TRAVIS, CHRISTOPHER J., BP Exploration Inc., Houston, TX; and ROY K. DOKKA and JEFF A. NUNN, Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA

ABSTRACT: Stratigraphic Architecture of a Detachment-Dominated Extensional Orogen: Early Miocene Mojave Extensional Belt, California

Recent studies of volcanic and sedimentary rocks of the early Miocene age Mojave Extensional Belt (MEB) provide new insights into the stratigraphic architecture of an evolving continental extensional orogen. A regional tripartite stratigraphy exists across the belt: (1) pre- to early synextension volcanic deposits, unconformably overlain by (2) syntectonic basement-derived megabreccia and breccia with local finer-grained units, overlain by (3) a post-tectonic fining-upward sequence of gravel, sand, shale, and limestone. Computer simulations using a diffusion model of sedimentation in half graben reproduce both the geometric and textural characteristics of the syn- and post-tectonic stages.

On a more local scale, stratigraphy and sediment dispersal within the MEB reflect the evolution of the major tectonic elements of the belt:

1. Breakaway Zone. Sediments deposited in the western Newberry Mountains record a complex history of basin formation and dissection as the upper plate of the terrane progressively broke up during extension.

2. Transfer Zone. Strike-slip elements had a variable effect on patterns of sediment accumulation. Miocene sedimentary rocks near the Kane Springs transfer zone were mostly derived from across the strike-slip boundary, but the Lane Mountain transfer zone appears to have had little affect on sedimentation patterns in the adjacent Mud Hills.

3. Core complex. Deposition of coarse-grained sedimentary rocks in the Mud Hills record the topographic evolution of the Mitchel Range-Hinkley Hills-Waterman Hills metamorphic core complex. Multidisciplinary studies of the upper and lower plates provide new constraints on models for extension of this area.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.