REY-Th-U Dynamics in the Critical Zone: Combined Influence of Reactive Bedrock Accessory Minerals, Authigenic Phases, and Hydrological Sorting (Mule Hole Watershed, South India)

ISI Document Delivery No.: GK9EATimes Cited: 0Cited Reference Count: 91Braun, Jean-Jacques Riotte, Jean Battacharya, Shrema Violette, Aurelie Oliva, Priscia Prunier, Jonathan Marechal, Jean-Christophe Ruiz, Laurent Audry, Stephane Subramanian, S.Institut de Recherche pour le Developpement (IRD); Centre National de la Recherche Scientifique (Institut National des Sciences de l'Univers) (CNRS/INSU); Toulouse University; IRD; INSU/CNRS through the French program EC2CO (Ecosphere Continentale et Cotiere); ACI-Eau; Karnataka Forest DepartmentData supporting text and tables are available in supporting information tables and Data Sets 1-5. The Mule Hole basin is part of the SNO-BVET project (Systeme National d'Observation-Bassin Versant Experimentaux Tropicaux; https://mtropics.obs-mip.fr/experimental-tropical-watersheds-2/) belonging to the French "Network of Drainage Basins'' (Reseau des Bassins Versants, RBV; http://rnbv.ipgp.fr/) and Infrastructure de Recherche OZCAR (Observatoire de la Zone Critique: Applications et Recherches). The Environmental Observatory BVET is supported by Institut de Recherche pour le Developpement (IRD), Centre National de la Recherche Scientifique (Institut National des Sciences de l'Univers) (CNRS/INSU), and Toulouse University. Our project benefited from funding from IRD and INSU/CNRS through the French program EC2CO (Ecosphere Continentale et Cotiere) and ACI-Eau. We thank the Karnataka Forest Department and the staff of the Bandipur National Park for all the facilities and support they provided. At GET, Toulouse, we thank the staff of the thin section workshop (Fabienne de Parseval and Jean-Francois Mena) and Philippe de Parseval and Thierry Algouy for EPMA and SEM-BSE. We are grateful to Olivier Bruguier University Montpellier 2, France for LA-ICPMS analyses. We would like to thank Mahesh Korakoppa for helping us with the EPMA analyses at GSI, Bangalore, India.Amer geophysical unionWashingtonInternational audienceThe sources of REY-Th-U and long-term mass balance were assessed in the gneissic tropical forested Critical Zone Observatory of Mule Hole, India. The study relies on the characterization of the solid compartments (bedrock, soils, streambed and suspended sediments), on batch leaching experiments of the parent gneiss and on extractions of cation-exchangeable and iron-related pools of selected soil samples. The REY-Th-U primary reservoir is controlled by monazite, xenotime, thorite, allanite, bastnesite, titanite, apatite, and, to a lesser extent, by zircon. This accessory mineral assemblage was profoundly modified by episodes of metamorphism and hydrothermal activity. Allanite, bastnesite, titanite, and apatite are prone to break down at incipient weathering stage while monazite, xenotime and zircon are resistant minerals. On a long-term basis, REY are roughly inert in the immature saprolite and depleted in the soil cover and are strongly redistributed among secondary phases. LREE and HREY are mainly controlled by poorly crystallized secondary iron oxides and oxyhydroxides, and, to a lesser extent, by secondary phosphates (e.g., rhabdophane). Th, inert in the saprolite, is controlled by well-crystallized secondary iron oxides and oxyhydroxides and likely by secondary thorianite (ThO 2). REY and Th are not easily mobilized during surface processes such as chelation by organic matter and uptake by plants. REY and Th are, by far, exported as suspended sediments associated with iron oxides. The U export by groundwater and suspended sediments dominates over those of streambed sediments and stream