Kluth, Charles F.¹
(1) Kluth & Associates, Colorado School of Mines, Golden, CO

ABSTRACT: Inversion and Re-inversion of the Northern Rio Grande Rift, Southern Colorado

The northern Rio Grande Rift in southern Colorado has been the site of inversion of different types of major structural features through Phanerozoic time. The area was a deep, narrow basin in the late Paleozoic. Over 5 km of arkosic redbeds and conglomerates filled the southern part of the Central Colorado Trough, part of the Ancestral Rocky Mountains. The Paleozoic basin was completely inverted by eastward thrusting and uplift during the Late Cretaceous-Early Tertiary Orogeny. The Sangre de Cristo Range preserves the eastern, frontal part of the Laramide uplift. A re-inversion of the uplift structure occurred when Late Tertiary extension related to the Rio Grande Rift caused the core of the Laramide uplift to subside. The Tertiary extension included early, low angle faulting and later, large, higher-angle planar faults. The northern Rio Grande Rift in the San Luis Basin in southern Colorado contains approximately 7 km of synrift basin fill. Hydrocarbon shows in core holes along the flanks of the rift suggest that a hydrocarbon system is present in the rift. Aeolian sands interbedded with lacustrine shales may have been accumulating since the inception of the rift, which has elevated heat flow. In addition to the rift-related plays, late Paleozoic source and reservoir rocks, preserved in the Sangre de Cristos, may be present in the footwall of the Laramide thrust faults, now in the down-dropped, hanging wall of the rift structures.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.