Temperature trends for reaction rates, hydrogen generation, and partitioning of iron during experimental serpentinization of olivine

McCollom, T. M.; Klein, Frieder; Robbins, Mark J.; Moskowitz, Bruce M.; Berquó, Thelma S.; Jöns, Niels; Bach, Wolfgang; Templeton, Alexis S.

doi:10.1016/j.gca.2016.03.002

Cited by 145 publications

(155 citation statements)

References 75 publications

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“…1 C and D ] decreased gradually during each of the experiments, except the one performed at 320°C (OLIV320), but in all cases, concentrations remained at 2.8 mmol kg −1 or higher at the end of the experiments (Table S1). The decrease in ΣCO 2 during heating is predominantly attributable to the formation of carbonate minerals, which were found dispersed among the product minerals in the experiments (29). Concentrations of C 2+ hydrocarbons were near or below detection limits in all samples (<0.01 μmol kg ) were generated in the experiment performed at 320°C (OLIV320) (Fig.…”

Section: Resultsmentioning

confidence: 82%

“…Solid reaction products of all experiments included chrysotile, Fe-bearing brucite, magnetite, and small amounts of carbonates (magnesite and dolomite) (29). In experiment OLIVOPX230, the products also included trace amounts of an Ni-Fe phase (presumably awaruite or other NiFe alloy) and native Pt (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…These experiments were performed using methods very similar to those of this study, except that the reaction vessel was periodically rotated during heating. After heating for [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] (Table 1). However, isotopic labeling indicated that the CH 4 in our experiments was not derived from reduction of dissolved inorganic carbon but instead, was derived entirely from background sources (i.e., composed of 99 mol % 12 CH 4 ).…”

Section: Discussionmentioning

confidence: 99%

“…Results reported here focus on carbon reduction and CH 4 synthesis during these experiments, whereas a detailed analysis of other products and reaction rates has been reported elsewhere (29). In all of the experiments, a 13 C-labeled compound was used as the inorganic carbon source (in the form of NaH 13 CO 3 ) to trace the conversion of inorganic carbon to CH 4 .…”

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confidence: 99%

“…The experiments were conducted over a temperature range of 200°C to 320°C. Experiments were not extended to lower temperatures, because the rates of serpentinization were found to be too slow below 200°C to be readily observable on laboratory timescales (29,30).…”

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confidence: 99%

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Abiotic methane formation during experimental serpentinization of olivine

McCollom

2016

Proc. Natl. Acad. Sci. U.S.A.

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Fluids circulating through actively serpentinizing systems are often highly enriched in methane (CH 4 ). In many cases, the CH 4 in these fluids is thought to derive from abiotic reduction of inorganic carbon, but the conditions under which this process can occur in natural systems remain unclear. In recent years, several studies have reported abiotic formation of CH 4 during experimental serpentinization of olivine at temperatures at or below 200°C. However, these results seem to contradict studies conducted at higher temperatures (300°C to 400°C), where substantial kinetic barriers to CH 4 synthesis have been observed. Here, the potential for abiotic formation of CH 4 from dissolved inorganic carbon during olivine serpentinization is reevaluated in a series of laboratory experiments conducted at 200°C to 320°C. A 13 C-labeled inorganic carbon source was used to unambiguously determine the origin of CH 4 generated in the experiments. Consistent with previous high-temperature studies, the results indicate that abiotic formation of CH 4 from reduction of dissolved inorganic carbon during the experiments is extremely limited, with nearly all of the observed CH 4 derived from background sources. The results indicate that the potential for abiotic synthesis of CH 4 in low-temperature serpentinizing environments may be much more limited than some recent studies have suggested. However, more extensive production of CH 4 was observed in one experiment performed under conditions that allowed an H 2 -rich vapor phase to form, suggesting that shallow serpentinization environments where a separate gas phase is present may be more favorable for abiotic synthesis of CH 4 .serpentinization | abiotic methane | hydrothermal systems

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Section: Resultsmentioning

confidence: 82%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Abiotic methane formation during experimental serpentinization of olivine

McCollom

2016

Proc. Natl. Acad. Sci. U.S.A.

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171

139

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Influence of pyroxene and spinel on the kinetics of peridotite serpentinization

et al. 2017

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Hydrothermal experiments were performed at 311°C and 3.0 kbar on natural olivine and peridotite to investigate the kinetics of serpentinization. The results show that the rates of reaction strongly depend on grain sizes of solid reactants, with smaller grain sizes resulting in faster kinetics. After 27 days of reaction, the reaction extent was 99% for peridotite with grain sizes of <30 μm, and the reaction extent was 28% for grain sizes of 100–177 μm. Compared to peridotite, olivine is serpentinized at much slower rates, e.g., 5.3% of reaction extent was achieved for olivine with grain sizes of 100–177 μm after 27 days, approximately five times lower than that reached during peridotite serpentinization. Such contrasting results are due to the presence of pyroxene and spinel, an interpretation which is supported by a marked increase in reaction extents for experiments with the addition of pyroxene and spinel. The reaction extent achieved in experiments with 3 wt % spinel greatly increased to 98% after 27 days, much higher than that achieved during olivine serpentinization. These results appear to be related to pyroxene and spinel releasing Al and Cr during serpentinization. As indicated by compositions of serpentine, orthopyroxene lost ~60% of Al at a reaction extent of 59%. Influence of Al and Cr is suggested by a dramatic increase in reaction extents with the addition of Al2O3 and Cr2O3 powders. Olivine in natural geological settings is commonly associated with pyroxene and spinel; consequently, serpentinization kinetics may be much faster than previously thought.

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Local Seismicity of the Rainbow Massif on the Mid‐Atlantic Ridge

et al. 2018

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The Rainbow massif, an oceanic core complex located in a nontransform discontinuity on the Mid‐Atlantic Ridge (36°N), is notable for hosting high‐temperature hydrothermal discharge through ultramafic rocks. Here we report results from a 9 month microearthquake survey conducted with a network of 13 ocean bottom seismometers deployed on and around the Rainbow massif as part of the MARINER experiment in 2013–2014. High rates (~300 per day) of low‐magnitude (average ML ~ 0.5) microearthquakes were detected beneath the massif. The hypocenters do not cluster along deeply penetrating fault surfaces and do not exhibit mainshock/aftershock sequences, supporting the hypothesis that the faulting associated with the exhumation of the massif is currently inactive. Instead, the hypocenters demarcate a diffuse zone of continuous, low‐magnitude deformation at relatively shallow (< ~3 km) depths beneath the massif, sandwiched in between the seafloor and seismic reflectors interpreted to be magmatic sills driving hydrothermal convection. Most of the seismicity is located in regions where seismic refraction data indicate serpentinized ultramafic host rock, and although the seismic network we deployed was not capable of constraining the focal mechanism of most events, our analysis suggests that serpentinization may play an important role in microearthquake generation at the Rainbow massif.

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Temperature trends for reaction rates, hydrogen generation, and partitioning of iron during experimental serpentinization of olivine

Abstract: A series of laboratory experiments were conducted to examine how partitioning of Fe among solid reaction products and rates of H 2 generation vary as a function of temperature during serpentinization of olivine. Individual experiments were conducted at temperatures

Cited by 145 publications

References 75 publications

Abiotic methane formation during experimental serpentinization of olivine

Abiotic methane formation during experimental serpentinization of olivine

Influence of pyroxene and spinel on the kinetics of peridotite serpentinization

Local Seismicity of the Rainbow Massif on the Mid‐Atlantic Ridge

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