FLEXURAL MODELING OF CONTINENTAL LITHOSPHERE DEFORMATION - A COMPARISON OF 2D AND 3D TECHNIQUES

The flexural isostatic response of the lithosphere in response to load ing caused by continental tectonics has been modelled in 3D. The model ling approach used has been to determine hanging wall deformation foll owing movement over a pre-defined fault surface. In addition, the lowe r crust is assumed to deform by a pure shear mechanism. The changes in crustal thickness resulting from these structural processes impose lo ads upon the lithosphere, which responds by isostatic adjustment. Algo rithms have been developed to quantify the flexural isostatic response to these loads in 3D. These deflections are then superimposed upon th e results from the structural modelling to generate isostatically comp ensated hanging wall, footwall and fault surfaces. Schematic models ar e presented for extensional, compressional and strike-slip deformation . Model results are dependent upon the interaction between fault geome try, displacement along the fault, which can be varied along strike, a nd the methodology used to quantify the flexural response of the litho sphere to loading. Emphasis has been placed upon contrasting models, w hich include a structural component only with those that incorporate b oth structural and flexural isostatic processes. Following extension, structural processes generate a relatively deep half-graben with no de formation at the basin edges. Isostatic compensation modifies this str ucture to produce a relatively shallow, but variable, basin depth with uplift (typically between 1 and 2 km) experienced at the basin edges. Compressional models have been generated which show the formation of large uplift structures, which are modified by isostatic compensation so that they are considerably reduced in magnitude. A regional depress ion (i.e. foreland basin) is also generated adjacent to the remaining uplift. Both 2D and 3D implementations of flexural isostasy have been investigated to provide insights into the validity of results provided by commonly applied 2D methods. A major advantage arising from 3D tec tonic modelling is the ability to investigate the effects of oblique o r entirely strike-slip components of fault movement. Strike-slip defor mation has been modelled in the context of a single fault surface, whi ch varies along strike, to show the development of pressure ridge and pull-apart basin structures. The isostatic compensation of these struc tures shows complex patterns of uplift and subsidence due to the inter ference of negative and positive loading and associated flexural defle ctions. (C) 1998 Elsevier Science B.V. All rights reserved.