No basalt accumulation and segregation atop the 660-km discontinuity beneath the Sea of Okhotsk  

作　　者：BingXin Zhou XiaoBo He 

机构地区：[1]Marine Science and Technology College,Zhejiang Ocean University,Zhoushan Zhejiang 316022,China

出　　处：《Earth and Planetary Physics》2024年第4期621-631,共11页地球与行星物理（英文版）

基　　金：support from the National Natural Science Foundation of China(Grant No.42276049);the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB42020103).

摘　　要：Recent seismic evidence shows that basalt accumulation is widespread in the mantle transition zone(MTZ),yet its ubiquity or sporadic nature remains uncertain.To investigate this phenomenon further,we characterized the velocity structure across the 660-km discontinuity that separates the upper mantle from the lower mantle beneath the Sea of Okhotsk by modeling the waveform of the S660P phase,a downgoing S wave converting into a P wave at the 660-km interface.These waves were excited by two regional>410-km-deep events and were recorded by stations in central Asia.Our findings showed no need to introduce velocity anomalies at the base of the MTZ to explain the S660P waveforms because the IASP91 model adequately reproduced the waveforms.This finding indicates that the basalt accumulation has not affected the bottom of the MTZ in the study area.Instead,this discontinuity is primarily controlled by temperature or water content variations,or both.Thus,we argue that the basalt accumulation at the base of the MTZ is sporadic,not ubiquitous,reflecting its heterogeneous distribution.

关 键 词：660-km discontinuity S660P basalt segregation mantle transition zone western Pacific subduction zone 

分 类 号：P588.145[天文地球—岩石学] P542.5[天文地球—地质学]