Oceanic lithospheric mantle beneath the continental crust of the Chinese Altai

Although subduction–accretion is proposed as a major regime in making new continental crust, how the lithospheric mantle forms
remains unclear. Formed after the closure of the Palaeo-Asian Ocean, the Ashele basalt shows normal mid-ocean ridge basalt
(N-MORB)-like characteristics with light REE-depleted patterns and extremely low contents of high field strength elements.
The low Zr/Y and Nb/Y ratios of the basalt are significantly different from those of asthenosphere-derived melts, and the
excess Eu and Sr suggest that the basalt was probably derived from accreted oceanic lithospheric mantle. The presence of the
N-MORB-like terrestrial basalt implies that subduction–accretion is an effective mechanism in building the refractory lithospheric
mantle of Phanerozoic continents.

尽管俯冲-增生被提出作为形成新大陆地壳的主要机制，但地幔形成的过程仍然不甚明了。阿谢勒玄武岩在古亚洲洋闭合之后形成，显示出类似正常中洋脊玄武岩（N-MORB）的特征，具有轻稀土元素贫化模式和极低的高场强元素含量。该玄武岩的Zr/Y和Nb/Y比值明显低于地幔源熔岩，且Eu和Sr的富集表明玄武岩可能源自增生的大洋地壳地幔。N-MORB类陆壳玄武岩的存在暗示了俯冲-增生过程是构建显生宙大陆地壳抗热地幔的有效机制。