Structural variations of arc crusts and rifted margins in the southern Izu‐Ogasawara arc–back arc system

Abstract

[1] We carried out a reflection/refraction seismic survey across the southern Izu-Ogasawara arc-back arc system, covering three arcs with different crustal ages. The oldest Eocene arc has middle and lower crust with high velocities of 6.4-6.6 and 6.8-7.4 km/s, respectively, suggesting denser crustal materials. The current volcanic arc has middle and lower crust with lower velocities of 5.7-6.5 and 6.7-7.1 km/s, suggesting advanced crustal differentiation. The crust-mantle transition layer, with a velocity of 7.5-8.0 km/s, is distributed beneath the current volcanic arc and the rear arc, suggesting a pool of dense materials emanating from the crust through the crustal growth. These structural differences between the Eocene arc and current arc indicate a difference of crustal growth based on basaltic and andesitic magmas according to known petrologic studies. Commonly, rifted crusts have lower crusts with high velocities of over 7.0 km/s, and the arc-back arc transition zone also has a thinner more reflective crust that may have been affected by postrifting magmatism.

Structural variation of the Bonin ridge revealed by modeling of seismic and gravity data

“…This observation strongly supports the view that forearc oceanic crust along the IzuBonin intra-oceanic arc was formed by forearc spreading during the initial stage of subduction (Kodaira et al, 2010). However, Kodaira et al (2010) pointed out that the seismic structure modeled to the north of Chichi-jima was not entirely consistent with the structure across the Bonin ridge reported by Takahashi et al (2009). The ridge-parallel profile of Kodaira et al (2010) and the cross-ridge profile of Takahashi et al (2009) intersect between Chichi-jima and Muko-jima, where the ridge-parallel profile shows a crust of about 10 km thickness, and the cross-ridge profile shows a crust of about 18 km thickness.…”

“…Since then, a series of high-resolution deep seismic studies in the IBM arc have presented new insights into the formation of arc crust Kodaira et al, 2010) and SPr2 (processed by Takahashi et al, 2009), respectively. Only the eastern half of line SPr2 (red solid line) was re-modeled in this study.…”

“…Kodaira et al (2008) proposed that the rear-arc crust is composed of a remnant arc crust that was separated from the volcanic front, probably in the Oligocene, and that most of the rear-arc crust was created before separation from the volcanic front. Takahashi et al (2009) provided an image from a seismic reflection/refraction profile across the central Izu-Bonin arc, which crossed three arcs of different ages: the Eocene forearc (Bonin ridge), the present arc (volcanic front), and the Oligocene rear-arc. For the Eocene arc crust, they observed seismic velocities of 6.4-6.6 and 6.8-7.4 km/s in the middle and lower crust, respectively, whereas those of the current volcanic front were slower (5.7-6.5 km/s for the middle crust and 6.7-7.1 km/s for the lower crust).…”

Subduction of the oceanic Hikurangi Plateau and its impact on the Kermadec arc

“…Tomography results from a trench-perpendicular ocean bottom seismometer array oriented east-west across the Kermadec trench to the Havre Trough at B37°S (refs 30,31) show zones of reduced seismic velocities (that is, Vp r7.8 km s À 1 compared with Z8 km s À 1 for mantle peridotite) beneath the arc front MOHO, consistent with Z10% of serpentenized mantle being present beneath the arc 44 . A similar B10-km thick crust-mantle transition layer with lower seismic velocities (that is, Vp ¼ 7.0-7.7 m s À 1 ) has also been identified beneath the Izu-Bonin-Mariana and Tonga arcs, interpreted to be composed of a mixture of crustal and mantle materials 45,46 . Likewise, beneath the central Taupo Volcanic Zone, a zone of reduced seismic velocities of ZVp ¼ 7.4 m s À 1 (Vp/Vs ¼ B1.87) extends from the Moho to the slab-mantle wedge interface suggesting diapirically rising hydrated and low density material 47 .…”

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

“…The mid-crustal layer is characterized by seismic velocities of around 6-6.5 km s −1 . This low velocity layer is often interpreted to be a layer of felsic to intermediate igneous rocks in many modern oceanic island arcs (South Sandwich; Leat et al, 2003; the Izu-Bonin-Mariana system; Kodaira et al, 2007a;Takahashi et al, 2007Takahashi et al, , 2009Tonga Arc;Crawford et al, 2003). The felsic mid-crustal unit is produced by repetitive anatexis of the mafic lower crust Rioux et al, 2010).…”