Serpentine alteration as source of high dissolved silicon and elevated δ30Si values to the marine Si cycle

Abstract Serpentine alteration is recognized as an important process for element cycling, however, related silicon fluxes are unknown. Pore fluids from serpentinite seamounts sampled in the Mariana forearc region during IODP Expedition 366 were investigated for their Si, B, and Sr isotope signatures (δ30Si, δ11B, and 87Sr/86Sr, respectively) to study serpentinization in the mantle wedge and shallow serpentine alteration to authigenic clays by seawater. While serpentinization in the mantle wedge caused no significant Si isotope fractionation, implying closed system conditions, serpentine alteration by seawater led to the formation of authigenic phyllosilicates, causing the highest natural fluid δ30Si values measured to date (up to +5.2 ± 0.2‰). Here we show that seafloor alteration of serpentinites is a source of Si to the ocean with extremely high fluid δ30Si values, which can explain anomalies in the marine Si budget like in the Cascadia Basin and which has to be considered in future investigations of the global marine Si cycle.

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Hydrothermal Sr contamination of the Dippin sill, Isle of Arran, Western Scotland

Mineralogical Magazine ◽

10.1180/minmag.1984.048.348.02 ◽

1984 ◽

Vol 48 (348) ◽

pp. 311-322 ◽

Cited By ~ 7

Author(s):

A. P. Dickin ◽

C. M. B. Henderson ◽

F. G. F. Gibb

Keyword(s):

Stable Isotope ◽

Hydrothermal Alteration ◽

Closed System ◽

Hydrothermal Systems ◽

Hydrothermal Fluids ◽

Drill Core ◽

Sr Isotope ◽

Core Section ◽

High Silica ◽

Isotope Measurements

Abstract The Dippin sill, which is emplaced into the Triassic sediments of SE Arran, is an alkaline basic sheet which displays pronounced hydrothermal alteration. The 40-m-thick sill has suffered pervasive contamination with radiogenic Sr, introduced from the Triassic sediments by hydrothermal fluids. Stable isotope measurements suggest that fluids were of meteoric origin, but were restricted to a small closed-system circulation. Initial 87Sr/86Sr ratios in the sill were raised from an original value of 0.7032 to a maximum of 0.7091, contamination being especially pronounced near the contacts at Dippin Head itself (localities 12 and 14) and in a drill core section through the sill above Dippin. Hydrothermal Sr was incorporated into an early-formed high-CaO, high-Sr analcime, which replaced unstable high-silica nepheline in interstitial patches. However, this high-CaO analcime, along with plagioclase, was later replaced by a low-CaO, low-Sr analcime, allowing Sr leaching from the margins of the sill. Hydrothermal fluids are thought to have migrated up to 1 km laterally, up the dip of the sill, mainly via tension joints forming in the cooling intrusion. Pooling of hot fluids at the upper end of the sill probably raised water/rock ratios in this region and allowed greater Sr contamination during mineralogical alteration. The undersaturated mineralogy of the sill accounts for its pervasive hydrothermal Sr contamination, which contrasts markedly with the relatively undisturbed Sr isotope compositions of Hebridean granites involved in hydrothermal systems.

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Stable Sr Isotope Fractionation between Fluids and Clay Minerals: Insight from Laboratory Batch Experiments

10.46427/gold2020.1590 ◽

2020 ◽

Author(s):

Hou-Chun Liu ◽

Chen-Feng You

Keyword(s):

Clay Minerals ◽

Isotope Fractionation ◽

Batch Experiments ◽

Sr Isotope

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Mantle wedge structure in the Miyagi Prefecture forearc region, central northeastern Japan arc, and its relation to corner-flow pattern and interplate coupling

Journal of Geophysical Research Atmospheres ◽

10.1029/2011jb008470 ◽

2011 ◽

Vol 116 (B10) ◽

Cited By ~ 16

Author(s):

Yojiro Yamamoto ◽

Ryota Hino ◽

Masanao Shinohara

Keyword(s):

Flow Pattern ◽

Mantle Wedge ◽

Corner Flow ◽

Interplate Coupling ◽

Northeastern Japan ◽

Miyagi Prefecture ◽

Wedge Structure ◽

Forearc Region

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The evolution of stable silicon isotopes in a coastal carbonate aquifer, Rottnest Island, Western Australia

10.5194/hess-2020-429 ◽

2020 ◽

Author(s):

Ashley N. Martin ◽

Karina Meredith ◽

Andy Baker ◽

Marc D. Norman ◽

Eliza Bryan

Keyword(s):

