Izu–Bonin–Mariana arc

The IBM arc system lies along the eastern margin of the Philippine Sea plate in the Western Pacific Ocean.

The consequent thin sedimentary cover makes it much easier to study arc infrastructure and determine the mass and composition of subducted sediments.

Active hydrothermal systems found on the submarine parts of IOCMs give us a chance to study how many of Earth's important ore deposits formed.

The trench is moving towards Eurasia, although a strongly extensional regime is maintained in the IBM arc system because of rapid PH-EU convergence.

Back-arc basin spreading is thought to be due to the combined effects of the sea-anchor force and rapid PH-EU convergence (Scholz & Campos 1995).

The IBM subduction zone began as part of a hemispheric-scale foundering of old, dense lithosphere in the Western Pacific (Stern & Bloomer 1992).

The beginning of true subduction localized the magmatic arc close to its present position, about 200 km away from the trench, and allowed the sub-forearc mantle to stabilize and cool.

Spreading also began in the northernmost part of the IBM arc about 25 Ma and propagated south to form the Shikoku Basin.

The Bonin segment to the south of the Sofugan Tectonic Line contains mostly submarine volcanoes and also some that rise slightly above sealevel, such as Nishino-shima.

The highest elevations in the IBM arc (not including the Izu Peninsula, where IBM comes onshore in Japan) are found in the southern part of the Bonin segment, where the extinct volcanic islands of Minami Iwo Jima and Kita Iwo Jima rise to almost 1000 m above sealevel.

Volcanoes erupting lavas of unusual composition – the shoshonitic province – are found in the transition between the Bonin and Mariana arc segments, including Iwo Jima.

The Mariana Trough shows marked variations along strike, with seafloor spreading south of 19°15’ and rifting farther north.

The forearc region is very narrow and the intersection of backarc basin spreading axis with the arc magmatic systems is complex.

The next section discusses some modifications of the lithosphere just prior to its descent and the age and composition of oceanic crust and sediments on the Pacific plate adjacent to the trench.

Each of these lineation sets comprises M-series (mid-Jurassic to mid-Cretaceous) magnetic anomalies that are essentially "growth rings" of the Pacific plate.

These anomaly sets indicate that the small, roughly triangular Pacific plate grew by spreading along three ridges (Bartolini & Larson 2001).

ODP site 801 lies on seafloor that isconsiderably older than M29 and the MORB basement there yields Ar-Ar ages of 167±5 Ma (Pringle 1992).

The oldest sediments at site 801C are middle Jurassic, Callovian or latest Bathonian (~162 Ma; Gradstein, Ogg & Smith 2005).

This occurred during mid-Cretaceous time, a ~35–40 Ma interval characterized by a lack of magnetic reversals known as the Cretaceous Superchron or Quiet Zone.

The compositions of sediments being subducted beneath the northern and southern parts of the IBM arc are significantly different, because of the Cretaceous off-ridge volcanic succession in the south that is missing in the north.

Castillo, Pringle & Carlson 1994 suggest that this province may reflect the formation of a mid-Cretaceous spreading system in the Nauru and East Mariana basins.

This crust is overlain by a 3 m thick, bright yellow hydrothermal deposit and about 60 m of alkali olivine basalt, 157.4±0.5 Ma old (Pringle 1992).

Spatial patterns of seismicity are essential for locating and understanding the morphology and rheology of subducting lithospheric slabs, and this is particularly true for the IBM Wadati–Benioff zone (WBZ).

More recently, Engdahl, van der Hilst & Buland 1998 provided an earthquake catalog containing improved locations (Figure 10).

They propose that transformational faulting, which occurs when metastable olivine changes to a more compact spinel structure, produces this zone of seismicity.

Samowitz & Forsyth 1981 suggested that unbending or thermal stresses in the upper 150 km of the slab may the primary cause of the seismicity.

They interpreted data from S to P converted phases and thermal modeling to propose that the DSZ results from transformational faulting of a metastable olivine wedge in the slab.

Bathymetry of the Mariana arc region (Baker et al. 2008), showing all 51 edifices presently named along the volcanic front between 12°30’N and 23°10’N.

Baker et al. 2008 estimated that intraoceanic arcs combined may contribute hydrothermal emissions equal to ~10% of that from the global mid-ocean ridge system.

The brown tree snake was accidentally introduced during World War II and has since devastated native birds on Guam.