Twinning, Reidite, and Zro in Shocked Zircon from Meteor Crater

Home , Coesite, Impact crater, Lechatelierite, Luna crater, Shock metamorphism, Stishovite

Transformations to granular zircon revealed: Twinning, reidite, and

ZrO2 in shocked zircon from Meteor Crater (Arizona, USA) Aaron J. Cavosie1,2,3, Nicholas E. Timms1, Timmons M. Erickson1, Justin J. Hagerty4, and Friedrich Hörz5 1TIGeR (The Institute for Geoscience Research), Department of Applied Geology, Curtin University, Perth, WA 6102, Australia 2NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA 3Department of Geology, University of Puerto Rico–Mayagüez, Mayagüez, Puerto Rico 00681, USA 4U.S. Geological Survey (USGS) Astrogeology Science Center, Flagstaff, Arizona 86001, USA 5NASA Johnson Space Center, Science Department/Jets/HX5/ARES, Houston, Texas 77058, USA

ABSTRACT Granular zircon in impact environments has long been recognized but remains poorly A N35° 2.0’ W111° 0.9’ understood due to lack of experimental data to identify mechanisms involved in its genesis. Meteor Crater in Arizona (USA) contains abundant evidence of shock metamorphism, includ- N

ing shocked quartz, the high-pressure polymorphs coesite and stishovite, diaplectic SiO2

glass, and lechatelierite (fused SiO2). Here we report the presence of granular zircon, a new shocked-mineral discovery at Meteor Crater, that preserve critical orientation evidence of specific transformations that occurred during formation at extreme impact conditions. The zircon grains occur as aggregates of sub-micrometer neoblasts in highly shocked Coconino Sandstone (CS) comprised of lechatelierite. Electron backscatter diffraction shows that each MCC2 site grain consists of multiple domains, some with boundaries disoriented by 65° around <110>, (main shaft) a known {112} shock-twin orientation. Other domains have {001} in alignment with {110}

of neighboring domains, consistent with the former presence of the high-pressure ZrSiO4 polymorph reidite. Additionally, nearly all zircon preserve ZrO + SiO , providing evidence 2 2 250 m of partial dissociation. The genesis of CS granular zircon started with detrital zircon that W111° 1.8’ N35° 1.3’ experienced shock twinning and reidite formation at pressures from 20 to 30 GPa, ultimately yielding a phase that retained crystallographic memory; this phase subsequently recrystal- B lized to systematically oriented zircon neoblasts, and in some areas partially dissociated to lechatelierite ZrO2. The lechatelierite matrix, experimentally constrained to form at >2000 °C, provided the ultrahigh-temperature environment for zircon dissociation (~1670 °C) and neoblast formation. The capacity of granular zircon to preserve a cumulative pressure-temperature granular record has not been recognized previously, and provides a new method for investigating his- tories of impact-related mineral transformations in the crust at conditions far beyond those zircon at which most rocks melt.

GRANULAR ZIRCON structure (South Africa) (Moser, 1997; Cavosie Granular zircon is of interest to studies of et al., 2015a). shock metamorphism as it is considered to rep- vesicle resent the highest-shock-intensity morphotype SHOCK METAMORPHISM AT 100 µm of zircon, resulting from recrystallization of dia- METEOR CRATER

plectic ZrSiO4 glass into newly grown domains Meteor Crater (also known as Barringer Cra- (neoblasts) at conditions in excess of 50 GPa ter) is a 1.2-km-diameter simple crater (Fig. 1A) Figure 1. A: Aerial photograph of Meteor Crater (Arizona, USA), showing main shaft (Wittmann et al., 2006). However, its formation that formed ~49 k.y. ago in northern Arizona where sample MCC2 was collected (image conditions remain poorly constrained as it has (Shoemaker, 1963; Kring, 2007). The impact source: NASA Earth Observatory, earthobser- not been produced by experiment. The Meteor punctured Permian and Triassic sedimentary vatory.nasa.gov). B: Backscattered electron Crater (Arizona, USA) granular zircon described rocks, however the CS has received the most image of sample MCC2, showing granular zircon in highly vesicular lechatelierite matrix. here consist of aggregates of sub-micrometer study for effects of shock metamorphism, as neoblasts and are similar to those found in most other lithologies at Meteor Crater are car- other impact environments, including distal bonates. The CS is a Permian eolianite that is ejecta (Bohor et al., 1993), impact melt (Kamo widespread across the Colorado Plateau; it is a CS have been recognized based on increasing

