In this paper we describe a variability mechanism centric approach for the representation of process family architectures, which act as the major blueprint for the implementation of families of process oriented software in process family engineering. We therefore analyze the role of variability mechanisms in process family architectures and define a set of variability mechanisms for process family architectures represented as a UML Activity Diagram. The variability mechanism centric approach for process family architecture modeling allows for representing explicitly and intuitively the variability in a process family architecture and supports the effective reuse of process family architecture parts for the process family members. Moreover, it allows to model the implementation of variability in the process family and thus to take into account the influence of the variability implementation on the non-functional properties of the process family during process family architecture design. Our approach thus supports a more model-driven variability implementation in process family engineering.