A dike in the common geological sense is a mostly tabular body of different materials (minerals, rocks, ores) cross-cutting the host rock. In impact structures, breccia dikes have played an important role in the understanding of the impact cratering process. They have been reported from many impact structures, and they have in detail been investigated e.g. for the Rochechouart (France) and Azuara (Spain) structures. It is generally suggested that for the most part the breccia dikes are formed in the excavation stage by injection of brecciated material into the walls and the floor of the expanding excavation cavity. Later formations of breccia dikes in the modification stage incorporating earlier formed ones may lead to generations of breccia dikes.

Although frequently very similar in outcrop conditions, breccia dikes should not be confused with impact pseudotachylites (see http://www.impact-structures.com/impact-rocks-impactites/impact-melt-page-impact-melt-rocks-impact-glasses-and-congeners/). By definition, pseudotachylites are characterized by a melt rock matrix clearly different from the clastic matrix of dike breccias.

Fig. 1. System of breccia dikes cutting through Liassic limestones. Azuara impact structure (Spain), near Belchite.

 

 

 

Fig. 2. Breccia dike, Rochechouart impact structure (France).

 

 

 

Fig. 3. Breccia dike sharply cutting through Jurassic limestone. Rim zone of the Rubielos de la Cérida impact basin, near Cervera del Rincón.

 

 

 

Fig. 4. System of impact breccia dikes cutting through heavily fractured Paleozoic siltstones. At the top well bedded post-impact Tertiary conglomerates. Rim Zone of the Rubielos de la Cérida impact basin near Lechago.

 

 

Fig. 5. Crossing breccia dikes (dike generations) in Malmian limestone. The first emplaced dike (N – S trending) is cut by the younger dike showing ribbon texture probably originating from chemical interactions between dike material and the host rock. Azuara impact structure; near Ventas de Muniesa, Corral de Cámaras. Match-box length 40 mm.

Fig. 6. Polymictic breccia dike cutting through Triassic dolostone. Rubielos de Cérida impact basin, near Teruel.

 

 

 

Fig. 7. Breccia dike in Jurassic limestone. Rubielos de la Cérida impact basin (Spain). Note the sharp-edged breccia clasts and the sharply fragmented host rock excluding any karstification features.

 

 

Fig. 8. Prominent breccia dike cutting through Paleozoic siltstones. Azuara impact structure, Virgin de Herrera.

 

 

Fig. 9. Breccia dike cutting through Muschelkalk limestone. Rubielos de la Cérida impact basin, near Corbalán. Sharp-edged fractures without any dissolution features exclude confusion with karst structures.

 

 

 

 

 

Fig. 10. Bifurcating breccia dike cutting through Lower Tertiary conglomerates. Rubielos de la Cérida impact basin, near Escorihuela.

 

 

 

Fig. 11. Breccia dikes in hand specimen. Muschalkalk limestone, Rubielos de la Cérida impact basin, near Escriche.

 

 

 

Fig. 12. Microscopic breccia dike in a quartzite clast of a strongly shocked polymictic dike breccia (breccia-dike generations). Azuara structure. Photomicrograph, plane light and xx polarizers; the field is 5 mm high. Note that the dikelet branching off from the principal dike cuts several quartz grains.