Nature2014-06-18 6:33 PM

板块构造是岩石圈受损的一个副产品 Plate tectonics, damage and inheritance


板块构造(地球表面分裂成被集中变形的线性区域分开的刚性板块的现象)在已知的陆地体系中是独特的。然而,关于该现象是怎样出现的仍没有共识。在这篇论文中,David Bercovici 和Yanick Ricard提出一个从变形物质的微观性质出发的解释。该理论认为,当足够的岩石圈受损积累时,剪切-局域化就会出现,长寿命的弱区域就会形成。然后,瞬时地幔流和迁移的原始消减会导致板块边界的积累,并最终导致构造板块的积累。作者通过一个颗粒演变和受损机制(将其耦合到一个关于由压力驱动的岩石圈流的理想化模型上)模拟了这一过程,发现构造板块边界和完全成形的构造板块能够在这种条件下形成.


The initiation of plate tectonics on Earth is a critical event in our planet’s history. The time lag between the first proto-subduction (about 4 billion years ago) and global tectonics (approximately 3 billion years ago) suggests that plates and plate boundaries became widespread over a period of 1 billion years. The reason for this time lag is unknown but fundamental to understanding the origin of plate tectonics. Here we suggest that when sufficient lithospheric damage (which promotes shear localization and long-lived weak zones) combines with transient mantle flow and migrating proto-subduction, it leads to the accumulation of weak plate boundaries and eventually to fully formed tectonic plates driven by subduction alone. We simulate this process using a grain evolution and damage mechanism with a composite rheology (which is compatible with field and laboratory observations of polycrystalline rocks), coupled to an idealized model of pressure-driven lithospheric flow in which a low-pressure zone is equivalent to the suction of convective downwellings. In the simplest case, for Earth-like conditions, a few successive rotations of the driving pressure field yield relic damaged weak zones that are inherited by the lithospheric flow to form a nearly perfect plate, with passive spreading and strike-slip margins that persist and localize further, even though flow is driven only by subduction. But for hotter surface conditions, such as those on Venus, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread, which corresponds to observations. After plates have developed, continued changes in driving forces, combined with inherited damage and weak zones, promote increased tectonic complexity, such as oblique subduction, strike-slip boundaries that are subparallel to plate motion, and spalling of minor plates.






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