Applications of morphochronology to the active tectonics of Tibet

Abstract

Abstract. The Himalayas and the Tibetan Plateau were formed as a result of the collision of India and Asia, and provide an excellent opportunity to study the mechanical response of the continental lithosphere to tectonic stress. Geophysicists are divided in their views on the nature of this response advocating either (1) homogeneously distributed deformation with the lithosphere deforming as a fluid continuum or (2) deformation is highly localized with the lithosphere that deforms as a system of blocks. The resolution of this issue has broad implications for understanding the tectonic response of continental lithosphere in general.Homogeneous deformation is supported by relatively low decadal, geodetic slip-rate estimates for the the Altyn Tagh and Karakorum Faults. Localized deformation is supported by high millennial, geomorphic slip-rates constrained by both cosmogenic and radiocarbon dating on these faults. Based upon the agreement of rates determined by radiocarbon and cosmogenic dating, the overall linearity of offset versus age correlations, and on the plateau-wide correlation of landscape evolution and climate history, the disparity between geomorphic and geodetic sliprate determinations is unlikely to be due to the effects of surface erosion on the cosmogenic age determinations. Similarly, based upon the consistency of slip-rates over various observation intervals, secular variations in slip-rate appear to persist no longer than 2000 years and are unlikely to provide reconciliation. Conversely, geodetic and geomorphic slip-rate estimates on the Kunlun fault, which does not have significant splays or associated thrust faults, are in good agreement, indicating that there is no fundamantal reason why these complementary geodetic and geomorphic methods should disagree. Similarly, the geodetic and geomorphic estimates of shortening rates across the northeasten edge of the plateau are in reasonable agreement, and the geomorphic rates on individual thrust faults demonstrate a significant eastward decrease in the shortening rate. This rate decrease is consistent with the transfer of slip from the Altyn Tagh Fault (ATF) to genetically-related thrust mountain building at its terminus. Rates on the ATF suggest a similar decrease in rate, but the current data set is too small to be definitive. Overall, the high, late Pleistocene-Holocene, geomorphic slip velocities on the the major strike-slip faults of Tibet, suggests that they absorb as much of India's convergence relative to Siberia as the Himalayan Main Frontal Thrust on the southern edge of the plateau.

Quaternary morphotectonic mapping of the Wadi Araba and implications for the tectonic activity of the southern Dead Sea fault

“…For each sample, the minimum and the maximum ages (calculated assuming no erosion and maximum erosion, respectively) are given in Table 1. For ages in the order of 70 ka, maximum erosion would lead to a 15% increase of the age, which is barely larger than the uncertainty, confirming the zero‐erosion hypothesis for surfaces F3 and younger [e.g., Ryerson et al , 2006]. The maximum erosion rate would imply very poor age control for surfaces older than F4.…”

The Pingding segment of the Altyn Tagh Fault (91°E): Holocene slip‐rate determination from cosmogenic radionuclide dating of offset fluvial terraces

“…The latter is younger than the youngest surface sample. Since the age of the surface cannot be older than the youngest sample at depth [ Ryerson et al , 2006], a mean inheritance of about 1.3 ka might be inferred (mean of the surface sample ages minus age of the youngest depth sample). A minimum inheritance of ∼820 years may similarly be derived from the difference between the ages of the youngest sample at depth and at the surface, assuming no inheritance on the depth sample.…”

“…The simulator yields a most likely minimum and maximum values of 1.5 ka and 3.5 ka, respectively, with a lowest Chi‐square for 2.4 ka (Figure Sup 5). Clearly however, two depth samples are insufficient to reliably estimate inheritance, especially in view of the variability of the inheritance inherent to the single cobble sampling strategy [ Ryerson et al , 2006] and the errors built in CRN model ages at depth, which imply knowledge of the density of the stratum above the sample and of the attenuation of the cosmic ray flux whose estimates vary from ∼140 to ∼180 g/cm 2 [ Gosse and Phillips , 2001]. Here, we used 177 ± 4 g/cm 2 [ Farber et al , 2008] for the attenuation length and 2.2 ± 0.2 g/cm 3 for the overburden density to calculate the two depth‐sample model ages and to run the Monte Carlo simulations [ Hidy et al , 2010].…”

Pleistocene alluvial deposits dating along frontal thrust of Changhua Fault in western Taiwan: The cosmic ray exposure point of view

“…Within this context, interplate fault slip rates are usually considered as constant due to steady plate boundary loading rates. However, on individual fault systems, comparisons of geological and geodetic fault slip rates suggest that they may have varied over long-spanned time scales (Grant and Sieh, 1994;Stein et al, 1997;Bendick et al, 2000;Dawson et al, 2003;Dixon et al, 2002;Friedrich et al, 2003;Ryerson et al, 2006). Measurements and comparison of fault slip rates integrated over different time spans are thus important not only to apprehend how plate convergence is accommodated by continental lithospheres but also to determine to what extend the slip rate variations may be related to the fault strength or to the transient accumulation of elastic strain in the lithosphere (e.g., Fay and Humphreys, 2005;Oskin et al, 2007;Chuang and Johnson, 2011).…”