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A comprehensive survey of faults, breccias, and fractures in and flanking the eastern Espanola Basin, Rio Grande Rift, New Mexico

Jonathan Saul Caine, Scott A. Minor, V. J. S. Grauch, James R. Budahn and Tucker T. Keren
A comprehensive survey of faults, breccias, and fractures in and flanking the eastern Espanola Basin, Rio Grande Rift, New Mexico
Geosphere (Boulder, CO) (October 2017) 13 (5): 1566-1609

Abstract

A comprehensive survey of geologic structures formed in the Earth's brittle regime in the eastern Espanola Basin and flank of the Rio Grande rift, New Mexico, reveals a complex and protracted record of multiple tectonic events. Data and analyses from this representative rift flank-basin pair include measurements from 53 individual fault zones and 22 other brittle structures, such as breccia zones, joints, and veins, investigated at a total of just over 100 sites. Structures were examined and compared in poorly lithified Tertiary sediments, as well as in Paleozoic sedimentary and Proterozoic crystalline rocks. Data and analyses include geologic maps; field observations and measurements; orientation, kinematic, and paleostress analyses; statistical examination of fault trace lengths derived from aeromagnetic data; mineralogy and chemistry of host and fault rocks; and investigation of fault versus bolide-impact hypotheses for the origin of enigmatic breccias found in the Proterozoic basement rocks. Fault kinematic and paleostress analyses suggest a record of transitional, and perhaps partitioned, strains from the Laramide orogeny through Rio Grande rifting. Normal faults within Tertiary basin-fill sediments are consistent with more typical WNW-ESE Rio Grande rift extension, perhaps decoupled from bedrock structures due to strength contrasts favoring the formation of new faults in the relatively weak sediments. Analyses of the fault-length data indicate power-law length distributions similar to those reported from many geologic settings globally. Mineralogy and chemistry in Proterozoic fault-related rocks reveal geochemical changes tied to hydrothermal alteration and nearly isochemical transformation of feldspars to clay minerals. In sediments, faulted minerals are characterized by mechanical entrainment with minor secondary chemical changes. Enigmatic breccias in rift-flanking Proterozoic rocks are autoclastic and isochemical with respect to their protoliths and exist near shatter cones believed to be related to a previously reported pre-Pennsylvanian impact event. A weak iridium anomaly is associated with the breccias as well as adjacent protoliths, thus an impact shock wave cannot be ruled out for their origin. Major fault zones along the eastern rift-flank mountain front are discontinuous and unlikely to impede regional groundwater flow into Espanola Basin aquifers. The breccia bodies are not large enough to constitute aquifers, and no fault- or breccia-related geochemical anomalies were identified as potential contamination sources for ground or surface waters. The results of this work provide a broad picture of structural diversity and tectonic evolution along the eastern flank of the central Rio Grande rift and the adjacent Espanola Basin representative of the rift as a whole and many rifts worldwide.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 13
Serial Issue: 5
Title: A comprehensive survey of faults, breccias, and fractures in and flanking the eastern Espanola Basin, Rio Grande Rift, New Mexico
Affiliation: U. S. Geological Survey, Denver, CO, United States
Pages: 1566-1609
Published: 201710
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 138
Accession Number: 2018-016581
Categories: Structural geologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
N31°30'00" - N37°00'00", W109°04'60" - W103°00'00"
N31°30'00" - N37°00'00", W107°30'00" - W105°30'00"
Secondary Affiliation: Colorado State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201804
Program Name: USGSOPNon-USGS publications with USGS authors
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