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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

Hydrogen isotope analysis of micro-scale apatite inclusions in Archaean zircon grains

Akizumi Ishida, Mizuho Koike, Naoto Takahata, Takuya Morita, Jean David, Daniele L. Pinti, Yuji Sano
Geochemical Journal, Vol. 52, No. 6, P. 457-466, 2018

ABSTRACT

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.

KEYWORDS

NanoSIMS, hydrogen isotope composition, U-Pb dating, Archean, apatite inclusion

Supplementary Materials(file)

https://www.jstage.jst.go.jp/article/geochemj/52/6/52_2.0534/_supplement/_download/52_2.0534_1.pdf

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