et al., 1996), tektites (Deloule et al., 2001), lunar mature, white, fine-grained quartz arenite (~97 shock intensity of SiO2 phases (Kieffer, 1971;

breccia (Grange et al., 2013), and meteorites wt% SiO2) that contains few minerals besides Kieffer et al., 1976). Class 1 includes fractured (Zhang et al., 2011). The examples cited above detrital quartz (Kring, 2007). Reports of shock detrital quartz grains (<1 GPa), classes 2 and are readily distinguished from grains consist- metamorphism of CS include the first discover- 3 feature collapsed pores and microcrystalline ing of neoblasts up to 100 µm across that have ies of both coesite (Chao et al., 1960) and stisho- coesite (5–13 GPa) as well as stishovite and only been reported from the Vredefort impact vite (Chao et al., 1962) in nature. Five classes of coesite (25–30 GPa), class 4 includes diaplectic

Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/44/9/703/3549653/703.pdf by guest on 25 September 2021 ABgrain 13 C n=14,577 pts I

III II

lechatelierite 1 µm 1 µm 1 µm DETwin orientations: domains I & II n=9,610 pts Reidite orientations: domains II & III n=12,027 pts (001) {110} {112} (001) {110} {112}red {100}dark blue aligned aligned aligned 67°

aligned

65°<110> aligned {112} (001) 90° apart {110} // to (001) {112}red // to {100}blue

Figure 2. Granular zircon (grain 13) with twin and reidite orientations. A: Backscattered electron image showing granular zircon in lechatelierite matrix. B: Band contrast image showing neoblasts. C: Orientation map color coded for Euler coordinate projection, showing three domains with distinct orientations (labeled I–III). D: Pole figures of domains I and II, showing twin relationships. E: Pole figures of domains II and III, showing reidite relationships.

glass and vesicular lechatelierite, and class 5 contact with vesicular lechatelierite (Fig. 1B; 2013a, 2013b; Thomson et al., 2014; Cavosie consists entirely of lechatelierite (>30 GPa and Item DR1), 12 of which were analyzed by EBSD et al., 2015b). In contrast, neoblasts in domains

>1000 °C). In addition to SiO2 phases, impact (Table DR2). The grains range from 5 to 37 II and III (Fig. 2C) have a different orientation melts also occur at Meteor Crater (e.g., Hörz et µm in length, and many appear to retain their relationship; poles to (001) for each domain al., 2015), however no other shocked minerals original shape; their small size and generally are aligned with a <110> direction in the other have been reported. round shape are consistent with detrital zircon. domain (Fig. 2E). This results in further align- On the polished surface, single grains expose ment of the second <110> for each domain, as SAMPLES AND METHODS between 111 and 2329 neoblasts each (Figs. 2A well as alignment of a {100} with {112} of the The sample of CS analyzed was collected and 2B), which range from 0.26 to 0.42 µm in other domain (Fig. 2E). The crystallographic from near the central mining shaft at Meteor mean diameter. relations described above for domains II and Crater (Fig. 1A). The rock originated from below III are the same orientation relations previously the current crater floor, and was excavated dur- Systematic Orientation Relationships described between zircon and the high-pressure

ing early mining operations. Sample MCC2 is Neoblasts in all of the granular zircon grains ZrSiO4 polymorph reidite, where (001)zircon is

