Peridotite xenoliths from the Takeshima seamount, Japan: an insight into the upper mantle beneath the Sea of Japan

Abstract

The Sea of Japan is one of the back arc basins distributed around the western rim of the Pacific. Nature of the plume for back arc basin (= BAB) opening is unknown partly because petrological characteristics of the BAB mantle are not well known compared with mid ocean ridge (= MOR) mantle.Peridotite xenoliths in an alkali basalt dredged from the Takeshima seamount (tentative name), ca. 230 km to the north of Oki islands, are examined to clarify the petrological feature of the Japan Sea mantle. They are spinel bearing lherzolite to harzburgite with equigranular to porphyroclastic textures. They can be classified into two types (Type 1 and Type 2 peridotites) in terms of REE (= rare earth elements) patterns of clinopyroxene (= cpx). Type 1 peridotites (Cr# of spinels, 0.4 0.5) are similar to abyssal peridotites in terms of major element chemistry and middle to heavy REE concentrations of cpx. The cpx in the former shows slight enrichment of LREE (= light REE), which is apparently due to metasomatism by slab derived fluids/melts. Type 2 peridotites have high REE cpx with flat to slightly LREE enriched patterns, and are quite similar to subcontinental peridotites obtained as xenoliths from China. The southern part of the Sea of Japan was formed by mainly thinning and rifting of the continental lithosphere. Type 2 peridotites are a remnant of the continental lithospheric mantle.Chemical characteristics of BAB basalts and Type 1 peridotites indicate that open system melting of peridotite affected by a flux from the downgoing slab was involved in the Japan Sea opening.

Trace element and Sr-Nd isotopic features of ultramafic xenoliths from Kurose, Southwest Japan

“…The flat to V -shaped KR375, KR202, and published clinopyroxene patterns are similar to clinopyroxene patterns of Type I Takeshima seamount xenoliths ( Fig. 2B; Ninomiya et al, 2007). The LREE enrichment cannot be explained by a simple partial melting event.…”

“…The clinopyroxene of the most fertile sample KR120 Ohara et al, 2002Ohara et al, , 2003, and Type I Takeshima seamount xenoliths (Ninomiya et al, 2007).…”

Insights into Petrological Characteristics of the Lithosphere of Mantle Wedge beneath Arcs through Peridotite Xenoliths: a Review

“…In addition, we report data for mantle xenolith localities within the Sea of Japan, one of the back-arc basins of the Western Pacific, including Oki-Dogo island, which has been interpreted as a remnant of continental lithosphere off the coast of Honshu (Takahashi, 1978a;Abe et al, 2003). Ninomiya et al (2007) reported peridotite xenoliths from a small seamount in the Sea of Japan.…”

Alkali basalt from the Seifu seamount of the Japan Sea: post-spreading magmatism in the back-arc region

“…The basalt sample contains peridotite xenoliths with variable size from a few millimetres to usually < 3cm (up to 10 10 cm) and their-derived xenocrysts (Ninomiya et al, 2007). The basalt sample shows porphyritic texture.…”

“…A basaltic block containing peridotite xenoliths was dredged from the Seifu Seamount (Ninomiya et al, 2007), located at northeast of the Tsushima Basin in the southwest Japan Sea (Fig. 1).…”