aims of the project

The aim of IGCP project 524 is the study of processes that occur in zones of collision between volcanic island arcs and continental margins in both fossil and active settings, with the objective of developing a general model for arc-continent collision. The key questions to be investigated include, but are not limited to;

1. Deep crustal and mantle structure through geophysical imaging.
2. Processes that take place deep within the subduction channel once the continental crust has entered the subduction zone (i.e. the subduction and exhumation of material as medium- or high-pressure rocks).
3. Continued evolution of the arc during collision (i.e. what deep-seated processes affect the retreat of the volcanic front to outboard of the subduction zone and the changes to the chemical composition of the volcanism).
4. Response of the continental crust to the collision (i.e. development of an accretionary complex above a basal detachment or whole-crustal failure).
5. Erosion of the developing mountain belt and the formation of a foreland and a suture forearc basin.
6. Emplacement of oceanic material in the form of ophiolite massifs.
7. Place constraints on the duration of arc-continent collision orogeny.

The project will also investigate the impact these collisions have (or have had) for human society in terms of economic development and geological risk. Zones of arc-continent collision are producers of much of the worlds economic wealth, especially gold, copper, and molybdenum, and are primary targets for exploration companies involved in the search for base and precious metals. The growing demand for these commodities has stimulated increasing exploration in third world countries and this in turn is speeding up their economic developemnt by catylysing transitoin to first world legal systems of tenement and mining law. It speeds up infrastructure development. It also leads to companies needing to manage risk to find world class deposits in countries with little infrastructure or an uneducated workforce. While models for the location and geochemical development of volcanic-hosted massive sulfide deposits in island arcs are very evolved, it is only recently that researchers have begun to place these deposits in a geodynamic context. IGCP 524 will investigate:

1. The timing of mineral deposit formation within the context of arc-continent collision.
2. The significance of the subduction of continental crust on the metals present in the various types of deposit
3. The effect that the entry of the continental crust into the subduction zone has on the generation of melting, fluid pathways, and deposit formation by causing stress reorientations in the colliding arc.

Finally, zones of active arc-continent collision are among some of the most populated in the world, as well as among the most seismically active. They are, therefore, zones of potentially high geological risk since a large magnitude earthquake in these areas could cause widespread human and economic damage. For example, seismic shaking and landsliding caused by the 1999 Chi-Chi earthquake in Taiwan killed an estimated 2,400 people and caused widespread damage to infrastructure. Also, the earthquake-generated sediment slump that caused the 1998 Papua New Guinea tsunami that killed more than 6,000 people occurred in the forearc region of the Finisterre arc that is actively colliding with the margin of Australia. IGCP 524 will investigate:

1. How the response of the continental crust to subduction (for example, whole crustal failure versus formation of a detachment level) affects the distribution of seismicity in the developing mountain belt.
2. What the effect of the crustal response is on the development of topography and landslide risk
3. Study seismically generated sedimentary deposits in both fossil and active collisions zones to assess tsunami risk.

To achieve the aims of the project, an international, multidisciplinary group of geoscientists has been put together whose expertise covers many aspects of plate tectonic processes, mineral deposit formation and geological risk assessment. Three field laboratories have been identified and a field excursion and conference will be held in each over the three year duration of the project. These field laboratories are; the Southern Urals of Russia, the north Caribbean margin (in particular Cuba), and Taiwan. These three examples represent arc-continent collisions that occurred over geological time, ranging from the Paleozoic (Urals) through the Mesozoic (Cuba), to currently active (Taiwan). By combining studies of fossil (inactive) and active arc-continent collision zones, insights will be gained into what happens at the surface (using currently active collision zones) and what happened at depth (using old, eroded collision zones). Well-constrained fossil arc-continent collision orogens can supply the third and fourth dimension (depth and time) that are generally missing from currently active examples. In active examples it is possible to observe tectonic processes, such as subduction, that is generally not available in older mountain belts. The integration of research on both active and fossil arc-continent orogens will provide key data for the understanding of how plate tectonics works today, and how it might have worked in the past.