white and powdery with no visible crystals and are crystallographically contiguous and may parallel to {110}reidite, there is alignment of a

is highly porous and vesicular, similar to pumice have different orientations relative to each other, {110} between the two phases, and {112}zircon 1 (see the GSA Data Repository , Item DR1). In whereby domains comprise groups of adjacent is aligned with {100}reidite (Leroux et al., 1999; thin section, it is extremely vesicular (Fig. 1B), neoblasts in similar orientation (Item DR3). Cavosie et al., 2015b; Reddy et al., 2015). Given contains very few crystals, and is almost com- Grain 13 (Figs. 2A and 2B) is an example of that domains I and II in grain 13 define a {112} pletely isotropic silica glass, typical for shock a granular zircon composed of three distinctly twin relation, it follows that the orientation class 5 (Kieffer, 1971). Zircon grains were iden- different orientation domains that each contain relation between domains II and III was estab- tified in a thin section using backscattered elec- from 48 to 134 similarly oriented neoblasts on lished by transformation of domain III to reidite tron (BSE) imaging, and analyzed by electron the polished surface (Fig. 2C, labeled I–III). The (Figs. 2C–2E). While reidite was not identified backscatter diffraction (EBSD) using a 50 nm orientation of individual neoblasts within each (indexed) during analysis of Meteor Crater zir- step size (Item DR2; Table DR1). domain show minor, non-systematic disper- con, orientation relationships consistent with the sion relative to each other that do not overlap former presence of reidite were found in eight RESULTS in orientation with adjacent domains [compare of 12 grains analyzed by EBSD, and {112} twin locations of poles to (001) in Figs. 2D and 2E]. orientations were found in seven of the 12 grains Granular Zircon Domain boundaries are irregular at the neoblast (Item DR3; Table DR2). A total of 14 zircon grains, all granular, scale but are otherwise approximately straight. were documented in one thin section, each in The boundary between domains I and II (Fig. Zirconia and Silica Oxides

2C) is defined by a 65° disorientation relation- Two morphologically distinct types of ZrO2 1 GSA Data Repository item 2016228, Item DR1 ship about <110>, which results in alignment of were found in BSE images for 11 of 14 grains (additional sample images), Item DR2 (location and both a {110} and a {112} (Fig. 2D). The unique (Figs. 3A and 3B). Rounded ~250-nm-sized method description), Item DR3 (additional EBSD disorientation of 65° about <110> in zircon is grains were indexed as baddeleyite (monoclinic maps), Table DR1 (analytical conditions), and Table a hallmark of {112} twinning, which has only ZrO ) by EBSD in 10 of 12 grains; the other DR2 (granular zircon characteristics), is available 2 online at www.geosociety.org/pubs/ft2016.htm, or on been reported in shocked zircon (e.g., Moser et type occurs as ~50-nm-sized ZrO2 grains that

request from [email protected]. al., 2011; Timms et al., 2012; Erickson et al., form vermicular intergrowths with SiO2 and did

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Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/44/9/703/3549653/703.pdf by guest on 25 September 2021 not yield EBSD patterns, indicating that they in high-pressure shock experiments from 53 A lechatelierite are either amorphous or composed of grains grain 11 to 94 GPa, where temperatures reach “several too small to yield unique diffraction patterns B,C thousand degrees” in porous targets (Kusaba et by EBSD (Figs. 3B and 3C). The occurrence al., 1985, p. 436). In the CS, jetting of molten

of ZrO2 phases is primarily along boundaries material into pore spaces has been cited as a pro- between zircon neoblasts, rather than occur- cess that created extreme temperatures, result- ring within neoblast interiors (Schmieder et ing in the formation of lechatelierite (Kieffer

al., 2015). In some grains ZrO2 was found only et al., 1976), which recent experiments have along the outer margin, whereas in others it confirmed forms at >2000 °C in tektites (Mac- occurs throughout the interior of the grain. ris et al., 2014). Given that the granular zircon 10 µm in shock-melted CS are entirely surrounded by DISCUSSION lechatelierite and vesicles (Fig. 1B; Item DR1), B they must have experienced heating to ~2000 °C Genesis of Granular Zircon during lechatelierite formation. The extremely high temperatures required for both lechatelier- Shock Twinning, Reidite, and Disordered type 1 ite formation and zircon dissociation only occur

