Pulsating diapiric flows: Consequences of vertical variations in mantle creep laws

Peter van Keken a, David A. Yuen b and Arie van den Berg a Received November 21, 1991, revision accepted June 17, 1992 Recent laboratory work has suggested that the rheology of the lower mantle may be Newtonian. We have studied the time-dependent dynamics of plumes interacting with a rheological interface separating an upper non-Newtonian mantle and a Newtonian lower mantle . Pulsating diapiric structures with fast time scales are promoted by the interaction of the rising plumes with this rheological boundary . Surface heat flow signals are discernible as pulses, which remain relatively stationary . They correlate well with the localized upwellings just below the surface . The presence of a mobile lithosphere from increasing the non-Newtonian power-law index helps to produce a large-scale circulation in the upper mantle which draws large hot patches away from nearby upwellings . In our calculations the resultant averaged effective viscosity of the non-Newtonian upper mantle is about two orders of magnitude lower than that of the Newtonian lower mantle . A viscously stratified Newtonian model produces more incoherent and broad-scale diapiric structures and is less efficient for generating sharply varying time-dependent thermal signatures .