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

Abstract

Abstract. A key component of subduction initiation rock suites is boninite, a high-magnesium andesite that is uniquely predominant in western Pacific forearc terranes and in select Tethyan ophiolites such as Oman and Troodos. We report, for the first time, the discovery of low-calcium, high-silica boninite in the middle Eocene Zambales ophiolite (Luzon Island, Philippines). Olivine–orthopyroxene microphyric high-silica boninite, olivine–clinopyroxene–phyric low-silica boninite and boninitic basalt occur as lapilli fall deposits and pillow lava flows in the upper volcanic unit of the juvenile arc section (Barlo locality, Acoje Block) of the Zambales ophiolite. This upper volcanic unit overlies a lower volcanic unit consisting of basaltic andesite, andesite to dacitic lavas and explosive eruptive material (subaqueous pahoehoe and lobate sheet flows, agglutinate and spatter deposits) forming a low-silica boninite series. The overall volcanic stratigraphy of the extrusive sequence at Barlo resembles holes U1439 and U1442 drilled by IODP Expedition 352 in the Izu–Ogasawara (Bonin) trench slope. The presence of depleted proto-arc basalts in the Coto Block (45 Ma) (Geary et al., 1989), boninite and boninite series volcanics in Barlo (Acoje Block (44 Ma)) and simultaneous and post-boninite moderate-Fe arc tholeiites in Sual and Subic areas of the Acoje Block (44–43 Ma) indicate that the observed subduction initiation stratigraphy in the Izu–Ogasawara–Mariana forearc is also present in the Zambales ophiolite. Paleolatitudes derived from tilt-corrected sites in the Acoje Block place the juvenile arc of northern Zambales ophiolite in the western margin of the Philippine Sea plate. In this scenario, the origin of Philippine Sea plate boninites (IBM and Zambales) would be in a doubly vergent subduction initiation setting.

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].…”

Subduction initiation from the earliest stages to self-sustained subduction: Insights from the analysis of 70 Cenozoic sites

“…Arc volcanism landward of Cotabato Trench belongs to the Sangihe Arc (Molucca Sea long-lived slab and not the <100 km-long Celebes Sea slab) according to Hall (2018). Perez et al (2018) , 1998). Failure within the Philippine Sea plate started either near Mindanao, propagating in both directions (Lallemand et al, 1998) or in the north, propagating southward (Macpherson, 2008).…”

Sluggish Slab Rollback at the Early Stage of Flux Melting During Subduction Initiation: Li Isotopic Evidence From the Coto High‐Al Chromite Deposit, Zambales Ophiolite, Philippines

“…Although the effects of slab components on the Li isotopic systems of sub‐arc mantle vary among different subduction zones, as revealed by the δ 7 Li values of arc lavas (∼−7‰ to +12‰; Figure 4c; Agostini et al., 2008; Chan et al., 2002; Elliott et al., 2004; Moriguti & Nakamura, 1998; Tang et al., 2010; Tomascak et al., 2000, 2002), addition of slab‐derived materials is the primary way of causing large‐scale heavy Li isotopic anomalies in the mantle. Given that the Coto block is thought to have a SI origin and was generated in a proto‐forearc setting (Geary et al., 1989; Perez et al., 2018; Yumul et al., 2020), the high‐δ 7 Li components required in the mantle sources of the high‐Al chromitites can be reasonably attributed to slab components.…”

“…However, systematic investigations show the two blocks are more likely different parts of the same oceanic fragment with transitional compositions (Geary et al, 1989). Although the Zambales blocks were dated to be formed at middle Eocene (46-44 Ma), they were possibly developed in the context of pre-Eocene lithospheres according to tectonic configuration (Perez et al, 2018;Wu et al, 2016), which can also be partly supported by the observation that the ophiolite is spatially bounded by a Western Mesozoic ophiolite belt and an Eastern Mesozoic-Eocene ophiolite belt (Queaño et al, 2017).…”

“…Especially, the MORB‐like rocks show subduction‐related features, for example, Nb‐Ta negative anomalies in spider diagram, indicating that they were generated at a spreading center with a slab below rather than at a typical MOR setting (Yu, 2015). By contrast, volcanic rocks in the adjacent younger Acoje block are mainly made of IAT and boninitic lavas at the lower and upper lava sequences, respectively, with boninites occurring as pillow lavas at the topmost sequence (Perez et al., 2018). Compared with the magmatism developed at different spreading settings (e.g., MOR, back‐arc basin, and proto‐forearc), such rapid continuous compositional variation of magmas in the Zambales ophiolite is best explained as the result of evolving magmatism in a proto‐forearc setting (Geary et al., 1989; Perez et al., 2018), consistent with the evolution trends of magmatism developed in the classical Troodos ophiolite, Oman ophiolite and the infant IBM arc (Whattam & Stern, 2011).…”