Petrological Characteristics of Peridotites from Serpentinite Seamounts in the Izu-Ogasawara-Mariana Forearc.

Abstract

Serpentinite diapiric seamounts have been reported exclusively from the forearc region of the Izu-Ogasawara-Mariana (hereafter, IOM) arc-trench system. This indicates that most mantle peridotites from these seamounts are residues derived from similar high degrees of partial melting related to the island arc volcanism.In contrast, mantle peridotites recovered from the southern Mariana exhibit wider range of compositions including more fertile peridotites, suggesting that they are residues of relatively lower degrees of partial melting. It is probable that they are related to volcanism that occurred during the formation of the back arc basin. Furthermore, mantle peridotites found in the Tonga forearc have wider compositional range than peridotites found in the IOM forearc region. These peridotites are considered to be derived from a layered sequence from upper crust through lower crust to the upper mantle rather than serpentinite diapiric

Dredge petrology of the boninite‐ and adakite‐bearing Hahajima Seamount of the Ogasawara (Bonin) forearc: An ophiolite or a serpentinite seamount?§

“…Several dredge hauls were also carried out by Tokai University (Kim et al . 2005), and two submersible dives along the northeast–southwest routes crossing the southern part of the seamount, using Shinkai 2000, were partly reported by Ishii et al . (2000) and Fujioka et al .…”

“…Spinel in harzburgite from northern KH80‐3‐32 and southern KH82‐4‐4 is Cr♯60–68 and Mg♯54–63, and spinel in dunite (KH82‐4‐4) is Cr♯57–61 and Mg♯61–62 (Ishii 1985). The peridotite samples obtained during two submersible dives (2K632 and 2K686) in the southern part of Hahajima Seamount bear spinels of highly diverse chemistry, Cr♯64–80 in 2K632 (southwestern site) and Cr♯50–70 in 2K686 (northeastern site) (Ishii 1986; Ishii et al . 2000).…”

“… Cr/(Al + Cr) − Mg/(Fe 2+ + Mg) relationship of spinels from the mantle harzburgite from Hahajima Seamount. The fields of spinels from the southern part of Hahajima Seamount (submersible samples; Ishii et al . 2000), Conical Seamount (Ishii et al .…”

“…(2005) reported that the Hahajima Seamount harzburgite gives a two‐pyroxene equilibration temperature (921°C) distinctly lower than that of MOR abyssal peridotite (1138°C), and bears various amphiboles ranging from edenitic hornblende to tremolite in composition. It can be said that the mantle peridotites of Hahajima Seamount are suitable as partial melting residues after production of IAT and boninitic magmas, later hydrated on cooling, but are not suitable for MORB residues (Ishii et al . 2000; Ishiwatari et al .…”

Evolution of the Earth as an andesite planet: water, plate tectonics, and delamination of anti-continent

“…The restite with and without 10 % olivine cumulate were then considered to be a possible crust/mantle component. The sub-IBM arc mantle was assumed to consist of harzburgite (Table 1) as it is commonly found as xenoliths in serpentine mud volcanoes in the IBM forearc (Ishii et al, 2000).…”