A
tectonic window (or
Fenster (lit. "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.