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Detrital shocked zircon provides first radiometric age constraint (<1472 Ma) for the Santa Fe impact structure, New Mexico, USA

Abstract

The Santa Fe structure in northern New Mexico is one of the few confirmed impact craters in the western USA. The history of the impact structure is obscure as it is tectonized and eroded to the extent that an intact crater is not preserved, and what remains is located in a complex geological setting. Shatter cones and shocked quartz were previously cited to confirm an impact origin; however, estimates for both impact age (350-1200 Ma) and crater diameter (6-13 km) remain poorly constrained. To further evaluate the extent of shock deformation, we investigated approximately 6600 detrital zircon grains for shock features, using material collected from 15 drainages and other sites within an approximately 5 km radius of known shatter cone outcrops. Six detrital shocked zircon grains were found at three locations, including two near shatter cones and one near brecciated granitoid. Follow-up studies of bedrock at two sites proximal to detrital shocked zircon occurrences led to the discovery of shocked zircon in situ in a shatter cone-bearing sample of biotite schist; shocked grains were not found in brecciated granitoid at the second site. Electron backscatter diffraction confirms the presence of {112} shock-twin lamellae in five shocked zircon grains, and secondary ion mass spectrometry U-Pb data for three detrital shocked grains yielded (super 207) Pb/ (super 206) Pb crystallization ages from 1715 + or - 22 to 1472 + or - 35 Ma. Laser ablation-inductively coupled plasma-mass spectrometry U-Pb ages for detrital zircon grains at five of the investigated sites provide the first broad constraints on the local distribution of Paleo- to Mesoproterozoic bedrock in the area. The presence of shock-twinned zircon indicates that some exposed rocks at the Santa Fe structure may record impact pressures up to approximately 20 GPa based on empirical studies, which is higher than previous reports of approximately 10 GPa based on planar deformation features in shocked quartz. The 1472 + or - 35 Ma date from a shock-twinned zircon yields the first direct radiometric maximum age constraint on the Santa Fe impact event, and expands the possible time period for impact to the Mesoproterozoic. Identification of shocked zircon in modern sediment led to the first discovery of shocked zircon in bedrock at this site, which is notable, as shocked zircon is otherwise not abundant in the studied rock samples. This study thus illustrates that detrital zircon surveys are an efficient way to search for diagnostic evidence of shock deformation at putative impact structures where shocked minerals may be present, but are not abundant in exposed bedrock.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 131
Serial Issue: 5-6
Title: Detrital shocked zircon provides first radiometric age constraint (<1472 Ma) for the Santa Fe impact structure, New Mexico, USA
Affiliation: University of Puerto Rico, Department of Geology, Mayaguez, Puerto Rico
Pages: 845-863
Published: 20181129
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 91
Accession Number: 2019-007063
Categories: GeomorphologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2018299
Illustration Description: illus. incl. 2 tables, geol. sketch maps
N35°45'00" - N35°45'00", W105°55'60" - W105°55'60"
Secondary Affiliation: Curtin University, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, 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: 201906
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