Contrib Mineral Petrol (2017) 172:6 DOI 10.1007/s00410-016-1322-0

ORIGINAL PAPER

Microstructural constraints on the mechanisms of the transformation to reidite in naturally shocked zircon

Timmons M. Erickson1 · Mark A. Pearce2 · Steven M. Reddy1 · Nicholas E. Timms1 · Aaron J. Cavosie1,3,4 · Julien Bourdet5 · William D. A. Rickard6 · Alexander A. Nemchin1,7

Received: 2 May 2016 / Accepted: 8 December 2016 / Published online: 12 January 2017 © Springer-Verlag Berlin Heidelberg 2017

Abstract Zircon (ZrSiO4) is used to study impact struc- using a combination of electron backscatter diffraction tures because it responds to shock loading and unload- (EBSD) and focused ion beam cross-sectional imaging ing in unique, crystallographically controlled manners. techniques. The zircon-bearing clasts were obtained from One such phenomenon is the transformation of zircon to within suevite breccia from the Nördlingen 1973 bore- the high-pressure polymorph, reidite. This study quan- hole, close to the center of the 14.4 Ma Ries impact crater, tifies the geometric and crystallographic orientation in Bavaria, Germany. We have determined that multiple relationships between these two phases using naturally sets (up to 4) of reidite lamellae can form in a variety of shocked zircon grains. Reidite has been characterized in non-rational habit planes within the parent zircon. How- 32 shocked zircon grains (shocked to stages II and III) ever, EBSD mapping demonstrates that all occurrences of lamellar reidite have a consistent interphase misori- entation relationship with the host zircon that is char-

acterized by an approximate alignment of a {100}zircon with a {112}reidite and alignment of a {112}zircon with a Communicated by Gordon Moore. conjugate {112}reidite. Given the tetragonal symmetry of zircon and reidite, we predict that there are eight possible Electronic supplementary material The online version of this variants of this interphase relationship for reidite trans- article (doi:10.1007/s00410-016-1322-0) contains supplementary material, which is available to authorized users. formation within a single zircon grain. Furthermore, laser Raman mapping of one reidite-bearing grain shows that * Timmons M. Erickson moderate metamictization can inhibit reidite formation, [email protected] thereby highlighting that the transformation is controlled by zircon crystallinity. In addition to lamellar reidite, 1 Department of Applied Geology, Curtin University, GPO Box U1984, Perth, WA 6845, Australia submicrometer-scale granules of reidite were observed in one zircon. The majority of reidite granules have a topo- 2 CSIRO Mineral Resources, Australian Resources Research Centre, 26 Dick Perry Avenue, Kensington, WA 6151, taxial alignment that is similar to the lamellar reidite, Australia with some additional orientation dispersion. We confirm 3 NASA Astrobiology Institute, Department of Geoscience, that lamellar reidite likely forms via a deviatoric transfor- University of Wisconsin-Madison, Madison, WI 53706, USA mation mechanism in highly crystalline zircon, whereas 4 Department of Geology, University of Puerto Rico- granular reidite forms via a reconstructive transformation Mayagüez, Mayagüez, PR 00681, USA from low-crystallinity ZrSiO4 within the reidite stability 5 CSIRO Energy, Australian Resources Research Centre, 26 field. The results of this study further refine the formation Dick Perry Avenue, Kensington, WA 6151, Australia mechanisms and conditions of reidite transformation in 6 Department of Imaging and Applied Physics, Curtin naturally shocked zircon. University, GPO Box 1984, Perth, WA 6845, Australia 7 Department of Geosciences, Swedish Museum of Natural Keywords Shock metamorphism · EBSD, zircon · History, 104 05 Stockholm, Sweden Reidite · Ries impact crater

1 3 6 Page 2 of 26 Contrib Mineral Petrol (2017) 172:6

Table 1 Locations of natural reidite occurrences Impact crater Age (Ma) Shock stage Method of identification Number of grains reported References

Ries impact structure, 14.7 II–IV Laser Raman spectroscopy II: 0, III: 1/12 (8%), IV: 0 Gucsik et al. (2004a) Germany II–IV Laser Raman spectroscopy II–III: 52/67 (78%), IV: 1/46 Wittmann et al. (2006) (2%) II–III EBSD, laser Raman 32/46 (70%) This study Eocene ejecta, New Jersey, 35.7 – X-ray diffraction 7/68 (10%) Glass and Liu (2001) Glass USAa et al. (2002) Eocene ejecta, Barbadosa 35.7 – – Glass et al. (2002) 4 Kamo et al. (2002) Chesapeake Bay impact 35.7 II–III Laser Raman spectroscopy – Wittmann et al. (2009) structure, USA II–III 1/27 (4%) Malone (2009) III–IV 1 Malone et al. (2010) Xiuyan Crater, China 0.1 II–III Laser Raman, XRD II: 7/30 (23%), III: 0/20 Chen et al. (2013) Rock elm impact structure, 460 II EBSD 2/135 (1%) Cavosie et al. (2015a) USA Proterozoic ejecta, Stac 1180 – EBSD 2/200 (1%) Reddy et al. (2015) Fada, Scotland Haughton Crater, Canada 39 IV Laser Raman 4/6 (67%) Singleton et al. (2015) a Ejecta horizons correlated to the Chesapeake Bay impact structure

Introduction the scheelite-structured reidite facilitates an approximately 10% increase in density, and is inferred to be complete

Zircon (ZrSiO4, space group I41/amd) is an important indi- at 900 °C and 12 GPa (Reid and Ringwood 1969; Ono cator and geochronometer of meteorite bombardment (Krogh et al. 2004). However, reidite forms well above 20 GPa in et al. 1984, 1993; Bohor et al. 1993). Shock microstructures shock experiments (Kusaba et al. 1985; Leroux et al. 1999; in zircon form at or above 20 GPa (Leroux et al. 1999) and Morozova 2015). The discrepancy in the pressure condi- provide diagnostic criteria to identify impact structures tions for reidite formation is likely the effect of an energy (French 1998; French and Koeberl 2010). Zircon is highly barrier associated with a transition state (Marqués et al. refractory, and shock microstructures can survive subse- 2008). quent metamorphism while similar shock microstructures Naturally occurring reidite was first identified using are obscured in phases such as quartz (Wittmann et al. 2006). X-ray diffraction (XRD) in zircon grains from Eocene Shock microstructures in zircon include {100}-parallel defor- ejecta associated with the ~90 km diameter, ca. 35.7 Ma mation bands (Erickson et al. 2013a; Timms et al. 2012), Chesapeake Bay impact structure (Glass and Liu 2001; mechanical twins along {112} (Moser et al. 2011; Timms Glass et al. 2002). Reidite has since been reported from et al. 2012; Erickson et al. 2013a, b; Thomson et al. 2014), the ca. 14.7 Ma, 24-km-wide Ries impact structure, south- decomposition of zircon to ZrO2 and SiO2 (El Goresy 1965; ern Germany, (Gucsik et al. 2004a; Wittmann et al. 2006), Wittmann et al. 2006; Timms et al. 2017), the development of bedrock at the Chesapeake bay structure (Wittmann et al. granular textured zircon (Bohor et al. 1993; Schmieder et al. 2009), the ca. 0.1 Ma, 1.8-km-diameter Xiuyan Crater, 2015; Cavosie et al. 2016; Timms et al. 2017), conversion northeastern China (Chen et al. 2013), the ca. 460 Ma, of zircon to reidite (Glass and Liu 2001; Glass et al. 2002), 6.5-km-wide Rock Elm impact structure, Wisconsin, USA and subsequent decomposition of reidite to ZrO2 and SiO2 (Cavosie et al. 2015a), the ca. 23 Ma, 23 km Haughton (Reddy et al. 2015). In the following study, we undertake a impact structure (Singleton et al. 2015), and within zircon microstructural study of zircon–reidite relationships to further grains from the ca. 1180 Ma Stac Fada ejecta deposit, Scot- refine the impact conditions that produce this transformation, land (Reddy et al. 2015) (Table 1). and establish the factors that control its development. Experimental shock deformation studies of zircon show

