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Title: Abiotic methane synthesis and serpentinization in olivine-hosted fluid inclusions
The conditions of methane (CH 4 ) formation in olivine-hosted secondary fluid inclusions and their prevalence in peridotite and gabbroic rocks from a wide range of geological settings were assessed using confocal Raman spectroscopy, optical and scanning electron microscopy, electron microprobe analysis, and thermodynamic modeling. Detailed examination of 160 samples from ultraslow- to fast-spreading midocean ridges, subduction zones, and ophiolites revealed that hydrogen (H 2 ) and CH 4 formation linked to serpentinization within olivine-hosted secondary fluid inclusions is a widespread process. Fluid inclusion contents are dominated by serpentine, brucite, and magnetite, as well as CH 4( g ) and H 2( g ) in varying proportions, consistent with serpentinization under strongly reducing, closed-system conditions. Thermodynamic constraints indicate that aqueous fluids entering the upper mantle or lower oceanic crust are trapped in olivine as secondary fluid inclusions at temperatures higher than ∼400 °C. When temperatures decrease below ∼340 °C, serpentinization of olivine lining the walls of the fluid inclusions leads to a near-quantitative consumption of trapped liquid H 2 O. The generation of molecular H 2 through precipitation of Fe(III)-rich daughter minerals results in conditions that are conducive to the reduction of inorganic carbon and the formation of CH 4 . Once formed, CH 4( g ) and H 2( g ) can be stored over geological timescales until extracted by dissolution or fracturing of the olivine host. Fluid inclusions represent a widespread and significant source of abiotic CH 4 and H 2 in submarine and subaerial vent systems on Earth, and possibly elsewhere in the solar system.  more » « less
Award ID(s):
1634032
PAR ID:
10126515
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Proceedings of the National Academy of Sciences
Volume:
116
Issue:
36
ISSN:
0027-8424
Page Range / eLocation ID:
17666 to 17672
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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