ZrSiO4 (?) in crustal rocks as a consequence of hyperve- The Meteor Crater results allow new con- type 2 locity impact; considered in this context, the straints to be placed on granular zircon genesis presence of baddeleyite in CS granular zircon based on preserved microstructures. System- is unambiguously attributed to high-temperature atic crystallographic orientations of neoblast dissociation of zircon, and is thus a product of

domains in the granular zircon described here the impact event. Natural occurrences of ZrO2 indicate that their pressure-temperature path in impact-dissociated shocked zircon have long involved both shock twinning and formation of been recognized (El Goresy, 1965). The striking reidite prior to recrystallization. The preserva- similarity in texture of the vermicular ZrO -SiO 1 µm 2 2 tion and identification of former twin domains intergrowths found in both Meteor Crater zir- in grains that have pervasively recrystallized has con (Fig. 3) and in experimentally calcinated not been reported in zircon previously. However, C zircon powders (Kaiser et al., 2008) provides EBSD has been used to identify inherited twin further microstructural support for an origin by orientations in recrystallized carbonate from baddeleyite high-temperature dissociation. We note further non-impact environments (Pearce et al., 2013). that the baddeleyite documented here may have Zircon {112} twins have been produced in static non-indexing reverted from a higher-symmetry polymorph ZrO + SiO experiments at 20 GPa (Morozova, 2015), and 2 2 of ZrO2 produced during dissociation, as bad- reidite forms from 30 to 40 GPa in shock experi- deleyite is not stable above 1200 °C (Kusaba et ments (Kusaba et al., 1985; Leroux et al., 1999). al., 1985; Kaiser et al., 2008). While the effects Thus, the {112} twins and evidence of reidite of high-pressure conditions in the formation of record minimum shock pressure of at least ~30 baddeleyite granular zircon remain unconstrained, these GPa, which is consistent for a porous rock com- zircon results clearly identify the role of ultrahigh tem- posed entirely of lechatelierite (Kieffer et al., perature in its formation. 1976; Stöffler and Langenhorst, 1994). Figure 3. Partially dissociated granular zircon Peak pressure experienced by the granular (grain 11). A: Backscattered electron image of Newly Identified Shocked Minerals at granular zircon with ZrO . B: Closeup show- zircon described here is difficult to constrain, as 2 Meteor Crater ing granular zircon with two types of ZrO2. there is no indication of what state the granular Type 1 is ~250-nm-sized grains, and type 2 The granular zircon from shocked CS is areas of vermicular ZrO + SiO . C: Phase zircon existed in above 30 GPa (e.g., a ZrSiO4 2 2 described here constitute the first new shocked polymorph, or constituent oxides). However, the map with band contrast, same area as B. Type mineral reported at Meteor Crater since stisho- 1 grains are baddeleyite; type 2 vermicular systematically oriented neoblasts indicate that intergrowths (black) do not index. vite in 1962 (Chao et al., 1962) and expand the the phase was unlikely to have been amorphous. current repertoire of shocked minerals beyond