Reidite (space group I41/a), the tetragonal high-pressure the conversion of zircon to reidite commences above 20 polymorph of ZrSiO4, was first recorded in experiments GPa and is complete by 52 GPa (Mashimo et al. 1983; by Reid and Ringwood (1969). Under static loading pres- Kusaba et al. 1985; Fiske et al. 1999; Leroux et al. 1999; sures at mantle conditions, the transformation of zircon to Morozova 2015). While conditions under which zircon

1 3 Contrib Mineral Petrol (2017) 172:6 Page 3 of 26 6 transforms to reidite during shock loading have been con- operate on the nanosecond to seconds timescale of shock strained experimentally, the mechanism by which the events because diffusion rates are too slow (Langenhorst conversion takes place is less constrained. The transfor- and Deutsch 2012); thus, a martensitic transformation mation mechanisms responsible for the conversion have mechanism is favored for impact-related reidite. been studied experimentally and investigated by transmis- While an experimental study by Leroux et al. (1999) sion electron microscopy (TEM) (Leroux et al. 1999). In used TEM to first establish the crystallographic relation- zircon grains experimentally shocked to 40 GPa, the par- ships between reidite and zircon lattices, studies of natu- tial transformation to reidite developed as 0.1 µm lamellae ral samples have primarily used XRD (e.g., Glass and Liu formed parallel to the {100} of the zircon, and contained 2001; Chen et al. 2013) or laser Raman (e.g., Gucsik et al. ~0.05-µm-wide {112} twins within its structure (Leroux 2004a; Wittmann et al. 2006, 2009; Chen et al. 2013) to et al. 1999). At 60 GPa, complete conversion of the zir- establish the presence of reidite. However, both XRD and con to reidite occurred and the reidite had many mechani- laser Raman analyses do not allow inter-crystalline rela- cal twins in {112}, along with localized aggregates of tionships to be quantified. In contrast, EBSD data provide nanocrystalline reidite. Based on TEM diffraction data, a rapid means of acquiring quantitative crystallographic the reidite lamellae were interpreted to have formed par- data with high spatial (~50 nm) and angular (~0.5°) resolu- allel to {100}zircon. The transformation was interpreted to tion (Cavosie et al. 2015a; Reddy et al. 2015). In this study, be martensitic, facilitated by shearing along {100}zircon in 32 reidite-bearing zircon grains are investigated by EBSD a [001]zircon direction, such that {100}zircon is parallel to and complementary electron microscopy, laser Raman, and 001 110 {112}reidite and zircon is parallel to the reidite. A FIB-based sectioning techniques to refine the three-dimen- martensitic transformation, analogous to the zircon–reidite sional crystallographic relationships between zircon and transformation, has also been invoked for the high-pressure reidite, correlate experimental shock results with natural transformation of zircon-structured GdVO4 to a scheelite samples, provide insight into the zircon–reidite transforma- structure in non-hydrostatic strain experiments (Yue et al. tion mechanism(s), and assess the effect of metamictization 2016). on the transformation to reidite. In contrast, other studies indicate that the nature of the transformation is unlikely to be due to just a simple mar- tensitic shear (Kusaba et al. 1986; Marqués et al. 2008). Geologic background A two-step transformation, which is first accommodated by translation of the Zr and Si cations by ¼ 010 glide on Ries impact structure {100} can achieve a partial transformation to reidite, and is subsequently completed by rotation of the oxygen atoms The Ries impact structure in Bavaria, Germany, is a around the cations (Kusaba et al. 1986; Turner et al. 2014). 24-km-diameter complex crater with an impact age of Parallelism of the {100} to {112} and 001zircon 14.68 0.11 Ma (2σ, Di Vincenzo and Skála 2009; Fig. 1). zircon reidite ± to 110reidite was also identified in the natural shocked zir- The impact punctured Triassic and Jurassic sedimentary con grains from Rock Elm (Cavosie et al. 2015a) and Stac units and shock-metamorphosed underlying Variscan gran- Fada (Reddy et al. 2015). However, three-dimensional ites, gneisses, and amphibolites (Sturm et al. 2013). With analysis of reidite lamellae in the Stac Fada zircon grains the discovery of high-pressure SiO2 polymorphs (both using focused ion beam milling and transmission Kikuchi coesite and stishovite), Ries was one of the first confirmed diffraction found that while {100}zircon and {112}reidite were terrestrial impact structures (Shoemaker and Chao 1961). coplanar, the lamellae interface did not form in {100}zircon Shock-produced planar deformation features (PDFs) were (Reddy et al. 2015). identified within quartz from suevitic breccia at Ries by A reconstructive transformation of zircon to reidite pro- Engelhardt and Bertsch (1969). Workers have since con- vides an alternative model to a shear (martensitic) trans- strained the development of shock-induced microstructures formation, which is supported by ab initio calculations within quartz from Ries, including PDFs (e.g., Engelhardt (Marqués et al. 2008). This transformation mechanism and Bertsch 1969; Goltrant et al. 1991; Ferrière et al. 2009), is achieved through a two-step transformation of zircon feather features (Poelchau and Kenkmann 2011), coesite, to reidite with an intermediate, monoclinic ZrSiO4 phase and stishovite (Stöffler 1971a; Stähle et al. 2007). So far, (Flórez et al. 2009). This process operates at a much lower at least five high-pressure minerals have been identified at activation energy barrier (88 kJ/mol) than that of a direct Ries, including coesite and stishovite (Stöffler 1971a), reid- transition from zircon to reidite (133 kJ/mol), but requires ite (Gucsik et al. 2004a), akaogiite (El Goresy et al. 2010), reconstruction of two Zr–O bonds (Smirnov et al. 2008; and diamond (Hough et al. 1995). Flórez et al. 2009). Despite these energy considerations, At the Ries impact structure, reidite was first described solid-state reconstructive transformations seem unlikely to in a zircon grain within a shock stage III (Stöffler 1971b)

1 3 6 Page 4 of 26 Contrib Mineral Petrol (2017) 172:6

AB 10° 30’ 10° 40’

N

49°00’

10° 20’ Aumühle

Zipplingen

48°54’ Nördlingen C 1973 C’

Nördlingen

Inner Ring

48°48’

Outer Rim 10 km Seelbronn

C Nördlingen C’ OR IR 1973 Fig. 2a IR OR

Post Impact Impactites Pre Impact Jurassic Malm Bunte breccia sediments Tertiary - Quaternary Jurassic Dogger sedimentary cover Suevite sediments Neogene freshwater Jurassic Lias limestone Basement sediments Gneisses and Triassic Keuper granitoids sediments

