Small graben in the southeastern ejecta blanket of the lunar Copernics crater: Implications for recent shallow igneous intrusion on the Moon
Small graben in the southeastern ejecta blanket of the lunar Copernics crater: Implications for recent shallow igneous intrusion on the Moon
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月球哥白尼陨石坑东南喷射物覆盖层中的小地堑：对最近月球浅层火成岩入侵的影响
DOI：
10.1016/j.icarus.2017.02.014
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发表时间：
2017
期刊：
影响因子：
3.2
通讯作者：
Long Xiao
中科院分区：
文献类型：
--
作者：
Zhiyong Xiao;Qian Huang;Zuoxun Zeng;Long Xiao
在哥白尼东南连续喷出物沉积中发现了数十个宽约10-400 m、长小于1 km的线状地堑，支持月球上曾发生过哥白尼时代的构造活动。断层几何学分析表明地堑的边界断层是在喷出物沉积物中形成的。地堑只位于局部高起伏地区，但它们不是由质量浪费形成的，因为地形坡度远小于典型月球物质的休止角，并且在哥白尼连续喷出物沉积物的类似高起伏地区看不到其他伸展结构。地堑的方位均指向哥白尼中心，但哥白尼地形在形成后补偿很小，表明地堑不是地壳均衡调整的结果。这个地堑系统是月球上三个被解释为由浅火成侵入体以岩盖岩的形式造成的例子之一。目前可用的GRAIL重力数据具有较低的空间分辨率比地堑的大小，所以重力数据不能解决假设的亚公里规模的岩盖下面的地堑。虽然需要约80米深的岩礁侵入来解释该地堑系统的形成，但岩礁侵入情景与地堑的地质背景并不一致。在地堑系附近可见挤压构造，它们的空间配置和相似的保存状态与一般相关一致。另外两组地堑也被解释为没有相关的挤压构造，对它们的仔细检查实际上揭示了附近空间上相关的叶状陡崖和褶皱脊。因此，用浅源火成岩侵入体来解释月球上哥白尼地堑的形成是不合理的，也是不必要的，它们很可能是由月球晚期全球收缩形成的。
Dozens of linear graben that are about 10–400 m wide and less than 1 km long are recognized in the.southeastern continuous ejecta deposits of Copernicus, supporting that Copernican-aged tectonism has.occurred on the Moon. Fault geometry analysis suggests that the bounding faults of the graben have.formed within the ejecta deposits. The graben are exclusively located on a local high-relief area, but they.are not formed by mass wasting, because the topographic slope is substantially less than the repose angle.of typical lunar materials, and no other extensional structures are visible on similar high-relief areas at.the continuous ejecta deposits of Copernicus. The orientations of the graben all point to the center of.Copernicus, but the topography of Copernicus is little compensated after formation, suggesting that the.graben were not caused by possible crustal isostatic readjustment. This graben system is one of the three.examples on the Moon that were interpreted to be caused by shallow igneous intrusions in the format of.laccoliths. The currently available GRAIL gravity data have a lower spatial resolution than the size of the.graben, so the gravity data cannot resolve the hypothesized sub-kilometer-scale laccoliths beneath the.graben. While laccolith intrusion to a depth of about 80 m is required to explain the formation of this.graben system, the laccolith intrusion scenario is not consistent with the geological context of the graben..A compressional structure is visible close to the graben system, and their spatial configuration and similar.preservation states are consistent with being generically related. A close examination of the other two.sets of graben that were also interpreted to have no associated compressional structures actually reveals.spatially-related lobate scarps and wrinkle ridges in the vicinity. Therefore, shallow igneous intrusion is.not plausible or necessary to explain to formation of Copernican-aged graben on the Moon, and they are.most likely formed by the late-stage global contraction of the Moon.