UPDATE ON AN OVERVIEW OF RIDGE-TRENCH INTERACTIONS IN MODERN AND ANCIENT SETTINGS

Nearly fifty years ago, ridge subduction was proposed by Delong and Fox (1977) for the Kula ridge entering the Aleutian trench. This led to further investigations along the southern Alaskan margin partly by Terry Pavlis and many others. His work on their structural evolution set the stage for other studies that integrate this with other signatures. A summary of the effects of ridge subduction resulted in GSA Special Publication 371 covering from Kodiak Island, AK to Vancouver Island, B.C. A primary signature of ridge-trench interactions are changes to the magmatic history in the overriding plate such arc magma chemistry, a cessation in arc magmatism, forearc magmatism as well as systematic changes in magmatic age relationships. In addition, there may be forearc ophiolites, gold mineralization, hydrothermal activity, forearc slivers and possible microplate interactions and high temperature/low pressure metamorphism and melting in the forearc. There are also changes in the sub arc mantle. To this day, this is still the best studied example of relict ridge subduction recording many different signatures related to this process.

Since this overview, there has been a recognition of other processes such as cold seeps in hot regions and a change in altimetry of the arc. Recent work has discussed the angle the ridge enters the trench as it can range from a high angle to parallel to the trench. In addition, mantle tomography has been used to decipher present and past ridge-trench interactions in the Cordillera and elsewhere. Increased geochronologic work has led to changes in some of the detailed processes and also recognition of the Resurrection plate. Further south, dike orientations across the Cascades probably reflect transtension and ridge=trench interactions. In summary, work by Terry Pavlis and others has led to recognition of more than 30 other regions of ancient ridge subduction. These occur on every continent and range in age from the present back into the Archean.