A new multidisciplinary project in southwest New Zealand that combines geological and geophysical data shows how and why deep lithospheric displacements were transferred vertically through the upper plate of an incipient ocean-continent subduction zone. A key discovery includes two zones of steep, downward-curving reverse faults that uplifted and imbricated large slices of Cretaceous lower, middle, and upper crust in the Late Miocene. Geochemical and structural analyses combined with 40 Ar/ 39

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... r geochronology and published images from seismic tomography suggest that the reverse faults formed at 8-7 Ma as a consequence of a deep (~100 km) collision between subducting oceanic lithosphere and previously subducted material. This collision localized shortening and reactivated two crustalscale shear zones from the upper mantle to Earth's surface. The event, which is summarized in a new lithosphericscale profile, is helping us answer some long-standing questions about the origin of Fiordland's unique lower-crustal exposures and what they tell us about how inherited structures can transfer motion vertically through the lithosphere as subduction initiates. GSA Today, v. 29, https://doi.GSSZ ICSZ Fault zones strike-slip, reverse J J J J J J