Rapid Uplift, yet Slow Denudation of the Suckling‐Dayman Metamorphic Core Complex in Tropical Papua New Guinea

A linear relationship between rates of physical erosion and chemical weathering is apparent in slowly eroding landscapes. Whether the relationship remains linear in rapidly eroding landscapes is less clear. Field‐based research into this relationship between erosion and weathering rates has largely been conducted in temperate climates with granitic bedrock. In tropical settings, the contribution of chemical mass loss to total denudation may approach, or even exceed, that of erosion. We report 10Be‐in‐quartz cosmogenic radionuclide and soil chemistry data from the Suckling‐Dayman Metamorphic Core Complex (SDMCC) in Papua New Guinea. Despite being exhumed at cm‐per‐year rates, its lower‐plate domed and striated morphology suggests minimal denudation, which is confirmed by our 10Be‐in‐quartz data (0.02–0.18 mm/yr). We suggest that rolling hinge‐style back‐rotation of the SDMCC's lower plate and the combination of a tropical climate and highly weatherable metabasalt bedrock have played a fundamental role in preserving the tectonic topography of this remarkable metamorphic core complex. Plain Language Summary Where mountains are raised (uplifted) slowly by plate tectonics, erosion (the removal of rocks/soils) tends to be slow. Where erosion is slow, chemical weathering (the local breaking down or dissolving of rocks/minerals) is usually slow as well. This observation has been made in mountainous regions around the world with temperate climates, and where mountains consist predominantly of granitic rocks. However, much less is known about how rates of erosion and weathering relate in tropical climates where mountains rise rapidly. We studied a unique geological structure in tropical Papua New Guinea (the Suckling‐Dayman Metamorphic Core Complex, SDMCC) to provide new data for addressing this knowledge gap. We measured denudation rates (the sum of physical and chemical mass loss) using a method that is based on the accumulation of atomic particles that form in the crystal lattice of minerals in rocks and soils by cosmic rays. Our denudation rates are much slower than the rate at which the SDMCC is being raised by tectonic processes, requiring some erosion‐limiting mechanism(s). The chemical compositions of basaltic soils from the SDMCC, however, imply intense weathering. We argue that the style of tectonic uplift and the tropical weathering regime are responsible for the slow denudation rates. Key Points 10Be‐in‐quartz denudation rates of the rapidly uplifting Su