Periodic climatic variations during collisional orogenesis – insights from coupled tectonic-surface-process models

Mountain building through continent-continent collision is typically accommodated by crustal thickening and creates topography as a consequence of isostatic compensation. Precipitation-fueled erosion, in-turn, counteracts orogen growth and provides a feedback-loop between tectonics, surface processes, and climate. Climate on Earth varies on different timescales and with variable dominant periodicity. Orbital forcings, e.g. Milankovitch cycles, change climate with periods up to in the order of 1e5 years, while internal “tectonic” forcings change climate on longer timescales in the order of (several) Myrs. The feedback between tectonics and climate-fueled erosion raises the question: How do collisional mountain belts respond to climatic variations on Earth? Here, we use numerical coupled tectonic-surface processes models to explore the influence of periodic climatic variations on collisional mountain building on Earth, specifically focusing on the evolution of sediment flux and topography. Our results from the coupled numerical models are compared to and supported by a simple analytical solution. We find that climatic forcings with a short period have a small effect on orogen height (Gain G < 0.1), that is lagging by 1/4 phase, while the effect on the sediment flux is in phase and strong (G ≈ 1). These results are independent of orogen type and expected to be observable in orogens limited in height by crustal strength or erosional efficiency. Climatic forcings with a long period result in a low gain in sediment flux (G < 0.3), that is lagging by up to 1/4 phase. The effect on topography is in phase and with a high gain of up to G ≈ 1. However, the effects of long-period forcings are not well expressed in strength-limited orogens and can primarily by observed in erosion-limited orogens. Comparing our modelling results with typical tectonic and surface processes timescales of orogens on Earth shows that variations in erosional efficiency due to orbital forcings, i.e. Milankovitch cycles, are likely detectable in the sedimentary record, while it is challenging to disentangle the autogenic dynamics of mountain building and periodic long-term climatic forcings.