Petrological diversity and origin of ophiolites in Japan and Far East Russia with emphasis on depleted harzburgite

Abstract

Ophiolites are divided into lherzolite-type (L-type) and harzburgite-type (H-type) by the lithology of their mantle peridotites. Rare depleted harzburgite-type (DH-type) is distinguished from the normal H-type by the more refractory nature of its mantle peridotite and the occurrence of orthopyroxene-type cumulate rocks including iron-rich harzburgite and orthopyroxenite. The Shelting (Sakhalin) and Krasnaya (Koryak Mountains) ophiolites in Far East Russia, which have both depleted harzburgite and orthopyroxene-type cumulate rocks, belong to this newly defined DH-type. The ophiolites in SW Japan-Primorye, NE Japan-Sakhalin, and the Koryak Mountains in the northwestern Pacific margin have diverse ophiolite types ranging from L- to DH-types. The wide petrological diversity, the common occurrence of DH-type, and the presence of thick crustal sections in these ophiolites suggest regionally inhomogeneous, commonly very high degrees of mantle melting over subduction zones, as in the modern Mariana forearc environment. The ophiolites of Japan and Far East Russia range in age from Early Palaeozoic to Cenozoic and are tectonically underlain by younger blueschists and accretionary complexes. The spatial association of these ophiolites with blueschists is analogous to the ophiolite-blueschist assemblages recovered from the Mariana forearc. This association might have formed in a period of non-accretion at an oceanic subduction zone that was followed by voluminous accretion of sediments, facilitating subsequent uplift of the ophiolites and blueschists.

Supra-subduction affinity in the Neoproterozoic serpentinites in the Eastern Desert, Egypt: Evidence from mineral composition

“…4). The highly depleted peridotite with high Cr# (>0.7) spinels can be produced in the mantle wedge beneath arcs or in plume-related within-plate mantle (Pearce et al, 1984;Arai, 1994;Ishiwatari et al, 2003). The TiO 2 content of spinel in the magma varies depending on the tectonic site of magma generation; TiO 2 is low in arc magma, intermediate in MORB and high in the intraplate magma (Arai, 1992).…”

“…The high Mg# accompanied by high contents of Ni, Cr and Co and depletion in the incompatible elements reflect the depleted and highly refractory nature of the parent rocks (Roberts, 1992). Moreover, the high Cr# of the disseminated chrome spinels combined with the high contents of Ni, Cr and Co in the bulk serpentinites suggest high degree of partial melting (Dick and Bullen, 1984;Arai, 1994;Ishiwatari et al, 2003).…”

Origin of magnetite veins in serpentinite from the Late Proterozoic Bou-Azzer ophiolite, Anti-Atlas, Morocco: An implication for mobility of iron during serpentinization

“…Vuollo et al, 1995;Ahmed et al, 2001;Gahlan et al, unpublished), and not uncommon in the Phanerozoic ones (e.g. England and Davies, 1973;Arai, 1997;Tamura et al, 1999;Ishiwatari et al, 2003 and references therein). The highly depleted Bou-Azzer mantle harzburgite with highCr# and low-TiO 2 spinel suggests mantle wedge or subarc mantle origin (e.g.…”

“…The high Ni, Cr and Co of the bulk serpentinites combined with the high Cr# (up to 0.8) of the intact spinels suggest high degrees of partial melting (e.g. Gü lacar and Delaloye, 1976;Dick and Bullen, 1984;Arai, 1994;Ishiwatari et al, 2003;Ahmed et al, 2005). The highly depleted harzburgite with high Cr# (P0.7) of spinel is very common to the Precambrian ophiolites (e.g.…”

The Neoproterozoic Abu Dahr ophiolite, South Eastern Desert, Egypt: petrological characteristics and tectonomagmatic evolution

“…Ahmed et al 2001 and references therein), and not uncommon in Phanerozoic examples (e.g. Ishiwatari et al 2003 and references therein).…”