月球火山作用的地貌学特征

Volcanic landforms on the Moon

火山活动是月球最主要的内动力地质作用之一,是研究月球地质历史和热演化的重要窗口,也是月球科学及探测的重点目标。本文概要总结了月球火山作用的基本原理,并重点介绍了"岩墙扩展"模型。基于此模型,列举了由于岩墙在月壳内部上升程度的不同,导致的不同形式的喷发活动,并在月表产生了一系列火山地貌特征:(1)当岩墙仅扩展到浅月表、未能穿透月壳并引起喷发活动时,可能会在月表产生坑链构造、地堑或底部断裂型撞击坑;(2)当岩墙穿透了整个月壳并引起爆裂式喷发活动时,会在月表产生小型火山锥、区域性火山碎屑堆积物、全月分布的微小火山玻璃、暗晕凹陷构造及环形火山碎屑堆积物;(3)当岩墙穿透了整个月壳并引起溢流式喷发活动时,随着岩浆喷发通量的逐步增高,会在月表产生小型熔岩流、月海穹窿、复合熔岩流、蜿蜒型月溪、巨型熔岩流及火山高原复合体。本文也简要介绍了在月表观测到的若干非典型火山地貌特征,包括不规则月海斑块、环形凹陷穹丘及非月海富硅质穹窿。近年来新的探月数据加深了对这些特殊火山地貌特征的认识,但是更多的地质特征及成因模型细节仍有待未来月球研究及探测去解决。

Volcanism, one of the major endogenic geological processes on Moon, provides an important window into lunar geological and thermal evolution history and is an important objective of lunar science and explorations. In this contribution, we first summarize the basic principles of lunar volcanism, especially the dike propagation model. In this scenario, depending on the differing status of dike emplacement, eruptive activities of different styles are envisaged, leading to the production of a wide range of volcanic landforms on the surface of the Moon:(1) dikes that propagate to the shallow crust and stall would not cause eruptions but produce crater chains, graben or floor-fractured craters;(2) dikes that propagate to the surface and cause explosive eruptions would produce small volcanic cones, regional pyroclastic deposits, Moon-wide dispersal of magma and gas droplets, dark-halo craters, and a dark pyroclastic ring;(3) dikes that propagate to the surface and cause effusive eruption, depending on the magma effusion rates, would produce small lava flows, mare domes, compound lava flow fields, sinuous rilles, extensive lava flows, and volcanic complexes. We also introduce some uncommon volcanic landforms observed on the lunar surface, including irregular mare patches, ring moat dome structures and silicic non-mare domes. Recent lunar exploration and analyses have provided many insights into these unusual volcanic features, while more details concerning their nature and origin are yet to be explored by future lunar missions and studies.