行星构造:寻求地球演化的踪迹

Planetary tectonics:indicatorsto earth’s evolution

地质构造是记录地球内、外动力地质作用过程的标志。和地球相似,太阳系其他天体上也发育丰富的地质构造。以研究天体表面的地质构造及其动力学机制为目的的"行星构造学"是建立在构造地质学、遥感地质学和地球物理学等学科基础上的一门新兴前沿学科。由于天体的大小、组分和轨道位置不同,表面构造特征及其形成机制各异。对比研究地球和其他天体上的构造特征,是完善地球动力学的重要途径。水星和月球的热演化轨迹大致相同,内部持续冷却造成全球收缩,表面形成大量的挤压构造,而伸展构造仅局部发育。火星的岩石圈主要通过热传导散热,表面发育大量的挤压构造,且其形成时间可能呈单峰式分布。同时,火星表面的伸展和挤压构造和大火山群紧密相关,表明深部动力过程影响了火星上的区域构造。金星和地球的大小相似,但金星表面的最大年龄远小于地球大陆地壳的平均年龄,~80%的早期地质记录完全被后期的岩浆-构造活动抹去,表面发育大量的火山-深大裂谷系,说明"幔柱"活动对金星的构造演化至关重要,因此热传导可能也是当前金星岩石圈的主要散热方式。以上天体的岩石圈形变均以垂直运动为主。在外太阳系,一些卫星的表壳主要由冰水和其他挥发分组成,有些卫星存在下伏的液态水圈,潮汐作用可能是驱动其构造演化的主要动力。在特殊的应力来源和物质特性的共同作用下,在这些卫星上发育大量的走滑断层和疑似俯冲消减带。行星地质构造从能量和物质属性的角度探究构造运动的物理和化学过程,与地球动力学研究相辅相成,对揭示地球早期动力学过程的关键科学问题具有重要的指示意义。

Tectonic features on Earth record the interior and exterior dynamics of our planet.Similar to the Earth,widespread tectonic features exist on the other planetary bodies.Planetary tectonics is targeted at resolving the tectonics features,their evolution,and the related dynamics on theplanetary bodies.This discipline is built on traditional structural geology,remote sensing,geophysics,and many others.Due to differences in size,bulk composition,and orbital positions of planetary bodies,tectonic features across our solar system exhibit rich diversity.Thermal evolution of the Moon,Mercury,and Mars follow a similar track,and currently their lithospheres lose heat primarily via conduction,so that tectonic features observed on the three bodies are highly comparable.Mars has witnessed a potential pulse of global contraction,while large volcanic provinces that were possibly driven by giant mantel plumes strongly affect the distribution of both extensional and constructional structures.The first~80%history of Venus has been completely removed by subsequent magmatic-tectonic activity,and the maximum surface age is much less than the average age of the Earth’s continental crust.Thermal conduction is perhaps the dominantheat dissipation mechanism of Venus lithosphere,andthe abundant volcanic-tectoniccomplexes on the surface(such as giant crustal rift systems)indicate that mantel plumes have played a critical role in the history of Venus.Vertical movements dominate tectonism on the above terrestrial bodies while horizontal shearing is minimum.On the other hand,most satellites of the giant planets in the outer Solar System exhibit icy or other volatile-rich crusts,underneath which some have warm oceans.Tide,instead of radioactiveheat,is the major source thatdrives the interior dynamics of many icy satellites.Due to both the special orbital characteristics and heterogeneous crustal structures,the stress fields on these bodies are highly variable with time,andboth vertical and horizontal movements are abundant.Long strike-slip faults and possible subduction zones have recently been discovered.The study of planetary tectonics is based onthe various energy sources and material properties,addressing the interior dynamics from both physical and chemical perspectives.Therefore,planetary tectonics and Earth dynamics are complementary.Referring to planetary tectonics is fundamentally important to solve persistentmysteries related with Earth(especially continental)dynamics,such as the origin of plate tectonics,formation of continents,and interior dynamics within continents.