Petrography and Geochemistry of the mantle xenoliths: Implications for lithospheric mantle beneath the Japan arcs

Abstract

Recent developments in instrumentation for in situ trace element analysis of peridotite minerals give us valuable data set of petrological and geochemical insights of the upper mantle. Here, we summarize petrographical, petrological and geochemical characteristics of mantle xenoliths from the Northeastern and Southwestern Japan arcs. They have clear correlations between microtexture and mineral compositions in terms of both major and trace elements. That suggests that influx assisted melt extraction occurs simultaneously with deformation/recrystalization in the upper mantle. Their characteristics of trace elements in clinopyroxene are distinguished from those of abyssal peridotite and peridotite xenoliths from continental regions. The geochemistry of Japan arcs clinopyroxenes have characteristics of arc type mantle source; i.e., low light rare earth element (LREE) and high field strength element (HFSE; Ti, Zr and so on), rather high heavy rare earth (HREE) relative to LREE elements and Sr concentrations. They also have a rather constant Ti/Zr ratio, variable REE patterns, and relatively low LREE/HREE ratios. The simple melt extraction model can not explain these characteristics. These features are due to metasomatism, which is different from carbonatite metasomatism.

Sulfide minerals in mantle xenoliths from the Kurose reef, Fukuoka Prefecture, Japan

“…In studies carried out on peridotite xenoliths from the Kurose reef, Abe and Arai (2005) suggested that the equilibrium temperature were in the range 900 -1100 °C on the basis of a two -pyroxene geothermometer (Wells, 1977). Since the samples of the present study were obtained from a geological environment similar to that described by Abe and Arai (2005), it is plausible that the lherzolite in the samples of this study crystallized at similar temperatures of 900 -1100 °C.…”

“…at temperatures >900 °C. On the basis of the equilibrium temperature (900 -1100 °C) of the Kurose mantle xenolith (Abe and Arai, 2005), it can be inferred that the sulfide inclusions of pentlandite were trapped as a sulfide liquid rather than in the solid phase. With decreasing temperature, the solid phase precipitated from the sulfide liquid.…”

“…The Fo# of olivine is 90.3 -90.7; this value is in accordance with the value obtained in a previous study of Kurose samples (Arai et al, 2001). Abe and Arai (2005) revealed that these peridotites were formed at temperatures between 900 and 1100 °C.…”

Constraints on the three-dimensional thermal structure of the lower crust in the Japanese Islands

“…We set Ichinomegata and Aratoyama as respective reference points for northeastern and southwestern Japan, and set the equilibrium temperatures to 950 • C and 1050 • C, respectively, using the research result of Arai et al (2007) as a reference. In most cases, the mantle xenoliths obtained in the Japanese Islands were spinel peridotite (Abe and Arai, 2005), which stably exists in the depth range shallower than about 60 km according to a P-T diagram (e.g., Gill, 2010). Therefore, we set the representative depth, at which the mantle xenoliths in the Japanese Islands had existed, to 45 km as the intermediate depth between the Moho boundary (about 30 km) and 60 km.…”

Lower crustal metasomatism inferred from mafic xenoliths from Ichinomegata crater, Northeast Japan arc

“…Xenoliths from the mantle wedge Arai and Ishimaru, 2008) have recorded mantle metasomatism (e.g., Arai and Kida, 2000;Abe and Arai, 2005;Ishimaru et al, 2007;Kawamoto et al, 2013). It is well known that ultramafic-mafic xenoliths from Ichinomegata, Northeast Japan arc, contain hydrous minerals (e.g., Kuno, 1967), some of which are of secondary origin (Arai and Saeki, 1980;Takahashi, 1986).…”