1 3 Contrib Mineral Petrol (2017) 172:6 Page 5 of 26 6

◂Fig. 1 Location map and cross section of the Ries impact crater A. electron microscope (SEM) at the Microscopy and Microa- Location of the Ries Crater (black dot) within the upper left-hand nalysis Facility, within the John de Laeter Centre (JdLC), insert map of Germany. B Geologic map of the Ries impact cra- ter modified after Schmidt-Kaler (2004). The locations of the town Curtin University. SEM imaging and analyses, including of Nördlingen and the Nördlingen 1973 Borehole are highlighted. secondary electron (SE), atomic number contrast backscat- The inner ring of the crater is defined by geophysical data while the ter electron (BSE), cathodoluminescence (CL), and energy- outer rim is defined by the structural rim of the crater (Stöffler et al. dispersive spectrometry (EDS), were undertaken. Further 2013). The reidite localities of Gucsik et al. (2004a) and Wittmann et al. (2006), Seelbronn, Aumühle, and Zipplingen, are also shown. C details on the operating conditions are given in Appendix Cross section of the Ries impact crater (C–C′) with the location of the 1 of supplementary material. Microstructural EBSD data Nördlingen 1973 borehole relative to the center of the impact crater, from the zircon grains were collected along orthogonal modified after Pohl et al. (2010) and Stöffler et al. (2013) grids (maps) with a step size of 50–200 nm, using a Nord- lys Nano high-resolution detector and Oxford Instruments fragment of a suevitic breccia from Seelbronn (Fig. 1; Aztec 2.2 acquisition system. Post-processing of the EBSD Gucsik et al. 2004a). The reidite could not be recognized data was undertaken with the Oxford Instruments Channel by backscatter electron (BSE) and cathodoluminescence 5.11 software suite. Maps and pole figures of the EBSD (CL) imaging (Figs. 1b and 10a in Gucsik et al. 2004a), data were produced with Tango and Mambo software, but was identified by distinct spectral peaks in laser Raman respectively. The interphase misorientation relationships spectra. Wittmann et al. (2006) documented zircon grains between different reidite lamellae and host zircon were also containing reidite in clasts that experienced shock stages visualized for all of the reidite lamellae using Mambo. To II–IV (Stöffler 1971b) from a Ries suevite breccia. In shock achieve this, the crystallographic orientation data for both stages II and III lithic fragments from the Zipplingen, phases were rotated so that each host zircon grain was in Seelbronn, and Aumühle quarries, Wittmann et al. (2006, the same reference orientation (Fig. 11; Appendix 2 of sup- Table 1) found 78% of zircon grains (52 of 67) analyzed by plementary material), such that each c-axis was aligned laser Raman contained reidite, while shock stage IV clasts with the z-direction of the pole figures and the a-axes were from Seelbronn and Aumühle contained 1 grain (2% of aligned with x and y. those investigated) with reidite (Fig. 1). The habit plane orientations of reidite lamellae within The samples analyzed in this study come from the the host zircon grains were reconstructed from their traces Nördlingen 1973 borehole, located within the central in two orthogonal polished surfaces. We used the Tescan region of the Ries impact structure, 3.65 km from the Lyra3 FIB-SEM in the Advanced Resource Characterisa- center of the structure (Fig. 1) and extending to a depth of tion Facility at Curtin University to cross section the host 1206 m (Bauberger et al. 1974; Reimold et al. 2011). The zircon grains to a depth of ~5 µm, from which the orienta- upper 264 m of drill core passes through post-impact lake tion of the reidite lamellae could be constrained relative to sediments (Fig. 2a). From 264 to 331.5 m depth, the sedi- the host zircon grain. The determination of the habit plane ments comprise of clasts of suevite, at the base of which was completed using standard structural plotting techniques are air-fall and “turbidity current-like” deposits (Reimold by reconstruction of a plane from the traces of the lamellae et al. 2011). A melt-rich package between 331.5 and 525 m on the two orthogonal surfaces using Stereonet9 software. depth represents a Flädle-type suevite derived from fallback To further quantify systematic orientation relationships of the impact vapor plume, below which is a melt-poor unit of the reidite lamellae with the host zircon grains, we devel- of suevite from 525 to 601.5 m depth (Stöffler 1977; Stöf- oped a MATLAB script to measure the crystallographic fler et al. 2013). Below 601.5 m depth lie shocked Variscan coincidence of specific planes between the two phases. basement gneisses and granitoids, which are crosscut by Firstly, the mean crystallographic orientations of the reidite impact breccias that were injected along large-scale frac- and zircon were measured from the EBSD data. The script

tures (Bauberger et al. 1974; Reimold et al. 2011). Two then calculated the orientation relationships of the (001)zircon, zircon-bearing clasts from the Flädle-type suevite breccia {100}zircon, {112}zircon, {110}reidite, and {112}reidite crystallo- were selected for this study (Fig. 2). Both clasts come from graphic planes with respect to the x–y–z coordinates of the a depth of 498 m and are located in a single thin section. acquisition surface. The angle between the following pairs of planes was then calculated using the dot product of the Analytical methods two direction vectors for each form (see Appendix 1 of sup-

plementary material for details): (001)zircon to {110}reidite, A standard petrographic thin section was polished and {100}zircon to {112}reidite, and {112}zircon to {112}reidite. given a final chemical–mechanical polish using 60 nm One zircon grain with reidite lamellae was selected colloidal silica in a NaOH dispersion. Zircon grains were for laser Raman mapping, allowing direct comparison identified by optical microscopy (Figs. 2, 3) and then of Raman and EBSD data for reidite. Laser Raman map- analyzed using a Tescan Mira3 field emission scanning ping was done at the CSIRO Energy Flagship, Australian

1 3 6 Page 6 of 26 Contrib Mineral Petrol (2017) 172:6

A 0 m B C Quaternary PPL sediments 23 Neogene 22 24 (001) 25 21 D 26 264 m suevite rich 30 331 m 20 27 19 18 29 36 Sample 16 17 28 suevite 13 12 498 m 11 14 10 9 601.5 m 31 33 6 35 brecciated 15 8 5 4 32 7 basement 3 gneisses and Clast 1 34 2 granites 5 mm 1 1206 m E PPL Nördlingen 1973 PPL 43 Borehole 45

D CL 40 44 39 38 46 37 F 42 41 zircon w. reidite Clast 2 200 μm 2 mm (001)

Fig. 2 Schematic of the Nördlingen 1973 borehole and petro- Clast 1, red points are from grains with reidite and green from grains graphic and SEM images of Ries Clasts 1 and 2. a The geology of without reidite. d CL image of typical shocked quartz from within the Nördlingen 1973 borehole with the location of Ries Clasts 1 and 2 Ries Clast 1 displaying multiple orientations of PDFs. e Plane-polar- from a depth of 498 m within the suevitic breccia. b Plane-polarized ized light image of highly altered and patchy Ries Clast 2 with the light (PPL) image of Ries Clast 1 with the location of zircon grains location of zircon grains. Reidite-bearing zircon grains are colored associated with the amphibole-rich melanosomes. Reidite-bearing red, while those without reidite are green. f Stereographic projection zircon grains are colored red, while those without reidite are green. of the poles to the (001) of the 10 zircon grains within Ries Clast 2, Note the distinct brown-beige-toasted appearance of the quartz red points are from grains with reidite and green from grains without domain. c Pole figures of (001) for the 32 zircon grains within Ries reidite

Resources Research Centre, using a Horiba LabRAM HR Further descriptions of the analytical methods are out- Evolution using a 600 g/mm grating and a Synapse Vis- lined in Appendix 1 of supplementary material, includ- ible detector. A 36 50 µm map was produced across ing SEM imaging, EBSD analysis, post-processing the × the shocked zircon. In addition to comparing the EBSD EBSD data, the FIB cross-sectioning method, the MAT- and Raman data, Raman analyses were used to assess the LAB script for determining the intra-crystalline mis- crystallinity of the zircon in order to test the effects of ini- orientation relationships, and the laser Raman analy- tial state (e.g., damage from metamictization, amorphous ses. Appendix 2 of supplementary material contains

ZrSiO4) on reidite formation. SEM images, EBSD maps, and pole figures from each

1 3 Contrib Mineral Petrol (2017) 172:6 Page 7 of 26 6

XPL CL BSE ig 4 Grain 21, F ig 5 Grain 12, F g 6 Fi Grain 14, ig 7 Grain 29, F

All scale bars 10 μm

Fig. 3 Petrographic and SEM images of shocked zircon from Ries Clast 1. Crosscutting lamellae can be seen in each grain ranging from 1 (e.g., Zircon 21) to 4 (e.g., Zircon 29) orientations, and are birefringent in cross-polarized light, dark in CL and bright in BSE images reidite-bearing zircon grain. Appendix 3 of supple- Results mentary material contains the reoriented pole figures of each reidite lamellae plotted in the zircon reference Ries Clast 1 frame, which are summarized in Fig. 11. Appendix 4 of supplementary material contains the input Euler angles Ries Clast 1 is a banded, quartz–plagioclase–hornblende– used for the MATLAB script and the reorientation of the biotite–magnetite gneiss with accessory apatite, zircon, and reidite pole figures, and the minimum angles between rutile (Fig. 2b). A total of 36 zircon grains were identified in (001)zircon to {110}reidite, {100}zircon to {112}reidite, and Ries Clast 1, all of which are found in plagioclase–amphi- {112}zircon to {112}reidite. bole–biotite–magnetite melanosomes; no zircon grains

