Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Sawada, Hikaru*; Niki, Sota*; Nagata, Mitsuhiro; Hirata, Takafumi*
Minerals (Internet), 12(1), p.107_1 - 107_15, 2022/01
Times Cited Count：2 Percentile：40.6(Geochemistry & Geophysics)The Oeyama ophiolite is one of the oldest components in Japanese Islands and important to reveal the initiation of plate subduction along proto-Japan. This study performed U-Pb-Hf isotopic and trace element analyses of zircon in gabbroic rocks. The weight mean of 
Pb/
U dates from zircons of the Oeyama ophiolite is 544 
4 Ma (2 sigma). Trace element analysis of the zircons exhibit that the host rock was derived from the mantle depleted of incompatible elements like mid-oceanic ridge basalt. The present igneous age and geochemical feature of the zircons is consistent with previous work for other part of the Oeyama ophiolite. Zircon Lu-Hf isotopic analysis also indicate that the gabbroic rock was derived from the depleted mantle domain. The Hf isotopic signature is more depleted than those of the zircons in jadeitite associated with the Oeyama ophiolite. This result implies that the older crustal material was involved into the initial oceanic plate subduction along the proto-Japan arc.
Nagata, Mitsuhiro; Fukuda, Shoma; Sueoka, Shigeru; Yokoyama, Tatsunori; Kagami, Saya; Niki, Sota*; Iwano, Hideki*; Danhara, Toru*; Ogita, Yasuhiro; Kajita, Yuya*; et al.
no journal, ,
no abstracts in English
Nakajima, Toru; Fukuda, Shoma; Niki, Sota*; Sueoka, Shigeru; Kawakami, Tetsuo*; Danhara, Toru*; Tagami, Takahiro*
no journal, ,
We conducted monazite fission-track (MFT) etching experiments for Quaternary monazite dating. Quite low-temperature annealing of the MFT system (45-25 degree: Jones et al., 2021) has been proposed, and application as an ultra-low-temperature thermochronometer is expected. The practical application of MFT dating gives us access to a geological event at ultra-low temperatures, such as shallow crustal denudation and faulting. Jones et al. (2019) examined the etching conditions and suggested that the etching rate can vary between grains depending mainly on the accumulated radiation damage. Since the monazites used in previous studies were pre-Mesozoic (Weise et al., 2009; Jones et al., 2021), younger monazites with less radiation damage would be expected to have higher etching resistance. In this study, we attempted to etch FT using the Quaternary monazites, which are expected to have less radiation damage, to investigate appropriate etching conditions and discuss a relation between etching rate and radiation damage. Monazites from the Toya Ignimbrite (ca. 0.1 Ma: Niki et al., 2022) and the Kurobegawa Granite (ca. 0.8 Ma: Ito et al., 2013) were used in this study. Euhedral monazite-(Ce) crystals have weak magnetism and can be separated by the conventional magnetic separation method. The Cretaceous monazite from the Kibe Granite (ca. 98 Ma: Skrzypek et al., 2016) was also etched for comparison.
Nakajima, Toru; Niki, Sota*; Kudo, Shumpei*; Kawakami, Tetsuo*; Higashino, Fumiko*; Hirata, Takafumi*; Sakai, Harutaka*
no journal, ,
no abstracts in English
