Did boninite originate from the heterogeneous mantle with recycled ancient slab?

Abstract

Boninites are widely distributed along the western margin of the Pacific Plate extruded during the incipient stage of the subduction zone development in the early Paleogene period. This paper discusses the genetic relationships of boninite and antecedent protoarc basalt magmas and demonstrates their recycled ancient slab origin based on the T-P conditions and Pb-HfNd-Os isotopic modeling. Primitive melt inclusions in chrome spinel from Ogasawara and Guam islands show severely depleted high-SiO 2 , MgO (high-silica) and less depleted low-SiO 2 , MgO (low-silica and ultralow-silica) boninitic compositions. The genetic conditions of 1 346 C at 0.58 GPa and 1 292 C at 0.69 GPa for the low-and ultralow-silica boninite magmas lie on adiabatic melting paths of depleted mid-ocean ridge basalt mantle with a potential temperature of 1 430 C in Ogasawara and of 1 370 C in Guam, respectively. This is consistent with the model that the low-and ultralow-silica boninites were produced by remelting of the residue of the protoarc basalt during the forearc spreading immediately following the subduction initiation. In contrast, the genetic conditions of 1 428 C and 0.96 GPa for the high-silica boninite magma is reconciled with the ascent of more depleted harzburgitic source which pre-existed below the Izu-Ogasawara-Mariana forearc region before the subduction started. Mixing calculations based on the Pb-Nd-Hf isotopic data for the Mariana protoarc basalt and boninites support the above remelting model for the (ultra)low-silica boninite and the discrete harzburgite source for the high-silica boninite. Yb-Os isotopic modeling of the high-Si boninite source indicates 18-30 wt% melting of the primitive upper mantle at 1.5-1.7 Ga, whereas the source mantle of the protoarc basalt, the residue of which became the source of the (ultra)low-Si boninite, experienced only 3.5-4.0 wt% melt depletion at 3.6-3.1 Ga, much earlier than the average depleted mid-ocean ridge basalt mantle with similar degrees of melt depletion at 2.6-2.2 Ga. K E Y W O R D Sancient slab recycle, boninite, depleted mid-ocean ridge basalt mantle, mantle heterogeneity, Mariana forearc, Ogasawara forearc, Pb-Nd-Hf isotopes, Re-Os model age | INTRODUCTIONThe upper mantle is mainly composed of the depleted mid-ocean ridge basalt (MORB) mantle (DMM), which was considered to be a relatively uniform reservoir through stirring and homogenization by convection for over 4 billion years, at least in major element terms (Allégre, 2002;Tatsumi, 1995). On the contrary, accumulating evidence of isotopic and trace element observations indicates that the DMM is heterogeneous consisting of fertile and refractory peridotites including recycled crust (e.g. Allégre, 2002;Walker, 2016;Zindler & Hart, 1986;Zindler, Staudigel, & Batiza, 1984 Nowell, & Noble, 1999). The radiogenic affinity of the Indian-type mantle is ascribed to time-integrated contamination of plumes that brought up the remnants of subducted slab beneath the Gondwana continent (Anderson, 1982;Staudigel et al., 1991) o...

Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics

“…The estimated parent magma requires cpx-undersaturated melting at an approximate pressure of 1 GPa (Fig. 3), well within error of the 0.96 GPa calculated by Umino et al (2017).…”

Editorial for Special Issue “Petrology, Geochemistry and Mineralogy of the Mantle as Tools to Read Messages from the Earth’s Interior”

“…This work is successful in that it succeeded in locating boninite magma production in the MTZ for the first time. This is consistent with the recent result on boninite genesis from erupted boninitic magmas [25,26].…”

Boninite and boninite-series volcanics in northern Zambales ophiolite: doubly vergent subduction initiation along Philippine Sea plate margins

“…In succeeding discussions, all samples are normalized to 100 % volatile free with total Fe recalculated as FeO * to enable comparison with compiled datasets. (Vollmer, 2015). Bedding plane orientations in Google Earth (Digital Globe, CNES/Astrium) images, viewed from southeast direction, are visualized using the S2K macro (Blenkinsop, 2012).…”