Abstract

An enhanced Landsat image of the northeastern Tadjik Depression in the Soviet Union was combined with field data to produce a 1:250,000 geologic map of the Vakhsh fold-and-thrust belt and adjacent autochthon. Mapping of the relatively continuous geologic structure in this region first required recognizing marker beds and contacts at or near the resolution of the Landsat sensor and then defining mappable units. Satellite image mapping was complemented by field study, which was necessary in this recently deformed area, both to verify the image mapping and to obtain more accurate structural dips. Deformation of the Cretaceous and Tertiary strata of the fold-and-thrust belt is, in the western half of the mapped area, conspicuously absent north of a buried basement fault that marks the hinge zone of the late Mesozoic passive margin. In the eastern half of the mapped area, however, the major thrusts (displacing rocks northward) have moved coherent sheets over the block fault. These sheets now lie flat atop the autochthon to the north. Tectonically, these observations indicate that (1) the crustal structure inherited from the Mesozoic extensional phase has strongly influenced the late Cenozoic pattern of deformation, (2) the thrust sheets that are displaced over the paleo-hinge zone actively load the basement rocks to the north, and (3) the development of the fold-and-thrust belt (which is markedly asymmetric) has included the progressive overlapping of thrusts. The later thrusts apparently formed internal to the older thrusts and subsequently overrode them.

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