Detailed geological mapping of the Ica-Pisco valleys in southern Peru has provided a strict control on K-Ar ages obtained from the plutonic rocks of the Arequipa Segment of the Coastal Batholith of Peru. It is concluded that although the batholith in the Ica-Pisco region was emplaced over a total time span of up to 26.5 Ma active plutonism was confined to two relatively short lived episodes between 107–97 Ma and 82.5-80.5 Ma. This is in contrast to the four main episodes of intrusion in the Lima Segment that spanned about 60 Ma. Correlation of the K-Ar ages and mineral fabrics contained within the plutonic rocks of the Arequipa Segment indicates that emplacement was associated with periods of regional compressive tectonism which, in turn, may be linked to variable rates of subduction.

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