Paleomagnetism of Lonar impact crater, India
Paleomagnetism of Lonar impact crater, India
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印度洛纳尔撞击坑的古地磁学
DOI：
10.1016/j.epsl.2008.08.025
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发表时间：
2008
影响因子：
5.3
通讯作者：
S. A. Soule
中科院分区：
文献类型：
--
作者：
K. Louzada;Benjamin P. Weiss;A. Maloof;Sarah T. Stewart;N. Swanson‐Hysell;S. A. Soule
印度洛纳尔陨石坑是在玄武岩中形成的保存最完好的陆地撞击坑，是陆地行星和月球上小型、简单的陨石坑的独特类似物。我们研究了直径1.88千米的陨石坑的古地磁和岩石磁性，以了解撞击对目标岩石磁化的影响。朗纳尔玄武岩中的磁化作用由原始的65 Ma德干磁化作用和最近的叠加作用组成。我们利用喷出沉积碎屑的砾岩测试和倾覆杂乱的边缘褶皱的褶皱测试相结合的方法，限制了Lonar获得磁化的时间。在一些地区，横卧的边缘褶皱被保存下来，可以近似为水平的圆柱形褶皱。在其他区域，在折叠过程中形成撕裂带的地方可能发生了相当大的垂直轴旋转。我们只观察到了对LONAR材料的岩石磁性的影响，其中包括受到冲击的喷出块中的矫顽力略有上升。我们表明，在没有冲击的岩石学证据的情况下，古地磁可以限制冲击加热(在这种情况下，<；187±15°C)。在Lonar，在陨石坑形成后，50kyr获得的粘性(和/或化学)剩余磁化掩盖了任何冲击波剩余磁化的证据。我们也没有发现冲击退磁的证据，也没有证据表明在较大的撞击结构周围存在强烈的冲击诱导或冲击放大的瞬变磁场。
Lonar crater, India, is the best preserved terrestrial impact crater formed in basalt and is a unique terrestrial analogue for small, simple craters on terrestrial planets and the Moon. We investigated the paleomagnetic and rock-magnetic properties of the 1.88 km diameter crater in order to understand the effect of impacts on magnetization in target rocks. The magnetization in the Lonar basalts consists of an original 65 Ma Deccan magnetization and a recent overprint. We constrained the timing of magnetization acquisition at Lonar using a combination of conglomerate tests on ejecta deposit clasts and fold tests on the overturned and jumbled rim fold. In some areas, the recumbent rim fold is preserved and can be approximated as a horizontal cylindrical fold. In other areas, substantial vertical axis rotation may have occurred where tear zones developed during folding. We observed only subtle effects from the impact on the rock-magnetic properties of Lonar materials, which include a slightly elevated coercivity in shocked ejecta blocks. We show that paleomagnetism can provide a constraint on shock heating in the absence of petrographic evidence of shock (in this case, <187±15 °C). At Lonar, viscous (and/or chemical) remanent magnetization acquired in the <50 kyr subsequent to crater formation has obscured any evidence of shock remanent magnetization. We also find no evidence of shock demagnetization or the presence of intense impact-induced or impact-amplified transient magnetic fields that have been proposed around larger impact structures.