Plinian eruptions and passive collapse events as mechanisms of formation for Martian pit chain craters
Plinian eruptions and passive collapse events as mechanisms of formation for Martian pit chain craters
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普林尼式喷发和被动塌陷事件作为火星坑链陨石坑的形成机制
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
L. Wilson
中科院分区：
文献类型：
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作者：
E. D. Scott;L. Wilson
[1]火星阿尔巴火山口附近存在三组不同且相交的地堑。其中一套是对阿尔巴火山口建筑演变的回应。第二组主要包括线性结构，广泛解释为响应非常大规模的区域应力而形成。第三组的成员包含许多坑陨石坑，我们认为，这些陨石坑形成的火山活动的结果以上的长期区域堤防从源南部的塔尔西斯地区。坑状陨石坑有两种形态：小的（小于2公里），形状规则，通常完全包含在地堑内，但偶尔无边界，和较大的（4-10公里），不规则的，通常彼此合并。我们认为，这两种类型的陨石坑形成的不同，但相关的机制。较小的火山口是在停滞的岩脉中的岩浆脱气，挥发物通过上覆地壳岩石的裂缝和断裂流失到大气中，然后坍塌到岩脉顶部的潜在空隙中，产生坑状陨石坑。更大的陨石坑是在堤壁内爆和坍塌时，由下面的堤产生的短暂爆炸性喷发形成的，破坏了任何喷口结构的证据。这些喷发没有可见的产物，因为火星周围的大气条件导致爆炸性喷发非常剧烈，将产物分散在非常广泛的区域。有证据表明，这两种形成机制都发生在同一岩脉上很短的距离内。先前存在的局部构造应力似乎影响了坑状火山口的位置，地下水可能参与了确定其位置和喷发活动的方式。
[1] Three distinct and intersecting sets of graben exist near the Martian volcano Alba Patera. One set formed as a response to the evolution of the Alba Patera edifice. A second set includes mainly linear structures widely interpreted to have formed in response to very large-scale regional stresses. The members of the third set contain numerous pit craters, and we propose that these craters formed as a result of volcanic activity above long regional dikes emanating from a source to the south within the Tharsis region. The pit craters are of two morphologies: small (<2 km), regular-shaped ones, usually completely contained within a graben but occasionally unbounded, and larger (4–10 km), irregular ones which commonly coalesce with one another. We argue that these two types of crater formed by different but related mechanisms. The smaller ones developed as the magma in a stalled dike degassed and volatiles were lost to the atmosphere via cracks and fractures in the overlying crustal rocks, which then collapsed into the potential void space at the top of the dike, producing the pit craters. The larger craters formed subsequent to short-lived explosive eruptions sourced from the underlying dike when the dike walls imploded and collapsed, destroying evidence of any vent structures. There are no visible products of these eruptions because the ambient Martian atmospheric conditions caused the explosive eruptions to be very vigorous, dispersing the products over very wide areas. Evidence indicates that both formation mechanisms occurred within very short distances over the same dike. Preexisting local tectonic stresses appear to have influenced the locations of the pit craters, and groundwater may have been involved in determining their locations and the style of eruptive activity.