Japan Geoscience Union Meeting 2015

Presentation information


Symbol B (Biogeosciences) » B-CG Complex & General

[B-CG28] Interrelation between Life, Water, Mineral, and Atmosphere

Tue. May 26, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Fumito Shiraishi(Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University), Tsubasa Otake(Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University), Yohey Suzuki(Graduate School of Science, The University of Tokyo), Ken Takai(Extremobiosphere Research Center, Japan Agency for Marine-Earth Science & Technology), Yuichiro Ueno(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Takeshi Naganuma(Graduate School of Biosphere Science), Takeshi Kakegawa(Graduate School of Science, Tohoku University), Tadashi Yokoyama(Department of Earth and Space Science, Graduate School of Science, Osaka University), Kentaro Nakamura(Precambrian Ecosystem Laboratory (PEL), Japan Agency for Marine-Earth Science and Technology (JAMSTEC))

6:15 PM - 7:30 PM

[BCG28-P11] Nitrogen and noble gas isotopes of Eoarchean Nuvvuagituq rocks

*Ko HASHIZUME1, Daniele Pinti1, Ryota HASUNAKA1, Luc Richard2, Jean David2, Arisai Valadez2 (1.Department of Earth and Space Science, Osaka University, 2.GEOTOP-UQAM, Montreal, Canada)

Keywords:Eoarchean, Atmosphere, Nitrogen, Noble gas

The Nuvvuagittuq greenstone belt is an Eoarchean volcano-sedimentary sequence located in northern Quebec. Rocks are gabbroic intrusions, volcano-sedimentary silicic rocks and banded iron formation (BIFs), enclosed by 3.66 Ga tonalitic gneiss. Rocks are metamorphosed to amphibolite facies and zircon U-Pb ages give a minimum age of 3.75-3.82 Ga to the belt. A deficit in 142Nd compared to the terrestrial Nd standard found in some igneous rock which were dated possibly at 4.28 billion years ago, making this rock suite one of the oldest on Earth. Characterization of the fluids in silicic rocks and BIFs, identified by previous works as chemical precipitates in seawater, might give precious constraints on the Earth superficial conditions in Late Hadean, following the Late Heavy Bombardment.
A preliminary survey intended to analyze the fluids trapped into several lithologies of the belt on the noble gas and nitrogen isotopic compositions. Selected samples are an ultramafic intrusion (POR21), a tonalitic gneiss (POR23), three felsic to intermediate silicic volcanoclastic rocks (POR27b, 28c, 28h), a meta-conglomerate (POR29) and a plagioclase-rich amphibolite (POR30). Preliminary noble gas isotopes where carried out at GEOTOP by using a quadrupole mass spectrometer. 4He, 22Ne, 36-40Ar, 84Kr and 129,132,136Xe were analyzed after crushing bulk rock and recovering gases in a purification line. All samples contain radiogenic 4He, from 3.7 x10-8 to 2.5 x 10-7 cm3STP/grock, although the calculated radiogenic 4He/40Ar* ratio is only 0.01 to 0.03 against the expected crustal ratio of 4.2. This could indicate large loss of helium during time (which is often observed in Archean rocks) or poor potassium content, the parent element of radiogenic 40Ar*. The measured 40Ar/36Ar ratios range from 403 to 9635, higher than the atmospheric value of 295.5. The sample that contains most radiogenic noble gas 4He and 136Xe (from U fission and alpha decay) and 40Ar* is the tonalitic gneiss (POR23). All other samples show atmospheric composition of noble gases (except 4He and 40Ar*) or slight 136Xe anomalies.
A new series of noble gas and nitrogen isotopic measurements are under way at Osaka University to determine the origin of gases into the Nuvvuagituq fluids and try to constrain crustal and igneous sources possibly feeding them.