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Abstract

The geometry of major basin-bounding faults in the central Rio Grande rift indicates that extension is characterized by overlapping and nested half grabens linked together by accommodation zones and bounded by tilted block uplifts. The Albuquerque-Belen Basin is composed of two separate, opposite-facing, structurally complex basins linked by an accommodation zone. South of the Albuquerque-Belen Basin, the rift broadens southwestward around the Colorado Plateau. A zone of distributed sinistral shear at the margin of the plateau accommodated differential extension between the little-extended plateau and the half grabens (Milligan Gulch, La Jencia, and Socorro) of the rift. Extension in the latter accommodation zone is expressed in the sedimentary cover rocks by north-striking, high-angle normal faults and a segmented, northeast-striking, sinistral fault. The Ladron horst and the Lucero uplift border the rift on the western side of the Albuquerque-Belen Basin and were isostatically uplifted as a result of tectonic denudation along the bounding faults of adjacent half grabens. Footwall structures include folded Paleozoic and Mesozoic rocks, intrabed thrust faults, and high-angle shear zones. We present new models for the Neogene evolution of the central Rio Grande rift and integrate contractional and extensional structures previously attributed to different stress regimes. Many of the structures in the central Rio Grande rift previously attributed to Laramide compression can be adequately explained by late Tertiary extension.