DOI: 10.1016/j.epsl.2020.116271
论文题名: Hydration of the crust and upper mantle of the Hikurangi Plateau as it subducts at the southern Hikurangi margin
作者: Herath P. ; Stern T.A. ; Savage M.K. ; Bassett D. ; Henrys S. ; Boulton C.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 541 语种: 英语
中文关键词: dehydration
; double seismic zone
; Hikurangi
; mantle hydration
; subduction
英文关键词: Cracks
; Dehydration
; Drops
; Faulting
; Hydration
; Kaolinite
; Offshore oil well production
; Seismic waves
; Serpentine
; Speed
; Controlled source
; Deformation front
; Dehydration process
; Low velocity zones
; Oceanic plateaux
; Seismic profiling
; Subducting plate
; Subduction zones
; Earthquakes
; antigorite
; continental margin
; crustal thickness
; earthquake event
; plate convergence
; seismic source
; seismic wave
; subduction zone
; upper mantle
; Hikurangi Margin
; Hikurangi Plateau
; Pacific Ocean
英文摘要: Controlled-source seismic studies at most subduction zones show that bending of the subducting plate results in reduced seismic wave-speeds in the crust and upper mantle near the trench. Similar studies also have found unusually high P-wave-speeds (Vp) in the upper mantle under oceanic plateaus. Onshore-offshore seismic profiling at the southern Hikurangi margin, where the ≈120 Ma old oceanic Hikurangi Plateau is subducting, indicates that a fast (Vp≈8.7±0.2 km/s) upper mantle layer lies beneath a ≈25 km thick mantle layer with more regular wave-speeds (Vp≈8.0±0.2 km/s) under the Hikurangi trough. This is consistent with previous findings of upper mantle Vp≈8.7-9.0 km/s in the margin-parallel direction under the North Island (≈100 km northwest of the deformation front) at depths ≈8-10 km below the Moho. Our profiles are margin-perpendicular, thus we show that the upper mantle lid of the subducting Pacific Plate is characterized by unusually high P-wave-speeds along all azimuths. We find an area of lowered Vp in the ≈12±1 km thick Hikurangi Plateau crust beneath the trough. This drop in Vp is ≈10%, and a similar drop in Vp is deduced to depths of 25±2 km into the upper mantle. We interpret that the increase in thickness of the regular mantle beneath the trough results from the formation of a low-velocity zone in the faster upper mantle layer; this zone formed from serpentinisation by hydration through bending-induced normal faults and/or due to crack porosity introduced by thermal cracking, further enhanced by bending-related faulting. Thus the “regular mantle” (Vp≈8 km/s) is not in fact regular, but rather the high-speed mantle has mechanically bent, fractured, and altered. The absolute depth of fast mantle Vp under the Hikurangi trough is around 50 km. The onset of the lower band of seismicity of the double seismic zone and high upper mantle Vp under the North Island is observed at similar depths. This is consistent with the hypothesis that the lower band of earthquakes in a double seismic zone is due to antigorite dehydration processes, a hydrous mineral formed in the low velocity zone in the upper mantle beneath the trough. Our study on the Hikurangi margin is different, as the subducting plate here contains a ≈120 Ma old oceanic plateau with a ≈12 km thick crust, but the results are similar to other subduction margins where regular oceanic crust is subducting. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165020
Appears in Collections: 气候变化与战略
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作者单位: School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington, 6140, New Zealand; GNS Science, 1 Fairway Drive, Avalon, Lower Hutt, 5011, New Zealand
Recommended Citation:
Herath P.,Stern T.A.,Savage M.K.,et al. Hydration of the crust and upper mantle of the Hikurangi Plateau as it subducts at the southern Hikurangi margin[J]. Earth and Planetary Science Letters,2020-01-01,541