Séminaire exceptionnel : Marie Catherine GENGE, Université de Hong Kong (Department of Earth Sciences)

« Increased exhumation along the Sutlej River, NW Indian Himalaya, at < 1 Ma triggered by river incision and climate »

Résumé : River erosion is considered a major driver of localized exhumation in contractional orogen systems and may be enhanced by tectonic processes, climate change or drainage reorganization. Extreme cases of focused river erosion regions (e.g., Himalayan syntaxes), where Earth’s most rapidly exhuming rock has been observed, are also characterized by tectonic indenters that may have affected the rock uplift. Constraining the effect of focused river erosion on crustal exhumation, and thus understand how it affects mountain building and landscape evolution, remains a major challenge. The Sutlej River region (NW Indian Himalaya) may represent an ideal laboratory to examine crustal response to focused erosion as i) it lacks the tectonic indenter, ii) it corresponds to the third largest erosive system crossing the Himalayan range, and iii) it is characterized by the development of an anticline, high relief, and rapid rock exhumation in the last 3 Myrs all spatially associated along the river course. The primary driver controlling the variability of crustal exhumation along the Sutlej River, which remains unexplored, has been investigated via diverse low-temperature thermochronology approaches. Thus, to constrain the last cooling events over the last ~100°C of rocks exposed, an extensive apatite (U-Th)/He dataset (n= 349) along the Sutlej River and its main tributaries have been integrated with a K-feldspar multi-optically stimulated luminescence dataset along the knickzone of the Sutlej River, where youngest cooling dates has been reported. Results evidenced three major exhumation phases:

i) an asymmetric exhumation of the anticline at > 2 Ma, younger in the north;

ii) a focused exhumation along the Sutlej River at < 1 Ma which is consistent with the capture of a large basin that increased water discharge into the Sutlej River;

iii) an increased erosion in the core of the Sutlej knickzone at < 20 ka probably triggered by deglaciation processes at 15 ka after the Last Glacial Maximum and enhanced by monsoon intensification at 10 ka.

These results evidence that the rapid exhumation in this area is most likely influenced by the erosive power of the river itself, enhanced by drainage reorganization and climate, and thus represents one of the few places on Earth where focused erosion affects significantly the exhumation rates of the crust (≥ 2 mm/year), with a limited tectonic impact.

Ce séminaire fait partie de la série de séminaires pour des candidats au poste de Maître de conférences ouvert en section 35 (Profil : Dynamique des surfaces continentales en réponse aux forçages tectoniques et/ou climatiques) pour le CEREGE cette année

Ce séminaire est ouvert à tout le monde et sera également accessible via zoom avec le lien suivant : https://univ-amu-fr.zoom.us/j/88351397273?pwd=ZGxiSG4xUTV5c2s4emRmd0d5cXA3UT09