Sentence:  Reflectance spectroscopy (Roush and others, 1993) suggests Mars has a dominantly basaltic crust, but this result may apply only to the surficial rocks, which could be <WSD>overplated</WSD> basalt (Lowman, 1989). 
Meaning of the word marked with <WSD> tags:  To move on top of and cover another tectonic plate.