Western Australia ◽

Isotope Analysis ◽

Inverse Correlation ◽

Silicon Isotopes ◽

Low Concentrations ◽

Groundwater Samples ◽

Si Isotopes ◽

Dissolved Silicon ◽

Si Isotope ◽

Few Data

Abstract. Dissolved silicon (DSi) is a key nutrient in the oceans, but there are few data available regarding Si isotopes in coastal aquifers. Here we investigate the Si isotopic composition of 12 fresh and 17 saline groundwater samples from Rottnest Island, Western Australia, which forms part of the world’s most extensive aeolianite deposit (the Tamala Limestone Formation). Two bedrock samples were also collected from Rottnest Island for Si isotope analysis. The δ30Si values of groundwaters ranged from −0.39 to +3.60 ‰ with an (average: +1.59 ‰) and the rock samples were −0.76 and −0.13 ‰. Due to the relatively low concentrations of DSi (64 to 196 μM) and clay-forming cations in fresh groundwaters, the correlation between δ30Si values and DSi concentrations (ρ = 0.59, p = 0.02) may be explained by Si adsorption onto Fe-Al (oxy)hydroxides present in the aquifer. An increase in groundwater δ30Si in association with the occurrence of water-rock interactions may explain the spatial pattern in δ30Si across the aquifer, and is consistent with the correlation between δ30Si and tritium activities when considering all groundwaters (ρ = −0.68, p = 0.0002). In the deeper aquifer, the inverse correlation between DSi and Cl concentrations (ρ = −0.79, p = 0.04) for the more saline groundwaters is attributed to groundwater mixing with local seawater that is depleted in DSi (

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Sr isotope fractionation in a karst river: case study of Krka, Croatia

10.5194/egusphere-egu21-6059 ◽

2021 ◽

Author(s):

Sonja Lojen ◽

Qasim Jamil ◽

Tea Zuliani ◽

Leja Rovan ◽

Tjaša Kanduč ◽

...

Keyword(s):

Trace Element ◽

Isotope Fractionation ◽

Solid Phase ◽

Isotope Composition ◽

Karst Water ◽

Carbonate Precipitation ◽

Sr Isotopes ◽

Sr Isotope ◽

Element Partitioning ◽

Karst River

Precipitation of calcite from water fractionates strontium (Sr) isotopes because of preferential incorporation of light (86Sr) isotopes into the solid phase, making continental carbonates one of the most 88Sr depleted reservoirs. It was suggested that carbonate precipitation is the most likely process controlling &#948;88/86Sr composition of karst water. Therefore, the 88Sr enrichment of river water could be used for the estimation of Sr and carbonate precipitation at catchment scale.In the present study, we report on trace element partitioning and Sr isotope fractionation between tufa and water in the groundwater fed karst river Krka (Croatia). Water and tufa along with samples of bedrock and soil as the main contributors of dissolved and particulate Sr at seven main waterfalls and cascades along a 33 km section of the river were analysed for trace element and Sr isotope composition (&#948;88/86Sr).The highest &#948;88/86Sr values were measured in soils and in siliciclastic rocks, while in limestone, the &#948;88/86Sr values were similar to those of old tufa precipitated in the period between 96 and 141 ky BP. Recent tufa, however, was considerably depleted in 88Sr. The isotope fractionation between water and recent tufa varied a lot and was inversely correlated with Mg and Sr partitioning coefficients, while correlations with precipitation rates and temperature were rather weak. The &#948;88/86Sr of recent tufa was strongly correlated with the stable isotope composition of organic carbon, which indicates that apart from hydrochemical, hydraulic parameters and temperature, plants and microbial communities that knowingly stimulate the tufa formation also affect the isotope fractionation of Sr.

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Silicon isotopes in Arctic and sub-Arctic glacial meltwaters: the role of subglacial weathering in the silicon cycle

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2019.0098 ◽

2019 ◽

Vol 475 (2228) ◽

pp. 20190098 ◽

Cited By ~ 6

Author(s):

Jade E. Hatton ◽

Katharine R. Hendry ◽

Jonathan R. Hawkings ◽

Jemma L. Wadham ◽

Sophie Opfergelt ◽

...

Keyword(s):

Primary Productivity ◽

High Latitude ◽

Critical Research ◽

Silicon Isotopes ◽

Contextual Framework ◽

Glacial Environments ◽

Marine Primary Productivity ◽

Dissolved Silicon ◽

Si Isotope

Glacial environments play an important role in high-latitude marine nutrient cycling, potentially contributing significant fluxes of silicon (Si) to the polar oceans, either as dissolved silicon (DSi) or as dissolvable amorphous silica (ASi). Silicon is a key nutrient in promoting marine primary productivity, contributing to atmospheric CO 2 removal. We present the current understanding of Si cycling in glacial systems, focusing on the Si isotope (δ 30 Si) composition of glacial meltwaters. We combine existing glacial δ 30 Si data with new measurements from 20 sub-Arctic glaciers, showing that glacial meltwaters consistently export isotopically light DSi compared with non-glacial rivers (+0.16‰ versus +1.38‰). Glacial δ 30 Si ASi composition ranges from −0.05‰ to −0.86‰ but exhibits low seasonal variability. Silicon fluxes and δ 30 Si composition from glacial systems are not commonly included in global Si budgets and isotopic mass balance calculations at present. We discuss outstanding questions, including the formation mechanism of ASi and the export of glacial nutrients from fjords. Finally, we provide a contextual framework for the recent advances in our understanding of subglacial Si cycling and highlight critical research avenues for assessing potential future changes in these environments.

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