In-situ cosmogenic 10Be constraints on non-steady-state denudation of granitic regolith from Changbaishan

In-situ cosmogenic nuclides are receiving growing attention in surface Earth system science in which the steady-state denudation is an important assumption for estimating the surface denudation of long-lived (103–106 years) surfaces. However, distinguishing steady-state denudation and deciphering a reliable denudation rate from non-steady state denudation region are difficult. Recent depth profile models for investigating the denudation rate, exposure age and inheritance are widely used for sediment and regolith of steady-state denudation region. Here we present in-situ cosmogenic nuclides 10Be and 26Al from two typical granite regolithes from Jixian in Tianjin and Tengchong in Yunnan to model non-steady landscape evolution process by using steady state (Model 1) and non-steady state (Model 2, continuous exposure; Model 3a, changed denudation rate; Model 3b, abrupt denudation event) models. The results of steady state model show that both regolithes are in non-steady state. 10Be non-steady state models of Jixian regolith reveal that the surface has likely experienced a denudation rate change or an abrupt denudation event during the past several millennia, resulting in a non-steady state. The similar Model 3a and 3b denudation rates of and mm kyr−1, respectively, might demonstrate the long-term denudation rate rather than the exaggerated rates of and mm kyr−1 calculated by assuming steady-state denudation and ignoring inheritance. The non-steady state model results of Tengchong regolith suggest that the surface has likely experienced a strong denudation about 157 ka (10Be) or 127 ka (26Al) ago. This timing is basically consistent with the termination of the MIS 6 (TII: 130 ka) and the climate change events in the Tibetan Plateau, suggesting a strong surface landscape denudation during the transition from glacial to interglacial. The compiling of basin-wide denudation rates in the Tibetan Plateau shows a good positive correlation with the regional tectonic activity, indicating that the denudation rate derived from non-steady state region with strong tectonic activity is likely to be overestimated by assuming steady state. We suggest that a combination of steady state and non-steady state depth profile models should be used to quantify denudation rate and exposure age more accurately and effectively in strong tectonic activity or climate change regions.