Late Cenozoic slip on the Talas-Ferghana fault, the Tien Shan, central Asia

Abstract

Although Cenozoic crustal shortening and thickening by thrust faulting have built the present Tien Shan, active right-lateral shear on the northwest-trending Talas-Ferghana fault appears to be the most rapid localized deformation in the belt. Ephemeral stream valleys have been offset right-laterally tens of metres. New and published radiocarbon dates of organic material deposited in depressions blocked by offset ridges place upper bounds on the average Holocene slip rate at 18 localities. Uncertainties allow 14 upper bounds to overlap the range of 8-16 mm/yr, and 95% confidence limits on such bounds at 11 sites are entirely within this range. We infer that the rate of ≈10 mm/yr is not simply an upper bound, but applies to the late Holocene Epoch. Although the bounds on rates permit more rapid slip in the northwest than the southeast, they do not place a useful constraint on variations in slip rate along the fault. Offsets of Paleozoic facies boundaries imply a total right-lateral shear of 180-250 km, but Early Cretaceous sedimentary rock appears to have been offset only 60 ± 10 km. Published paleomagnetic declinations of Cretaceous-Miocene rock demonstrate 20°-30°of counterclockwise rotation of the Ferghana Valley, which lies just west of the Talas-Ferghana fault, with respect to stable parts of Eurasia and 20°± 11°with respect to the central Tien Shan east of the fault. These declinations are consistent with a maximum northwestward translation of 70-210 km of the Ferghana Valley at the Talas-Ferghana fault and, therefore, with a similar maximum horizontal shortening across the Chatkal Ranges, which lie between the Ferghana Valley and the Kazakh platform. Estimates of crustal thickness beneath the Chatkal Ranges, however, permit only 60-100 km of Cenozoic shortening. If <100 km of slip on the Talas-Ferghana fault accumulated at a constant rate of 10 mm/yr, it would imply an initiation of slip more recently than ca. 10 Ma, long after India collided with the rest of Eurasia.

Tien Shan Geohazards Database: Earthquakes and landslides

“…The initial dextral strike slip movements along the Talas-Fergana Fault crossing the Tien Shan from SE to NW (Fig. 1) occurred in the Late Permian (Burtman et al, 1996). Cumulative displacements along this nearly 1000 km long fault amount to some 250 km.…”

The late Quaternary slip-rate of the Har-Us-Nuur fault (Mongolian Altai) from cosmogenic 10Be and luminescence dating

“…The collision between India and Eurasia is a key testing ground for these models (Avouac & Tapponnier, 1993;Peltzer & Saucier, 1996;England & Molnar, 1997, 2005Holt et al, 2000;Liu & Bird, 2008), but quantitative slip-rate data are primarily concentrated in the southern and central parts of this zone, in and around the Tibetan plateau (early papers include Van der Woerd et al, 1998;Lasserre et al, 1999;and Brown et al, 2002) and the Tien Shan range (e.g. Burtman et al, 1996;Brown et al, 1998;Thompson et al, 2002). North of the Tien Shan such data become very sparse, with the notable exception of the Gobi-Altai region in southern Mongolia (Ritz et al, 1995(Ritz et al, , 2003(Ritz et al, , 2006Owen et al, 1999;Vassallo et al, 2005Vassallo et al, , 2007.…”

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

“…Generally, strike-slip faults within continental interiors often move in response to distal plate collisions (e.g. Burtman et al 1996;Yin et al 2002). Constraining the spatio-temporal distribution of activity along such faults is therefore of great significance in terms of our understanding of how oblique deformation is accommodated in transpressional settings.…”