EarthByte Group, School of Geosciences, Madsen Building F09, University of Sydney, Sydney, New South Wales 2006, Australia.
Seismological Laboratory, California Institute of Technology, Pasadena, California 91125, USA.
Nat Commun. 2017 Jan 18;8:14164. doi: 10.1038/ncomms14164.
A unique structure in the Earth's lowermost mantle, the Perm Anomaly, was recently identified beneath Eurasia. It seismologically resembles the large low-shear velocity provinces (LLSVPs) under Africa and the Pacific, but is much smaller. This challenges the current understanding of the evolution of the plate-mantle system in which plumes rise from the edges of the two LLSVPs, spatially fixed in time. New models of mantle flow over the last 230 million years reproduce the present-day structure of the lower mantle, and show a Perm-like anomaly. The anomaly formed in isolation within a closed subduction network ∼22,000 km in circumference prior to 150 million years ago before migrating ∼1,500 km westward at an average rate of 1 cm year, indicating a greater mobility of deep mantle structures than previously recognized. We hypothesize that the mobile Perm Anomaly could be linked to the Emeishan volcanics, in contrast to the previously proposed Siberian Traps.
在欧亚大陆下方，最近发现了地球最底层地幔中的一个独特结构，即永久异常区。它在地震学上类似于非洲和太平洋下方的大型低速剪切速度省（LLSVPs），但规模要小得多。这对当前关于板块-地幔系统演化的理解提出了挑战，该系统中地幔柱从两个 LLSVPs 的边缘升起，在时间上是固定的。过去 2.3 亿年来地幔流动的新模型再现了下地幔的现今结构，并显示出类似永久异常区的特征。该异常区在大约 1.5 亿年前之前，在一个周长约为 22000 公里的封闭俯冲带网络内孤立形成，然后向西迁移约 1500 公里，平均迁移速度为每年 1 厘米，表明深部地幔结构的活动性比之前认为的要大。我们假设，与之前提出的西伯利亚陷阱相比，这种可移动的永久异常区可能与峨眉山火山岩有关。
