The mountains of Io: Global and geological perspectives from Voyager and Galileo
The mountains of Io: Global and geological perspectives from Voyager and Galileo
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木卫一山脉：航海者号和伽利略号的全球和地质视角
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发表时间：
2001
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通讯作者：
P. Thomas
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作者：
Paul Schenk;H. Hargitai;R. Wilson;A. McEwen;P. Thomas
为了寻找可能与lo内部动力学有关的局部和全球尺度的地质联系，我们完成了所有山脉和火山中心的全球目录。我们已经确定了115个山结构（覆盖地表的约3%）和541个火山中心，包括火山口和暗斑和盾状火山。爱奥尼亚山脉的平均长度为157公里，最长的为570公里。爱奥尼亚山脉的平均高度为6.3公里，已知最高的山是Boosaule Montes（17.5±3公里）。已经确定了五种基本的山地形态类型；台地，高原，山峰，山脊和地块。很少有山脉与经典的火山地貌有任何物理上的相似之处，但许多类似于地球上的熨斗山，被解释为倾斜的地壳块。这与大多数山脉是逆冲块体的假设是一致的，这是由于火山层随着时间的推移而被埋在地下，全球沉降导致下地壳中形成的压应力的结果[Schenk和Bulmer， 1998]。然而，可能不止一种机制导致了所有的爱奥尼亚山脉。一些山脉靠近paterae可能表明一些山脉和火山活动之间有直接联系，尽管并不总是清楚哪个先出现。与先前的研究相反，在山脉和火山中心的全球分布中观察到明显的双峰模式。火山中心面积密度最高的地区靠近亚木星区和反木星区，但在经度上与两个山脉最集中的地区相差约90°。这种反相关关系可能表明，由于沉降，在全球压应力上叠加了第二个应力场。火山中心和山脉的双峰分布与Tackley等[2001]发展的软流圈潮汐加热和内部对流模式相一致。在地幔上升流的地区，全球沉降引起的下地壳压应力可能会减少，从而促进火山活动，阻止造山活动。在地幔下移的地区，下地壳的压应力可能会增加，从而抑制火山活动，促进造山活动。或者，全球模式可能与lo的可能（但没有记录）非同步旋转有关，这将在地壳中产生两个区域，每个区域都是压缩和拉伸。在爱奥尼亚山脉上发现的分层和大量浪费的证据，包括滑坡、块体滑动、碎片夹带和下坡蠕变，表明洛的地壳本质上是由部分固结的火山熔岩和羽流沉积物组成的层状堆积，随着深度的增加而变得更加固结。特别是下地壳也可能发生韧性变形，不时受到火山侵入和断层作用的破坏，并破碎成块体，其中一些已经隆起形成山脉。
To search for local and global scale geologic associations that may be related to the internal dynamics of lo, we have completed a global catalog of all mountains and volcanic centers. We have identified 115 mountain structures (covering ∼3% of the surface) and 541 volcanic centers, including paterae (calderas and dark spots) and shield volcanoes. The average length of an Ionian mountain is 157 km, with the longest being 570 km. The mean height of Ionian mountains is 6.3 km, and the highest known mountain is Boosaule Montes (17.5 ±3 km). Five basic morphologic types of mountains have been identified; mesa, plateau, peak, ridge, and massif. Very few mountains bear any physical similarity to classic volcanic landforms, but many resemble flatiron mountains on Earth and are interpreted as tilted crustal blocks. This would be consistent with the hypothesis that most mountains are thrust blocks formed as a result of compressive stresses built up in the lower crust due to the global subsidence of volcanic layers as they are buried over time [Schenk and Bulmer, 1998]. More than one mechanism may be responsible for all Ionian mountains, however. The proximity of some mountains to paterae may indicate a direct link between some mountains and volcanism, although it is not always clear which came first. In contrast to earlier studies, a pronounced bimodal pattern is observed in the global distribution of both mountains and volcanic centers. The regions of highest areal densities of volcanic centers are near the sub- and anti-Jovian regions, but are offset roughly 90° in longitude from the two regions of greatest concentration of mountains. This anticorrelation may indicate the overprinting of a second stress field on the global compressive stresses due to subsidence. The bimodal distribution of volcanic centers and mountains is consistent with models of asthenospheric tidal heating and internal convection developed by Tackley et al. [2001]. Over regions of mantle upwelling, compressive stresses in the lower crust induced by global subsidence might be reduced, encouraging volcanism and discouraging mountain building. In regions of mantle downwelling, these compressive stresses in the lower crust might be increased, discouraging volcanism and encouraging mountain building. Alternatively, the global pattern may be related to possible (but undocumented) nonsynchronous rotation of lo, which would produce two regions each of compression and extension in the crust. Evidence of layering and of mass wasting, including landslides, block sliding, debris aprons and downslope creep, on Ionian mountains suggests that the crust of lo is essentially a layered stack of partially consolidated volcanic lavas and plume deposits, becoming more consolidated with depth. The lower crust especially may also be ductily deformed, punctuated by volcanic intrusions and faulting at paterae, and broken into blocks, some of which have been uplifted to form mountains.