Inferring the rheology of the crust from the uplift observed above the Altiplano-Puna Magma Body

Geophysical imaging techniques together with numerical models have shown that the surface uplift measured above the Altiplano-Puna Magma Body (APMB) can be explained by the presence and propagation of a diapir from the top of the APMB itself. In this work, we model deformation that characterizes the crustal region above and around APMB through the use of a viscoplastic rheology. That is, we assume that at large scale the crust that surround the magmatic mushy diapir behaves as a yield-stress fluid described by the Herschel-Bulkley (HB) model, whereby motion develops only when the local deviatoric stress is greater than a critical value, the yield stress. In this scenario, laboratory and numerical results show that there are two main critical conditions needed for the growth and subsequent rise of a diapir: (1) the ratio between the yield stress and viscous stresses, namely the Bingham number Bi, has to be less than 1, that is Bi <= 1 and (2) the ratio between buoyancy stresses and the yield stress, namely the inverse Yield number Y-inv, has to be larger than a critical value Y-invC. Using these two conditions allows us to estimate the bulk rheological properties of the heterogeneous crust above APMB as a function of the diapir's size and density contrast with the crust. For the development of a 10-100 km wide diapir, 100-400 kgm(-3) lighter than the surrounding crust, the crust yield stress should range between 0.5 and 15 MPa. Then, the regional uplift velocity measured at the surface implies a strain rate greater than similar to 10(-15)-10(-16) s(-1) and a crust maximum bulk effective viscosity of eta c=10(21) Pa.s.