Bounds on the viscosity coefficient of continental lithosphere from 3 removal of mantle lithosphere beneath the Altiplano and

8 [1] The rapid rise of the central Andean plateau 9 between 10 and 6.8 Ma implies that mantle 10 lithosphere, including eclogitized lower crust, was 11 removed from beneath the region in that time interval; 12 we infer from that removal that the average viscosity 13 coefficient of mantle lithosphere was quite low when 14 removal occurred. Using scaling laws for the growth 15 of perturbations to the thickness of a dense layer over 16 an inviscid substratum (Rayleigh-Taylor instability), 17 we place bounds on the average viscosity coefficient 18 for central Andean lithosphere. When compared with 19 laboratory measurements of flow laws for olivine and 20 eclogite, the allowed range of viscosity coefficients 21 yields bounds on the temperature of 500–800 C at 22 the Moho beneath this region and suggests that mean 23 stresses across mantle lithosphere during continental 24 deformation are less than 50 MPa. This range of 25 temperature is comparable with, if a slightly lower, 26 than we might expect for lithosphere approximately 27 doubled in thickness and not yet equilibrated with the 28 doubled crustal radioactivity. The mean deviatoric 29 stress is comparable to that associated with stresses 30 that drive plates and hence shows that lithospheric 31 material is not too strong to prevent removal of its 32 mantle part. Citation: Molnar, P., and C. N. Garzione (2007), 33 Bounds on the viscosity coefficient of continental lithosphere 34 from removal of mantle lithosphere beneath the Altiplano and 35 Eastern Cordillera, Tectonics, 26, XXXXXX, doi:10.1029/ 36 2006TC001964.