Corrigendum to “Alteration of basaltic glass within the Surtsey hydrothermal system, Iceland – Implication to oceanic crust seawater interaction” [Journal of Volcanology and Geothermal Research 429 (2022) 107581] (Journal of Volcanology and Geothermal Research (2022) 429, (S0377027322001123), (10.1016/j.jvolgeores.2022.107581))

Prause S, Weisenberger TB, Kleine-Marshall B, Monien P, Rispoli C, Stefánsson A (2024)

Publication Type: Journal article, Erratum

Publication year: 2024

Journal

Journal of Volcanology and Geothermal Research Elsevier

Article Number: 108135

DOI: 10.1016/j.jvolgeores.2024.108135

Abstract

The authors regret to report a problem with the original bulk rock mass balance calculations published in their 2022 paper, requiring corrections. The changes affect part of the discussion and the conclusions regarding the mobility of elements (details below) during hydrothermal seawater-tuff interaction at Surtsey volcano. In our original paper, bulk rock mass balance was calculated using a single “unaltered parent” bulk rock composition assumed to be that of scoria erupted from the Surtla vent in late December 1963 during the same eruption phase that deposited the Surtur tephra (Schipper et al., 2015). However, a recent re-evaluation of the existing bulk-rock data in Jackson et al. (2019) by Dr. T.J. Barrett (independent research geochemist, Ontario, Canada) shows that the Surtsey pyroclastic deposit exhibits an igneous fractionation trend. This is expressed as a linear positive correlation between TiO2 and FeOtot concentrations in the samples used in our bulk rock mass balance calculations, which in turn leads to downhole variations in the Al2O3/TiO2 ratios (Fig. 1). Based on previous investigations (Schipper et al., 2015), fractionation is likely driven by the formation of clinopyroxene as well as, to a lesser extent, plagioclase and potentially olivine. The formation of accessory (Fe-)Ti-oxides may also contribute to this process. Observed Al2O3/TiO2 ratios increase between ∼180–100 m depth from bottom to top, reflecting ongoing fractionation under relatively oxidized conditions as the magma became less mafic over time. Above ∼80 m Al2O3/TiO2 ratios decrease as TiO2 and FeO concentrations increase. We suggest that this effect is caused by replenishment as a new pulse of less evolved, more mafic melt enters the conduit and begins to fractionate under reduced conditions. Considering the evidence for fractionation, the use of a single parent composition needs to be corrected. We therefore recalculate the bulk rock mass changes by first estimating the magmatic fractionation trend using the previously considered scoria as well as the three least altered samples from the Surtsey drill cores. The least altered samples are from 37.3 m and 145 m depth in SE-01 and 180.8 m depth in SE-02b. This selection was based on previous petrographic investigations of palagonitization extent and secondary mineral abundance (Prause et al., 2020). Reconstructed altered and precursor compositions for each sample and the corresponding mass changes were calculated following the method introduced by MacLean (1990) and applied to Icelandic altered rocks by Libbey and Williams-Jones (2016). Note that, due to the lack of trace element data for altered bulk rock samples, we used Al2O3 and TiO2 as compatible/immobile and incompatible/immobile elements, respectively (Fig. 2). Following the estimation of individual unaltered precursor compositions for each sample, mass changes were recalculated analogously to our original paper. The new results, summarized in Figures 8_corr, 9_corr, and 10_corr, update those displayed in Figures 8, 9, and 10 and supplementary table A.1 in Prause et al. (2022). Corrections to the text are included below. Revised mass changes were found to be minor for FeOtot and MgO in most samples from the SE-01 and SE-02b drillholes (Fig. 8_corr). Such small changes, which are <5% of the initial concentrations of these elements in the precursor rock in most cases, are likely within the margin of error of the mass balance calculations. In the case of MgO, however, two samples from SE-01, at 157.1 and 171 m depth, provide an exception, having gained between +2.2 to +1.6 wt% MgO. These enrichments are significant, representing gains of +32 and + 23 wt%, respectively, relative to the estimated MgO contents of the precursor. Furthermore, the MgO enrichment in the sample from 157.1 m depth coincides with an unusually high loss of −4.0 wt% CaO. The reason for these compositional anomalies is currently unclear but may be related to the fact that the tuff in SE-01 remained relatively unconsolidated below ∼160 m and recovered material mainly consisted of cuttings. The chemical composition of cuttings may be biased towards the preservation of least altered primary minerals and more resistant alteration minerals, which can obscure the effects of alteration (Fowler and Zierenberg, 2016). The SE-01 sample from 170 m depth also displays enrichment in CaO of +2.5 wt% (Fig. 8_corr). Bulk rock chemical analyses in Jackson et al. (2019) indicate unusually high SO3 content for this sample and petrographic observations by Prause et al. (2020) document an increase of the abundance of anhydrite at this depth in the SE-01 drill core. The mass gains of +2.5 wt% CaO in the sample from 170 m depth is therefore interpreted as being due to the increased formation of anhydrite. Additionally, it is possible that gypsum contributes to CaO gains, as this phase was identified at the bottom of hole SE-02b (Prause et al., 2020). Mass changes for Na2O and K2O are variable but generally small with no discernible vertical trends (Fig. 8_corr). Those samples with higher mass gains of Na2O as well as higher losses of CaO and SiO2 are considered to reflect local mineralogical reactions, e.g., palagonitization of basalt glass and plagioclase dissolution (Prause et al., 2020) combined with the formation of analcime in the seawater-saturated part of the hydrothermal system (below 55 m depth). The inferred immobility of Al2O3 on the bulk rock scale changes our previous assessment regarding the Surtsey hydrothermal system acting as an Al source for seawater (Figs. 8-10_corr). Rather, a more likely interpretation is that Al2O3 is mobilized on a small scale (possibly millimetres) during palagonitization before being quickly incorporated into zeolites, Al-tobermorite, and clay minerals. This revised interpretation of the data is more in line with previous assessments of Al solubility and mass fluxes in comparable hydrothermal systems (Barrett et al., 1991, 2005; Barrett and MacLean, 1994; MacLean and Barrett, 1993). The authors would like to apologise for any inconvenience caused. 5.3 Overall mass movement and elemental fluxes in the hydrothermal system at Surtsey (…) Our bulk rock mass balance calculation indicates that the mass changes in most elements are too small to be related to specific alteration processes. However, some sections of the altered tuff below sea level between ∼55–180 m depth have lost up to −3.4 wt% SiO2 and − 1.6 wt% CaO and gained up to +1.8 wt% Na2O. (…) Negative mass changes for SiO2 and CaO were generally highest between ∼80 and 120 m depth. (…) Overall, combined bulk rock and fluid data at Surtsey volcano suggest that 50+ years of submarine water-rock interaction at drillhole depths of up to 180 m has transferred up to 1.24·10−2 mol kg−1 yr−1 Ca and 1.68·10−2 mol kg−1 yr−1 Si from rocks to porewaters, while removing up to 1.17·10−2 mol kg−1 yr−1 Na from porewaters. (…) These findings suggest that, at least in the shallower portion of the volcanic pile, low-temperature hydrothermal alteration of basaltic tuff at Surtsey acts as a source for seawater Ca and Si, but a sink for seawater Na. (…) 6. Conclusions (…) Bulk rock elemental fluxes resulting from water-rock interaction indicate minor losses of SiO2 and CaO to porewaters as well as minor uptake of Na2O. Sodium gains notably become evident below sea level, likely because of interaction of Na-rich seawater with the basaltic tuffs, leading to the formation of zeolites, in particular analcime. Mass changes of SiO2 are generally greater in samples from the 2017 drill core, SE-02b, compared to those from the 1979 drill core, SE-01, indicating continued release of silica to seawater. Mass changes of FeOtot, MgO, and K2O are too small relative to their initial concentrations to accurately assess the fluxes of these elements.[Formula presented] Fig. 1 Downhole changes in bulk rock Al2O3/TiO2 and linear positive correlation between TiO2 and FeOtot (data from Jackson et al., 2019). The TiO2-FeOtot correlation indicates that magmatic fractionation has affected the sample suite; the variation in TiO2 content from sample to sample produces variations in the downhole Al2O3/TiO2 ratio.[Formula presented] Fig. 2 Altered sample compositions and estimated primary fractionation trends (black lines) based on least altered samples. Data from Jackson et al. (2019) and Schipper et al. (2015). Immobile elements: Al2O3 (compatible) and TiO2 (incompatible).[Formula presented] Fig. 8_corr. Updated bulk rock mass balance results for individual mobile elements. Negative values denote a loss from the rock to the hydrothermal solution while positive values indicate rock gains. This figure replaces the original fig. 8 in Prause et al. (2022).[Formula presented] Fig. 9_corr. Updated annual molar flux estimates. This figure replaces the original fig. 9 in Prause et al. (2022).[Formula presented] Fig. 10_corr. Summary of results including updated overview of bulk rock alteration effects. This figure replaces the original fig. 10 in Prause et al. (2022).

