气候变化领域集成服务门户(CCPortal): Small-scale heterogeneity in the lowermost mantle beneath Alaska and northern Pacific revealed from shear-wave triplications

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DOI	10.1016/j.epsl.2021.116768
	Small-scale heterogeneity in the lowermost mantle beneath Alaska and northern Pacific revealed from shear-wave triplications
	Li Y.; Miller M.S.; Tkalčić H.; Sambridge M.
发表日期	2021
ISSN	0012821X
卷号	559
英文摘要	The D″ layer, regarded as a thermal boundary layer and a chemically distinct region above the core-mantle boundary (CMB), has been associated with the phase transition from bridgmanite (Bm) to post-perovskite (pPv) in the lowermost mantle. However, the composition of the lowermost mantle and thermal conditions where Bm-pPv phase-transition occurs is still debatable. The methods typically used to study the fine-scale seismic features in the D″ layer has provided important information. However, trial-and-error seismic waveform modelling cannot uniquely quantify D″-layer properties because of subjective model-parameterization choices and inherent non-uniqueness of solutions and the waveform inversion method has a limited resolution of the velocity gradient and depth of the D″ discontinuity. We develop a grid-search scheme to constrain the detailed 1-D shear-wave velocity structure in the lowermost mantle beneath Alaska and the northern Pacific, accompanied with quantitative assessment of the uncertainty of 1D models. Our results show strong lateral variations of the D″ discontinuity from west to east beneath Alaska, along with the existence of smaller-scale heterogeneities in the east. We find a broad velocity increase, as thick as 240 km, at the top of D″ that indicates this region may involve a composite of downwelling thermo-chemical anomalies at the CMB. There are even smaller scale heterogeneities of approximately 120 km×120 km in size with larger lateral variations in the lowermost mantle beneath northern Pacific. Both the magnitude and gradient of the velocity at the top of the D″ layer vastly change in adjacent regions, with an increase from 2.8% to 4.5% in magnitude and from 0.08% to 1.2% in gradient, but with a relatively consistent depth of the D″ discontinuity at ∼340 km above the CMB. The weak correlation between D″ topography and velocity variations indicate chemical heterogeneities must be present beneath the northern Pacific, which might come from north-westward subducted Pacific oceanic lithosphere. Our characterisation of the spatial pattern of small-scale heterogeneities in the lowermost mantle supports a hybrid thermo-chemical boundary layer (TCBL) model beneath Alaska and northern Pacific. © 2021 Elsevier B.V.
关键词	lowermost mantle non-linear inversion phase transition slab debris small-scale chemical heterogeneities waveform modelling
英文关键词	Boundary layers; Perovskite; Seismology; Shear waves; Structural geology; Topography; Velocity; Wave propagation; Waveform analysis; Chemical heterogeneities; Model parameterization; Quantitative assessments; Scale heterogeneities; Shear wave velocity structure; Small-scale heterogeneity; Thermal boundary layer; Thermo-chemical boundary layer; Shear flow; core-mantle boundary; data inversion; heterogeneity; lower mantle; nonlinearity; numerical model; S-wave; seismic wave; velocity structure; waveform analysis; Alaska; Pacific Ocean; Pacific Ocean (North); United States
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/203186
作者单位	Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia
推荐引用方式 GB/T 7714	Li Y.,Miller M.S.,Tkalčić H.,et al. Small-scale heterogeneity in the lowermost mantle beneath Alaska and northern Pacific revealed from shear-wave triplications[J],2021,559.
APA	Li Y.,Miller M.S.,Tkalčić H.,&Sambridge M..(2021).Small-scale heterogeneity in the lowermost mantle beneath Alaska and northern Pacific revealed from shear-wave triplications.Earth and Planetary Science Letters,559.
MLA	Li Y.,et al."Small-scale heterogeneity in the lowermost mantle beneath Alaska and northern Pacific revealed from shear-wave triplications".Earth and Planetary Science Letters 559(2021).