DENSITY, TEMPERATURE, AND RHEOLOGICAL MODELS FOR THE SOUTHEASTERN CANADIAN CORDILLERA - IMPLICATIONS FOR ITS GEODYNAMIC EVOLUTION

Two-dimensional density, temperature, and rheological models are const ructed for a 350 km northeast-trending transect of the southeastern Ca nadian Cordillera. All models highlight several major physical differe nces between foreland and hinterland lithosphere. Significant features of the density model are the presence of an anomalously low-density ( 3.10 x 10(3) kg . m-3) layer, with a maximum thickness of 12 km, benea th the Moho in the hinterland; the similar densities of the Monashee T errane and the cratonic crust of the foreland; and an increase in crus tal thickness beneath the Southern Rocky Mountain Trench. The temperat ure model shows steeper gradients and higher Moho temperatures beneath the hinterland than beneath the foreland. In the rheological model th e hinterland is characterized by a thin, brittle, upper crust beneath which the entire lithosphere is hot, weak, and ductile. In contrast, t he foreland is composed of a thick, brittle, upper crust, with an addi tional brittle zone in the upper mantle. The Moho is a large strength discontinuity beneath the foreland, and the total lithospheric strengt h there is an order of magnitude larger than in the hinterland. The mo dels are constrained and supported by geological mapping and a number of independent geophysical data sets. Palinspastic cross sections, tog ether with paleotemperature and paleopressure information, are used to generate a time series of one-dimensional paleorheological profiles a t a number of times during deformation. This sequence of profiles indi cates that the foreland and hinterland have been rheologically distinc t since pre-Late Cretaceous times. The profiles are used to clarify th e geodynamic evolution of the area and to explain why deformation rema ined thin skinned in the foreland whereas in the hinterland the entire lithosphere was deformed.