Full waveform tomographic images of the peak ring at the Chicxulub impact crater
Full waveform tomographic images of the peak ring at the Chicxulub impact crater
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希克苏鲁伯撞击坑峰环的全波形断层扫描图像
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
P. Barton
中科院分区：
文献类型：
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作者：
J. Morgan;M. Warner;G. Collins;R. Grieve;G. Christeson;S. Gulick;P. Barton
峰环是类地行星上大型撞击坑的一个特征，通常认为是由深埋的岩石在陨石坑形成过程中隆起而形成的。然而，峰环形成的精确岩性和运动学仍不清楚。先前的工作已经揭示了一套明亮的向内倾斜的反射层，位于希克苏鲁布撞击坑的峰环之下，峰环是由地震速度相对较低的岩石形成的。新的二维、全波形层析速度图像显示，峰环的最上层岩性是由一层薄的（100-200米厚）低速（1000 -3200米/秒）岩石形成的。这个低速层很可能是由高度多孔的、同种异体的撞击角砾岩组成的。我们的模型还表明，峰值环内外岩性之间的速度变化比以前实现的更突然，发生在倾斜反射体的位置附近。在整个峰环中，速度似乎与陨石坑形成的动态模型预测的冲击压力有很好的相关性，其中形成峰环的岩石起源于受到高冲击压力（10-50 GPa）的隆起基底，并位于受到<5 GPa冲击压力的下沉沉积岩之上。这些观察结果表明，低速度内的峰值环可能与冲击效应和倾斜的反射峰环下可能代表高度冲击基底和弱冲击沉积物之间的边界。
Peak rings are a feature of large impact craters on the terrestrial planets and are generally believed to be formed from deeply buried rocks that are uplifted during crater formation. The precise lithology and kinematics of peak ring formation, however, remains unclear. Previous work has revealed a suite of bright inward dipping reflectors beneath the peak ring at the Chicxulub impact crater and that the peak ring was formed from rocks with a relatively low seismic velocity. New two-dimensional, full waveform tomographic velocity images show that the uppermost lithology of the peak ring is formed from a thin (∼100–200 m thick) layer of low-velocity (∼3000–3200 m/s) rocks. This low-velocity layer is most likely composed of highly porous, allogenic impact breccias. Our models also show that the change in velocity between lithologies within and outside the peak ring is more abrupt than previously realized and occurs close to the location of the dipping reflectors. Across the peak ring, velocity appears to correlate well with predicted shock pressures from a dynamic model of crater formation, where the rocks that form the peak ring originate from an uplifted basement that has been subjected to high shock pressures (10–50 GPa) and lie above downthrown sedimentary rocks that have been subjected to shock pressures of <5 GPa. These observations suggest that low velocities within the peak ring may be related to shock effects and that the dipping reflectors underneath the peak ring might represent the boundary between highly shocked basement and weakly shocked sediments.