A moderately disordered phase would provide the known SiO2 phases. Baddeleyite is not an energetically favorable medium for neoblast uniquely a shocked mineral, but its occurrence nucleation, given impact conditions favoring original orientation (domain II) (Figs. 2C and in CS is here shown to be a consequence of the high nucleation and rapid crystal growth rates. 2E). While this observation is new in studies of Meteor Crater impact. Reidite was not encoun- Evidence for the former presence of reidite shock-deformed zircon, the former existence of tered during this study, but the data presented in Meteor Crater zircon is indirect and based on high-pressure phases has been demonstrated in a here provide compelling evidence for its former preserved systematic crystallographic relations baddeleyite megacryst in a kimberlite from twin presence based on preservation of systematic among zircon neoblasts that are not known to relationships that could have only have arisen orientation relationships among neoblasts in form by any process other than shock defor- through transformation from cubic and tetrago- granular zircon. More broadly, the recognition

mation. Transformation of zircon to reidite nal ZrO2 (Kerschhofer et al., 2000). that granular zircon can preserve evidence of occurs via the specific systematic orientation its transformation history, as well as survive relationships described above; reversion back High-Temperature Dissociation and in fused rocks, provides new opportunities for to zircon could occur via several possible sym- Neoblast Formation investigating the extreme formation conditions metrically equivalent relationships, resulting in Zircon dissociation is experimentally well of impact melts, tektites, meteorites, and other neo-formed zircon with the observed crystallo- constrained to occur at 1673 °C at 1 atm (Kai- highly shocked materials from Earth and other graphic orientation of domain III relative to the ser et al., 2008) and has also been documented planetary bodies.

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Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/44/9/703/3549653/703.pdf by guest on 25 September 2021 ACKNOWLEDGMENTS 15 melt breccia: Journal of Geophysical Research, (EBSD, CL, EDS) and isotopic U-Pb and (U-Th)/ B. Hess prepared the sample. Editor J.B. Murphy, v. 118, p. 2180–2197, doi:10.1002/jgre.20167. He analysis of the Vredefort Dome: Canadian S. Kamo, W. Cordua, and an anonymous reviewer pro- Hörz, F., Archer, P.D., Jr., Niles, P.B., Zolensky, M.E., Journal of Earth Sciences, v. 48, p. 117–139, doi: vided helpful comments. Support was provided by the and Evans, M., 2015, Devolatilization or melting 10.1139/E11-011. National Science Foundation (grant EAR-1145118), of carbonates at Meteor Crater, AZ?: Meteoritics Pearce, M.A., Timms, N.E., Hough, R.M., and Clev- the USGS Meteor Crater Sample Collection, the NASA & Planetary Science, v. 50, p. 1050–1070, doi:10 erley, J.S., 2013, Reaction mechanism for the Astrobiology program, a Curtin Research Fellowship, .1111/maps.12453. replacement of calcite by dolomite and siderite: and the Microscopy and Microanalysis Facility at Kaiser, A., Lobert, M., and Telle, R., 2008, Thermal Implications for geochemistry, microstructure,

