In geology, a slab window or slab tear is a gap that forms in a subducted oceanic plate due to localization of stress in the subducting slab (i.e., the subducted oceanic plate). Several mechanisms may trigger the formation of a slab window. It can form when a mid-ocean ridge meets with a subduction zone and plate divergence at the ridge and convergence at the subduction zone continue, causing the ridge to be subducted. Another process that can initiate a slab window is the presence of an oceanic plate joint (i.e., pre-existing weakness in the plate that results from the intersection of two mid-ocean ridges) where the stress in the slab can be focused, leading the slab to break at depths. Formation of a slab window produces an area where the crust of the overriding plate is lacking a rigid lithospheric mantle component and thus is exposed to hot asthenospheric mantle (for a diagram of this, see the link below). This produces anomalous thermal, chemical and physical effects in the mantle that can dramatically change the overriding plate by interrupting the established tectonic and magmatic regimes. In general, the data used to identify possible slab windows comes from seismic tomography, heat flow studies, and geochemistry.
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👉 Slab window in the context of Chile Rise
The Chile Ridge, also known as the Chile Rise, is a submarine oceanic ridge formed by the divergent plate boundary between the Nazca plate and the Antarctic plate. It extends from the triple junction of the Nazca, Pacific, and Antarctic plates to the Southern coast of Chile. The Chile Ridge is easy to recognize on the map, as the ridge is divided into several segmented fracture zones which are perpendicular to the ridge segments, showing an orthogonal shape toward the spreading direction. The total length of the ridge segments is about 550–600 km (340–370 mi; 300–320 nmi).
The continuously spreading Chile Ridge collides with the southern South American plate to the east, and the ridge has been subducting underneath the Taitao Peninsula since 14 million years (Ma). The ridge-collision has generated a slab window beneath the overlying South America plate, with smaller volume of upper mantle magma melt, proven by an abrupt low velocity of magma flow rate below the separating Chile ridge. The subduction generates a special type of igneous rocks, represented by the Taitao ophiolites, which is an ultramafic rock composed of olivine and pyroxene, usually found in oceanic plates. In addition, the subduction of the Chile Ridge also creates Taitao granite in Taitao Peninsula which appeared as plutons.