1 3 6 Page 8 of 26 Contrib Mineral Petrol (2017) 172:6

A B (001) and {110} IPFZ reidite (001) (010)

(001)z, {110}r (110)

{110}z, {110}r {110}z, (001)r Fig. C, D {100}z and {112}r F

CL dark domain

20 μm F’ Pole to z = 104941 step = 0.2 μm habit plane r= 474 v1(SiO ) v3(SiO ) E 4 4 C 1. Crystalline reidite Zircon y (a.u.) 3 zz z z zzz 2. Metamict 2 1 tensit

In Zircon 3. Reidite & zircon rrr r r

-1 -1 -1 0 500 1000 1500 992-1012 cm 345-365 cm 392-412 cm Raman Shift (cm-1)

D F F F’ CL dark domain

3

2 1

10 μm 10 μm

1 3 Contrib Mineral Petrol (2017) 172:6 Page 9 of 26 6

◂Fig. 4 EBSD and laser Raman data from Zircon 21 from Ries Clast calculated to range between 0.1 and 9.1%, indicating that 1 with a well-pronounced set of lamellae in {100}zircon equivalent to the transformation was highly localized and incomplete. A {112}reidite. a EBSD map of the reidite lamellae (with inverse pole figure (IPF) color scheme) and zircon (grayscale band contrast map). thorough microstructural description of four grains (21, 12, b Pole figures for zircon and reidite (note all pole figures are lower 14, and 29) from Clast 1 follows. These grains are selected hemisphere, equal area stereographic projections). Close alignment of because they contain the full range of both reidite develop- the poles to {100}zircon and {112}reidite is highlighted and the pole to ment and other deformation features found in this study. the habit plane, as determined from the FIB-milled cross section, is marked on the pole figures (see Appendix 1 of supplementary mate- In Zircon 21 (Fig. 4a, b), a single set of reidite lamel- rial for how this was calculated). c Overlain Raman intensity map for lae is well developed throughout the grain. The lamellae 1 1 two zircon peaks (blue 353 cm− wave number and green 1003 cm− show close alignment of the {100}zircon to {112}reidite, while wave number), which relate to the symmetric, v1(SiO4), and asym- (001)zircon and {110}reidite are more scattered (Fig. 4b). metric, v3(SiO4), stretching vibrations of the tetrahedral SiO4, respec- 1 However, while the trend of the lamellae on the polished tively, and one reidite peak (red 402 cm− wave number). The reidite lamellae, which can be correlated to the lamellae within the EBSD surface (Fig. 4a) is close to that of the {100}zircon, three- map, show up as bright red while the most crystalline zircon is yellow dimensional observations of the geometry of the reidite– green. d Map of the ratio of v3(SiO4) peak to the v1(SiO4), v3(SiO4) zircon interface (Fig. 4b, f) show that the habit plane is is sensitive to short-range order of the crystal structure and thus is a proxy for metamictization. Locations 1–3 mark the Raman spectra ~20° from {100}zircon. This relationship is consistent with shown in Fig. 4. e The lower-crystalline dark domain, which reidite parallelism of {512}zircon with {122}reidite. For additional lamellae do not crosscut, is outlined by a dashed white line. e Raman pole figures, including {512}zircon and {122}reidite, addi- spectra for (1) crystalline zircon, (2) metamict zircon core, and (3) tional images of Zircon 21 refer to Appendix 2 of supple- reidite lamellae (see text for further discussion). Peaks labeled z and r correlate to those published in the literature for zircon and reidite, mentary material. respectively. f BSE atomic number contrast imaage of the cross- In Zircon 12, four distinct sets of lamellae were iden- sectional F–F′ exposing the reidite lamellae, which the three-dimen- tified (Fig. 5). In all cases, a consistent orientation rela- sional orientation of the lamellae was refined from (see Appendix 2 of tionship between reidite and host zircon is seen, whereby supplementary material, Zircon 21 for more details) 110 one reidite is aligned subparallel to [001]zircon and the conjugate 110reidite is subparallel to 110zircon. The were found in the quartz-rich segregations (Fig. 2b). The greatest dispersion of reidite poles is about 110 parallel

zircon grains have a crystallographic preferred orientation to [001]zircon, which is the crystallographic direction about (CPO), which is exhibited by alignment of (001) (Fig. 2c). which the parent zircon is plastically deformed (Fig. 5). Quartz grains from Clast 1 contain up to five sets of PDFs While there is general alignment of the {001} and {110} (Fig. 2d) and have a distinct “toasted” appearance (White- poles between the two phases, analysis of different sets

head et al. 2002). No high-pressure polymorphs of SiO2 of lamellae shows that for each set, one {112}reidite is were found in Clast 1. Plagioclase is highly altered and in closely aligned with {100}zircon (Fig. 5b). Additionally, places isotropic, having partially transformed to maskel- there is alignment between {112}zircon and one of the other ynite during shock metamorphism. Based on the presence {112}reidite lattice planes. Three-dimensional analysis of the of diaplectic plagioclase and PDFs within the quartz, Ries interface between the reidite lamellae and the host zircon Clast 1 experienced shock stage II, which corresponds to shows that the two well-developed reidite lamellae (L1 and

peak shock pressures of 25–30 GPa (Stöffler 1971b). L2) lie along a {112}zircon which is parallel to {112}reidite The zircon grains are subhedral to euhedral and range (Fig. 5b, Appendix 2 of supplementary material Zircon 12). in length from 12 to 145 µm (mean 59 µm, Table 1). Of The habit plane of the other two reidite lamellae is ~20° = the 36 zircon grains, 25 exhibit thin ( 1 µm) lamellae that from the {100} , similar to the lamellae in Zircon 21, ≤ zircon crosscut the grains in up to 4 orientations (Table 1; Fig. 3). and is consistent with {512}zircon (see Appendix 2 of sup- In transmitted light, the lamellae are transparent, have a plementary material, Zircon 12 for additional pole figures higher relief than zircon, and appear brighter in reflected and images). light. In cross-polarized light, the lamellae show a maxi- In Zircon 14, two sets of reidite lamellae are well devel- mum birefringence of second-order blue. Imaging of the oped. In addition, the grain contains a set of shock twins zircon grains by BSE identifies bright lamellae, consistent along {112}, with 65° misorientation about 110 (Fig. 6). with those detected optically, which range from 0.1 to 1 µm At the intersection of one of the zircon twins with one of in width. In CL images, the lamellae are dark and crosscut the reidite lamellae, a small domain (~0.15 µm wide) of rei- compositional growth zonation (Fig. 3). dite is misoriented 75° about 110, and is likely a twinned 110 Mapping by EBSD confirms that the lamellae are reid- domain within the reidite (TR; Fig. 6b, c). The reidite, ite. In Ries Clast 1, reidite was only found in lamellar form; aligned with the twin misorientation axis, is subparallel 58 distinct sets of aligned lamellae were identified within to the zircon twin 110zircon misorientation axis. In addi- 25 zircon grains (Table 1). The total area of reidite exposed tion, one of the {112} planes of the twinned reidite is on the polished surfaces of individual zircon grains was closely aligned with a {100} plane of the twinned zircon,

1 3 6 Page 10 of 26 Contrib Mineral Petrol (2017) 172:6

A Texture component L4 IPF reidite B (001) and {110} zircon X (001)(010) {110}z, 0° 15° (001)r

(110)

