Fault offsets and lateral crustal movement on Europa - Evidence for a mobile ice shell
Fault offsets and lateral crustal movement on Europa - Evidence for a mobile ice shell
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欧罗巴上的断层偏移和横向地壳运动——移动冰壳的证据
DOI：
10.1016/0019-1035(89)90109-7
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发表时间：
1985
期刊：
影响因子：
3.2
通讯作者：
W. McKinnon
中科院分区：
文献类型：
--
作者：
P. Schenk;W. McKinnon
在冰冷的伽利略卫星欧罗巴上已经确定了125公里的右侧结构偏移。这些发生在沿着与楔形带正交的深色线性构造上，楔形带也有25公里宽。楔形带被解释为扩张的张性断裂，它是由50-100公里宽的地壳块体（或板块）沿着两侧的走滑断层相互分离和滑动而形成的。这种变形方式似乎并不是其他线性构造类型的特征，除了地球之外，似乎是欧罗巴所独有的。在反木星点附近，近平行的楔形B带共同形成了一条宽约1500 km、宽小于500 km的NW-SE带。这条带被解释为一个主要的地壳断裂（或裂谷）带，其旋转极（由走滑断层决定）位于47°S，144°W附近，最大张应力大致为NE-SW方向。伸展可能在拉张带或拉张带（可能是挤压成因的亮带）得到了区域补偿。全球膨胀、潮汐扭曲和非同步旋转不能解释推断的最小主成分（即，最小压缩）应力方向。另外，反木星点附近的断裂可能是由于（i）下冰壳中的固态对流（可能是由硅酸盐内部不均匀的热流引发的），（ii）由纬度岩石圈厚度变化引起的冰壳围绕亚和反木星点旋转，或者（iii）冰壳其余部分的优先应变积累。在断裂和旋转过程中，地壳块体没有发生明显的变形，这表明在断裂的时间尺度上，冰壳可能与该地区的硅酸盐内部机械分离。在全球范围内的解耦也可能是简单的几何形状的线性构造主张形成在一个冰冷的岩石圈，而不是硅酸盐的，和其他证据断裂造成的非同步旋转应力是不兼容的潮汐锁定硅酸盐内部（我们显示是可能的），除非冰壳独立旋转。脱钩可能是由于温暖的冰或冰壳底部附近的液态水。岩石圈厚度的力学界限（几到10公里）导致热流估计，承认这两种可能性，但有利于液态水去耦。
Right-lateral structural offsets of ∼25 km have been identified on the icy Galilean satellite Europa. These occur along dark lineaments oriented orthogonally to wedge-shaped bands, which are also ∼25 km wide. Wedge-shaped bands are interpreted as dilated tension fractures, which formed as crustal blocks (or plates) 50–100 km across separated and slipped past each other along flanking strike-slip faults. This style of deformation does not appear to be characteristic of other lineament types, and with the exception of Earth appears to be unique to Europa. Together, the subparallel wedge-shaped b bands form a broad NW-SE trending belt, ∼1500 km long and less than 500 km across, near the anti-Jovian point. This belt is interpreted as a major crustal fracture (or rift) zone, with a pole of rotation (determined by the strike-slip faults) near 47°S, 144°W, and an approximate NE-SW direction of maximum tensile stress. Extension may have been areally compensated at Agenor Linea, a bright band of possible compressional origin. Global expansion, tidal distortion, and nonsynchronous rotation do not explain the inferred minimum principal (i.e., least compressive) stress directions. Alternatively, fracturing near the anti-Jovian point may be a result of (i) solid-state convection in the lower ice crust (possibly triggered by uneven heat flow from the silicate interior), (ii) rotation of the icy shell about the sub- and anti-Jovian points induced by latitudinal lithospheric thickness variations, or (iii) preferential strain accumulation from the rest of the icy shell. No significant distortion of the crustal blocks occurred during fracturing and rotation, indicating that the icy crust was probably mechanically decoupled from the silicate interior in this region over the time scale of fracturing. Decoupling on a global scale is also likely the simple geometry of lineaments argues for formation in an icy lithosphere, not a silicate one, and other evidence for fracturing caused by nonsynchronous rotation stress is not compatible with a tidally locked silicate interior (which we show is likely) unless the ice shell rotates independently. Decoupling could have been due to either warm ice or liquid water near the base of the icy crust. Mechanical bounds on lithospheric thickness (a few to ∼10 km) lead to heat flow estimates that admit both possibilities but favor decoupling by liquid water.