Why the Mariana Islands?

In 1998, the National Science Foundation launched the MARGINS program, a research venture that would explore the world's tectonic boundaries through a number of initiatives. One of those initiatives is called The Subduction Factory. Its goal is to understand how subduction zones around the world work and how they influence the chemistry and dynamics of the deep Earth, the crust at Earth's surface and even the living creatures inhabiting Earth.

Scientists assigned to the task chose two locations that they believe hold the greatest potential for yielding breakthroughs in the understanding of the Subduction Factory. In 2001, the Central American margin was targeted (See Volcano Expedition in Costa Rica) and work commenced on the string of volcanoes from the Mexico/Guatemala border through Honduras, El Salvador and Nicaragua to Costa Rica in the south.

This year many of the same researchers are examining the Izu-Bonin-Mariana (IBM) volcanic arc in the western Pacific. Both are subduction zones where material is both entering the Earth's mantle and being ejected from it in close proximity. The two selected areas have much in common but also several key differences:

• Unlike in Central America, where an oceanic plate is colliding with a continental plate, two oceanic tectonic plates are colliding with each other in IBM. This means there will be less contamination by continental plate material in the samples collected by the MARGINS team. It will make it easier for scientists to distinguish the effects of other forces on the materials produced by the zone.

• IBM is one of the few sites in the world that provides every aspect of subduction zones in one relatively small area. In addition to the convergent margin where the Pacific plate subducts under the Philippine plate, a divergent margin, or back-arc basin, where seafloor spreading takes place, lies to the west of the IBM volcano chain.

• At the IBM locale, the sedimentary section is almost completely subducted. It is also of different composition to Central America. This will allow the team to assess and contrast the influence of the down-going sediments in more detail.