L1 (001)z, {110}r

{110}z, {110}r {112}z and {112}r

L1

L3

L2

{100}z and {112}r L3

L4

10 μm r= 46085 step = 0.05 μm L2 z = 450187

Fig. 5 EBSD maps and pole figures for Zircon 12 from Ries Clast 1 tion, highlighting the reidite lamellae (labeled L1–L4). b Pole figures showing four lamellar orientations for reidite (L1–4). a EBSD map for zircon and reidite, reidite lamellae 1 (L1) and lamellae 2 (L2) are with a texture component exhibiting cumulative misorientation of in {112}zircon//{112}reidite orientations, while reidite lamellae 3 and 4 15° across the zircon, accommodated by a combination of brittle and (L3, 4) are in an orientation that cannot be a low-order rational habit crystal–plastic intragrain deformation, and the development of low- plane but is close to {512}zircon (see Appendix 2 of supplementary angle grain boundaries. Reidite lamellae are colored using IPF nota- material, Zircon 12 for more details)

consistent with the relationship observed for other reidite by ~10°, {100}zircon and {112}reidite have a mean misori- lamellae (see Appendix 2 of supplementary material, Zir- entation of ~5° and {112}zircon and {112}reidite also have a con 14 for further details). The habit plane of the two sets mean misorientation of ~5° (Appendix 4 of supplementary of reidite lamellae (L1 and L2) is ~20° from {100}zircon// material). The most common habit plane for reidite lamel- {112}reidite and is consistent with {512}zircon. lae in Clast 1 is {512}zircon, which occurs in 15 sets, and Zircon 29 contains 4 well-developed sets of reidite is parallel to either {122}reidite, {133}reidite, or {124}reidite. lamellae. All lamellae show close crystallographic align- The second most common habit plane is {112}zircon, which ment of {112}reidite with the same {100}zircon (Fig. 7a, b). accounts for 5 sets of lamellae, and is parallel to {112}reidite However, each lamella shows alignment of {112}reidite with in all cases. Additionally, 3 sets of lamellae were identified a unique {112}zircon, so that the lamellae are in 4 different which lie in {100}zircon and are coplanar with {112}reidite, crystallographic orientations relative to the host zircon (see and 3 sets of lamellae were found that lie in {111}zircon and Appendix 2 of supplementary material, Zircon 29). Addi- are coplanar with {100}reidite (Table 2). However, for 29 tionally, the zircon contains many low-angle boundaries sets of lamellae cross-sectioned by FIB, the planes are typi- that are subparallel to the zircon–reidite interfaces of the cally irrational and do not occur in a consistent orientation four sets of reidite lamellae. (Appendix 2 of supplementary material). In all instances, reidite lamellae show close crystallo- In addition to shock-produced reidite and twin lamellae, graphic alignment of one {112}reidite with {100}zircon and the zircon grains contain a combination of crystal–plastic alignment of another {112}reidite with a {112}zircon (see strain and brittle fractures. Plastic strain includes planar Appendices 2, 3, and 4 of supplementary materials for deformation bands, low-angle (<10°) subgrains, and high- details). While (001)zircon is misoriented from (110)reidite angle (>10°) grain boundaries, typically misoriented about

1 3 Contrib Mineral Petrol (2017) 172:6 Page 11 of 26 6

A IPFY C (001) and {110} Zircon (001) (010) {110}

(110) (001) TZ Twin boundary, 65° <110> (001) LAB >1° {110} LAB >2° T Z {110} >10° TZ

(001) and {110} {110} (001) {110}

TR {110} T {110} Z {110} (001) (001) TR B T Z

{100}z and {112}r L1

L2 L2

L1 T R

10 μm

z = 720633 step = 0.2 μm B r= 18529

Fig. 6 EBSD maps and pole figures for Zircon 14 from Ries Clast intersection of the reidite lamellae and the shock twins, the reidite is 110 1, exhibiting two orientations of reidite lamellae and a set of shock disoriented 75° about . Tz and TR denote zircon and reidite twins, twins. a IPF colored EBSD map displaying two orientations of reidite respectively. c Pole figures for zircon and reidite, the shock twins in lamellae (L1 colored purple and L2 colored red) and the shock twins zircon and reidite are systematically rotated about the pole to {110}, (colored pink). Low-angle boundaries (LABs) between adjacent pix- which in tetragonal symmetry is parallel to 110, as described by els within the zircon with disorientation angles of >1° (thin, gray), Timms et al. (2012). While lamellae 1 (L1) and lamellae 2 (L2) both >2° (yellow), >10° (red) and twin boundary relationship 65° about have alignment of {112}reidite to {100}zircon, the three-dimensional 110 disorientation axis (green) are shown. Note that the appar- control on the lamellae orientations (marked on the pole figures) ent curvature of the reidite lamellae was caused by beam drift dur- reveals that each lamella is instead in a {512}zircon orientation (see ing SEM mapping. See BSE image in Fig. 3 for a drift-free image. Appendix 2 of supplementary material, Zircon 14 for further details) The white box shows the location of Fig. 6b. b Area of interest at the

001 and/or 110 (Figs. 5, 6, 7). Crystal–plastic defor- lamellae crosscut the bright rim but then pinch out, and do mation microstructures typically accommodate 5–18° of not occur in the dark core. Raman mapping of the grain cumulative misorientation across the grains containing confirms the lamellae as reidite, which supports results of reidite (Table 2). However, a zircon that contains 2 sets of EBSD mapping (Fig. 4c–e). Spectra from the rim of the reidite lamellae (see Zircon 18, Appendix 2 of supplemen- host zircon have peaks at 198, 209, 220, 353, 434, 970, 1 tary material) also contains a shear band with up to 43° of and 1003 cm− , consistent with values from unshocked misorientation about the [001]zircon and highlights extreme zircon (e.g., Gucsik et al. 2004b). Raman analysis of zir- plastic behavior of zircon during shock metamorphism. con from the rim of the grain shows the v3(SiO4) peak has Zircon 21 was selected for laser Raman mapping a high amplitude and narrow width (spectra 1, Fig. 4c, e). because it has a well-developed set of reidite lamellae Using Eq. 2 of Nasdala et al. (2001), the calculated full that heterogeneously crosscuts the parent zircon grain width at half-maximum (FWHM) value for the v3(SiO4) 1 (Fig. 4a). Imaging of the zircon by CL reveals a dark core is ~3.64 cm− . Raman spectra from the reidite lamellae with minor overprinting along its boundaries and a bright, (spectra 3, Fig. 4e) exhibit a unique set of peaks at 402, 1 concentrically zoned rim (Fig. 3). The CL-dark reidite 455, 543, 846, and 883 cm− , in addition to the peaks

1 3 6 Page 12 of 26 Contrib Mineral Petrol (2017) 172:6

L3 A IPFZ reidite B Local misorientation (001) (010) Host Zircon zircon

0˚ 5˚ {110} (110)

(001) L4 L2 L1

{110}

Reidite lamellae

{110}L3,4

(001)L1,2

{110} L1,2,3&4

(001)L3,4

{110}L1,2

{100}z and {112}r L2 L3

L4 10 μm L1 z = 431290 step = 0.05 μm r= 35186

Fig. 7 EBSD maps and pole figures of reidite-bearing Zircon many of the low-angle grain boundaries within the host zircon. 29 from Ries Clast 1, displaying 4 unique orientations of rei- b Pole figures for zircon and reidite. This grain has four orienta- dite lamellae within the grain. a EBSD map with local misori- tions of reidite lamellae, and all show close alignment of {112}reidite entation color scheme for zircon and IPF color scheme for rei- to one {100}zircon orientation. Additionally, one of the poles to dite. Each pixel of zircon is colored according to the mean {110} for all reidite lamellae plots in the vicinity of (001)zircon. disorientation value from the surrounding 7 7 pixel grid and The poles to the habit planes for the 4 lamellae cluster around the × shows the low-angle boundary microstructures of the host zir- {100}zircon parallel to {112}reidite (see Appendix 2 of supplementary con. The four reidite lamellae (labeled L1–4) are subparallel to material, Zircon 29 for further details of this grain) detected in the zircon (spectra 1). Raman peaks from diffuse peaks that are ambiguous (e.g., 633, 698, 811, and 1 the reidite lamellae are consistent with data from experi- 850 cm− ). mental studies (Knittle and Williams 1993; Gucsik et al. 2004a, b; van Westrenen et al. 2004) and natural reidite Ries Clast 2 (Wittmann et al. 2006, 2009; Chen et al. 2013). In contrast to the rim (spectra 1, Fig. 4e), the v3(SiO4) zircon peak Ries Clast 2 consists of equant plagioclase and quartz from the core (spectra 2, Fig. 4e) is shifted relative to the with minor biotite and an overprint of iron oxide alteration more crystalline zircon in the rim, and has a lower ampli- (Fig. 2e). Quartz grains within the clast contain PDF lamel- 1 tude and larger corrected FWHM of 14.15 cm− . In addi- lae or are entirely diaplectic glass, the latter are isotropic tion to zircon peaks, the core spectrum has low-amplitude in cross-polarized light. The majority of feldspar grains

