Assessing the behaviour of lithium and the distribution of Li isotopes during river weathering is of major importance for studying water/rock interactions at the surface of the Earth. Lithium (6Li ~ 7.5% and 7Li ~ 92.5%) is a fluid-mobile element and, due to the large relative mass difference between its two stable isotopes, it is subject to significant low temperature mass fractionation which provides key information on the nature of erosion processes. The Loire River in central France is approximately 1010 km long and drains a surface area of 117 800 km2. In the upper basin, the bedrock is old plutonic rock overlain by much younger volcanic rocks. In the intermediate basin, the Loire River drains the sedimentary series of the Paris Basin, mainly carbonate deposits. Then, the lower Loire basin drains pre-Mesozoic basement of the Armorican Massif and its overlying Mesozoic to Cenozoic sedimentary deposits. In the rivers of the Loire Basin, Li isotopes were measured using the Neptune MC-ICP-MS, 7Li/6Li ratios were normalized to the L-SVEC standard solution (NIST SRM 8545) following the standard-sample bracketing method. Lithium concentrations in river waters of the Loire River main stream and the main tributaries span a wide range from 2.0 to 46.5 µg/L, whereas d7Li are comprised between +5.0 and +13.3‰. There is a clear contrast between the headwaters upstream and rivers located downstream in the lowlands, with a siginificant decrease of the d7Li with the distance from the source. This feature is observed for both low (summer time) and high water stages (spring time) . In addition, one of the major tributaries in the Massif Central (the Allier River) is clearly influenced by inputs from mineralized waters resulting of hydrothermal activities having lower 7Li values. More generally, the Li isotopic composition measured in the rivers of the Loire Basin shows that 7Li is enriched in the dissolved load. On going analysis will focus on suspended sediments and the distribution of lithium and its isotopes between dissolved and solid products of erosion at the scale of the whole Loire River Basin.

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卢瓦尔河流域（法国）的锂同位素：两个互补尺度的水文地球化学特征

评估河流风化过程中锂的行为和锂同位素的分布对于研究地球表面的水/岩石相互作用具有重要意义。锂（6Li ~ 7.5% 和 7Li ~ 92.5%）是一种流体可移动元素，由于其两种稳定同位素之间的相对质量差异较大，因此会发生显着的低温质量分馏，这提供了有关其性质的关键信息侵蚀过程。法国中部的卢瓦尔河长约 1010 公里，流域面积为 117 800 平方公里。在盆地上部，基岩是古老的深成岩，上面覆盖着更年轻的火山岩。在中间盆地，卢瓦尔河排出了巴黎盆地的沉积系列，主要是碳酸盐沉积物。然后，下卢瓦尔河盆地排放了 Armourican 地块的前中生代基底及其上覆的中生代至新生代沉积物。在卢瓦尔河流域的河流中，使用 Neptune MC-ICP-MS 测量锂同位素，按照标准样品包围法将 7Li/6Li 比率标准化为 L-SVEC 标准溶液 (NIST SRM 8545)。卢瓦尔河干流和主要支流河水中的锂浓度范围很广，从 2.0 到 46.5 µg/L，而 d7Li 在 +5.0 到 +13.3‰之间。低地上游源头与下游河流形成鲜明对比，d7Li随着源头距离的增加而显着降低。对于低水位（夏季时间）和高水位（春季时间）均观察到该特征。此外，地块中央的主要支流之一（阿列河）明显受到热液活动产生的矿化水输入的影响，其 7Li 值较低。更一般地说，在卢瓦尔河盆地的河流中测量的 Li 同位素组成表明 7Li 在溶解负荷中富集。正在进行的分析将集中在整个卢瓦尔河流域范围内的悬浮沉积物和锂及其同位素在溶解和固体侵蚀产物之间的分布。