Curtin University. stability of zircon (ZrSiO4): Journal of the Euro- and porosity evolution during hydrothermal min- pean Ceramic Society, v. 28, p. 2199–2211, doi: eralisation: Contributions to Mineralogy and Pe- REFERENCES CITED 10.1016/j.jeurceramsoc.2007.12.040. trology, v. 166, p. 995–1009, doi:10.1007 /s00410 Bohor, B.F., Betterton, W.J., and Krogh, T.E., 1993, Kamo, S.L., Reimold, W.U., Krogh, T.E., and Col- -013-0905-2. Impact-shocked zircons: Discovery of shock-in- liston, W.P., 1996, A 2.023 Ga age for the Vre- Reddy, S.M., Johnson, T.E., Fischer, S., Rickard, duced textures reflecting increasing degrees of defort impact event and a first report of shocked W.D.A., and Taylor, R.J.M., 2015, Precambrian shock metamorphism: Earth and Planetary Sci- metamorphosed zircon in pseudotachylytic brec- reidite discovered in shocked zircon from the Stac ence Letters, v. 119, p. 419–424, doi:10.1016 cias and granophyre: Earth and Planetary Science Fada impactite, Scotland: Geology, v. 43, p. 899– /0012-821X(93)90149-4. Letters, v. 144, p. 369–387, doi:10 .1016/S0012 902, doi:10 .1130 /G37066 .1. Cavosie, A.J., Erickson, T.M., Timms, N.E., Reddy, -821X(96) 00180-X. Schmieder, M., Tohver, E., Jourdan, F., Denyszyn, S.M., Talavera, C., Montalvo, S.D., Pincus, M.R., Kerschhofer, L., Scharer, U., and Deutsch, A., 2000, S.W., and Haines, P.W., 2015, Zircons from the Gibbon, R.J., and Moser, D., 2015a, A terrestrial Evidence for crystals from the lower mantle: Acraman impact melt rock (South Australia): perspective on using ex situ shocked zircons to Baddeleyite megacrysts of the Mbuji Mayi Shock metamorphism, U-Pb and 40Ar/39Ar sys- date lunar impacts: Geology, v. 43, p. 999–1002, kimberlite: Earth and Planetary Science Letters, tematics, and implications for the isotopic dating doi:10.1130/G37059.1. v. 179, p. 219–225, doi:10 .1016 /S0012 -821X (00) of impact events: Geochimica et Cosmochimica Cavosie, A.J., Erickson, T.M., and Timms, N.E., 2015b, 00132-1. Acta, v. 161, p. 71–100, doi:10.1016/j.gca.2015 Nanoscale records of ancient shock deformation: Kieffer, S.W., 1971, Shock metamorphism of the .04.021. Coconino Sandstone at Meteor Crater, Arizona: Shoemaker, E.M., 1963, Impact mechanics at Meteor Reidite (ZrSiO4) in sandstone at the Ordovician Rock Elm impact crater: Geology, v. 43, p. 315– Journal of Geophysical Research, v. 76, p. 5449– Crater, Arizona, in Middlehurst, B.M., and Kui- 318, doi:10 .1130 /G36489 .1. 5473, doi:10.1029/JB076i023p05449. per, G.P., eds., The Moon, Meteorites and Comets Chao, E.C.T., Shoemaker, E.M., and Madsen, B.M., Kieffer, S.W., Phakey, P.P., and Christie, J.M., 1976, (The Solar System, Volume 4): Chicago, Univer- 1960, First natural occurrence of coesite: Sci- Shock processes in porous quartzite: Transmis- sity of Chicago Press, p. 301–336. ence, v. 132, p. 220–222, doi:10.1126/science sion electron microscope observations and the- Stöffler, D., and Langenhorst, F., 1994, Shock meta- .132.3421.220. ory: Contributions to Mineralogy and Petrology, morphism of quartz in nature and experiment: I. Chao, E.C.T., Fahey, J.J., Littler, J., and Milton, D.J., v. 59, p. 41–93, doi:10 .1007/BF00375110. Basic observation and theory: Meteoritics, v. 29, Kring, D.A., 2007, Guidebook to the Geology of Bar- p. 155–181, doi:10.1111/j.1945-5100.1994 1962, Stishovite, SiO2, a very high pressure new mineral from Meteor Crater, Arizona: Journal of ringer Meteorite Crater, Arizona (a.k.a. Meteor .tb00670.x. Geophysical Research, v. 67, p. 419–421, doi:10 Crater): Lunar and Planetary Institute Contribu- Thomson, O.A., Cavosie, A.J., Moser, D.E., Barker, I., .1029/JZ067i001p00419. tion 1355, 150 p. Radovan, H.A., and French, B.M., 2014, Preser- Deloule, E., Chaussidon, M., Glass, B.P., and