1 3 Contrib Mineral Petrol (2017) 172:6 Page 13 of 26 6 32 21 225 145 122 124 112 221 001 133 112 112 122 122 122 121 104 122 122 118 132 125 122 221 100 112 habit plane reidite 1332 habit plane zircon 511 311 512 512 100 414 110 320 313 11 112 112 512 512 211 332 411 512 512 221 112 214 212 103 421 111 112 FIB transect Yes Yes Yes Yes Yes Yes No Yes Yes Plucked Plucked Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Lamellae number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 # of planes 0 1 1 1 4 2 0 2 2 0 0 4 3 2 3 0 1 2 4 Reidite No Yes Yes Yes Yes Yes No Yes Yes No No Yes Yes Yes Yes No Yes Yes Yes {112} twins Yes a 8.11 8.97 8.31 9.7 9.48 7.88 3.28 8.08 5.02 10.87 16.29 12.51 12.34 12.77 14.22 10.31 15.52 43.34 10.21 MOS (°) 21 37 42 27 64 66 36 54 52 60 10 43 49 60 51 27 68 36 100 Width (µm) Width 25 55 63 34 80 60 86 63 64 27 45 55 77 63 42 93 55 125 145 Length (µm) Characteristics of zircon and reidite from Ries Clast 1 a depth 498 m within the Nördlingen 1974 borehole 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2 Table Zircon grain #

1 3 6 Page 14 of 26 Contrib Mineral Petrol (2017) 172:6 112 122 125 144 122 100 112 133 133 133 133 112 510 213 100 142 122 231 122 102 124 121 121 112 102 112 111 134 habit plane reidite habit plane zircon 112 512 212 201 512 111 100 512 512 512 512 100 212 314 111 432 512 215 512 512 512 310 311 120 302 112 103 101 FIB transect Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes 55 Yes Lamellae number 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 # of planes 2 1 0 2 4 0 4 1 3 4 2 0 0 1 0 0 2 58 Reidite Yes Yes No Yes Yes No Yes Yes Yes Yes Yes No No Yes No No Yes 25 {112} twins 1 a 9.05 9.52 9.08 5.02 6.44 3.36 17.22 14.5 11.31 11.931 12.74 11.69 12.65 11.95 16 15.24 18.2 11.8 MOS (°) 8 8 69 67 43 26 50 37 51 58 41 31 38 14 19 10 26 41.6 Width (µm) Width 70 89 86 32 65 48 60 78 78 51 60 18 27 12 22 14 42 58.6 Length (µm) MOS: Maximum deviation from mean orientation (°) calculated with grain detect function in Channel5 MOS: Maximum deviation

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 a 36 Total Zircon grain # 2 Table continued

1 3 Contrib Mineral Petrol (2017) 172:6 Page 15 of 26 6

A B T C Z TZ L1

TZ

PDB L2 LAB >1° >10° (001)(010) 10 μm step = 0.05 μm LAB >2° twin, 65° about (110) IPFX (110) D Host Reidite {100}z and Zircon {110} {112}r TZ

(001) {110}

(001) (001) {110} TZ

{110} {110} z = 113088 r= 133

Fig. 8 Scanning electron images and pole figures for Zircon 42 the lower left corner of the grain (green in IPF). c EBSD map of the from Ries Clast 2, which exhibits 2 orientations of reidite lamellae reidite lamellae (with IPF color scheme) and zircon (grayscale band and 1 set of shock twins. a BSE atomic number contrast image, the contrast map), with the reidite lamellae colored red (L1) and orange two reidite lamellae observed crosscutting the zircon approximately (L2). d Pole figures for zircon and reidite. The twins are misoriented N–S and E–W. b IPF colored EBSD map of the zircon grain. The from the host grain 65° about 110, while misorientation about 001 boundaries between adjacent pixels within the zircon with disorienta- is associated with the a-plane deformation band with a slip system tion angles of >1° (thin, gray), >2° (yellow), >10° (red) and the 65° of <010> (100). The reidite lamellae both show close alignment of 110 about  twin relationship (green) are shown, TZ denotes zircon {112}reidite to {100}zircon, but are aligned with the different {100}zircon twins. An a-plane parallel deformation band (PDB) is also visible in lattice planes are optically isotropic, which indicates near-complete con- One to three distinct orientations of reidite lamellae were version to maskelynite. In addition to minor remnants of identified in each reidite-bearing zircon, totaling 15 differ- crystalline plagioclase, there are skeletal feldspar grains, ent sets of lamellae. In addition to reidite lamellae, other consistent with rapid growth from quenched feldspar melt deformation microstructures in the Clast 2 zircon grains generated by the impact. The presence of quenched feld- include planar deformation bands, low-angle grain bounda- spar glass and diaplectic SiO2 indicates a pressure range of ries, and shock twins (e.g., Fig. 8). Detailed microstructural 30–35 GPa and shock stage III for Ries Clast 2 (Stöffler description of Zircons 42 and 37 from Clast 2 follows. 1971b). The clast contains 10 euhedral to subhedral zircon Zircon 42 exhibits characteristic lamellar reidite in grains ranging in length from 18 to 45 µm (mean 25 µm, addition to a range of other deformation microstructures, = Table 2). Unlike Ries Clast 1, there is no evidence of a pre- while Zircon 37 contains both lamellar reidite and a unique existing gneissic fabric, and zircon grains do not appear to granular form, which is not present elsewhere in this study. have a CPO (Fig. 2f). EBSD mapping confirms that reid- Zircon 42 from Clast 2 contains a variety of shock micro- ite is present in seven of ten zircon grains (70%) (Table 2). structures, including two sets of reidite lamellae, planar

1 3 6 Page 16 of 26 Contrib Mineral Petrol (2017) 172:6

A B C

L G

G

IPFX (001) (010) 10 μm G (110) step = 0.05 μm D Host zircon Misoriented zircon Reidite granules {112} reidite lamellae (001), {110} (001), {110} (001), {110} {100} host zircon (001), (001), {110} {110} {110} (001), (001), {110} {110} {110}

Pole to {110}, (001) {110} habit r = 19 n = 75728 n = 1431 {110} n =7744 plane z = 75728

Fig. 9 Scanning electron images and pole figures for Zircon 37 from contrast map for zircon. The reidite lamella and the majority of the Ries Clast 2 with lamellar (L) and microgranular (G) reidite. a BSE granules are colored orange to purple indicating two dominant crys- atomic number contrast image exhibiting bright reidite granules tallographic orientations. d Pole figures for zircon and reidite, the in the lower half of the grain and a reidite lamella crosscutting the majority of the granular reidite showing an epitaxial alignment of 110 110 110 upper section. b EBSD map with IPF color scheme for the zircon and zircon// reidite and [001]zircon// reidite, similar to the lamel- grayscale band contrast map for reidite. The majority of the zircon lae. The majority of the granular zircon (G in Fig. 9b) is in the same is colored in the green scale, but a variety of granules (labeled G) crystallographic orientation as the reidite, suggesting the zircon gran- are misoriented from the host. Many of the zircon granules are sys- ules are potentially a reversion product. The orientation of the habit tematically misoriented ~90° 110 from the host zircon orientation. plane for the lamellar reidite is also marked on one of the pole figures c EBSD map with IPF color scheme for reidite and grayscale band

deformation bands along {100}zircon with a slip system of significantly misoriented with respect to the host grain. A <010> (100), and a set of shock twins in {112}zircon with total of 275 granules of reidite were identified via EBSD a misorientation relationship of 65° about 110 (Fig. 8). mapping, ranging in diameter from to 0.10 to 1.3 µm Zircon 37 has a combination of lamellar and submicrom- (mean 0.24 µm). The majority of the reidite granules = eter granular reidite (Fig. 9). Part of this grain is more crys- (97%) have the same topotaxial relationship to the host zir- talline (upper domain, Fig. 9a, c) and is cut by lamellae, con as the reidite lamellae, such that 110reidite aligns with which appear bright in BSE images (Fig. 9a). One set of [001]zircon, while 9 granules (3%) are in random orientation. lamella index as reidite via EBSD mapping and show close In the portion of the grain that contains reidite granules, 25

