Erosion and weathering of the Northern Apennines with implications for the tectonics and kinematics of the orogen
Embargoed until 2021-01-23
- Doctoral Thesis
Mountainous landscapes reflect the competition between denudation, uplift, and climate, which produce, modify, and destroy relief and topography. Bedrock rivers are dynamic topographic features and a critical link between these processes, as they record and convey changes in tectonics, climate, and sea level across the landscape. River incision models, such as the stream power model, are often used to quantify the relationship between topography and rock motion in the context of landscapes at steady state. At steady state, the stream power model predicts higher denudation rates for steeper river channels, while accounting for only the vertical motion of rock due to rock uplift or denudation. However, natural landscapes often have more complicated histories, particularly in convergent orogens with asymmetric topography, where steady state requires that denudation must balance both vertical and horizontal rock motion. This thesis addresses this central issue by comparing the spatial and temporal pattern of denudation with metrics of topographic steepness in the Northern Apennine Mountains of Italy, a young and active orogen with asymmetric topography. New and existing catchment-averaged denudation rates from cosmogenic 10Be concentrations demonstrate that the steeper flank of the Northern Apennines is eroding more slowly than the gentler flank. Long-term denudation rates inverted from low-temperature thermochronometers show that this pattern of denudation across the orogen is long-lived, since at the least 3—5 Ma, and that denudation rates have decreased on the Ligurian side through time. The apparent decoupling between denudation rates and topography is resolved with a kinematic model of the orogenic wedge that accounts for the full vertical and horizontal rock velocity field. This model reconciles the 10Be concentrations, geomorphic observations, and geodetic rates of rock motion with the topography of the Northern Apennines, and provides new estimates for slab retreat rates consistent with recent estimates from tomography, surface geology, and morphology. This thesis also explores the partitioning of denudation into physical erosion and chemical weathering in the Northern Apennines. Chemical weathering in particular is an important control on landscape evolution and the global CO2 budget. Most studies have focused on weathering in orogens comprised of silicate-rich lithologies, which can remove CO2 from the atmosphere over geologic timescales, whereas carbonate weathering is generally considered to be CO2 neutral. However, even in silicate-rich landscapes, carbonate weathering dominates total solute fluxes. Recently uplifted orogens in particular are often characterized by carbonate-rich, marine sedimentary sequences, so the global weathering flux of carbon and calcium to the oceans should be more strongly influenced by these orogens. However, the partitioning of denudation fluxes remains largely unexplored in mixed lithology orogens, so, it is unclear whether the same processes that control erosion and weathering apply to both silicate-rich and mixed lithology settings. Here, denudation fluxes from the Northern Apennines are partitioned into carbonate and silicate chemical weathering and physical erosion fluxes. These fluxes demonstrate that denudation is dominated by physical erosion of both silicate and carbonate rocks; carbonate physical erosion is controlled by lithology; weathering fluxes are dominated by carbonate dissolution; and denudation is negatively correlated with runoff. Finally, denudation fluxes from the Northern Apennines are similar to other temperature mountain ranges (e.g. Southern Alps of New Zealand), although total weathering fluxes from this study are generally higher, due to greater carbonate weathering fluxes. The results from this thesis challenge current interpretations regarding denudation rates through space and time and contribute to a broader understanding of surface and crustal processes in the Northern Apennines. Show more
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ContributorsExaminer: Willett, Sean
Examiner: Picotti, Vincenzo
Examiner: Gallen, Sean F.
Examiner: Pazzaglia, Frank J.
Organisational unit03754 - Willett, Sean / Willett, Sean
154434 - SWISS-AlpArray - Assessing Alpine Orogeny in 4D-space-time Frame (SNF)
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