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Publication . Article . 2014

Garnets within geode-like serpentinite veins: Implications for element transport, hydrogen production and life-supporting environment formation

Oliver Plümper; Andreas Beinlich; Wolfgang Bach; Emilie Janots; Håkon Austrheim;
Closed Access
Published: 01 Sep 2014 Journal: Geochimica et Cosmochimica Acta, volume 141, pages 454-471 (issn: 0016-7037, Copyright policy )
Publisher: Elsevier BV

Geochemical micro-environments within serpentinizing systems can abiotically synthesize hydrocarbons and provide the ingredients required to support life. Observations of organic matter in microgeode-like hydrogarnets found in Mid-Atlantic Ridge serpentinites suggest these garnets possibly represent unique nests for the colonization of microbial ecosystems within the oceanic lithosphere. However, little is known about the mineralogical and geochemical processes that allow such unique environments to form. Here we present work on outcrop-scale vein networks from an ultramafic massif in Norway that contain massive amounts of spherulitic garnets (andradite), which help to constrain such processes. Vein andradite spherulites are associated with polyhedral serpentine, brucite, Ni–Fe alloy (awaruite), and magnetite indicative of low temperature (<200 °C) alteration under low fO2 and low aSiO2,aq geochemical conditions. Together with the outcrop- and micro-scale analysis geochemical reaction path modeling shows that there was limited mass transport and fluid flow over a large scale. Once opened the veins remained isolated (closed system), forming non-equilibrium microenvironments that allowed, upon a threshold supersaturation, the rapid crystallization (seconds to weeks) of spherulitic andradite. The presence of polyhedral serpentine spheres indicates that veins were initially filled with a gel-like protoserpentine phase. In addition, massive Fe oxidation associated with andradite formation could have generated as much as 600 mmol H2,aq per 100 cm3 vein. Although no carboneous matter was detected, the vein networks fulfill the reported geochemical criteria required to generate abiogenic hydrocarbons and support microbial communities. Thus, systems similar to those investigated here are of prime interest when searching for life-supporting environments within the deep subsurface.

Subjects by Vocabulary

Microsoft Academic Graph classification: Awaruite geography geography.geographical_feature_category biology Brucite Geochemistry Massif engineering.material biology.organism_classification Abiogenic petroleum origin chemistry.chemical_compound chemistry Andradite Ultramafic rock engineering Vein (geology) Geology Magnetite


Geochemistry and Petrology