Jadeitites and associated metasomatic rocks from serpentinite mélanges in the Nishisonogi unit, Nagasaki Metamorphic Complex, western Kyushu, Japan: a review

Abstract

The Nishisonogi jadeitite is a peculiar example among Japanese jadeitites in terms of the age of formation and its genesis as metasomatic replacement (R-type). The Nishisonogi jadeitite is characterized by jadeite with a quartzinclusion-rich core and quartz-free rim. The pressure-temperature (P-T ) conditions of the Nishisonogi jadeitite is constrained by the assemblage of jadeite + quartz and of clinozoisite + paragonite + quartz. The jadeitite occurs as tectonic blocks in a sepentinite mélange together with metasomatic rocks such as omphacitite, albitite and zoisite rock. The protolith of the jadeitite is likely plagiogranite or adakitic granite as suggested by the rare earth element (REE) pattern of zircon. The zircon has a euhedral core with a U-Pb age of 126 ± 6 Ma with exhibiting sharp and flat boundary with metamorphic rim, which has a U-Pb age of 84 ± 6 Ma. The rim age is almost consistent with the 95-90 Ma age of the peak metamorphism of the coherent schists, as a host of the serpentinite mélange, as determined by 40 Ar/ 39Ar method applied to glaucophane and phengite. Some jadeitite blocks show lithological zonations with albitite and other rocks in scale of several tens of centimeters. These zonations likely formed in the stability field of albite during exhumation of the serpentinite mélange. The isocon analysis of whole rock compositions and the singular value decomposition analysis of mineral reactions show that SiO 2 , Na 2 O, and Fe 2 O 3 evolved from the jadeitite towards serpentinite according to the retrograde reactions.

Determination of reaction kinetics using grain size: An application for metamorphic zircon growth

“…Zircons from the pelitic schists of the Nishisonogi unit (Nishiyama, Mori, & Shigeno, ) of the Nagasaki Metamorphic Complex on the Nishisonogi Peninsula, Kyushu, southwest Japan, were used for our experiments (Figure ). The Nagasaki Metamorphic Complex represents the western extension of the Sanbagawa Metamorphic Complex that extends along the Japanese islands for approximately 1,000 km (Miyazaki, Ozaki, Saito, & Toshimitsu, ) and is a typical high‐pressure and low‐temperature, intermediate‐type metamorphic complex.…”

“…The Nagasaki Metamorphic Complex represents the western extension of the Sanbagawa Metamorphic Complex that extends along the Japanese islands for approximately 1,000 km (Miyazaki, Ozaki, Saito, & Toshimitsu, ) and is a typical high‐pressure and low‐temperature, intermediate‐type metamorphic complex. The Nishisonogi unit comprises pelitic schists with minor mafic schist, serpentinite, quartz schist and psammitic schist (Nishiyama, ; Nishiyama et al., ). The protolith of the pelitic schist is a mudstone containing carbonaceous material (CM).…”

Jadeitite (jadeite jade) from Japan: History, characteristics, and perspectives

“…Jadeite-rich metasomatic rocks and metasomatic jadeite veins cutting metamorphic rocks have been described from both Paleozoic and Mesozoic metamorphic belts in Japan [e.g., Kochi, Yatsushiro, Yorii, and Kamuikotan Gorge (Tsujimori, 2017;Nishiyama et al, 2017;Hirajima, 2017)]. Such local jadeitite veins and pods are normally associated with lawsonite blueschist localities, like the case in the Dominican Republic (Maresch et al, 2012) and Ward Creek (Banno et al, 2000).…”

Gem sparkles deep: Preface of the special issue on ‘Jadeite and jadeitite’

“…Based on the authors' experience in jadeitite study, current perspectives on jadeitite are also documented. Nishiyama et al (2017) present an invited review of the Nishisonogi jadeitites in the Nagasaki Metamorphic Complex. The authors summarize geochemical and geochronological data of the jadeitites with interpretations on their petrogenesis.…”

“…The JAMS invited two review articles on Japanese jadeitites (Tsujimori and Harlow, 2017;Nishiyama et al, 2017) and requested another four review articles (Tsujimori, 2017;Miyajima, 2017;Hirajima, 2017;Ohtani et al, 2017) from experts with JAMS membership. In addition, in response to a call for papers to the Japanese geoscience community, five research articles Goto et al, 2017;Fukuyama et al, 2017;Takahashi et al, 2017;Sakamaki, 2017) were contributed from the authors and authors' groups conducting research on jadeite and jadeitite.…”