Impact breccias in carbonate rocks, Sierra Madera, Texas

GSA Bulletin
By: , and 



Two main types of deformational breccia occur in the Sierra Madera cryptoexplosion structure: monolithologic breccias composed of shattered rock of a single lithology and mixed breccias composed of rocks of several lithologies. Monolithologic breccias generally show no mineralogic signs of shock deformation, but a few samples are shatter-coned in a manner suggesting simultaneous formation of breccias and shatter cones. Mixed breccias, forming irregular, cross-cutting bodies, consistently contain moderately to highly shocked material, with mineralogic evidence of shock pressures of 50 kb to more than 200 kb, which, with evidence from the structural geometry of Sierra Madera and orientation of shatter cones, indicate an impact origin of the breccias.

The mode of occurrence of the breccias, petrographic characteristics, and association with shock features are shared by breccias in many other cryptoexplosion structures in both carbonate and crystalline rock terranes, suggesting that such breccias have a common origin.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Impact breccias in carbonate rocks, Sierra Madera, Texas
Series title GSA Bulletin
DOI 10.1130/0016-7606(1971)82[1009:IBICRS]2.0.CO;2
Volume 82
Issue 4
Year Published 1971
Language English
Publisher Geological Society of America
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 10 p.
First page 1009
Last page 1018
Country United States
State Texas
Other Geospatial Sierra Madera crater