Active near-surface mobilisation of slab-derived geochemical signatures by hyperalkaline waters in brecciated serpentinites
Active near-surface mobilisation of slab-derived geochemical signatures by hyperalkaline waters in brecciated serpentinites
Unusual hyperalkaline meteoric groundwaters on Troodos massif, Cyprus, issue from highly deformed and completely serpentinized ultramafic brecciated rock masses of the Artemis Diapir and have high salinity (25–30% seawater total dissolved solids) and some of the highest recorded pH values (11−13) for natural waters. These waters have elevated dissolved Na, K, Li, B, Ba, Rb, Cs, Cl and SO4 with ion/chloride substantially above seawater ratios, overprinting minor contributions from marine aerosols. For example, K concentrations are similar to seawater values. Water stable isotope ratios imply extensive water-rock interaction and 87Sr/86Sr is rock-dominated (0.705) and significantly lower than seawater. These rare fluids contrast with surface and shallow ground waters draining the ultramafic Troodos Mantle Sequence that have pH of 8.5–9, meteoric stable isotope ratios, 87Sr/86Sr similar to early Miocene seawater (0.7085) and low dissolved salts albeit with ion/chloride ratios also greater than seawater. The combination of high pH and salinity is unusual in ophiolites and these hyperalkaline waters are most similar to end-member fluids emanating from serpentine mud volcanoes in the Mariana forearc. Rainwater rapidly transiting terraces of asbestos mine tailings on Troodos mostly resemble the surface waters but show slight contamination by a saline component. We propose that inclusions within the serpentinite that contain highly soluble salts have been made accessible by tectonic deformation during uplift and diapirism, or comminution during mining activity. A multistage process is proposed whereby alkali and other signatures have been released from the stalled subducting slab beneath the Troodos massif and have infused the mantle wedge. Some of these rocks have been carried to the surface by diapiric uplift and erosion, where tectonic deformation or mining activities have enabled the near-surface mobilisation of slab-derived geochemical signatures by modern meteoric waters.
Evans, Aled D.
41a3083e-fb13-4f18-a35b-c0763afa7716
Craw, Dave
c5701ce3-cff8-41c0-916a-5479e18b9bfc
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
17 November 2023
Evans, Aled D.
41a3083e-fb13-4f18-a35b-c0763afa7716
Craw, Dave
c5701ce3-cff8-41c0-916a-5479e18b9bfc
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Evans, Aled D., Craw, Dave and Teagle, Damon A.H.
(2023)
Active near-surface mobilisation of slab-derived geochemical signatures by hyperalkaline waters in brecciated serpentinites.
Chemical Geology, 643, [121822].
(doi:10.1016/j.chemgeo.2023.121822).
Abstract
Unusual hyperalkaline meteoric groundwaters on Troodos massif, Cyprus, issue from highly deformed and completely serpentinized ultramafic brecciated rock masses of the Artemis Diapir and have high salinity (25–30% seawater total dissolved solids) and some of the highest recorded pH values (11−13) for natural waters. These waters have elevated dissolved Na, K, Li, B, Ba, Rb, Cs, Cl and SO4 with ion/chloride substantially above seawater ratios, overprinting minor contributions from marine aerosols. For example, K concentrations are similar to seawater values. Water stable isotope ratios imply extensive water-rock interaction and 87Sr/86Sr is rock-dominated (0.705) and significantly lower than seawater. These rare fluids contrast with surface and shallow ground waters draining the ultramafic Troodos Mantle Sequence that have pH of 8.5–9, meteoric stable isotope ratios, 87Sr/86Sr similar to early Miocene seawater (0.7085) and low dissolved salts albeit with ion/chloride ratios also greater than seawater. The combination of high pH and salinity is unusual in ophiolites and these hyperalkaline waters are most similar to end-member fluids emanating from serpentine mud volcanoes in the Mariana forearc. Rainwater rapidly transiting terraces of asbestos mine tailings on Troodos mostly resemble the surface waters but show slight contamination by a saline component. We propose that inclusions within the serpentinite that contain highly soluble salts have been made accessible by tectonic deformation during uplift and diapirism, or comminution during mining activity. A multistage process is proposed whereby alkali and other signatures have been released from the stalled subducting slab beneath the Troodos massif and have infused the mantle wedge. Some of these rocks have been carried to the surface by diapiric uplift and erosion, where tectonic deformation or mining activities have enabled the near-surface mobilisation of slab-derived geochemical signatures by modern meteoric waters.
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Accepted/In Press date: 7 November 2023
e-pub ahead of print date: 9 November 2023
Published date: 17 November 2023
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Local EPrints ID: 490318
URI: http://eprints.soton.ac.uk/id/eprint/490318
ISSN: 0009-2541
PURE UUID: 72939139-00ae-4ca9-8f67-725fa5b19453
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Date deposited: 23 May 2024 16:47
Last modified: 25 May 2024 02:03
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Author:
Aled D. Evans
Author:
Dave Craw
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