地幔转换带是联系上下地幔的纽带,对于认识整个地幔的组成和演化、地幔对流、岩石圈深俯冲及深源地震等地球深部动力学问题具有重要意义。一般认为,转换带地震不连续面主要与橄榄石的高压相变密切相关。最新的高温高压实验研究表明,地幔中非橄榄石组分的相变,如辉石和石榴子石的相变,对不连续面的深度和宽度以及转换带内的波速和密度梯度也起到很大的影响。另外地幔全岩成分、端员组分、温度和水也对相变和不连续面具有重要影响,这些精细的实验研究成果更好地解释了转换带地震不连续面一些相对局部的性质和变化,促进了我们对地球深部性质和动力学过程的了解。因为缺少直接来自地球深部的样品,而地球物理和地球化学研究也有它们的相对局限性,所以高温高压实验仍然是我们了解地球深部成分和性质的重要手段之一。
Mantle transition zone (MTZ) is the link between the upper and lower mantle.It has important implications for our understanding of the composition and evolution of the whole mantle,mantle convection and the geodynamics of the deep subduction of lithosphere and deep-focus earthquakes.The seismic discontinuities in transition zone are generally interpreted in terms of phase transformations in olivine component at high pressures.Recent high-pressure-temperature experiments indicate that the transformations in non-olivine components (e.g.pyroxene and garnet) contribute significantly to the depth and sharpness of these discontinuities as well as the gradients in seismic velocities and density.In addition,the bulk composition,elemental partitioning,temperature and H2O have great impacts on these phase transformations and relative discontinuities,as well.These subtle experiment results explained some relative local characteristics and variations very well,and advanced our knowledge of the Earth's deep interior and its geodynamic process.Because of the lack of samples directly from deep Earth,and the relative limitation of geophysical and geochemical methods,the high-pressure-temperature experiments are still the indispensable method for our understanding of the composition and characteristics of the Earth's deep interior.