start-ver=1.4 cd-journal=joma no-vol=334 cd-vols= no-issue= article-no= start-page=105475 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2019 dt-pub=201911 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Tourmaline in a Mesoarchean pelagic hydrothermal system: Implications for the habitat of early life en-subtitle= kn-subtitle= en-abstract= kn-abstract= The RNA World hypothesis requires the synthesis of RNA to allow the emergence of life on Earth. Hydrothermal systems have been proposed as potential candidates for constructing complex biomolecules. However, in order to successfully form RNA, it is necessary to stabilize ribose, a RNA carbohydrate component. Borate has been found to stabilize ribose. Therefore, boron rich hydrothermal systems are important environments concerning the origin of life on Earth.
The 3.2-Ga Dixon Island Formation of the West Pilbara Superterrane, Western Australia, is a volcano-sedimentary sequence. The Formation represents a Mesoarchean pelagic hydrothermal system, which formed adjacent to an immature island arc. Fine-grained tourmaline, in addition to biogenic carbonaceous matter and spherulitic and tubular bacteriomorphs, are found in black chert. A boron-rich environment was responsible for the formation of these deposits. To explore the implications of such a boron enriched environment on microbial activity, modes of occurrence and chemical compositions of the tourmaline were examined.
The tourmaline is schorl or dravite of the alkali tourmaline group and the boron isotope compositions range in 11B from -7.3 to +2.6. The tourmaline occurs in microcrystalline quartz matrix of black chert veins that cross cut a volcanic unit and also in a bedded black chert, which overlays the volcanic unit. The volcanic unit contains highly altered zones with hydrothermal veins. The associated lithologic and stratigraphic features suggest that the black chert veins were the conduits for upward moving hydrothermal fluids, which reached the sea floor. Subsequently, the volcanic unit was covered by organic matter-rich cherty sediments that in part were fed, and/or altered, by the hydrothermal fluids.
These results suggest that the origin of boron enrichment to form Dixon Island tourmaline is not the associated sedimentary mineral assemblage, which includes diagenetic clay, low-grade metamorphic mica, and organic matter. Instead, the tourmaline was directly precipitated from hydrothermal fluid, enriched in boron. Furthermore, the hydrothermal fluids had already concentrated the boron, in the Mesoarchean pelagic system, prior to the apex of organic matter production and microbial activity. Our findings support a hypothesis that the boron-enriched hydrothermal environment aided the survival and evolution of early life. en-copyright= kn-copyright= en-aut-name=OtaTsutomu en-aut-sei=Ota en-aut-mei=Tsutomu kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=AiharaYuhei en-aut-sei=Aihara en-aut-mei=Yuhei kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=KiyokawaShoichi en-aut-sei=Kiyokawa en-aut-mei=Shoichi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=TanakaRyoji en-aut-sei=Tanaka en-aut-mei=Ryoji kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= en-aut-name=NakamuraEizo en-aut-sei=Nakamura en-aut-mei=Eizo kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=5 ORCID= affil-num=1 en-affil=Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University kn-affil= affil-num=2 en-affil=Department of Earth and Planetary Sciences, Kyushu University kn-affil= affil-num=3 en-affil=Department of Earth and Planetary Sciences, Kyushu University kn-affil= affil-num=4 en-affil=Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University kn-affil= affil-num=5 en-affil=The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University kn-affil= en-keyword=Mesoarchean kn-keyword=Mesoarchean en-keyword=Hydrothermal system kn-keyword=Hydrothermal system en-keyword=Early life kn-keyword=Early life en-keyword=Boron kn-keyword=Boron en-keyword=Tourmaline kn-keyword=Tourmaline END