URLhttps://www.bco-dmo.org/dataset/663969
Download URLhttps://www.bco-dmo.org/dataset/663969/data/download
Media Typetext/tab-separated-values
CreatedNovember 4, 2016
ModifiedNovember 2, 2017
StateFinal no updates expected
Brief DescriptionSulfur geochemistry of the Santa Elena (Costa Rica) ultramafics

Acquisition Description

Santa Elena samples:
Sample preparation and mineralogy: Ultramafic basement rocks were sampled throughout the Santa Elena Ophiolite. Carbonate deposits associated with Mg-HCO3 and Ca-OH springs in the eastern part of the ophiolite were sampled at various locations within riverbeds. All analytical measurements and sample preparation of the Santa Elena peridotites and carbonates were performed at the Department of Geosciences at Virginia Tech. The carbonate samples were prepared by drilling out individual depositional layers of carbonates to reveal heterogeneities within different layers or crushed with an agate mortar for bulk rock analysis. Carbonate precipitates from the rivers were first dried at 40 degrees C in the oven. Before sample analyses all samples were homogenized by hand with the agate mortar. The mineralogy of the carbonates was then determined by X-ray diffraction on a Rigaku MiniFlex XRD using the powder diffraction analysis package PDXL.

Bulk rock powders were prepared for all the ultramafic rocks. To remove contamination from weathering, the outermost 1-2 cm of the rock samples were cut away. The samples were then cleaned in an ultrasonic bath prior to powdering them with a shatter box using an alumina dish. These bulk rock powders were subsequently analyzed for their carbon and sulfur geochemistry.

Sulfur geochemistry:
We determined the isotopic composition and contents of the acid volatile sulfide (AVS or also referred to elsewhere as the monosulfide fraction), chromium reducible sulfide (CRS or also called disulfide fraction) and the sulfate. Sulfur extractions were performed following a modified version of the methods of Canfield et al. (1986). Acid volatile sulfide was first extracted by reacting 20-25g of bulk rock powder with 6N HCl in an inert N2-atmosphere. The residual sample was then reacted with an acidified CrCl2 solution to extract the chromium-reducible sulfide. In both cases the liberated H2S was precipitated as ZnS in a zinc acetate solution and subsequently converted to Ag2S through reaction with a 0.1M AgNO3 solution. The sulfate fraction was recovered by reacting the solution from the AVS extraction with BaCl2 to form BaSO4. The amounts of AVS, CRS and sulfate were determined gravimetrically and were subsequently corrected based on the sulfur content of the precipitate as determined on the EA, since co-precipitation of other phases during the wet chemical extraction could not be completely prevented.

The isotopic composition of the AVS, CRS and sulfate were determined on a Vario ISOTOPE EA attached to an Isoprime 100 IRMS. To ensure complete combustion during EA-analyzes, vanadium pentoxide (V2O5) was added to the samples. Sulfur isotope values are reported in standard delta-notation relative to the Vienna-Canyon Diablo Troilite (V-CDT) standard. During measurements the international sulfide (Ag2S) standards IAEA-S-1 (d34S = -0.3‰), IAEA-S-2 (d34S = +22.7‰) and IAEA-S-3 (d34S = -32.3‰) and the sulfate (BaSO4) standards IAEA-SO-5 (d34S = +0.5‰), IAEA-SO-6 (d34S = -34.1‰), and NBS127 (d34S =+20.3‰) were used to place our samples on the V-CDT scale. Reproducibility is better than 0.2‰ for all sulfur analyses (samples and standards), and the relative precision of sulfur contents is within 3%.

Processing Description

Total sulfide = S content AVS + S content CRS
Total sulfur content = S content AVS + S content CRS + Sulfate

Detection limits:
Sulfide and sulfate contents: Determined by the sulfur extraction procedure and the total amount available to perform bulk rock sulfur extractions. Approximately 4ppm

BCO-DMO Processing:
- moved group/sample type into its own column;
- replaced "n.d." with nd and "<l.o.d." with BDL;
- replaced spaces with underscores;
- replaced commas with semi-colons;
- removed % signs from data column "degre of serpentinization";
- modified parameter names to conform with BCO-DMO naming conventions.

Instruments

Rigaku MiniFlex XRD [X-ray diffractometer]
Details
Instance Description (Rigaku MiniFlex XRD)

The mineralogy of the carbonates was then determined by X-ray diffraction on a Rigaku MiniFlex XRD using the powder diffraction analysis package PDXL.

Instruments that identify crystalline solids by measuring the characteristic spaces between layers of atoms or molecules in a crystal.

Vario ISOTOPE elemental analyzer [Elemental Analyzer]
Details
Instance Description (Vario ISOTOPE elemental analyzer)

TC contents, d13CTC and d13CTOC were determined on a Vario ISOTOPE elemental analyzer (EA) coupled to an Isoprime 100 isotope ratio mass spectrometer (IRMS). 

Instruments that quantify carbon, nitrogen and sometimes other elements by combusting the sample at very high temperature and assaying the resulting gaseous oxides. Usually used for samples including organic material.

Details
Instance Description (Isoprime 100)

TC contents, d13CTC and d13CTOC were determined on a Vario ISOTOPE elemental analyzer (EA) coupled to an Isoprime 100 isotope ratio mass spectrometer (IRMS). 

The d13CTIC and d18OTIC and TIC contents were analyzed on a MultiFlowGeo headspace sampler attached to an Isoprime 100 IRMS.

