Identifying Blind Thrust Anticlines in the Subsurface using Drainage Patterns: Andean Foreland of Central Argentina
Peter A. Enderlin
The Ohio State University, School of Earth Sciences, Columbus, OH;
Blind thrust faults are faults that have not propagated to intersect the Earth’s surface. In some cases, blind thrusts can be identified by anticlinal hills above the projected fault tip. However, even if there is no topographic expression, blind thrust faults can be identified geomorphically by deviations in drainage patterns or overall changes of basin shape. The purpose of this study is to test if a geomorphic method can be used to identify blind thrust faults associated with subdued topographic expression in the Andean Foreland, Central Argentina. Active deformation in this region has resulted in the topographic expression of several blind thrust faults, and their affect on drainage morphology can be used for comparison.
This approach requires both lab- and field-based components. Regional drainage of the basin was mapped in the lab by comparing a stream-network vector file, derived from 3 arc-second digital elevation models, to stream locations seen on high-resolution satellite imagery. Anomalies in the drainage patterns associated with tectonics, such as longitudinal and lateral changes in stream gradient (e.g. river diversions, shifts in sinuosity, and gradient changes) were identified in order to recognize areas with potentially active, buried tectonic structures. Preliminary findings show a number of river diversions between lat 32°30’-33°30’S and long 67°30’-68°W. The influence of blind thrusts on drainage morphology will be verified in the field during a Fall 2009 field-season and using regional seismic profile lines. If a previously unknown blind-thrust anticline is indentified, this structure could be further explored as a potential hydrocarbon trap.
AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid