@misc{10481/58918,
year = {2019},
month = {10},
url = {http://hdl.handle.net/10481/58918},
abstract = {We present a detailed study of the water geochemistry, mineralogy and textures in serpentinizationrelated
hyperalkaline springs in the Ronda peridotites. Ronda waters can be classified into hyperalkaline
fluids and river waters that are broadly similar to Ca2+
-OH- and Mg2+
-HCO3 - water types described
in serpentinite-hosted alkaline springs elsewhere. At the discharge sites of the fluids (fractures or human
made outlets) and ponds along the fluid flow paths, the fluids are hyperalkaline (10.9 < pH < 12) and
characterized by low Mg and high Na, K, Ca, and Cl- concentrations. River waters, occurring near the
spring sites, are mildly alkaline (8.5 < pH < 8.9) and enriched in Mg and DIC compared to Na, K, Ca and
Cl-. The chemistry of Ronda MgeHCO3 river waters is likely due to the hydrolysis of ferromagnesian
peridotite minerals in equilibrium with the atmosphere by infiltrated meteoric water and shallow
groundwater in the serpentinized peridotite. The Ronda CaeOH hyperalkaline fluids are generated by the
combination of low temperature serpentinization reactions from infiltrated surface Mg-HCO3 river
waters -or Ca-HCO3 waters from near karst aquifers- and deep carbonate precipitation isolated from
atmospheric CO2. Mass balance calculations indicate that the weathering of Ca-bearing peridotite silicates,
such as diopside, is a feasible source of Ca in Ronda Ca-OH hyperalkaline fluids; however, it requires
steady-state dissolution rates substantially greater than those determined experimentally.
Travertine, crystalline crusts and sediment deposits comprise the types of solid precipitates observed
in Ronda hyperalkaline spring sites. Calcite, aragonite, dolomite and Mg-Al-rich clays are the main
mineral phases identified in the spring sites. As illustrated in the Ba~nos del Puerto spring site, (i) calcitedominated
precipitation is due to uptake of atmospheric CO2 by CaeOH hyperalkaline fluids during
discharge, and (ii) aragonite-dominated precipitation is due to mixing of CaeOH hyperalkaline fluids
with Mg-HCO3 river waters. Aragonite and dolomite contents increase away from the springs and toward
the river waters that uniquely reflects the effect of Mg ions on the precipitation of aragonite versus
calcite. Other potential factors controlling the precipitation of these CaCO3 polymorphs are the Mg/Ca
ratio, the CO2 content, and the temperature of the fluids. Dolomite forms during lithification of travertine
due to periodic flooding of river water combined with subsequent evaporation.},
organization = {The present research has been funded by the European Commission
in the framework of the FP7 Marie Curie Action-ITN
“ABYSS” under REA grant agreement no. 608001, and European
Research Council Advanced Grant “PROMETHEUS” under REA grant
agreement no. 340863. CJG acknowledges funding from the Junta
de Andalucía (grant nº RNMe131). Research and infrastructure
grants leading to this research have been (co)funded by the European
Regional Development Fund (ERFD) and the European Social
Fund (ESF) of the European Commission.},
publisher = {Elsevier BV},
keywords = {Ronda peridotites},
keywords = {Serpentinization},
keywords = {Alkaline springs},
keywords = {Carbonate precipitation},
keywords = {Magnesium ion effect},
title = {Geochemistry and mineralogy of serpentinization-driven hyperalkaline springs in the Ronda peridotites},
author = {Giampouras, Manolis and Garrido, Carlos J. and Benavente Herrera, José and García Ruiz, Juan Manuel},
}