  The Lindblad generators of the master equation define which kind of
decoherence happens in an open quantum system. We are working with a two qubit
system and choose the generators to be projection operators on the eigenstates
of the system and unitary bilocal rotations of them. The resulting decoherence
modes are studied in detail. Besides the general solutions we investigate the
special case of maximally entangled states - the Bell singlet states. The
results are depicted in the so-called spin geometry picture which allows to
illustrate the evolution of the (nonlocal) correlations stored in a certain
state. The question for which conditions the path traced out in the geometric
picture depends only on the relative angle between the bilocal rotations is
addressed.