(<5.0°) crystallographic coincidence between {100}zircon// granules of zircon, ranging in size from 0.18 to 1.00 µm {112}reidite (Fig. 9c, d). The rest of the grain (lower domain, (mean 0.35 µm), are systematically misoriented 90° about Fig. 9a, c) contains granular reidite, and some domains that <110> relative to the host zircon, and are in the same crys- index as zircon. The majority of the indexed lower por- tallographic orientation as the reidite granules (Fig. 9d). tion of the zircon has retained the crystallographic orien- Reidite lamellae from Clast 2 have the same misorienta- tation of the more crystalline domain of the grain (upper tion relationship to the host zircon as those in Clast 1, such 110 portion of the zircon in Fig. 9b, c). However, discrete that reidite is aligned subparallel to [001]zircon (e.g., domains (subgrains or granules) that index as zircon are Fig. 8d) with a mean misorientation of 8.1°. Similarly,

1 3 Contrib Mineral Petrol (2017) 172:6 Page 17 of 26 6

there is crystallographic coincidence between {100}zircon Crystallographic control on lamellar reidite: nature with {112}reidite, which has a mean misorientation of ~5° and experiments for each lamellae from Clast 2. Likewise, {112}zircon is subparallel with another {112}reidite lattice plane and has Reidite occurs in 1–4 distinct sets of lamellae in 32 of the a mean misorientation of ~5° (5.5°). In the reidite-bearing grains analyzed (Fig. 10). The EBSD data show that there is grains from Clast 2, one set of lamellae is consistent with a consistent crystallographic relationship between the host a {512}zircon habit plane and one lamellae is consistent zircon and the reidite lamellae. In all instances, {112}reidite with {112}zircon, while the 7 other lamellae transected by is closely aligned with {100}zircon, which is in agreement FIB milling are not in any consistent, rational habit planes with the experimental results of Leroux et al. (1999), and

(Table 3). the mean misorientation between {100}zircon and {112}reidite is ~5° (see Appendix 4 of supplementary material). However, while Leroux et al. (1999) also reported coinci- 110 Discussion dence of [001]zircon to reidite, our results indicate that these directions are not exactly coincidental, but are mis- Comparison with natural reidite from other localities oriented by ~10° (Appendix 4 of supplementary material), such that 110reidite are systematically dispersed around

The results of this study show that reidite most commonly [001]zircon (Fig. 11). In all cases of lamellar reidite from this forms as thin crosscutting lamellae; however, it may also study, there is close alignment of {112}zircon to one of the occur as submicrometer granules. The form of reidite other {112}reidite lattice planes. The average misorientation within zircon parent grains is often ambiguous (e.g., Guc- between {112}zircon and {112}zircon for all reidite lamellae sik et al. 2004a), because previous studies of reidite have is also ~5° (Appendix 4 of supplementary material). either used XRD (Glass and Liu 2001; Chen et al. 2013) Therefore, the data presented in this study lead to an or laser Raman (Gucsik et al. 2004a; Wittmann et al. 2006, alternative and more robust definition of interphase orienta- 2009; Chen et al. 2013), while EBSD has only been uti- tion relationship between reidite lamellae and host zircon lized in two previous studies (Cavosie et al. 2015a; Reddy grains, such that an a-plane of the zircon, (100) or (010), et al. 2015). However, petrographic and SEM images of is aligned with one {112}reidite, while another {112}reidite reidite from Chesapeake Bay impact ejecta (Glass et al. is aligned with respect to one of the {112}zircon. This rela- 2001), the Ries impact structure (Wittmann et al. 2006) and tionship results in up to eight unique crystallographic the Xiuyan Crater (Chen et al. 2013) all share similar char- orientations of lamellar reidite with respect to a host zir- acteristics to the reidite lamellae documented in this study. con (Fig. 11; for pole figures for individual sets of reidite At the Seelbron and Aumühle quarries in the Ries Crater, lamellae from each grain please, see Appendix 3 of sup- reidite-bearing shocked zircon grains from the shock stages plementary material). The interphase relationship of this III and IV clasts exhibit “subparallel lamellae of subµm study is consistent with zircon–reidite crystallographic thickness” or “a high density of planar microstructures,” data from Rock Elm and Stac Fada, where lamellar reidite respectively (Wittmann et al. 2006, their Fig. 5). Likewise, shows close alignment of the {100}zircon with (112}reidite, petrographic and SEM images of shocked zircon grains and {112}zircon with another {112}reidite (Cavosie et al. from the Xiuyan Crater exhibit lamellae that crosscut the 2015a; Reddy et al. 2015). While the transformation of zircon grains and are bright in BSE (Chen et al. 2013, their zircon to reidite has been postulated to occur by the con- 110 Figs. 7 and 8). Similarly to this study, EBSD analysis of version of one of the zircon to [001]reidite (Kusaba et al. reidite-bearing shocked zircon from Rock Elm (Cavosie 1986; Leroux et al. 1999), this would result in the align- 110 et al. 2015a) and Stac Fada (Reddy et al. 2015) identifies ment of [001]zircon with reidite, which is inconsistent reidite most commonly formed as sets of multiple crosscut- with the misorientation relationships reported in our study ting lamellae. In all cases, the reidite lamellae are brighter and requires further consideration. than the host zircon in BSE, due to its ~10% denser crys- Even though there is consistent crystallographic align- tal structure (Glass et al. 2002), dark in CL, and crosscut ment of the reidite lamellae to the host zircon, the habit the primary zonation patterns of the zircon (Cavosie et al. planes (or interfaces) between the zircon and the reidite 2015a; Reddy et al. 2015, this study). At Rock Elm, reid- lamellae are highly variable (Fig. 12). The most common ite was also found a submicrometer granules (Cavosie et al. planes along which lamellar reidite formed are {512}zircon 2015a), similar to those found in Zircon 37 of this study. (16 out of 64, 25%) and {112}zircon (6 out of 64, 9%). The crystallographic relationships between reidite habit However, the majority of lamellae formed along irra- (lamellar and granular) and the host zircon are discussed tional planes that show no discernible systematic orienta- further below. tion relationships with the host zircon (Fig. 12). A similar

1 3 6 Page 18 of 26 Contrib Mineral Petrol (2017) 172:6 Habit plane reidite 201 221 122 118 112 101 123 120 121 Habit plane zircon 203 104 512 221 112 414 203 113 124 FIB transect Yes Yes Yes Yes Plucked Plucked Plucked Plucked Plucked Yes Yes No Yes Yes Yes 9 Lamellae number 59 60 61 62 64 65 63 66 67 68 69 70 71 72 73 1 0 3 0 3 2 0 3 2 1 # of planes 15 Reidite Yes No Yes No Yes Yes No Yes Yes Yes 7 {112} Twins Yes 1 a 8.63 3.85 9.56 13.37 16.55 17.42 15.7 10.34 11.9 MOS (°) >20 Width (µm) Width 22 11 24 19 19 18 15 21 10 14 17.3 Length (µm) 27 18 38 19 45 22 20 23 18 18 24.8 Characteristics of zircon and reidite from Ries Clast 2 a depth 498 m within the Nördlingen 1974 borehole MOS: Maximum deviation from mean orientation (°) calculated with grain detect function in Channel5 MOS: Maximum deviation

