Intraoceanic unroofing of eclogite facies rocks in the Omachi Seamount, Izu-Bonin frontal arc

Abstract

Electron-microscope and electron-microprobe observations of amphibolites from the Omachi Seamount in the Izu-Bonin frontal arc show that they contain micrometer-sized inclusions of omphacite ؎ kyanite, indicating eclogite facies metamorphism. The garnetzoisite amphibolite was subjected to metamorphic conditions of 600-700 ؇C and ϳ2 GPa in the early stage of metamorphism. These metabasites were subducted to a depth of ϳ70 km beneath the Izu-Bonin arc and were exhumed together with serpentinite schist. Their intraoceanic unroofing was probably induced by backarc extension of the upper plate, whose axes were intersected and cooled by the newly formed Izu-Bonin subduction system. This intraoceanic exhumation associated with suprasubduction extension can be a modern analogue for ancient on-land eclogite terranes accompanied by ophiolites.

Subduction Zone Geodynamics

“…At the regional scale, a network of normal shear zone underline by sheared serpentinites or sheared metasediments separated several metabasite blocks recording contrasted P-T conditions. The possible exception is the eclogitic blocks of andesite origin dredged near the Omachi forearc serpentinite diapir (Izu-Bonin arc) (Ueda et al, 2004). CT: Costa Ticino; PG: Passo Galarino; LS: Lago Superiore; TU: Tour Real; VM: Viso Mozzo; SP: Basal Serpentinite; TU: (b) Geological and structural map of the Erro Tobio serpentine mélange (Southwestern Alps).…”

New interpretation of the Franciscan mélange at San Simeon coast, California: tectonic intrusion into an accretionary prism

“…The seamount consists of high-pressure metamorphic rocks entrained in serpentinite diapirs close to the Palaeogene volcanic front (Ueda et al 2004(Ueda et al , 2011. One serpentinite body is tens of kilometres in diameter (of mostly wehrlite and dunite origin, now largely serpentinized into antigorite schist), which is associated with garnet-hornblende schist with eclogitic facies relics (Ueda et al 2004(Ueda et al , 2011.…”

“…This strongly supports some shearing during diapiric intrusion of blueschist-bearing mélanges that were further intruded into turbidite beds of the trench accretionary prism body as discussed above. (2003), where it is applied to occurrences of serpentinite encasing high-pressure blocks of Ueda et al (2004Ueda et al ( , 2011 in the Izu forearc.…”

Serpentinite textural evolution related to tectonically controlled solid‐state intrusion along the Kurosegawa Belt, northwestern Kanto Mountains, central Japan

“…However, some serpentinite bodies lack any association with basaltic or ophiolitic rocks, and instead are found in association with high‐pressure metamorphic suites (blueschist to eclogite facies), commonly along fault zones (Fryer et al . 1999; Ueda et al . 2004).…”