Elastoviscoplastic relaxation of impact crater topography with application to Ganymede and Callisto
Elastoviscoplastic relaxation of impact crater topography with application to Ganymede and Callisto
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DOI：
10.1029/2005je002445
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发表时间：
2006-01-10
影响因子：
4.8
通讯作者：
McKinnon, WB
中科院分区：
文献类型：
--
作者：
Dombard, AJ;McKinnon, WB
我们使用弹粘塑性流变模型来研究木卫三和木卫四上陨石坑地形的长期松弛。我们采用一套完整的流变参数在冰的韧性蠕变和实现一个新的，较浅的初始形状模型。在高热流条件下，应力在较深、粘性较低的材料中被释放，剩余的应力在粘性较硬的近表层集中为弯曲（弯曲）应力。从本质上讲，机械岩石圈的形成集中了应力，但其隆起和应力水平总是大于纯粘性半空间所获得的应力水平。我们讨论了经典弹性弯曲和纯粘性松弛是这种更广义流变模型的特殊情况。在足够高的热流条件下，弯曲层（即弯曲层）的应力集中可以超过冰的塑性屈服强度，这在一定程度上削弱了冰层，增加了总松弛量。这些塑性应变往往局限于火山口底部浅层区域的小震级（< 0.5%）；这些特征可以在可用的图像中观察到。冰中主要蠕变机制的晶粒尺寸敏感性代表了冰卫星上陨石坑松弛研究的一个新的输入参数（以及弹性和塑性模量，尽管程度较小）。然而，我们发现，在合理的输入参数下，我们的模拟再现了在木卫三和木卫四上看到的连续松弛状态。较高的表面温度（类似于120-130 K）和较大的晶粒尺寸（> -1 mm）的组合允许在预期热流范围的低端和高端分别保持和松弛地形。考虑到马里乌斯地区的松弛陨石坑以及改写坑和近改写坑，表明古代热流超过10 mW m(-2)，与其他估计一致。
We use an elastoviscoplastic rheological model to study the long-term relaxation of impact crater topography on Ganymede and Callisto. We employ a complete set of rheological parameters for ductile creep in ice I-h and implement a new, shallower initial shape model. Under high heat flow conditions, stresses are relieved in deeper, less viscous material, and the remainder concentrates as flexural ( bending) stresses in a viscously stiffer near-surface layer. Essentially, a mechanical lithosphere forms that focuses stresses but with uplifts and stress levels that are always greater than those obtained for a purely viscous half space. We discuss how classic elastic flexure and purely viscous relaxation are special cases of this more generalized rheological model. Stress concentration in the flexing (i.e., bending) layer can exceed the plastic yield strength of ice for high enough heat flows, weakening the layer somewhat and increasing the total amount of relaxation. These plastic strains tend to be limited to small magnitudes (< 0.5%) in a shallow region on the crater floor; such features may be observable in available imagery. The grain size sensitivity of the dominant creep mechanism in ice represents a new input parameter in crater relaxation studies on icy satellites ( along with the elastic and plastic moduli, although to a lesser extent). Nevertheless, we find that for reasonable input parameters our simulations reproduce the continuum of relaxation states seen on Ganymede and Callisto. A combination of higher surface temperatures (similar to 120-130 K) and larger grain sizes (> 1 mm) permits both retention and relaxation of topography at the lower and higher ends, respectively, of the anticipated heat flow range. Consideration of relaxed craters in Marius Regio and of the palimpsests and penepalimpsests suggests ancient heat flows in excess of 10 mW m(-2), consistent with other estimates.