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Abe, Takeyasu; Kuribayashi, Takahiro*; Nakamura, Michihiko*
European Journal of Mineralogy, 29(6), p.949 - 957, 2017/12
Times Cited Count：2 Percentile：6.18(Mineralogy)Polarised infrared spectra of synthetic single crystals and radiation-damaged natural samples were collected to examine hydroxyl incorporation in monazite. The IR spectra of pure synthetic monazite contain two OH stretching bands at 3163 and 3335 cm
with contrasting bandwidths of 40 and 90 cm, respectively. The two OH bands show strong pleochroism and dominant infrared absorption in the Y direction. The IR spectra of natural monazite contains a weak pleochroic OH band centered around 3400 cm with a bandwidth of more than 200 cm. During step-heating experiments, this broad OH band split into several bands, and these bands differ from those observed in the spectra of synthetic samples. The OH stretching signals in the spectra of both natural and synthetic samples disappeared after heating at 1000
C. Based on these results, OH defects in natural monazite arise because of secondary hydration facilitated by radiation damage, as in the case of natural zircon and xenotime.
Abe, Takeyasu
no journal, ,
REE- and actinide-bearing minerals contain geochemical and geochronological information, which is important to discuss rock-formation process (cf. Harlov, 2016 review article, Journal of the Indian Institute of Science). In metamorphic petrology, many researchers have focused on the minerals such as zircon, garnet, apatite, monazite and xenotime. Many previous studies of those minerals have been reported (e.g. Hoskin and Schaltegger, 2003, Reviews in Mineralogy and Geochemistry; Meagher, 1982, Reviews in Mineralogy and Geochemistry; Spear and Pyle, 2002, Reviews in Mineralogy and Geochemistry). Here, current understanding of REE- and actinide-bearing minerals is reviewed. Based on the review, future work direction of mineralogical studies on geochronometers is discussed focusing on monazite.
monazite; Investigation of impurity incorporation into interstitial siteAbe, Takeyasu; Kuribayashi, Takahiro*; Nakamura, Michihiko*
no journal, ,
no abstracts in English
Fukuda, Shoma; Nakajima, Toru; Suzuki, Ayase*; Sueoka, Shigeru; Tagami, Takahiro*
no journal, ,
The monazite fission-track method has been expected to be a powerful tool as an ultra-low temperature (below 50 degrees Celcius) thermochronometers. Jones et al., (2019) proposed the optimum for the MFT etching (6 M HCl at 90 degrees of Celcius for 60-90 min) by using 252Cf-derived semi-tracks of the Devonian monazite. In our preliminary experiments, spontaneous tracks in the Cretaceous monazites of Japan were successfully etched within 90-120 min as FT densities attain a plateau. However, Quaternary monazites in Japan yielded few and very thin (i.e., under-etched) spontaneous tracks even after step-etching for 600 min. Our results from Raman spectrometry and EPMA analyses suggested that less-damaged monazites tend to require a longer etching time. Therefore, we proposed a termination criterion for MFT step-etching: to etch until the thinnest track width reaches approximately 1.0 
0.5 micron, similar to zircon FT step-etching. This 1-micon width criterion is valid regardless of monazite characteristics, e.g., radiation damage and chemistry.
