THE POTENTIAL OF ABIOTIC ORGANIC SYNTHESIS IN ALKALINE ENVIRONMENTS OF SUBDUCTION ZONES
2010 (English)Conference paper (Other academic)
Reduced carbon and nitrogen precursor compounds may be formed under off-axis hydrothermal conditions in oceanic lithosphere in the presence of native Fe and Ni and are adsorbed on authigenic layer silicates and zeolites. The native metals as well as the molecular hydrogen reducing CO2 to CO/CH4 and NO3-/NO2- to NH3/NH4+ are a result of serpentinization of mafic rocks. Once the reduced carbon and nitrogen compounds have been formed the synthesis of hydrogen cyanide is, in principle, possible . HCN is central to most of the reaction pathways leading to abiotic formation of simple organic compounds containing nitrogen, such as amino acids, purines and pyrimidines. Oceanic plates are conveyor belts of reduced carbon and nitrogen compounds from the off-axis hydrothermal environments to the subduction zones, where compaction, dehydration, desiccation and diagenetic reactions affect the organic precursors. CO/CH4 and NH3/NH4+ in fluids distilled out of layer silicates and zeolites in the subducting plate at an early stage of subduction will react upon heating and form the HCN, which is then available for further organic reactions. Since the released fluids will rise through hydrated ultramafic mantle rocks of the lower part of the overriding plate, they will experience a strong pH increase. The reason for this increase is that the serpentinization of ferromagnesian minerals in ultramafic rocks in contact with the water leads to the formation of the secondary magnesium hydroxide mineral brucite, which causes high pH. The high pH may promote abiotic formation of carbohydrates like pentose sugars, particularly ribose, as well as nucleosides and even nucleotides, since pyrophosphate is stable under alkaline conditions at low water-rocks ratios . Convergent margins in the initial phase of subduction must, therefore, be considered the most potent sites for prebiotic organic reactions on terrestrial planets, provided that some type of plate tectonics occurs.
Place, publisher, year, edition, pages
Oslo: Norsk Geologisk Forening , 2010.
Astrobiology, abiotic organic geochemistry
Other Earth and Related Environmental Sciences
Research subject Geochemistry
IdentifiersURN: urn:nbn:se:su:diva-48380OAI: oai:DiVA.org:su-48380DiVA: diva2:375483
Nordic Geological Winter Meeting