Fold-thrust system overprinting syn-rift structures on the margin of an inverted rift basin: Indio mountains, west Texas.

摘要

Detailed mapping in the central Indio Mountains in west Texas, reveal a complex stacking of thrust sheets that record inversion of the Mesozoic Chihuahua Trough rift basin. Important newly recognized structural complexities include both folding of older thrust sheets and development of younger, out-of-sequence thrusts that cut across older folds; detachment fold horizons within thrust sheets; and a regional anticlinorium that exposes the Squaw thrust in a structural half-window bounded on the west by the Neogene Indio normal fault. The Chihuahua trough originated as part of the late Mesozoic border rift system and was inverted during Laramide thrusting. Remnants of Mesozoic rifting are preserved in Cretaceous strata as facies and stratigraphic thickness variations between different thrust sheets. Statigraphic thickness variations are particularly prominent in the Yucca Formation. A well exposed transgression divides the upper yucca into a fluvial lower interval and a coastal upper interval. The Upper Yucca is 650m thick in the hanging wall of the Squaw thrust and 280 m in the structurally lowest footwall of the thrust system. Reported klippe-fenster relationships indicate a minimum displacement of 7-10km for the structurally highest thrust (Squaw thrust). However, after evaluating the newly identified duplex and incorporating a lower decollement, balanced cross-section reconstructions give a new minimum displacement of 17.3 km. Section reconstruction also indicates that a cryptic basin margin normal fault is carried in the hanging wall of the Squaw Peak thrust to account for both stratigraphic variations and hanging-wall cutoff relationships. Similarities between the structures and models of the Atlas Mountains to those presented in this study suggest the Atlas Mountains and its continuous deformation could be a modern analog for the Indio Mountains.