Saikia Ashima, Frost Daniel J, Rubie David C
Bayerisches Geoinstitut, University of Bayreuth, D-95444 Bayreuth, Germany.
Science. 2008 Mar 14;319(5869):1515-8. doi: 10.1126/science.1152818.
Seismic studies indicate that beneath some regions the 520-kilometer seismic discontinuity in Earth's mantle splits into two separate discontinuities (at approximately 500 kilometers and approximately 560 kilometers). The discontinuity near 500 kilometers is most likely caused by the (Mg,Fe)2SiO4 beta-to-gamma phase transformation. We show that the formation of CaSiO3 perovskite from garnet can cause the deeper discontinuity, and by determining the temperature dependence for this reaction we demonstrate that regional variations in splitting of the discontinuity arise from variability in the calcium concentration of the mantle rather than from temperature changes. This discontinuity therefore is sensitive to large-scale chemical heterogeneity. Its occurrence and variability yield regional information on the fertility of the mantle or the proportion of recycled oceanic crust.
地震研究表明，在某些区域之下，地球地幔中520公里处的地震不连续面分裂成两个单独的不连续面（分别在约500公里和约560公里处）。500公里附近的不连续面很可能是由（Mg,Fe）2SiO4的β相向γ相转变引起的。我们表明，石榴石形成硅酸钙钛矿会导致更深的不连续面，并且通过确定该反应的温度依赖性，我们证明不连续面分裂的区域变化源自地幔钙浓度的变化，而非温度变化。因此，这种不连续面对大规模化学不均一性很敏感。它的出现和变化产生了关于地幔肥力或再循环洋壳比例的区域信息。
