Geochemistry of metasomatized peridotites above subducting slab: a case study of hydrous metaperidotites from Happo-O'ne complex, central Japan

Abstract

Hydrous peridotites from the Happo -O'ne area in central Japan, which form a serpentinite mélange in the high -P/T Renge metamorphic belt, vary from depleted lherzolites to harzburgites with subordinate dunite that contains primary chromian spinel with Cr# = 0.72 on average. Systematic variations of major and trace elements of bulk -rock compositions possibly resulted from various degrees of partial melting experienced by their protoliths (15% to <30% fractional melting). Some hydrous peridotites from the tremolite zone are representatives of the mantle peridotite facies with Ti -rich chromian spinel (up to 5.7 wt% TiO 2 ), and these peridotites have the same compositions as other peridotites except for enrichment in Na 2 O, Ba, and Ti. Their bulk rocks show U -shaped PM (primitive mantle) -normalized REE (rare earth elements) patterns (0.05 -0.5 times PM) and are enriched with Cs, Pb, Sr, Ba, and Rb (0.2 -20 times PM), indicating metasomatism by fluids derived from the subducting slab. The hydrous peridotites contain low amounts of Zr, Hf, Ta, and Nb (HFSEs), which possibly indicate that metasomatizing melts are not involved. These results are confirmed by in -situ analysis of tremolites that show U -shaped REE patterns (0.1 -3 times PM) and are highly enriched with fluid -mobile elements (B, Li, Cs, Sr, and Pb; 1 -100 times PM) and Sc relative to HFSEs.Keywords: Bulk -rock compositions, Hydrous metaperidotites, Tremolites, Happo -O'ne, Japan INTRODUCTIONThe characteristics of trace elements of the mantle wedge reveal the nature of metasomatic fluids or melts derived from the subducting slab (e.g., Maury et al., 1992). Mantle -wedge peridotites are expected to be metasomatized by slab fluids/melts according to the temperature distribution of subduction zones (e.g., Kawamoto, 2006). Mantlewedge peridotites hydrated by slab -derived fluids are enriched in LILEs (large ion -lithophile elements) and depleted in HFSEs (high -field -strength elements) (e.g., Scambelluri et al., 2004; Marrochi et al., 2007). Peridotites from Happo -O'ne, central Japan, which have been metamorphosed to various degrees along with associated high -P/low -T metamorphic rocks, are a good analogy to mantle -wedge peridotites just above the slab. We focus mainly on peculiar hydrous peridotites with Ti -rich chromian spinel from the tremolite zone (cf., Khedr and Arai, 2009), which are possible representatives of some part of the mantle wedge above the slab. The aim of this study is to further unravel the petrogenesis of these hydrous peridotites with Ti -rich chromian spinel and to provide important information about the nature of slab -derived fluids and enrichment processes occurring within the mantle wedge. GEOLOGICAL SETTING AND PETROGRAPHYThe Happo -O'ne complex is located in the northeastern part of the Hida Marginal Tectonic Zone on Honshu Island, central Japan (Nozaka, 2005 and references therein). Happo -O'ne peridotites, which are hydrated to various degrees, are partly massive in the central part and foliated in the marginal part,...

The blueschist-associated perovskite-andradite-bearing serpentinized harzburgite from Dobšiná (the Meliata Unit), Slovakia

“…Low-degree batch melting (E2 event) could not influence the REE (especially the HREE) and HFSE contents sufficiently. An increased content in Cs and Ba is usually interpreted as an impact of slab-derived (metamorphic) fluids (Scambelluri et al 2004;Khedr and Arai 2009). Therefore these signatures in the studied samples should be the result of the E3 and E4 events.…”

“…Perovskite was however also found from medium-to low-temperature reaction domains between the chemically contrasting rocks metamorphosed in blueschist to eclogite facies, as reported further. Alteration and reaction-metasomatic zones in ultramafics are reliable indicators of fluid-rock interaction processes (Grégoire et al 2001;Scambelluri et al 2004Scambelluri et al , 2006Khedr and Arai 2009;Kodolányi et al 2012;Uysal et al 2012). For example, abyssal peridotites are generally strongly affected by oceanic (seafloor) hydrothermal alterations like serpentinization (Bodinier and Godard 2007).…”

Perovskite, reaction product of a harzburgite with Jurassic– Cretaceous accretionary wedge fluids (Western Carpathians, Slovakia): evidence from the whole-rock and mineral trace element data

“…Our samples, enriched in LREE(La,Ce), Cs, ±Ba, U, Nb, Pb, As, Sb, ±Nd and Li in comparison with HREE, Rb and Sr (Fig. 7a, b) can therefore be interpreted as having been overprinted by slab-derived metamorphic fluids (e.g., Scambelluri et al 2004Scambelluri et al , 2014Khedr & Arai 2009;Putiš et al 2012). Our LA-ICP-MS mineral study revealed behaviour of trace elements during the harzburgite alterations in relationship to Prv genesis.…”

“…Element mobility in accretionary wedges using the LA-ICP-MS data was searched, for example, by Scambelluri et al (2004Scambelluri et al ( , 2014 and Khedr & Arai (2009) in HP peridotites and serpentinites with implications for fluid processes and trace-element recycling. Kodolányi et al (2012) investigated fluid-rock interaction processes in ocean floor and fore-arc serpentinites.…”

飛騨外縁帯，小滝地域の超苦鉄質岩：大江山オフィオライトかんらん岩とその変成作用について

“…CaCa-NaNa- Ishizuka, 1980Ishizuka, , 1987 Na Type 2 Na K , Ozawa, 1988;Ohara and Ishii, 1998;Zanetti et al, 1999;Chen and Zeng, 2007;Spandler et al, 2008 Khedr andArai 2009 , Na Evans, 1977Arai, 1975, 1984;Nozaka, 2003Nozaka, , 1951Fujimaki and Yomogida, 1986 …”