The Isotope-ratio Mass Spectrometer is a particular type of mass spectrometer used to measure the relative abundance of isotopes in a given sample (e.g. VG Prism II Isotope Ratio Mass-Spectrometer).

Parameters

sample_group [sample_descrip]
Details
sample_group
Sample group/type
text description of sample collected
sample_name [sample]
Details
sample_name
Sample name

unique sample identification or number; any combination of alpha numeric characters; precise definition is file dependent

lat [latitude]
Details
lat
Latitude; positive values = North

latitude, in decimal degrees, North is positive, negative denotes South; Reported in some datasets as degrees, minutes

lon [longitude]
Details
lon
Longitude; positive values = East

longitude, in decimal degrees, East is positive, negative denotes West; Reported in some datsets as degrees, minutes

description [sample_descrip]
Details
description
Sample description
text description of sample collected
degree_of_serpentinization [unknown]
Details
degree_of_serpentinization
Degree of serpentinization (percent)
association with a community-wide standard parameter is not yet defined
S_content_AVS [unknown]
Details
S_content_AVS
Sulfur concentration of the Acid volaltile sulfur (AVS) fraction of the bulk rock
association with a community-wide standard parameter is not yet defined
S_content_CRS [unknown]
Details
S_content_CRS
Sulfur concentration of the chromium reduceable sulfur (CRS) fraction of the bulk rock
association with a community-wide standard parameter is not yet defined
total_sulfide [unknown]
Details
total_sulfide
Total sulfide
association with a community-wide standard parameter is not yet defined
S_content_sulfate [unknown]
Details
S_content_sulfate
Sulfur content of sulfate
association with a community-wide standard parameter is not yet defined
total_S_content [unknown]
Details
total_S_content
Total sulfur content
association with a community-wide standard parameter is not yet defined
SO4_to_total_sulfur [unknown]
Details
SO4_to_total_sulfur
Ratio of SO4 to total sulfur
association with a community-wide standard parameter is not yet defined
delta34S_AVS [unknown]
Details
delta34S_AVS
Delta 34S of AVS relative to the V-CDT (Vienna Canon Diablo Troilite) standard
association with a community-wide standard parameter is not yet defined
delta34S_CRS [unknown]
Details
delta34S_CRS
Delta 34S CRS relative to the V-CDT (Vienna Canon Diablo Troilite) standard
association with a community-wide standard parameter is not yet defined
delta34S_sulfate [unknown]
Details
delta34S_sulfate
Delta 34S of sulfate relative to the V-CDT (Vienna Canon Diablo Troilite) standard
association with a community-wide standard parameter is not yet defined
mineralogy [unknown]
Details
mineralogy

Sulfide/metal mineralogy: dissem. sulfides = disseminated sulfides; ptl = pentlandite; po = pyrrhotite; hz = heazlewoodite; mgt = magnetite; aw = awaruite; cc = chalcocite; cp = chalcopyrite; bn = bornite; cub = cubanite; sm = smythite; vl = violarite; sug = suggakiite; sam = samaniite; Cu = native Cu or Cu-Fe-Ni alloys; (Santa Elena data from Schwarzenbach et al., 2014; Voltri Massif data from Schwarzenbach, 2011)

association with a community-wide standard parameter is not yet defined

Dataset Maintainers

NameAffiliationContact
Esther M. SchwarzenbachFreie Universität Berlin
Shannon RauchWoods Hole Oceanographic Institution (WHOI BCO-DMO)

BCO-DMO Project Info

Project TitleIdentifying the controls on biological activity in serpentinites
AcronymControls on biological activity
URLhttps://www.bco-dmo.org/project/654267
CreatedAugust 18, 2016
ModifiedOctober 31, 2016
Project Description

Project description from C-DEBI:
Serpentinization – the hydrothermal alteration of ultramafic rocks – is a unique mineralogical process that results in H2 and CH4 – rich fluids that can support microbial communities. Using a combination of petrographic observations, bulk rock and in-situ sulfur isotope signatures of variably serpentinized peridotites from four different geotectonic environments we provide new constraints on the factors that support microbial activity. The studied samples overall suggest that redox conditions reflected by the presence of pyrite and pyrrhotite represent the fluid chemistry that favors microbial activity. This fluid chemistry, i.e., the prevailing hydrogen and sulfur fugacities of the fluid, are thereby correlated to high water-rock ratios and increased incorporation of seawater-derived species such as sulfate and carbonate. These species serve as major energy sources of microbial activity. In contrast, highly reducing conditions and limited fluid input limits or even prevents microbial activity within serpentinites due to insufficient availability of these species. Interaction with carbonate and sulfate-bearing meteoric waters is likely an essential process that supports microbial activity in continental serpentinization environments. Overall, this study shows that apart from fluid temperatures being within the limits of life, the fluid chemistry (redox conditions and availability of e.g. carbonate and sulfate) are the primary factors that control the presence or absence of microbial communities within serpentinizing peridotites. This study highlights the importance of combining bulk rock and in-situ stable isotope data with petrographic and mineralogical observations in order to better constraint the presence of microbial communities within the subsurface of peridotite-hosted hydrothermal systems.

Note: This project was funded by a C-DEBI Research Grant.

Project Maintainers
NameAffiliationRoleContact
Esther M. SchwarzenbachFreie Universität BerlinLead Principal Investigator
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