Koeberl, Kusaba, K., Syono, Y., Kikuchi, M., and Fukuoka, K., vation of detrital shocked minerals derived from C., 2001, U-Pb isotopic study of relict zircon in- 1985, Shock behavior of zircon: Phase transition the 1.85 Ga Sudbury impact structure in modern clusions recovered from Muong Nong–type tek- to scheelite structure and decomposition: Earth alluvium and Holocene glacial deposits: Geologi- tites: Geochimica et Cosmochimica Acta, v. 65, and Planetary Science Letters, v. 72, p. 433–439, cal Society of America Bulletin, v. 126, p. 720– p. 1833–1838, doi:10.1016/S0016-7037(01) doi:10.1016/0012-821X(85)90064-0. 737, doi:10.1130/B30958.1. 00548-8. Leroux, H., Reimold, W.U., Koeberl, C., Hornemann, Timms, N.E., Reddy, S.M., Healy, D., Nemchin, A.A., El Goresy, A., 1965, Baddeleyite and its signifi- U., and Doukhan, J.-C., 1999, Experimental Grange, M.L., Pidgeon, R.T., and Hart, R., 2012, cance in impact glasses: Journal of Geophysi- shock deformation in zircon: A transmission Resolution of impact-related microstructures in cal Research, v. 70, p. 3453–3456, doi:10 .1029 electron microscopic study: Earth and Planetary lunar zircon: A shock-deformation mechanism /JZ070i014p03453. Science Letters, v. 169, p. 291–301, doi:10 .1016 map: Meteoritics & Planetary Science, v. 47, Erickson, T.M., Cavosie, A.J., Moser, D.E., Barker, /S0012-821X(99)00082-5. p. 120–141, doi:10.1111/j.1945-5100.2011 I.R., Radovan, H.A., and Wooden, J., 2013a, Macris, C.A., Badro, J., Asimow, P.D., Eiler, J.M., .01316.x. Identification and provenance determination of and Stolper, E.M., 2014, Seconds after impact: Wittmann, A., Kenkmann, T., Schmitt, R.T., and Stöf- distally transported, Vredefort-derived shocked Insights from diffusion between lechatelierite and fler, D., 2006, Shock-metamorphosed zircon in minerals in the Vaal River, South Africa using host glass in tektites and experiments: Meteorit- terrestrial impact craters: Meteoritics & Planetary SEM and SHRIMP-RG techniques: Geochimica ics & Planetary Science, v. 49, p. A5–A454, doi: Science, v. 41, p. 433–454, doi:10.1111/j .1945 et Cosmochimica Acta, v. 107, p. 170–188, doi: 10.1111/maps.12359. -5100.2006.tb00472.x. 10.1016/j.gca.2012.12.008. Morozova, I., 2015, Strength study of zircon under Zhang, A.-C., Hsu, W.-B., Li, X.-H., Ming, H.-L., Erickson, T.M., Cavosie, A.J., Moser, D.E., Barker, high pressure [M.S. thesis]: London, University Li, Q.-L., Li, Y., and Tang, G.-Q., 2011, Impact I.R., and Radovan, H.A., 2013b, Correlating of Western Ontario, 111 p. melting of lunar meteorite Dhofar 458: Evidence planar microstructures in shocked zircon from Moser, D.E., 1997, Dating the shock wave and ther- from polycrystalline texture and decomposition the Vredefort Dome at multiple scales: Crystal- mal imprint of the giant Vredefort impact, South of zircon: Meteoritics & Planetary Science, v. 46, lographic modeling, external and internal imag- Africa: Geology, v. 25, p. 7–10, doi:10 .1130 /0091 p. 103–112, doi:10.1016/j.epsl.2011.01.021. ing, and EBSD structural analysis: The American -7613(1997)025<0007:DTSWAT>2.3.CO;2. Mineralogist, v. 98, p. 53–65, doi:10 .2138/am Moser, D.E., Cupelli, C.L., Barker, I.R., Flowers, Manuscript received 29 April 2016 .2013.4165. R.M., Bowman, J.R., Wooden, J., and Hart, R.J., Revised manuscript received 21 June 2016 Grange, M.L., Nemchin, A.A., and Pidgeon, R.T., 2011, New zircon shock phenomena and their Manuscript accepted 21 June 2016 2013, The effect of 1.9 and 1.4 Ga impact events use for dating and reconstruction of large im- on 4.3 Ga zircon and phosphate from an Apollo pact structures revealed by electron nanobeam Printed in USA

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