SLAB WINDOWS: FROM UNDERSTANDING THE CENOZOIC TO SOLVING THE PRECAMBRIAN (Invited Presentation)

Appealing to ridge subduction as a way to explain anomalies of convergent plate margins began in the 1970s. Early workers focused on Cenozoic forearcs in the Pacific rim and recognized that a subducting ridge was likely to generate anomalously high heat flow in the overriding plate. This “blow torch effect” has been successfully applied to many locations where thermal metamorphism and forearc magmatism are evident. Toward the end of the 1970s and into the early 1980s, the understanding of ridge subduction broadened to include anomalies in the arc and backarc regions of convergent margins. Major advances included a geometrical approach to slab edge positions, and the recognition of slab windows as gaps between the subducting slabs. The outcome was a new paradigm in which the sizes and shapes of slab windows could be modeled using plate motion vectors. As well, the magmatic response to ridge subduction became increasingly evident. A connection between intraplate magmatism and slab windows was demonstrated, and modifications to the mantle wedge in subduction zones became a widely accepted corollary. In the late 1980s and through the 1990s, slab windows became recognized as transient but potentially long-lived features with diachronous consequences. Confidence in the recognition of slab window manifestations grew, and researchers began using on-land geology to constrain ridge-trench locations and propose new plate configurations in the Pacific basin. Since 2000, refinements have included a better appreciation for the degradation of slab window margins caused by microplate formation and thermal erosion. The success of the slab window paradigm to Cenozoic geology of the Pacific rim prompted greater acceptance among a sometimes-critical tectonics community, and widespread application of ridge subduction tectonics to more distant locations. As well, researchers increasingly applied the hypothesis to older orogenic belts. A resemblance to modern Pacific slab window environments has been noted, for example, in the Early Cenozoic of Turkey, the Paleozoic of the Central Asian Orogenic Belt, and the Precambrian of the southwestern United States. Current advancements through the use of seismic tomography and enhanced global plate modeling are providing a more complete understanding of the life cycle of slab windows.