Concentric impact structures in the Palaeozoic of Sweden – the Lockne and Siljan craters
Concentric impact structures in the Palaeozoic of Sweden – the Lockne and Siljan craters
复制标题
瑞典古生代的同心撞击结构——Lockne 和 Siljan 陨石坑
作者：
Anette E. S. Högström;E. Sturkell;J. R. Ebbestad;M. Lindström;J. Ormö
奥陶纪时期的洛克内和泥盆纪时期的西尔扬陨石坑是北方欧洲最大的两个撞击结构。两者都形成于具有厚的低强度上层的目标中。已知该靶配置产生同心凹坑结构，该同心凹坑结构具有在低强度层中的外部浅凹坑，围绕在更耐腐蚀的基底中的中心较深凹坑。洛克内和西尔扬的同心圆陨石坑是研究地球和太阳系其他地方类似同心圆陨石坑的绝佳模型。一些结构问题仍然存在，瑞典深层钻探方案打算钻透陨石坑，以解决以下问题：陨石坑与撞击时间的关系;陨石坑对基底的影响;基底结构对陨石坑形成的作用。洛克内陨石坑的一个问题是与加里东造山带和喷出物覆盖层的横向延伸的关系-边缘被一个径向凹陷中断，该凹陷被解释为主要和次要的构造诱导。第二个要研究的特征是切割基底的更深更老的（1.82-1.80 Ga）NNW-SSE剪切带。在西尔扬地区，由地堑充填组成的巨型块体组合的发展存在争议。这些断块可能是由断块外围部分的下陷形成的，也可能是由涉及千米长搬运的主要径向运动形成的。
The Ordovician age Lockne and Devonian Siljan craters are two of the largest impact structures in northern Europe. Both formed in targets with a thick, low-strength upper layer. This target configuration is known to generate concentric crater structures with an outer, shallow crater in the low-strength layer, surrounding a central, deeper crater in the more resistant substrate. The concentric craters of Lockne and Siljan are excellent models for studies of similar concentric craters on Earth and elsewhere in the Solar system. Several structural issues remain, and drilling through the craters within the Swedish Deep Drilling Program intends to address the following: the extent of the craters with respect to the time of impact; the effects of cratering on the basement; and the role of basement structure for the crater formation. A problem for the Lockne crater is the relation to the Caledonian orogeny and the lateral extension of the ejecta blanket – the rim is interrupted by a radial depression that has been interpreted both as primary and secondary, tectonically induced. A second feature to study is the deeper and older (1.82–1.80 Ga) NNW–SSE shear zones that cut the basement. In the Siljan area the development of mega block associations comprising the infilling of the graben is disputed. The blocks may either be formed by sagging of peripheral parts of the fault blocks or alternatively by major radial movement involving kilometre long transport.