The term allochthonous refers to rocks or sediments that have been transported from their place of origin and deposited in a different location, typically by tectonic forces. In geology, allochthonous units are often contrasted with autochthonous units, which have remained in their place of formation. Allochthonous materials provide insights into the dynamics of tectonic processes, such as thrust faulting and subduction.
Source Davis, G. H., & Reynolds, S. J. (1996). Structural Geology of Rocks and Regions. John Wiley & Sons.