Contractional Regime Research Articles

Review of Precambrian-Palaeozoic relationships at the craton margins of southeastern Australia and adjacent Antarctica

Abstract Similarities in the evolution of late Proterozoic-early Palaeozoic mobile belts flanking the southeast Australian and adjacent Antarctic craton margins support the evidence provided by Archaean-early Proterozoic terranes for former juxtaposition of these two cratons in a Gondwanaland context. The mobile belts show an inversion from an extensional to a contractional regime during this evolution of the active palaeo-Pacific margin of Gondwana. Accretion of outboard terranes along the eastern margin of the mobile belts appears to be preceded by subduction in the Antarctic section whereas, in Australia, contraction of the mobile belt resulted in southeastward transpression at its eastern margin, following obduction of oceanic crust, prior to terrane accretion and collision. Further crustal extension expressed by the subsequent formation of basins in both continents led to lateral displacement of formerly contiguous geologic structures.

Spatially heterogeneous strength in thrust fault zones

Deformation in the hanging wall of the Lewis thrust fault at Marias Pass, northwest Montana, is heterogeneous in space, with regions dominated by either large‐scale contraction or extension faults. The distribution of mesoscopic structures within the two regions also differs. The density of fractures is highest in the extensional region, whereas the density of solution seams is highest in the contractional regime. This spatial heterogeneity of structures at the base of the Lewis thrust sheet may result from spatially heterogeneous fault zone strength. In analytical models of an elastic thrust sheet overlying a fault represented by spatial heterogeneity in shear traction or displacement, stress magnitudes and principal directions vary with position within the model thrust sheet. With the application of a Mohr‐Coulomb criterion, contraction and extension faults initiate within localized regions at the base of the model thrust sheet. Spatial variations in mean stress at the base of the thrust sheet predicted by the models may explain both the greater density of solution seams in the contractional region than in the extensional region and the greater density of mesoscopic faults and veins in the extensional region than in the contractional region of the Marias Pass exposure. The spatial heterogeneity of pressure solution and cataclasis in response to variable mean stress within a fault zone of heterogeneous strength may facilitate thrust sheet movement relative to movement over a fault zone of uniform strength, because a decrease in mean stress enhances cataclasis and an increase in mean stress maintains a constant shear stress during pressure solution.

Neoclassical and Marxian conceptions of production

Incorporating information deficiencies into the neoclassical paradigm has introduced some broad similarities with the Marxian analysis of the labor process. Both approaches predict the existence of a variety of contractual regimes and that workers with equal productivities can be adjudged unequal in the market place. And, while the Marxian approach sees unemployment as inevitable, the new neoclassical models also allow for equilibrium unemployment. These similarities, and areas of divergence, in the assessment of productive efficiency and welfare are explored. A crucial difference arises from the individualism of the neoclassical model, as opposed to the class approach in the Marxian model. Copyright 1988 by Oxford University Press.