克拉通地幔形成与演化及对大陆命运制约因素的思考

Formation and evolution of cratonic roots and its bearing on the fate of continents.

岩石圈地幔属性主要由熔体抽取和交代作用程度共同决定,与岩石圈起源、大陆稳定性、宜居环境演变等密切相关。全球古老大陆的命运差别很大,有的长期稳定、有的遭受破坏,其控制因素可能包括大陆根地幔形成时熔融条件和后续交代改造过程等。本文总结前人研究资料发现,南非克拉通长期处于板块离散背景下,并经历了多期地幔柱活动,岩石圈地幔主体保持难熔属性、局部发生富集;华北克拉通长期处于板块汇聚背景下,并在显生宙发生强烈岩石圈减薄、改造和地幔置换作用,仅局部有难熔地幔残留。我们认为,亟需对不同命运克拉通之下的岩石圈地幔开展早期熔融条件和交代演化历史对比研究,寻找控制大陆命运的先天条件和后天因素。研究结果可以为大陆起源、宜居星球演化等关键科学问题提供制约。

The nature of lithospheric mantle is the accumulative effect of melt extraction and metasomatism,and is closely related to the origin and stability of continents and the evolution of habitable environment.Global ancient continents,namely cratons,have highly variable fates and the possible controlling factors behind include the formation conditions of the underlying mantle roots and the metasomatic events superimposed in the prolonged tectonic histories.Our literature review shows that the South African Craton,a typical stable craton,has been involved in divergent tectonic regimes for billions of years and impinged by several episodes of mantle plumes,but retains the originally attached thick and refractory mantle root with localized mantle refertilization.In contrast,the disrupted North China Craton has long been surrounded by subduction episodes and experienced remarkable lithospheric thinning,modification and mantle replacement in the Phanerozoic,with locally preserved refractory relics.We propose that comparative studies on the melting condition and metasomatic history of cratonic mantle root with contrasting evolution paths are vital and urgently in need to reveal the fate of continents,especially for the congenital conditions associated with craton formation in the deep time and the nurture processes linked to the continental evolution histories.The knowledge arising from the endeavor in this field will have significant bearing for the origin of continents and the evolution of habitable planets.