001;Cunningham et al 2003;Jolivet et al 2010Jolivet et al , 2013Jolivet et al , 2015, providing sediments to these newly forming extensional basins (Brookfield & Hashmat 2001;Klett et al 2006;Fü rsich et al 2015;Brunet et al 2017).…”