Erosion of the Southern Alps Changed by Deglaciation
We estimated how mountain erosion evolves under a changing climate, through a sediment provenance analysis of marine and fluvial deposits. Raman spectroscopy of carbonaceous material (RSCM) is used as a novel sediment tracer. RSCM is a method often used in metamorphic geology, to estimate the peak temperature a rock experienced during its burial history. Here we use the temperature measured on single sediment grains collected from the West Coast rivers and submarine canyon to trace their schist or semischist source rocks in the Southern Alps of New Zealand. The results (Jiao et al., 2018) show that the sediments predominantly derived from high regions near the Main Divide, probably mainly erosion products from large landslides. Samples of different ages (~21–1 ka) also indicate a marked change in erosion pattern of the source region from Last Glacial Maximum to the Holocene, with a decreased proportion of sediment contribution from lower parts of the catchments and increased from high-elevation areas. We interpret this change to be driven by the upstream retreat of the glaciers. This work involved researchers based in Switzerland (Frédéric Herman, Thierry Adatte, and myself at that time), France (Olivier Beyssac), and New Zealand (Simon Cox, Faye Nelson, Helen Neil).
25-Million-Year Rock Exhumation of New Zealand
During my postdoc with Frédéric Herman, I constrained a large-scale exhumation model of the basement rocks of New Zealand during the late Cenozoic plate convergence since 25 Ma, using the published thermochronological ages. The modelling uses the same method as Herman and Brandon (2015), modified from Fox et al., (2014). The rock exhumation model (Jiao et al., 2017) is compared to a plate tectonic model. The comparison highlights the importance of tectonics in controlling the rock exhumation pattern at a convergent margin, and suggests that the impact from climate on mountain erosion can only be detected in regions with slow to moderate tectonic deformation.
Exhumation History of North Island, New Zealand
Based on application of low-temperature thermochronology, my PhD thesis studied the exhumation process of the basement rocks of North Island, New Zealand. In the central part of the island, new data and modelled thermal histories (Jiao et al., 2014) reveal rock exhumation processes during the Gondwana (Mesozoic) and Hikurangi (late Cenozoic) subduction cycles of the New Zealand plate margin. On the Hikurangi margin due to the coupling between the overriding and subducting plates, the crust of eastern North Island is subject to horizontal compression. The estimated rock exhumation pattern (Jiao et at., 2015) suggests crustal shortening and thickening to be the most important tectonic processes that drive the uplift and unroofing of the inner forearc, which are chiefly accommodated by seaward thrusting on the margin-parallel North Island Dextral Fault Belt. My PhD was supervised by Diane Seward, Tim Little and Barry Kohn.