NUMERICAL SIMULATIONS OF CHICXULUB CRATER FORMATION BY OBLIQUE IMPACT
NUMERICAL SIMULATIONS OF CHICXULUB CRATER FORMATION BY OBLIQUE IMPACT
复制标题
斜向撞击希克苏鲁伯陨石坑形成的数值模拟
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
S. Gulick
中科院分区：
文献类型：
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作者：
G. Collins;N. Patel;A. Rae;T. Davison;J. Morgan;S. Gulick
简介：撞击轨迹方向和与靶面的角度是重要的撞击参数，它们决定了最严重环境后果的方向、气化靶的体积和深度[1]以及喷出物[2]和弹坑的不对称性[3]。希克苏鲁布陨石坑地下结构的不对称性与撞击前目标的不对称性[4、5]以及撞击角度和方向[1、6]有关，但这些参数仍有争议。在这里，我们使用3D数值模拟来研究的影响角度和结构的陨石坑不对称性之间的关系，在一个希克苏鲁伯规模的峰环陨石坑没有预撞击目标不对称。研究方法：希克苏鲁布撞击是使用iSALE 3D冲击物理代码[7，8]模拟的，状态方程[9，10]和强度模型[11]适用于地壳和地幔岩石。模型参数的选择是基于先前使用iSALE 2D [12、5、13]进行的垂直撞击模拟和希克苏鲁布撞击早期阶段的倾斜撞击模拟[14]。使用的地壳平均厚度为33公里。材料数量的限制排除了列入流变学不同的沉积层的目标，但是，示踪剂颗粒允许在这个地层水平的材料在模拟过程中被跟踪，以及峰值冲击压力和峰值环材料的来源。我们考虑了四个冲击角度：90°（垂直），60°，45°和30°。为了计算方便，采用了低碰撞速度（12 km/s），并将垂直碰撞情况与以前的二维模拟进行了直接比较。撞击器直径随着撞击角度的减小而增加（从90°时的16公里增加到30°时的21公里），以实现大致相等的最终弹坑直径（差异<12%）。在所有模拟中使用常见的声学流化参数（粘度和衰减时间）。最小单元尺寸为500 m，根据撞击角度，每个撞击器半径的分辨率为16-21个单元。结果与讨论：对希克苏鲁布陨石坑形成的斜撞击模拟在陨石坑演变、最终峰环和陨石坑结构以及表面形态方面产生了长距离的不对称性，这些不对称性一般随着与目标表面的撞击角度的减小而变得越来越明显（图1和图2）。1和2）。与垂直撞击情况相比，斜向撞击导致瞬态陨坑边缘在上向方向上的抬升较小，而在下向方向上的抬升较大。在火山口塌陷过程中，火山口底部随后的反弹开始于火山口中心的上升段，但有一个下降段的组成部分，使得中央隆起向下降段倾斜，而隆起的中心在塌陷之前位于火山口中心的下降段（图2）。相反，中央隆起的向下和向外的塌陷优先发生在隆起方向上，导致中央隆起在隆起方向上的瞬态火山口边缘顶部的逆冲推覆作用增强。中央隆起的下行方向上升和上行方向下降的最终结果是一个峰值环，其中心仅在下行方向上适度偏移（图1）。
Introduction: Impact trajectory direction and angle to the target plane are important impact parameters that determine the direction of most severe environmental consequences and the volume and depth of origin of vaporized target [1], as well as ejecta [2] and crater asymmetries [3]. Asymmetries in the subsurface structure of the Chicxulub crater have been linked to asymmetry in the preimpact target [4, 5], as well as impact angle and direction [1, 6], but those parameters are debated. Here we use 3D numerical modeling to examine the relationship between impact angle and structural crater asymmetries in a Chicxulub-scale peak-ring crater without preimpact target asymmetry. Methods: The Chicxulub impact was simulated using the iSALE3D shock physics code [7, 8], with equations of state [9, 10] and a strength model [11] appropriate for crustal and mantle rocks. The choice of model parameters was based on previous vertical impact simulations using iSALE2D [12, 5, 13] and oblique impact simulations of the early stages of the Chicxulub impact [14]. A mean crustal thickness of 33 km was used. Material number limitations precluded inclusion of a rheologically distinct sedimentary layer in the target; however, tracer particles allowed material at this stratigraphic level to be tracked during the simulation, as well as the peak shock pressure and provenance of peak ring materials. We considered four impact angles: 90° (vertical), 60°, 45° and 30°. A low impact speed (12 km/s) was used for computational expediency and to afford direct comparison of the vertical impact case with previous 2D simulations. Impactor diameter was increased with decreasing impact angle (from 16 km at 90° to 21 km at 30°) to achieve approximately equivalent final crater diameters (<12% difference). Common acoustic fluidization parameters (viscosity and decay time) were used in all simulations. The minimum cell size was 500 m, affording resolutions of 16-21 cells per impactor radius, depending on impact angle. Results & Discussion: Oblique impact simulations of Chicxulub crater formation produce along-range asymmetries in crater evolution, final peak-ring and crater structure and surface morphology that in general become increasingly pronounced with decreasing impact angle to the target surface (Figs. 1 & 2). Compared with the vertical impact case, oblique impact results in less uplift of the transient crater rim in the uprange direction and more uplift in the downrange direction. Subsequent rebound of the crater floor during crater collapse begins uprange of the crater centre, but has a downrange component such that the central uplift is tilted downrange and the centre of the uplift prior to its collapse is downrange of the crater centre (Fig. 2). Conversely, downward and outward collapse of the central uplift occurs preferentially in the uprange direction, resulting in enhanced overthrusting of the central uplift on top of transient crater rim in the uprange direction. The net result of the downrangedirected rise and uprange-directed fall of the central uplift is a peak ring with a centre only modestly offset in the downrange direction (Fig. 1).