| Strontium isotope composition of the Arno River Valley waters （Tuscany, Italy） as a natural tracer of water-rock interaction and mixing processes |
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| 作者姓名： | Barbara Nisi Orlando Vaselli Antonella Buccianti Giulia Perini Angelo Minissale Giordano Montegrossi Franco Tassi |
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| 作者单位： | [1]Department of Earth Sciences, Via G. La Pira, 4, 50121 Florence, Italy [2]CNR- IGG, Via G. La Pira, 4-50121 Florence, Italy |
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| 摘 要： | Sr isotope studies of surficial waters have highlighted that differences in the ^87Sr/^86Sr ratio and Sr concentration are primarily caused by mixing of waters of various origins with specific isotopic and chemical characteristics, resulting from water-rock interaction processes. In this paper we reported the first Sr isotopic ratios, coupled with water chemistry, the measurement was carried out on samples related to （1） the Amo River （Tuscany, central-northern Italy）, between the source and the mouth, （2） the most important tributaries and to （3） the thermal water discharges seeping out in the southern part of the basin. The main goals are： a） to use the ^87Sr/^86Sr ratio as a discriminative parameter of source areas, b） to define its variation along both the main course and principal tributaries, and c） to estimate the effects of the mixing process of the different end-embers. The outcropping rocks in the Amo River Basin are predominantly sedimentary, mainly made up of Mesozoic limestones, Oligocene sandstones and Plio-Pleistocene marine-lacustrine formations. Triassic and Mesosinian evaporites crop out in the Elsa and Era reaches, whereas Paleozoic quartzitic formations occur in the Mrs. Pisani area. Strontium isotopic composition is generally controlled by lithology and does not seem to be affected by anthropic input and flow rate. The ^87Sr/^86Sr ratios in the Arno Basin vary between 0.707963 and 0.712743, the highest ratios being related to waters circulating in the Palezoic rocks and Oligocene sandstone formations. Less radiogenic values pertain to the Elsa and Era tributaries where contributions related to the dissolution of evaporitic sequences, and mixing processes with the thermal discharges have been distinguished. The tributaries show that water samples in the pristine area have higher ^87Sr/^86Sr ratios than the respective tributaries from which water samples were collected near the confluence. Eventually, water samples collected along the Arno River, close to the mouth, tend to have Sr isotopic ratios similar to those of the present seawater.
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| 关 键 词： | 意大利 河流 锶 同位素 水文化学 |
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