Stagnant lids and mantle overturns: Implications for Archaean tectonics, magmagenesis, crustal growth, mantle evolution, and the start of plate tectonics
Stagnant lids and mantle overturns: Implications for Archaean tectonics, magmagenesis, crustal growth, mantle evolution, and the start of plate tectonics
复制标题
DOI：
10.1016/j.gsf.2017.01.005
复制
发表时间：
2018-01-01
影响因子：
8.9
通讯作者：
Bedard, Jean H.
中科院分区：
文献类型：
--
作者：
Bedard, Jean H.
下板块是现代会聚边缘的主导因素，其特征是活跃的俯冲作用，负浮力的海洋岩石圈在其自身重量的作用下沉入软流圈。这是一个强大的板块驱动力，因为板块拉力是通过坚硬的大洋下岩石圈地幔传递的。由于地质和地球化学数据似乎与现代风格的脊和弧的存在不一致，而提出了一个不稳定的滞流盖地壳系统。停滞盖间隔可能对应于分层地幔对流的时期，有效的冷却被限制在上地幔，扰乱地球的热量产生/损失平衡，最终触发地幔翻转。中生代玄武岩来源于翻转上升流区（OUZO）的肥沃地幔，比后中生代地幔柱更大，寿命更长。由于大量的玄武岩和科马提岩被长期输送，早期的火山岩/大陆可能形成于OUZO之上，从而允许基底地壳的自食作用、含石榴石的地壳残岩脱层作用以及大陆地壳和次大陆岩石圈地幔的耦合发展。反转期间的周期性混合和再均一化阻碍了同位素亏损的MORB（洋中脊玄武岩）地幔的发育。只有在真正的俯冲开始后，俯冲板片在核幔边界的隔离才导致亏损MORB地幔源的发展。在侏罗纪地幔翻转期间，位于OUZO上方的先前存在的大陆将被强烈改造;而OUZO远端大陆将响应地幔流而漂移。漂移的大洋大陆前缘是以不俯冲洋壳岩石圈的增生、叠瓦、俯冲和深熔作用为特征的会聚边缘。随着地球冷却和背景海洋岩石圈变得更致密和更坚硬，海洋地壳段可能以有组织的方式建立的可能性越来越大，产生了俯冲前会聚边缘逐渐演变为现代风格的活跃俯冲系统。今天的板块构造包括：（1）一个大陆漂移系统，开始于早白垩世，由深部地幔流驱动，挤压太古代的亚大陆岩石圈地幔龙骨，构成早白垩世的板块;（2）一个俯冲驱动系统，开始于晚白垩世末期。(C)2017年，中国地质大学（北京）和北京大学。制作和主办：Elsevier B. V.
The lower plate is the dominant agent in modern convergent margins characterized by active subduction, as negatively buoyant oceanic lithosphere sinks into the asthenosphere under its own weight. This is a strong plate-driving force because the slab-pull force is transmitted through the stiff sub-oceanic lithospheric mantle. As geological and geochemical data seem inconsistent with the existence of modern-style ridges and arcs in the Archaean, a periodically-destabilized stagnant-lid crust system is proposed instead. Stagnant-lid intervals may correspond to periods of layered mantle convection where efficient cooling was restricted to the upper mantle, perturbing Earth's heat generation/loss balance, eventually triggering mantle overturns. Archaean basalts were derived from fertile mantle in overturn upwelling zones (OUZOs), which were larger and longer-lived than post-Archaean plumes. Early cratons/continents probably formed above OUZOs as large volumes of basalt and komatiite were delivered for protracted periods, allowing basal crustal cannibalism, garnetiferous crustal restite delamination, and coupled development of continental crust and sub-continental lithospheric mantle. Periodic mixing and rehomogenization during overturns retarded development of isotopically depleted MORB (mid-ocean ridge basalt) mantle. Only after the start of true subduction did sequestration of subducted slabs at the core-mantle boundary lead to the development of the depleted MORB mantle source. During Archaean mantle overturns, pre-existing continents located above OUZOs would be strongly reworked; whereas OUZO-distal continents would drift in response to mantle currents. The leading edge of drifting Archaean continents would be convergent margins characterized by terrane accretion, imbrication, subcretion and anatexis of unsubductable oceanic lithosphere. As Earth cooled and the background oceanic lithosphere became denser and stiffer, there would be an increasing probability that oceanic crustal segments could founder in an organized way, producing a gradual evolution of pre-subduction convergent margins into modern-style active subduction systems around 2.5 Ga. Plate tectonics today is constituted of: (1) a continental drift system that started in the Early Archaean, driven by deep mantle currents pressing against the Archaean-age sub-continental lithospheric mantle keels that underlie Archaean cratons; (2) a subduction-driven system that started near the end of the Archaean. (C) 2017, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.