2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 317-2
Presentation Time: 9:15 AM

EXPANDING THE DISTRIBUTION OF SHOCKED BEDROCK AT THE SANTA FE IMPACT STRUCTURE (NM, USA) BASED ON NEW DETRITAL SHOCKED MINERAL LOCALITIES


MONTALVO, Pedro E., Department of Geology, University of Puerto Rico, P.O. Box 9000, Mayaguez, PR 00681 and CAVOSIE, Aaron J., Department of Geology, University of Puerto Rico, Po Box 9000, Mayaguez, PR 00681

Shocked minerals provide diagnostic evidence for the confirmation of impact structures. Previous studies have documented that detrital shocked minerals can survive post-impact metamorphism, erosion, and distal transport in modern alluvium at the Vredefort Dome [1,2] and Holocene glacial deposits at Sudbury [3]. Detrital shocked minerals can thus be used to identify eroded or obscure impact structures. The Santa Fe impact structure in NM, USA is highly tectonized; both the age (1200-300 Ma) and size (6-13 km) are poorly constrained [4]. In this study we document new occurrences of detrital shocked minerals in regional drainages to expand the distribution of shocked bedrock in the region, beyond where shatter cones have been previously reported.

Detrital grains were surveyed using SEM methods (BSE) to search for diagnostic shock microstructures on grain surfaces. We report the presence of detrital shocked zircon and apatite in sediments (colluvium and alluvium) collected in drainages in all directions away from known shatter cone outcrops on NM Hwy 475 [4]. A total of 1612 zircons were surveyed from 6 samples of colluvium and alluvium, yielding 4 confirmed shocked grains (4/1612 = 0.25%). A total of 792 apatites [5] were surveyed, yielding 26 shocked grains (26/792 = 3.3%).

The results from this study extend occurrences of shocked minerals (and thus rocks) beyond known shatter cone localities. We have documented the presence of detrital shocked zircon and/or apatite in samples 0.4 km south of Hwy 475, on the west side of Chamisa Trail, and 1.7 km north of Hwy 475, all from areas where previously documented shocked bedrock could not have contributed to the sediments. Previous estimates of crater diameter (6-13 km) were calculated from scaling laws based on a 3 km diameter central uplift, derived from shatter cone distribution [4]. As we continue to document new occurrences of detrital shocked minerals, and rocks, the size of the Santa Fe impact structure is predicted to increase.

Support for this work was provided by NSF (EAR 1145118) and NASA Astrobiology.

[1] Cavosie et al. 2010 GSA Bulletin. [2] Erickson et al. 2013 GCA. [3] Thomson et al. 2014 GSA Bulletin. [4] Fackelman et al. 2008 EPSL. [5] Cavosie and Lugo, 2014 LPSC.

Session No. 317

T229. The Holey Solar System (Posters)
Wednesday, 22 October 2014: 9:00 AM-6:30 PM
Exhibition Hall C (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.760
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