Abstract:

An upper mantle discontinuity topography map of southern Nazca Plate and western South America Plate (120°W?60°W, 30°S?5°N) was obtained by using common mid-point stacking in bins of 5 degree radius over ten thousand USArray teleseismic records. The resolution was higher than that of previous studies because the records more densely sampled the region so that stacking bins were smaller. Discontinuity topography corresponding to high temperature anomalies in deep mantle was observed beneath Galapagos, Easter and San Felix hotspots. Other findings include a depression of 410 km discontinuity beneath Southern East Pacific Rise and depressions of both 410 km and 660 km discontinuities beneath the subduction zone.

Key words: upper mantle discontinuity, mantle transition zone, hotspot, slab, Southern East Pacific Rise

摘要：

利用USArray的远震记录资料, 对1万多条地震记录的SS前驱波进行共反射点叠加分析(叠加范围是半径为5°的球冠), 得到纳斯卡板块南部及南美板块西部(120°W—60°W, 30°S—5°N)上地幔间断面的起伏形态。由于数据很好地覆盖了研究区域, 叠加范围更小, 因此比以往的结果具有更高的空间分辨率。在Galapagos, Easter和 San Felix这3个热点下方观测到的间断面起伏形态符合地幔深部存在高温异常的假设。还观测到: 在东太平洋洋隆南段下方, 410 km间断面深度增加; 在俯冲带下方, 410 km和 660 km间断面深度增加。

关键词: 上地幔间断面, 地幔过渡带, 热点, 俯冲板块, 东太平洋洋隆南段