The degree to which the chain was affected by the erosion depended mainly on the structure of the terrain, which explains the diversity in the topography of the area. The topography of Sarek, similar to that of Kebnekaise, is divided into sharply defined zones, particularly in respect to the two neighbouring national parks. This is mainly due to the existence of diabase and diorite dikes which are more resistant to erosion. The park is intersected by a tangle of dikes created 608 million years ago, an era that probably corresponds with the first appearance of the rift during the formation of the Iapetus ocean. These dikes represent intrusions into the Sarektjåkkå nappe, which is composed of sediments probably deposited in the rift basin.