Authors with CRIS profile

Barbara Kleine-Marshall Professur für Geochemie von Lagerstätten

Involved external institutions

University of Iceland (UI) / Háskóli Íslands IS Iceland (IS) Universität Bremen DE Germany (DE) Università degli Studi di Napoli Federico II IT Italy (IT)

How to cite

APA:

Prause, S., Weisenberger, T.B., Kleine-Marshall, B., Monien, P., Rispoli, C., & Stefánsson, A. (2024). Corrigendum to “Alteration of basaltic glass within the Surtsey hydrothermal system, Iceland – Implication to oceanic crust seawater interaction” [Journal of Volcanology and Geothermal Research 429 (2022) 107581] (Journal of Volcanology and Geothermal Research (2022) 429, (S0377027322001123), (10.1016/j.jvolgeores.2022.107581)). Journal of Volcanology and Geothermal Research. https://doi.org/10.1016/j.jvolgeores.2024.108135

MLA:

Prause, Simon, et al. "Corrigendum to “Alteration of basaltic glass within the Surtsey hydrothermal system, Iceland – Implication to oceanic crust seawater interaction” [Journal of Volcanology and Geothermal Research 429 (2022) 107581] (Journal of Volcanology and Geothermal Research (2022) 429, (S0377027322001123), (10.1016/j.jvolgeores.2022.107581))." Journal of Volcanology and Geothermal Research (2024).

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