Serpentinization and blueschist-facies metamorphism beneath the Mariana forearc

DOI Web Site Web Site 2 Citations 39 References

Bibliographic Information

Other Title
  • マリアナ前弧域直下の蛇紋岩化作用と低温高圧型変成作用
  • マリアナ ゼン コイキ チョッカ ノ ジャモンガンカ サヨウ ト テイオン コウアツガタ ヘンセイ サヨウ

Search this article

Abstract

<p>A zone of dome-shaped diapiric seamounts occurs along the trench axis in the Mariana forearc. The seamounts mainly comprise blocks of serpentinized peridotite of varying sizes and fine-grained serpentinite matrix. The serpentine minerals are mostly chrysotile and/or lizardite, but antigorite is also found in peridotites recovered from the Raijin, Conical, Twin Peaks, Big Blue, Celestial, and South Chamorro seamounts. Antigorite is commonly associated with iron-rich secondary olivine (Fo86–89) as rim overgrowths or along the cleavage traces of primary olivine (Fo90–92). The assemblage is indicative of high-temperature serpentinization at ~500°C. Chrysotile and/or lizardite veins, both predating and postdating antigorite formation, are also present in antigorite-bearing samples. This may reflect a complex serpentinization history, suggesting the tectonic migration of serpentinized peridotites from the shallow mantle wedge to greater depths, and then back to the surface. Blueschist-facies rocks recovered from the Conical, Twin Peaks, and South Chamorro seamounts have a variety of mineral assemblages and chemistries, suggesting a wide range of metamorphic conditions, but all formed under low-temperature, blueschist-facies conditions (150–300°C, 0.5–0.7 GPa). The protolith of some blueschist-facies clasts from the Twin Peaks Seamount was amphibolite. The clasts contain metamorphic pargasite, Al-rich epidote and rutile, which are indicative of higher-grade epidote-amphibolite-facies metamorphism prior to blueschist-facies metamorphism. It is likely that these samples were initially metamorphosed at depths of ca. 40 km within the subduction zone, and then ascended along the subduction boundary to depths of 20–25 km, where they were metamorphosed under blueschist-facies conditions. Although the progressive metamorphic evidence cannot be detected from metamorphic rocks, the P-T histories obtained from the serpentinized peridotites and metamorphic rocks are broadly consistent, implying that both the serpentinized peridotites and metamorphic rocks experienced similar transport histories within the subduction zone.</p>

Journal

Citations (2)*help

See more

References(39)*help

See more

Keywords

Details 詳細情報について

Report a problem

Back to top