Window (geology)

"window" in German), is a geologic structure formed by erosion or normal faulting on a thrust system.

In such a system the rock mass (hanging wall block) that has been transported by movement along the thrust is called a nappe.

When erosion or normal faulting produces a hole in the nappe where the underlying autochthonous (i.e. un-transported) rocks crop out this is called a window.

This process results in an outlier of exotic, often nearly horizontally translated strata overlying autochthonous strata.

Windows can be almost any size, from a couple of metres to hundreds of kilometres.

Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a nappe . If an erosional hole is created in the nappe that is called a window. A klippe is a solitary outcrop of the nappe in the middle of autochthonous material.