Science. 1991 May 10;252(5007):827-30. doi: 10.1126/science.252.5007.827.
The seismologically delineated transition zone, at depths between 400 and 670 kilometers, is a fundamental discontinuity in the earth that separates the upper mantle from the lower mantle. Xenoliths from within or close to the transition zone are dominated by pyropic garnet and associated pyroxene or mineralogically heterogeneous garnet lherzolite. These xenoliths show evidence for the high-pressure (90 to 120 kilobars) transformation of pyroxene to a solid solution of pyroxene in garnet (majorite) and silicon in octahedral coordination; low-pressure (less than 80 kilobars) exsolution of clinopyroxene or orthopyroxene from the original majorite is preserved. Although mineral modes and rock proportions below the transition zone and the relative amount of eclogite present cannot be accurately assessed from the xenoliths, it is likely that both majorite and beta-spinel help produce the observed seismic gradient of the transition zone.
地震学划定的过渡带，深度在 400 至 670 公里之间，是地球内部的一个基本不连续面，将上地幔与下地幔分隔开来。来自过渡带内部或附近的捕虏体主要由尖晶石石榴石和与之共生的辉石或矿物学上不均匀的石榴石二辉橄榄岩组成。这些捕虏体显示出辉石在高压（90 至 120 千巴）下向石榴石（镁铝榴石）和八面体配位硅的固溶体转变的证据，以及原始镁铝榴石中低压（小于 80 千巴）的单斜辉石或正交辉石出溶。尽管不能从捕虏体准确评估过渡带以下的矿物模式和岩石比例以及存在的榴辉岩的相对数量，但很可能镁铝榴石和β-尖晶石都有助于产生过渡带的观测到的地震梯度。
