10:45 AM - 12:15 PM
[BBG01-P05] Relation between Deep-sea Hydrothermal Fluid and Life Activity Deciphered from Accreted Deep-sea Sedimentary Rocks in Japan
Keywords:ridge hydrothermal system, deep-sea biosphere, Mesozoic, origin of life, chert-basalt
One of the oldest micro-fossil was discovered from the silica dyke (quartz vein) in the chert-barite sequence on the Archean ridge hydrothermal system (e.g Ueno et al., 2004). The deep-sea-hydrothermal activity has played an important role in the origin and evolution of life. Phanerozoic ridge hydrothermal activity is well-recognized in accreted oceanic crust in the continental margin, such as circum Pacific orogenic belt. Organic carbon with negative carbon isotope signature, preserved in iron sulfide (pyrite) from the Besshi-type ore (Volcanic Massive sulfide) deposit in the Sanbagawa metamorphic rocks. The carbon is originated from hydrothermal activity of the Jurassic Mid-Ocean Ridge and subsequently suffered subduction zone metamorphism at Cretaceous (Ando, 2016). Presence of the Besshi-type deposit in Sanbagawa high P/T metamorphic rocks reveals that the ridge hydrothermal activity in the late Jurassic was one of the largest in the history of the earth (Nozaki et al., 2013). Nozaki et al (2013) proposed that global oceanic anoxic event and global warming due to high CO2 emission from the late Jurassic ridge activity. However, there are a few examples of analysis of hydrothermal deposits from the Jurassic accretionary complex accreted to the Japanese archipelago and associated biofossils. In this study, in order to confirm the relation between the deep-sea biosphere and the ridge activity through the Mesozoic, we conducted petrological investigations, microscopic observations, and chemical studies of the chert-basalt association from the accreted Triassic, Jurassic and Cretaceous terranes in Japanese Islands.
Our preliminary observation of the Early Triassic black chert concludes that numerous high angle veins against the chert layers contain FeS, graphite and quartz. It suggests that the ridge hydrothermal activity played major role after global mass extinction at the end of Permian. Jurassic red cherts contain minor amount of FeS overgrown by Fe-oxide. That is, Jurassic oxidation state in the global ocean was still higher although the deep-sea redox condition was well-operated by the ridge hydrothermal activity. The Cretaceous Shimanto accretionary complex, chert-basalt association was also observed. Calcite + quartz vein is abundant, and its margin is characterized with titanite-chlorite assemblage. It suggests that CO2 concentration was comparable to the Archean-ridge-hydrothermal condition (e,g Kitajima et al., 2007). Thus, the deep-sea redox state was not completely correlated with whole ocean oxidation condition and CO2 concentration.
Our preliminary observation of the Early Triassic black chert concludes that numerous high angle veins against the chert layers contain FeS, graphite and quartz. It suggests that the ridge hydrothermal activity played major role after global mass extinction at the end of Permian. Jurassic red cherts contain minor amount of FeS overgrown by Fe-oxide. That is, Jurassic oxidation state in the global ocean was still higher although the deep-sea redox condition was well-operated by the ridge hydrothermal activity. The Cretaceous Shimanto accretionary complex, chert-basalt association was also observed. Calcite + quartz vein is abundant, and its margin is characterized with titanite-chlorite assemblage. It suggests that CO2 concentration was comparable to the Archean-ridge-hydrothermal condition (e,g Kitajima et al., 2007). Thus, the deep-sea redox state was not completely correlated with whole ocean oxidation condition and CO2 concentration.