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Ongoing and recent projects

Erosion and relief evolution of volcanic islands

Volcanic islands present exceptional natural laboratories for landscape evolution. On one hand, volcanic islands present advantages for geomorphologists: they are numerous, composed of relatively homogeneous bedrock, and in many cases, the initial topography can be quantified from reconstructions of the volcano shape. On the other hand, volcanic islands are complex because of their time-varying vertical motion (uplift and subsidence), multiple construction and destructions phases through volcanic activity, and Quaternary climatic variations. Erosion on volcanic islands is characterized by shallow landslides, flank collapses and landscape dissection by river incision. What is the evolution of fluvial incision through time? What is the long-term response of rivers to extreme precipitation events? To tackle these questions, my colleagues and I have been working on hotspot volcanic islands to quantify erosion rates and model incision over a wide time range (kyr to Myr) using Bayesian inversion techniques.

Collaborators: Vincent Famin & Laurent Michon (Géosciences Réunion), Sean Gallen (Colorado State University), Miangaly Olivia Ramanitra (student, Université de La Réunion), Xavier Quidelleur (GEOPS), Eric Gayer (IPGP), Maëlis Arnould (ENS Lyon)

Funding: TelluS program of the Institut National des Sciences de l’Univers to LG & VF

River network reorganization in SE Tibet

The eastern Tibetan plateau-southern China-Burma-Vietnam area is characterized by a monsoonal climate regime, numerous active faults (some of them being responsible for deadly earthquakes such as the 2008 Sichuan earthquake), a gradual topographic transition from 5000 m to sea level, and major rivers draining the interior of the Tibetan plateau and the Himalaya. These characteristics have directed my research toward a number of exciting questions. How are the river courses, such as the Yangtze River, and active faults geometry related? How has the climate evolved since ~40 Myr? How has the landscape co-evolved with climate and tectonics? 

2-km-deep valley incised by the Upper Mekong, Sichuan

Collaborators: Maria Giuditta Fellin (ETH), Rong Yang (Zhejiang University), Sean Willett (ETH), Colin Maden (ETH), Jean-Louis Paquette (Laboratoire Magmas et Volcans), Gweltaz Mahéo (LGLTPE), Hervé Leloup (LGLTPE), Philippe Sorrel (LGLTPE), Marie-Luce Chevalier (CASG, Beijing), Anne Replumaz (ISTerre)

Funding: ETH postdoctoral fellowship to LG, National Natural Science Foundation of China Grant to Rong Yang

Completed projects

Landscape evolution of the western Tibetan Plateau

During my PhD I employed sedimentology, topography analysis, U-Pb dating and the recently developed 4He/3He thermochronometer combined with conventional (U-Th)/He dating. My work showed that some of the present-day geomorphic features of western Tibet formed prior to the Miocene. This area maintained high topographic relief and was connected to the Indus River in the past. Subsequent motion on the dextral Karakorum fault caused a major drainage reorganization leading to the internally drained landscapes observed today. 

Late Oligocene, 100-m-thick trachytic lava flow overlaying red sandstones and conglomerates (photo by P.H. Leloup)

Collaborators: Gweltaz Mahéo (LGLTPE/UCBl), Hervé Leloup (LGLTPE/UCBL), David Shuster (UC Berkeley / Berkeley Geochronology Center), Jean-Louis Paquette (Laboratoire Magmas et Volcans)

Funding: ENS Graduate Student Research Grant, Cai Yuanpei research grant to Leloup, Région Rhône-Alpes Mobility Explora’doc Grant

Neon diffusion kinetics in mafic minerals

I focused on constraining neon diffusion kinetics in olivine, feldspar, and pyroxene, with my MSc mentor David Shuster at Berkeley Geochronology Center. We conducted stepwise degassing experiments in order to assess whether Ne is quantitatively retained in these minerals over geological times. Our observations show that olivine and pyroxene are highly retentive to neon; thus, cosmogenic 21Ne dating can be applied to olivine and pyroxene. In contrast, 21Ne retention is unlikely to occur in most granitic alkali feldspars.

Neon diffusion behavior in orthopyroxene and clinopyroxene, olivine, and feldspars (sanidine and anorthoclase). From Gourbet et al. (2012).

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