Gypsum speleothems in lava tubes from Lanzarote (Canary Islands). Ion sources and pathways



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Huerta, Pedro and Martín Pérez, Andrea and Martín García, Rebeca and Rodríguez Berriguete, Álvaro and La Iglesia, Á. and Alonso-Zarza, Ana María (2019) Gypsum speleothems in lava tubes from Lanzarote (Canary Islands). Ion sources and pathways. Sedimentary Geology, 383 . pp. 136-147. ISSN 0037-0738

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Lava tubes from Lanzarote Island in the Canary Archipelago commonly show white speleothems that stand out from the black basaltic rock. Mineralogical analyses of the speleothems from El Covón and Chifletera lava tubes show that gypsum is the dominant mineral with minor amounts of halite. Speleothems composed of microcrystalline gypsum (up to 150 μm long) are: coatings, globules, or extensive white powder accumulations covering the tube floor. Those composed of macrocrystalline gypsum with millimetric-size tabular and lenticular crystals are: crusts and stalactites. Uranium series dating of speleothems show ages ranging from 6217 ± 1644 yr to 40,039 ± 4748 yr. δ34S and the δ18O of gypsum speleothems (δ34S is 20.97‰ V-CDT and δ18O is 9.78‰ V-SMOW) is similar to that of sulphate dissolved in seawater. 87Sr/86Sr from speleothems (0.708665–0.708976) suggests that the main source of Ca is seawater, but additional Ca contributions from aeolian dust have reduced the Sr isotope values. These data support the idea that gypsum precipitates in the lava tube by evaporation of marine spray or solutions derived from marine spray. Two probable vias for ions input into the lava tube are considered: 1) sea spray circulating through the lava tube; 2) low-frequency rain infiltration leaching the marine spray salts precipitated at the surface. The constant supply of ions from sea spray, air currents in the cave, and the fast, but partial, evaporation due to the high relative humidity in the lava tube favours accumulation of major amounts of gypsum and subordinately halite. Scarcity of precipitation in the western Canary Islands prevents dissolution of gypsum speleothems.

Item Type:Article
Uncontrolled Keywords:Gypsum speleothems, Sulphur isotopes, Strontium isotopes, Marine spray, Lava tube
Subjects:Sciences > Geology > Geochemistry
Sciences > Geology > Mineralogy
Sciences > Geology > Petrology
ID Code:51767
Deposited On:06 Mar 2019 18:20
Last Modified:21 Sep 2020 10:21

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