Along-strike variation in subducting plate seismicity and mantle wedge attenuation related to fluid release beneath the North Island, New Zealand

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• 作者：Donna Eberhart-Phillips ; Martin Reyners ; Manuele Faccenda ; John Naliboff
• 关键词：Subduction ; Slab seismicity ; Dehydration ; New Zealand ; Volcanism
• 刊名：Physics of the Earth and Planetary Interiors
• 出版年：December, 2013
• 年：2013
• 卷：225
• 期：Complete
• 页码：12-27
• 全文大小：5720 K

文摘

We analyze seismicity in the subducted slab of the Hikurangi subduction zone, along a 600-km length beneath the North Island, New Zealand. The volcanic character changes along strike with extremely productive rhyolitic volcanism in the central Taupo Volcanic Zone, moderate andesitic volcanism in the northern and south-central zones, and subduction without volcanism in the southernmost Hikurangi zone. We have relocated slab earthquakes with 3-D velocity models. The relocated seismicity shows more detail of the varied distribution and abundance of slab seismicity, which below 50-km depth may be related to embrittlement from high fluid pressure. The depth of the buoyant subducted Hikurangi Plateau ranges from 40 to 140 km depth.

At depths where the subducting slab interacts with the mantle wedge, along-arc variation in slab seismicity is a fundamental characteristic, with patches of abundant seismicity separated by low seismicity zones. The largest most numerous patch, at 150-220 km depth, underlies a pronounced low Qp zone in the mantle wedge, which is associated with the rhyolite-dominant Taupo caldera. Extensive melt in the region of low Qp requires high H₂O flux from the underlying slab. The abundant Taupo seismicity suggests a correlation between melt production and regions of earthquake fracture permeability following embrittlement which promote migration of dehydration fluid. The hydration history of the incoming slab may be a key factor in producing variations in dehydration and intraslab fluid migration. Broader, extensive outer-rise yielding and hydration may have occurred near the approach of the re-entrant Hikurangi Plateau, forming the slab section that currently has high seismicity. Slab seismicity deepens from 240 to 330 km along-arc as the subduction rate increases from <20 to >40 mm/yr. The southwestern slab seismicity is bounded by an unusually narrow zone with 110-km depth extent. This is inferred to be a dehydration front related to heating at a slab edge that is located 70 km further southwest.