Hot orogens, tectonic switching, and creation of continental crust

Many granulite terrains were too hot to have formed during continental collision. Rather, along with many high-grade metamorphic terrains that typify continental crust, most formed in accretionary orogens during tectonic switching, when prolonged lithospheric extension was interrupted by intermittent, transient contraction. Based on modern and ancient examples, tectonic switching occurs when slab retreat induces upper plate extension, causing arc splitting, formation of microcontinent slivers, and backarc basins; then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction (or slab flip) and crustal thickening. During slab retreat, basaltic magmas produced from decompressed…