水诱导的地幔反转与大陆起源  

Water Induced Mantle Overturn and Origin of the Archean Crust

作　　者：吴忠庆 WU Zhongqing(Laboratory of Seismology and Physics of Earth’s Interior,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;Center for Excellence in Comparative Planetology,Chinese Academy of Sciences,Hefei 230026,China;Deep Space Exploration Laboratory,Hefei 230026,China)

机构地区：[1]中国科学技术大学地球和空间科学学院,地震与地球内部物理实验室,安徽合肥230026 [2]中国科学院比较行星学卓越创新中心,安徽合肥230026 [3]深空探测实验室,安徽合肥230026

出　　处：《地球科学进展》2024年第6期551-564,共14页Advances in Earth Science

基　　金：国家自然科学基金项目(编号:41925017,42350004)资助。

摘　　要：岛弧模型和地幔柱的海底高原模型是大陆起源的两个主流模型。相较于岛弧模型,地幔柱模型能更好地解释太古宙大陆的特征,但在解释太古宙陆壳源区富水这一关键特征时遇到了困难。最近提出的水诱导的地幔反转模型较好地解决了这个问题,同时还能解释太古宙多个令人困惑的现象。该模型指出,在地幔发生整体熔融的情况下,岩浆洋在中地幔深度开始结晶,形成外层和基底两个岩浆洋。由于下地幔矿物含水能力低,随着岩浆的结晶,最初含一定量水的基底岩浆洋将逐渐富水。水降低基底岩浆洋的密度。当水富集到一定程度时,基底岩浆洋的密度将不再高于上覆地幔,从而导致重力失稳,形成地幔反转。这种反转将水带到地球浅部,促进了大陆和克拉通岩石圈地幔等的形成。因此,太古宙大陆是基底岩浆洋演化的产物。当地幔反转耗尽基底岩浆洋后,太古宙型的大陆不再形成。太古宙末期对应着大陆形成机制的转变期,水诱导的地幔反转可以自然地解释为什么太古宙前后的大陆具有完全不同的特性。类似的,水诱导的地幔反转还可以解释其他多个长期困扰的现象,如:为什么几乎没有冥古宙的大陆,为什么太古宙的镁铁质岩石的源区具有原始地幔的组分且在整个太古宙几乎不变,为什么内太阳系只有地球具有大陆等。形成全地幔岩浆洋和岩浆洋含水是水诱导的地幔反转的2个前提。由于大撞击在全地幔岩浆洋形成中扮演了关键角色,月球远比我们想象的重要。The island arc and oceanic plateau models of a mantle plume are two popular models for the origin of the crust.In contrast to the island arc model,the oceanic plateau model can account for most of the features of the Archean crust but meets the fundamental challenge of explaining the water-rich features of the magma source for the Archean crust.The recent water-induced mantle overturn model accounts for not only water-rich features but also several puzzling phenomena in the Archean.The whole-mantle Magma Ocean(MO)separated into outer and basal MO because the crystallized mantle floated in the middle mantle.The water-induced mantle overturn model shows that with crystallization,basal MO became increasingly enriched in water because lower-mantle minerals can only contain a limited amount of water.Water reduced the density of basal MO.The basal MO eventually became less dense than the overlying solid mantle and became gravitationally unstable because of water enrichment.The triggered mantle overturned transport a large amount of water to the shallow part of the Earth and resulted in large pulses of crust and thick subcontinental lithospheric mantle(SCLM)generation.Therefore,the Archean crust was the result of the evolution of the basal MO.Once the mantle overturned from the basal MO,Archean-type crust no longer formed.Thus,the water-induced mantle overturn model can account for global change at the end of the Archean and other puzzling phenomena.For example,why were Tonalite-Trondhjemite-Granodiorite(TTG)and thick SCLM rare in the Hadean,why does the source of Archean basalts remain the primitive mantle from ca 4.0 to 2.5 Ga,and why does only Earth have continental crust?

关 键 词：太古宙 基底岩浆洋 水循环 高温高压 

分 类 号：P534.2[天文地球—古生物学与地层学]