Evolution of volcanism and magmatism during initial arc stage: constraints on the tectonic setting of the Oman Ophiolite

Abstract

Based on detailed stratigraphy, petrology and geochemistry, the initial arc magmatism of the Oman Ophiolite consisting of tholeiitic lavas followed by boninite flows and tephras is studied in the Wadi Bidi area, northern Oman Mountains. An 1110-m-thick V2 sequence is divided into the lower 970 m (LV2) and upper 140 m (UV2) thick subsequences by a 1.0-m-thick sedimentary layer. Pahoehoe flows dominate in the lower part of the LV2, while the upper part consists mainly of sheet flows with sparse interbedded pelagic sediments and a cylindrical plug. In addition to the presence of a feeder conduit, the flow-dominant lithofacies with a few thin sedimentary interbeds in the LV2 indicates that the study area was the centre of a volcano grown in a short period. The UV2 is composed of boninite sheet flows overlain by a 2.0-m-thick pyroclastic fall deposit. A small amount of boninite lavas at the end of the V2 sequence overlain by thick pelagic sediments suggests that the subduction-related arc volcanism was short lived and terminated long before the ophiolite obduction.Supplementary material:Locations, mode of occurrence, phenocryst assemblages and bulk-rock major and trace element compositions of lavas in the Wadi Bidi area are available at http://www.geolsoc.org.uk/SUP18684.

Reply to referee Y. Kusano's comment

“…In fact, V2-I rather appears to correspond to the Tholeiitic Alley unit, as suggested by the alongstrike continuity of V2-I described by Godard et al (2003). Lavas directly comparable to V2-II were not recovered during this study nor by Kusano et al (2014). However, as noted by Kusano et al (2014), the spoon-shaped incompatibleelement patterns of V2-II fit those of an evolved Boninitic or "Transitional Alley" lava ( Fig.…”

“…While Boninitic Alley and Tholeiitic Alley have previously been grouped on the basis of their appearance and stratigraphic intercala- Figure 2. Semail ophiolite volcanostratigraphy with capping pelagic sediments (Suhaylah Formation) and sheeted dyke complex (SDC), with approximate stratigraphic thicknesses revised according to field observations in this study after Alabaster et al (1982), Gilgen et al (2014), and tions, their source composition and geochemical fractionation trends are clearly distinct from one another (Gilgen et al, 2014;Kusano et al, 2014), thereby justifying their definition as distinct volcanostratigraphic units.…”

Petrology of mantle diopsidite from Wadi Fizh, northern Oman ophiolite: Cr and REE mobility by hydrothermal solution

“…They were possibly derived from the seawater or of magmatic origin, however, their genesis is still enigmatic because of the complex history of the Oman ophiolite since its generation at a mid-ocean ridge to obduction onto the Arabian Peninsula through an intra-oceanic subduction zone (e.g. Lippard et al 1986;Nicolas et al 2000;Cowan et al 2014;Kusano et al 2014).…”

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

“…On the other hand, LSB crystallization sequence is controlled by olivine and clinopyroxene fractionation (Kostopoulos and Murton, 1992;Natland, 1982). LSB 30 differentiation series is typified by suites from northern Zambales, Holes U1439 and U1442 of Expedition 352 and Hole 458, ODP Leg 60 (Meijer, 1982;Sharaskin, 1982 (Reagan & Meijer, 1984), Tonga Trench (Falloon et al, 2007;Falloon and Crawford, 1991), Troodos ophiolite (Cameron, 1985;König et al, 2008;Osozawa et al, 2012;Pearce & Robinson, 2010) and Oman ophiolite (Ishikawa et al, 2002;Kusano et al, 2017;Kusano et al, 2014;Nagaishi, 2008).…”