T253 Celebrating Dr. John W. Valley's Contributions to Isotope Geochemistry and Beyond, from the Hadean to the Holocene (Posters)

Tuesday, 24 October 2017
9:00 AM - 6:30 PM
Halls 4EF

DETRITAL SHOCKED ZIRCON PROVIDES FIRST MAXIMUM AGE CONSTRAINT OF 1472 MA FOR THE SANTA FE IMPACT STRUCTURE, NEW MEXICO (USA)

Paper number: T253-15
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Shocked minerals provide diagnostic evidence of impact structures, which are prone to erosion, burial and tectonic deformation. Zircon {112} twins are considered diagnostic evidence of shock deformation, and have been identified at several impact structures such as Vredefort [1,2,3,4], Sudbury [5], Ries [6], Rock Elm [7], and in lunar impact breccia [8]. The Santa Fe impact structure contains shatter cones and shocked quartz, but is highly tectonized and eroded; previous reports of impact age (1200–300 Ma) and size (6–13 km) are poorly constrained [9]. Here, we report the first occurrence of shock-twinned zircon in both sediments and bedrock at the Santa Fe impact structure.

A total of 6619 grains from fifteen sediment samples and two rock samples were surveyed; seven shocked grains were identified (7/6619 = 0.1%). One shocked zircon was identified in a biotite schist shatter cone. Five of the seven shocked zircon grains were EBSD mapped; three were analyzed with multiple SIMS spots. EBSD mapping revealed {112} deformation twin lamellae in each of the five zircon grains. U-Pb geochronology for three grains yield crystallization ages from 1715±22 to 1472±35 Ma.

This study revealed the first confirmed shocked zircon at Santa Fe. Zircon, in addition to xenotime and quartz [9,10], is the third confirmed shocked mineral at Santa Fe; its occurrence indicates that exposed bedrock experienced shock pressures of ~ 20 GPa. The crystallization age for a shocked zircon of 1472±35 Ma offers the first and only reliable maximum impact age constraint. The new detrital shocked zircon sites indicate that shocked rocks and minerals may be distributed over an area up to 9 km2, from which scaling laws indicate a crater diameter of 9-14 km.

References: [1] Moser et al. (2011) Can. Jour. Earth Sci., 48, 117-139, [2] Erickson et al. (2013a) Am. Min., 98, 59-65, [3] Montalvo et al. (2017) Am. Min. 102, 813-823, [4] Cavosie et al. (2017) AGU Mon., in press, [5] Thomson et al. (2014) GSA Bull., 126, 720-730, [6] Erickson et al. (2017) Cont. Min. Pet., 172, 6 , [7] Cavosie et al. (2015) Geo., 43, 315-318, [8] Timms et al. (2012) Met. Plan. Sci., 47, 120-141, [9] Fackelman et al. (2008) EPSL, 270, 290-299, [10] Cavosie et al. (2016) Geo., 44, 803-806.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-301967

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