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Abstract:

The Permian Basin of west Texas and southern New Mexico is located in the foreland of the late Paleozoic Marathon-Ouachita orogenic belt. This complex foreland area consists of several sub-basins that are separated by intraforeland uplifts. In an accompanying paper in this volume, regional structural and stratigraphic relationships are used to constrain the tectonic history of the Permian Basin region. A kinematic model for the origin of the Central Basin Platform (CBP), a prominent intraforeland uplift that separates the Midland and Delaware Basins, is also presented. In this paper, we show the results of two-dimensional flexural models for the Permian Basin region.

The Marathon orogenic belt is generally considered to be the dominant topographic load that caused flexural subsidence in the Permian Basin region. Basement shortening and uplift associated with the CBP, however, require that the CBP is an additional topographic load that must be considered when modeling the late Paleozoic evolution of the adjacent basinal areas. The CBP was treated as a distributed tectonic load that produced lithospheric flexure of the adjacent basinal areas. To calculate the effects of this load, loading geometries were determined from the excess basement material measured on structural cross sections. These loading geometries were then used to calculate static profiles of the deflected lithosphere using flexural models for elastic lithosphere. Results from flexural analyses compare well with reconstructed synorogenic geometries of the Midland, Delaware, and Val Verde Basins, indicating that subsidence of these basins most likely was produced by the combined topographic loads of the Marathon orogenic belt, the CBP, and probably structures associated with the Diablo Platform and cryptic loads near the Eastern Shelf on the eastern side of the Midland Basin.

Best-fit model profiles for the Val Verde and Delaware Basins indicate that values for the flexural rigidity of lithosphere in the Permian Basin region are lowest near the southwest corner of the CBP. The Val Verde Basin is narrowest and the Delaware Basin is deepest near this corner. The apparently low rigidities at this corner also coincide with a prominent salient in the Marathon orogenic belt and with the greatest amount of shortening measured along the boundaries of the CBP. These low calculated rigidities reflect locally weaker lithosphere that might be related to inherent lateral strength variations in the Marathon foreland. Alternatively, high bending stresses produced by the combined loads of the southwest corner of the CBP and the prominent salient of the Marathon orogenic belt may also have weakened the lithosphere in this area.

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