Carpenter, James A.¹
(1) Crain Energy, Ltd. / R. Lacy, Inc, Longview, TX

ABSTRACT: Nevada-Arizona-Utah: Pattern Recognition & 3D Visual-Spatial Analyses of Fold-Thrust Structure with Multi-Phase Reactivation and Inversion

Matthews’ (1988-1989) model for a Goodspring thrust duplex and gravity-glided Red Spring segment of the Keystone thrust system is supported by new mapping, 3D geospatial analyses, stratigraphic constraints and structure contouring on faults to examine the alternative models (Carpenter-Carpenter, 2003). C&C’s discovery of the La Madre Mountain gravity slide detachment surface beneath Red Spring klippen is exactly what Matthews' model predicted; and recognition of the Red Rock Canyon clastic unit as a fault rock (i.e., not a synorogenic deposit), with a fabric dipping west 37-46 degrees immediately beneath the Keystone thrust in the Wilson Cliffs, ties up extraneous loose-ends. Matthews’ Single Thrust Sheet model is substantiated. The greater than three-decades-old Dual Thrust Sheet model of Burchfiel-Davis-Axen seems soundly defeated. However, diverse and inclusive written and verbal public debates with gentle hearts and clear heads are encouraged.
Longwell’s footwall ramp geometry for the Keystone-Muddy Mountain thrust system is confirmed for the Mormon Mountains - a Mississippian footwall flat is not present. The North Buffington-Moapa Peak backthrust system (C&C, 1987) is part of a west-vergent backthrust salient that formed at the latitude of an Albian-initiated basement-buttress (Black Ridge salient). Paleostructural analyses show that the east-vergent Muddy Mountain thrust sheet advanced while the Virgin-Beaver Dam Mountains uplifted. The reverse fault that propagated the V-BDM uplift acted as a normal fault in late Precambrian time, and this fault is active today (third time/negative inversion) as a normal fault during Cenozoic Basin-Range extension.
Paleostructural analyses show that while the Roberts Mountains allochthon advanced eastward during the Devonian-Mississippian Antler orogeny autochthonous uplifts formed contemporaneously. The Devonian-Mississippian uplifts experienced renewed propagation during Ancestral Rockies tectonism and again during Sevier tectonism. Some faults that propagated these structures reactivated a fourth time with normal slip during Basin-Range extension (negative inversion). A preceding fifth phase of fault movement, i.e., normal slip, can be inferred in the late Precambrian.

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