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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 6. (June)

First Page: 794

Last Page: 794

Title: Thermomechanical Properties and Evolution of Small Pull-Apart Basins: ABSTRACT

Author(s): J. F. Dewey, G. D. Karner, W. C. Pitman, III


Small pull-apart basins are generally characterized by 2 component subsidence: an initial essentially instantaneous isostatic subsidence (Si) dependent on the ratio of crustal to lithospheric thickness (Cz/lz) and the stretching factor ß, followed by a slower decaying thermal subsidence (St) controlled by the thermoelastic properties of the continental lithosphere, which in turn can be characterized by a thermal time constant ^tgr. Rapid short-lived subsidence (e.g., Vienna basin, Californian Miocene basins) is indicative of either (1) inhomogeneous crustal stretching without major sublithospheric involvement, or (2) extremely small lithospheric diffusivities. The former implies a thin-skinned origin for pull-apart basins nd suggests that the spatial and temporal distribution of bounding faults and splays typical of pull-apart basins, result from inhomogeneous brittle failure of the upper crust. However, the effects of lateral heat flow decrease the thermal time constant by allowing a basin to subside more quickly due to both lateral and vertical cooling. The size of this effect is dependent on the width of the stretched lithosphere (the effective ^tgr of a 100 km wide rift is 36 m.y., for a 25 km rift, 6 m.y., whereas the actual thermal time constant in both cases is 62.8 m.y.). Lateral heat flow amplifies rift subsidence while producing complementary time-transgressive uplift in adjacent unstretched regions. However, the flexural rigidity of the lithosphere severely attenuates the deformation caused by he lateral flow of heat. Whereas the deformation is highly dependent on the mechanical properties of the lithosphere, ^tgr is independent.

Continental lithospheric rigidities appear to increase with age following an orogenic or thermal event, suggesting that the long-term mechanical behavior of the continental lithosphere is similar to that of the oceanic lithosphere. However, high rigidities (1032 dyne-cm) associated with Archean/Proterozoic terranes and modeling of plate deformation suggest that the long-term thermal behavior of continental lithosphere is governed by a cooling plate model with a 200-250 km lithospheric thickness, nearly twice the 125 km estimates for the oldest oceanic lithosphere. This has important implications for the evolution of sedimentary basins. A doubling of the lithospheric thickness implies a quadrupling of ^tgr, yet basin subsidence models have assumed that ^tgr for the oceanic a d continental lithospheres are similar. A large ^tgr allows basin subsidence to continue over significantly longer times, but now lateral heat flow, in addition to vertical, must be included in basin models to obtain accurate subsidence and temperature estimates. In particular, Si is highly dependent on the age of the underlying basement. These principles are illustrated both theoretically and with reference to the European Alpine foreland, upper Paleozoic foreland basins of North America, and Californian Neogene basins.

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