Denudation rates of granitic regolith along climatic gradient in Eastern China

Abstract

In order to assess the impact of the monsoonal climate on denudation, physical erosion, and chemical weathering processes, we measured cosmogenic nuclides 10Be, 26Al and immobile element Zr in five granitic regolith profiles across Northeast to South China. The 10Be and 26Al concentrations are 2.98 × 104–25.20 × 104 atoms g−1 and 2.18 × 105–16.62 × 105 atoms g−1, respectively. Compiling previous depth profile data from Leymon and Beacon Heights, we find that the 26Al/10Be ratios systematically increase or decrease with the depth. Our numerical model shows that muons contributions can produce higher 26Al/10Be ratios (greater than 6.75) in both steady-state and non-steady state scenarios, which can result in underestimated burial age (initial 26Al/10Be ratio) and exaggerated denudation rates (due to non-negligible production from muons) for the application of dual-nuclide in Earth Science. The denudation rates, chemical weathering rates and physical erosion rates derived from cosmogenic nuclides and Zr are 28–45, 9–31 and 6–22 m Ma−1, respectively. Chemical weathering rates, excluding the JLN profile, comprise a large proportion of the denudation rates (greater than 50%). Despite the wide range of mean annual precipitation (MAP) and mean annual temperature (MAT), the denudation rates vary without an apparent gradient from northeast to south. However, the physical erosion and chemical weathering results show good relationships with climate, suggesting the limitation type changed from kinetic-limited in the north, to supply-limited in the south. Chemical weathering indices (chemical index of alteration, CIA and weathering intensity factor, WIF) also indicate that the extent of chemical weathering strengthens from northeast to south and increases with chemical weathering rates, but decreases with physical erosion rates.