Climate and tectonic controls on glaciated critical-taper orogens

Abstract

In this work we present the results of a new analytical model that examines the coupling between glacial erosion and orogen development. Surface processes are assumed to be glacially dominated, and tectonic activity is controlled by critical wedge mechanics. In these circumstances, we find that orogen width is strongly dependent on both the rate of accretion and on the rate of precipitation. The orogen size is linked to tectonic and climate changes via proportionality constants: the orogen width scales with the rate of accretion to between the 2/3rd and 2nd powers, and with the rate of precipitation to the 1/3rd and 5/4th powers. The value of the proportionality constants varies with the taper angle and the relative rates of ice deformation and sliding. In all cases, the sensitivities are higher than those calculated for fluvially-eroding critical wedge orogens. Analytical solutions are supported by the results of a numerical flow-line model. The flow-line model further predicts that uplift rates will be highest at, and just below, the equilibrium line altitude. If glacial ablation is largely a calving process, rock uplift in the wedge will be strongly focused towards the toe. The predicted response time of glaciated orogens to changes in climate and tectonic forcing is dependent upon the constants of erosion, the rheology, and the rate of precipitation. These analyses predict that actual orogens have variable e-folding response times, for example approximately 1.5 Myr for the Southern Alps of New Zealand and the Olympic Mountains of Washington State, and approximately 5.5 Myr for the European Alps.

Feedbacks among climate, erosion, and tectonics in a critical wedge orogen

“…Even without this steady-state balance, provided that the time scale of interest is longer than that over which the deformation responds to changes in stresses, and longer than that over which the erosion adjusts to deformation of the landscape, the orogen will tend to approximate a self-similar form and the feedbacks will apply. On million-year time scales these appear to be reasonable assumptions-they were the basis of the timedependent studies of Whipple and Meade (2006) and Tomkin and Roe (2007), and are in agreement with the numerical results of others (2006, 2007a).…”

“…Calculations using a similar framework to this one show that the extreme case of a fully-glaciated orogen is more sensitive to precipitation than the fluvial case here (Tomkin and Roe, 2007). The reason is that glacial erosion laws depend more sensitively on the discharge of ice along a flow line than fluvial erosion depends on the discharge of water along a channel (for example, Hallet, 1979;Tomkin and Braun, 2002).…”

“…This basic physical mechanism is a strong constraint on the system dynamics, and its operation essentially depends only on there being some tendency for the orogen to grow self-similarly (that is, as an orogen builds up it also builds out), and some tendency for erosion to increase with increasing discharge and channel slope. The concepts have been applied to a fold-and-thrust belt in the Andes (Hilley and others, 2004), to Taiwan (Whipple and Meade, 2006), and to the Olympic Mountains of Washington State (Stolar and others, 2007a), and a glacial-erosion version to the southern Alps of New Zealand (Tomkin and Roe, 2007). Coupled numerical models of crustal deformation and landscape evolution also obey the scaling relationship very closely (Stolar and others, 2006), suggesting that, although severe assumptions were used in its derivation, the scaling relationship captures the important behavior, despite the many possible degrees of freedom by which the numerical system might adjust (and by analogy, the richer natural system).…”

Seismic and non-seismic influences on coastal change in Alaska--Fieldtrip guide and conference abstracts, 5th International Conference of IGCP 588

“…Most active mountain ranges have been extensively shaped throughout Quaternary glaciation, but have only remnants of glaciers and glacial landforms today. For that reason our understanding of coupling between glacial erosion and tectonic processes is mostly based on the study of the geomorphology of deglaciated landforms (Brocklehurst and Whipple, 2002Whipple, , 2007Champagnac et al, 2009), and on conceptual (Whipple et al, 1999), analytical (Tomkin and Roe, 2007), and numerical models (Tomkin and Braun, 2002;Tomkin, 2007;Herman and Braun, 2008;Yanites and Ehlers, 2012). The St. Elias Range provides the opportunity for direct field investigations of glacial erosion processes in an active orogen and testing glacial erosion models (e.g.…”

On the Milankovitch sensitivity of the Quaternary deep-sea record

“…The MS changes considerably both within the 100 kyr cycles (as exemplified by the presence of terminations; that is, threshold events) and it changes noticeably on longer timescales as well, presumably largely owing to a strong link to the size of the ice mass present in the Northern Hemisphere and its stability (Dolan et al, 2011). In addition, the MS is strongly influenced, presumably, by tectonic processes and associated erosion rates (Roe and Baker, 2007;Tomkin and Roe, 2007;A. Berger et al, 2008;Brocklehurst, 2008;Champagnac et al, 2012).…”