OLD MARINE WATER IN FUERTEVENTURA ISLAND DEEP FORMATIONS
OLD MARINE WATER IN FUERTEVENTURA ISLAND DEEP FORMATIONS
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富特文图拉岛深层的古老海水
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
R. Rosas
中科院分区：
文献类型：
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作者：
C. Herrera;E. Custodio;Gran Capità;R. Rosas
在波兰博林岛米日兹德罗耶举行的SWIM会议期间，介绍了关于西班牙加那利群岛富埃特文图拉火山地下咸水起源的第一批结果。现在，他们完成了第一作者博士论文的最终结果（Herrera，2001年），在第二个的学费。该研究考虑了岛屿的中部，那里有最大海拔（约800 m），并且火山建筑物下方的海底地层和侵入岩也露出来。地下水溶解固体含量高，浓度向下增加。上部单元含有2.5至5.5 mS cm-1和18至25 o C的氯化钠型地下水，具有中等碱度、硫酸盐和二氧化硅含量，并且通常具有相当高的人为来源的硝酸盐含量。下层单元地下水产量为5.5至24.0 mS cm-1，25至30 oC，氯化钠-硫酸盐型，溶解硅含量高，不含硝酸盐。上部地层的高盐度主要是由于岛上的气候干旱，平均降雨量在100至200 mma-1之间变化。上部单元地下水的化学成分可以很容易地解释为雨水蒸发与水-岩相互作用的次生矿物贡献，这主要是由于斜长石风化导致钠增加。然而，为了解释下单元的溶解固体含量，必须考虑其他贡献。考虑到Cl/Br比、水同位素组成、最具特征的离子比和化学建模，存在海水成分，假设其为截留在侵入岩体中的残余海水。它在岛屿海拔较低的阶段渗透，可能在最后一次第四纪火山爆发之前。这些侵入岩的体积渗透率非常小，尽管局部的不均匀性允许一些钻孔产生显著的水流，但这可能解释了即使在海平面以上，一些海水仍然没有被冲洗。这些沃茨中的高硫酸盐含量是由于火成硫溶解所致，如S同位素组成所示。
During the SWIM meeting in Miedzyzdroje, Bolin Island, Poland, first results on the origin of saline groundwater in volcanic Fuerteventura, Canary Islands, Spain, were presented. Now they are completed with the final results of the doctoral thesis of the first author (Herrera, 2001), under the tuition of the second one. The study considers the central part of the island, where there are the maximum elevations (ca.800 m) and the submarine formations and intrusive rocks underlying the volcanic edifices crop out. Groundwater presents high dissolved solids content and the concentration increases downwards. An Upper Unit contains groundwater of 2.5 to 5.5 mS cm -1 and 18 to 25o C, of the sodium-chloride type, with moderate alkalinity, sulphate and silica contents, and often with quite high nitrate contents of anthropic origin. A Lower Unit yield groundwater of 5.5 to 24.0 mS cm -1 and 25 to 30oC, of the sodium chloride-sulphate type, high in dissolved silica and nitrate free. The high salinity of the Upper formation is due mostly to the climatic aridy of the island, in which average rainfall varies between 100 a 200 mma -1 . Chemical composition of groundwater from the Upper Unit can be easily explained by rainfall water evaporation with a secondary mineral contribution from water-rock interaction, which mostly results in a sodium increase due to plagioclase weathering. However, to explain the dissolved solids contents of Lower Unit other contributions have to be considered. Considering the Cl/Br ratio, the water isotope composition, the most characteristic ion ratios and chemical modelling, there is a marine water component, which is assumed to be relict seawater trapped in the intrusive rock bodies. It penetrated during stages in which the island was at a lower elevation, possibly before the last Quaternary volcanic eruptions. The very small bulk permeability of these intrusive rocks, in spite of local heterogeneities that allow some boreholes to yield significant water flows, may explain that some marine water is still not flushed, even above sea level. The high sulphate content of these waters is due to igneous sulphur dissolution, as shown by S isotope composition.