Quantification of growth and lateral propagation of the Kashi anticline, southwest Chinese Tian Shan

Abstract

[1] The Kashi anticline is a north vergent, asymmetric, doubly plunging detachment fold located in the SW Tian Shan foreland. We combine structural, magnetostratigraphic, and topographic data to define the fold's lateral propagation, surface uplift, and concomitant exhumation. Two new magnetostratigraphic sections indicate that the fold began growing at $1.4 Ma and by 1.07 Ma, deformation had propagated eastward $13 km at an average rate of $40 km/Myr. Subsequently, propagation rates increased at least twofold, until the fold reached >60 km in length by 0.8 ± 0.3 Ma. Since then, eastward fold propagation slowed to $15 km/Myr, and the eastern 15-25% of the fold remains buried in the rapidly aggrading foreland. The structure and topography of the emergent fold support interpretations of fold growth in three stages: initial symmetric lateral growth both east and west to a total length of $30 km followed by, first, rapid and, then, slower eastward lengthening to 72 ± 10 km total length. Shortening rates as high as 1.9 À0.2 +0.3 mm/yr characterize the western part of the fold but decrease toward the east. Significant dissection of the emergent fold does not occur until topographic relief is sufficient ($200 m) to permit stripping of protective conglomerates from across the fold's upper surface. As differential rock uplift continues following breaching of the conglomerate, $75% of the rock raised above local base level is subsequently eroded at rates as high as 2.4 km/Myr. Despite extensive erosion, the modern fold topography mimics spatial patterns of both long-term shortening and variations in rock uplift.

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

“…Four stages of tectonic deformation in the Atushi Basin in front of the SW Chinese Tian Shan at 20 ~ 25 Ma, ca.16.3 Ma, 4 ~ 13.5 Ma and after 4 Ma were constrained by magnetostratigraphic study, which lead to a total north south shortening of 10 -32 km (Heermance et al, 2008). The kinematic mechanism of the Atushi and Kashi folds were well constrained by Scharer et al (2004) and Chen et al (2007).…”

Three-Dimensional Growth of Flexural Slip Fault-Bend and Fault-Propagation Folds and Their Geomorphic Expression

“…For example, using in situ cosmogenic 10 Be measurements in quartzites, Jackson et al [28] obtained average uplift and propagation rates of 0.10-0.15 m/ka and 1.0-2.0 m/ka, respectively, over the last 450 ka for a Late Quaternary anticline forming above a blind reverse fault in Central Otago, New Zealand, whereas Chen et al [24,65] reported shortening rates of 2.0-4.4 m/ka and lateral propagation rates of c. 15-40 m/ka from the Chinese Tien Shan.…”

“…Of specific interest here, the geomorphic expression of active fault-related fold structures provides a potential opportunity to decipher both fold kinematics and mechanisms of lateral growth, although data from natural examples is not abundant [4,6,15,19,23,24]. Recently, the geometry of drainage basins and river networks (including stream profile analysis) has been used to interpret the spatial and temporal evolution of fault-related structures in both extensional [25][26][27] and contractional settings [10,18,23,[28][29][30][31][32] due to the strong control that fault-or fold-related uplift has on drainage basin development, stream initiation and diversion.…”

Climate Evolution in Central Asia during the Past Few Million Years: A Case Study from Issyk Kul

“…Fault plane solutions of earthquakes consistently show reverse or thrust faulting. Evidence of active faulting is widespread (Abdrakhmatov et al, 2007;Chedia, 1986;Laverov and Makarov, 2005), and rates of slip on several faults exceed 1 mm yr -1 (Chen et al, 2007;Thompson et al, 2002).…”