GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
Hydrogen isotope analysis of micro-scale apatite inclusions in Archaean zircon grains
Akizumi IshidaMizuho KoikeNaoto TakahataTakuya MoritaJean DavidDaniele L. PintiYuji Sano
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2018 年 52 巻 6 号 p. 457-466

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A novel study of in situ hydrogen isotope composition (δD) measurements of micron-scale apatite inclusions hosted in zircon crystals was carried out by lateral high-resolution secondary ion mass spectrometry. The host rock of zircon is a tonalite belonging to the Nuvvuagittuq Supracrustal belt, Canada, which is considered to be one of the oldest supracrustal belts of Hadean-Archean age. Uranium-lead dating of host zircon crystals yielded an age of 3636 ± 20 Ma, which is consistent with previously reported ages of this unit. The δD values were measured for seven apatite inclusions, and range from –225 to +65‰ (vs. SMOW). A negative correlation was observed between δD values and the 18O/1H ratios of the examined apatite inclusions. This relationship can be explained by a mixing trend between the original hydrogen in the apatite inclusions and contamination from the analytical environment. The pristine δD value estimated for the apatite inclusion is +53 ± 60‰, which was clearly distinct from the δD value resulting from bulk rock analysis, –49 ± 2‰. The pristine δD value of the tonalitic magma source may provide new constraints on the formation of the primitive crust and/or the ocean of the early Earth.

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© 2018 by The Geochemical Society of Japan
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