Allègre Claude J
Laboratoire de Géochimie and Cosmochimie, Institut de Physique du Globe de Paris, Boite 89, 4 place Jussieu, 75252 Paris cedex 05, France.
Philos Trans A Math Phys Eng Sci. 2002 Nov 15;360(1800):2411-31. doi: 10.1098/rsta.2002.1075.
We present a geochemical overview of the canonic model that suggests a two-layer mantle for most of the Earth's history. A change in the Rayleigh number may have modified the convection and now allows the subduction of oceanic plates into the lower mantle, which was not the case in the past. The measurement of stirring time in the source of mid-ocean-ridge basalt, together with Xe- and Pb-isotopic ratios in the mid-ocean-ridge-basalt source, suggests that the upper mantle is separated into two domains, one above the 400 km discontinuity (asthenosphere) with rapid mixing and short residence time, and another between the 400 and 670 km discontinuities with sluggish mixing and a residence time of ca. 1.5 x 10(9) yr.
我们展示了经典模型的地球化学概述，该模型表明在地球历史的大部分时间里地幔分为两层。瑞利数的变化可能改变了对流，现在允许海洋板块俯冲到下地幔中，而过去并非如此。对大洋中脊玄武岩源区搅拌时间的测量，以及大洋中脊玄武岩源区的氙和铅同位素比率，表明上地幔被分为两个区域，一个在400公里不连续面之上（软流圈），混合迅速且停留时间短，另一个在400至670公里不连续面之间，混合缓慢且停留时间约为1.5×10⁹年。
