Continental weathering and sedimentary recycling processes: insights from lithium (Li) isotope and alkali elements in river-borne materials,

• Main Authors: Dellinger, Mathieu, Gaillardet, Jérôme
• Other Authors: Institut de Physique du Globe de Paris (IPG Paris), Institut de Physique du Globe de Paris (IPGP), Université du Québec à Montréal, Jérôme Gaillardet, Claude Hillaire-Marcel
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2013
• Subjects: Lithium isotopes; Sedimentary recycling; Alkali elements; Weathering geology; Erosion; Rivers; River sediments; Isotopes du lithium; Recyclage sédimentaire; Eléments alcalins; Altération (géologie); Cours d'eau; Sédiments fluviaux; [SDE]Environmental Sciences; Arctic; Arctic Ocean; Mackenzie River; Mackenzie river
• Online Access: https://tel.archives-ouvertes.fr/tel-03092831; https://tel.archives-ouvertes.fr/tel-03092831/document; https://tel.archives-ouvertes.fr/tel-03092831/file/Dellinger_2013_Apport%20des%20isotopes%20du%20lithium%20et%20des%20e%CC%81le%CC%81ments%20alcalins%20a%CC%80%20la%20compre%CC%81hension%20des.pdf

Alkali elements (Li, Na, K, Rb, Cs) form a group of chemical elements essentially found in silicateminerals and partitionned between dissolved and particulate phases during water-rock interactions. Inthis thesis, we have investigated alkali element concentrations and Li isotopes (the lighter alkali element)in the erosion and weathering products transported by large rivers (Mackenzie, Amazon, Ganges), inorder to constrain erosion processes of silicate rocks at a global scale and explore the complementaritybetween dissolved and particulate loads.Large river sediments sampled along depth profiles show that rivers are stratified chemically. Afterthe Amazon and Ganges rivers, previously investigated, we confirm, in this study, this important featurefor the Mackenzie river and we calculate depth-integrated particulate geochemical fluxes transported tothe Arctic Ocean by this river.We show in this thesis that, based on alkalis and Li isotopes contrasted behaviours, river-sedimentsdepth-profiles can be interpreted as a mixture between fine surface particles, produced by modern weatheringprocesses and particles, variable in size, derived from non chemically-weathered rocks. We calculatethat more than 60% of the sediments transported by those rivers are actually non weathered particlesand we find that most of the sediments derive from the erosion and weathering of sedimentary rocks alreadydepleted in soluble elements during the past weathering events that they have experienced duringtheir geological history. Alkali elements therefore trace the cannibalistic nature of erosion and weatheringprocesses. In addition, the fractionation of alkali elements in erosion products of the Mackzenzie riverallow us to calculate that bedload transport never exceed 20-30% of the total solid load.In the dissolved load, we have analyzed the Li isotopes in the Amazon river basin. We show that thedissolved Li isotopic composition of the Amazon and its main tributaries is clearly enriched in the heavyisotope (compared to bedrocks) and can well ...