3 Table Zircon grain # a 37 38 39 40 41 42 43 44 45 46 Total

1 3 Contrib Mineral Petrol (2017) 172:6 Page 19 of 26 6

is inconsistent with the pervasive mechanical twinning in 12 Clast 1 11 {112}reidite reported by Leroux et al. (1999). (n=36) The high abundance of reidite-bearing zircon grains 10 in each studied clast allows a systematic investigation of 9 Clast 2 whether reidite lamellae formation is controlled by intrin- (n=10) y 8 sic or extrinsic factors. While the zircon grains from Ries 7 Clast 1 show a CPO within the x–y–z-coordinate frame- 6 6 work of the sample (Fig. 2), this is likely due to passive equenc

Fr grain rotation and alignment during the development of the 4 pre-impact gneissic fabric (cf. Kaczmarek et al. 2011). Fur- 3 3 3 thermore, there is no CPO developed in the zircon grains 2 2 2 from Clast 2, and therefore, CPO development in Clast 1 probably predates the impact event and is not a result of 0 0 shock deformation. The habit plane orientations from rei- 0 1234 dite lamellae in Ries Clast 1 (with a CPO) and Ries Clast Number of lamellae per grain 2 (without a CPO) are both heterogeneously distributed (Fig. 13). Therefore, these results suggest that the initial Fig. 10 Histogram of the number of unique reidite lamellae orienta- zircon grain orientation has no discernible control on the tions within individual zircon grains from Ries Clasts 1 and 2 most energetically favorable transformation orientations within the zircon crystal structure with respect to the propa- observation was made for reidite lamellae identified from gation direction of the shock wave (Table 4). Instead, the shocked zircon from Stac Fada (Reddy et al. 2015). transformation of zircon to lamellar reidite appears to be The formation of reidite as multiple discrete lamel- dominantly controlled by the preexisting microstructure lae during rapid shock conditions produced in an impact of the zircon and the rheological properties of the adjacent environment is inconsistent with a diffusion-driven trans- phases. formation and instead supports the interpretation that the transformation occurs in a displacive manner (Langenhorst Formation mechanisms of granular reidite and Deutsch 2012). Likewise, the volume change between the zircon and reidite phases rules out a potential shuffle Granular reidite was found in the analyzed Ries sample transformation (Delaey 2006). Furthermore, the system- in a zircon that also contains lamellar reidite (Zircon 37). atic misorientation relationship between reidite and zircon The granular reidite grains are submicrometer in size with is consistent with an invariant direction of transformation, an average diameter of 0.24 µm. This is consistent with supporting a deviatoric, rather than dilatation, dominated granular reidite reported from Rock Elm with average grain transformation. While a deviatoric shear transformation is diameters of 0.19 µm (Cavosie et al. 2015a). Furthermore, supported by our data, the large number of crystal planes nanogranular reidite ranging from 20 to 100 nm has been along which this transformation occurs suggests that there reported in zircon grains experimentally shocked to 60 GPa is also a rotational element to the transformation, as pro- (Leroux et al. (1999). posed by Kusaba et al. (1986). The active slip systems The reidite granules occur in domains of low crystallin- within the host zircon prior to reidite formation may also ity within the host zircon (interpreted from EBSD pattern play a role in the development of different habit planes. quality, e.g., Zircon 37; Fig. 9) or along the edges of the Further work is required to refine this displacive mecha- zircon grains and within vugs (Rock Elm Grain 9; Cavo- nism, which accommodates both the large number of crys- sie et al. 2015a). Additionally, the majority of the submi- tallographic planes that reidite may form along, and the crometer reidite granules reported in this study and Cavosie systematic crystallographic alignment between the reidite et al. (2015a) have specific crystallographic misorientation and zircon. relationships with the host zircon. Granular reidite shares Leroux et al. (1999) reported the formation of numer- a topotaxial alignment similar to that of the reidite lamel- ous twins within the lamellar reidite in {112}, resulting lae, with one of the 110reidite subparallel to 110zircon from localized buildup of strain (Delaey 2006). However, and the conjugate 110reidite subparallel to 001zircon (e.g., in our analyzed Ries zircon grains, only one example of Fig. 9d), although the crystallographic coincidence of the twinned reidite was found (Fig. 6). The twinned reidite is granular reidite is more relaxed compared to the strict located where a reidite lamella and a zircon twin intersect, relationship of lamellar reidite. This topotaxial relation- and has a misorientation relationship 75° about 110 that ship was observed for 97% of the submicrometer granules

1 3 6 Page 20 of 26 Contrib Mineral Petrol (2017) 172:6

A Zircon Reidite measured Reidite theoretical {100} {110} {110}

{112} {112} {100} {001} {112} {112}

n = 73

B Reidite with {112} // {100}A Host Zircon Reidite with {112} // {100}B

{110} {110}

{001} {001} {112} {112} {001}

{110} {110}

{001} {001} {112} {112}

{100}A {110} {100}B

{112} {112}

{001} {001}

{110} {110}

{112} {112}

{001} {001}

{110} {110}

Fig. 11 Pole figures and diagram of the 8 distinct alignments of the Virtual Chamber function of Channel5 (i.e., -ϕ2, -Φ, -ϕ1). This lamellar reidite with the host zircon. a Pole figures of the fixed zircon aligns the c-axis of the zircon with the vertical axis of the pole fig- orientation, the reidite orientations measured for all 73 lamellae iden- ure and the a-planes with x and y, respectively. b Schematic diagrams tified, and the 8 crystallographic alignments of the reidite within the and pole figures to illustrate the 8 different crystallographic orienta- host zircon. Note the close agreement of the theoretical orientations tion variants of lamellar reidite (blue crystals) with zircon (orange and the measured orientations (see Appendix 2 of supplementary crystal), created by coincidence of {112}reidite with {100}zircon and material for further pole figures). To orient the reidite lamellae into {112}reidite with {112}zircon. Poles to reidite planes are colored red or a reference frame relative to the zircon, the mean orientation of the green relative to the fixed zircon orientation, depending on the spe- host zircon was measured using the Grain Detect function of Tango, cific {100} pole with which they are aligned then the average Euler angles were subtracted from each grain using within Zircon 37 of Ries Clast 2 (this study) and 71% of It is unlikely that the reidite granules identified at the reidite granules in Zircon 9 from Rock Elem (Cavosie Ries (Zircon 37) and Rock Elm (Zircon 9 in Cavosie et al. 2015a). et al. 2015a) formed via displacive shearing along the

1 3 Contrib Mineral Petrol (2017) 172:6 Page 21 of 26 6

Habit plane orientations of Ries Clast 1 Ries Clast 2 reidite lamellae in parent zircon (001) zircon (001) zircon 001 100

(001) lamellar reidite (001) lamellar reidite Clast 1 (n=55) Clast 2 (n=9) 110

Fig. 12 Inverse pole figure plot of the habit planes of each reidite lamellae relative the host zircon. The three-dimensional orientations of each lamellae that were transected using the FIB were rotated by the mean crystallographic orientation of the zircon. The orientations Pole to habit plane Pole to habit plane of the zircon were measured using the same method as described in Fig. 11, but the habit planes were rotated using Stereonet9, so that the lamellae could be viewed relative to the crystallographic orienta- tion of the host zircon. The symmetry of the host zircon was then col- lapsed into an IPF plot so that symmetrical equivalent planes could be removed. The data from Clast 1 (black) and Clast 2 (white) each show a large amount of scatter, confirming the many irrational planes that reidite has formed along, but there is a cluster of poles at {512}zircon n=55 n=9 from Clast 1

Fig. 13 Pole figures for zircon and reidite from Ries Clasts 1 and 2. The zircon grains in Ries Clast 1 have a preexisting crystallographic crystal lattice because the granules occur along the zir- preferred orientation (CPO) of their [001] caused by the gneissic fab- con grain boundary or within domains of decreased crys- ric. While the c-axis of the reidite lamellae from Clast 1 shows a sys- tallinity, where it would be difficult to impose a shear tematic alignment, this distribution is likely to be caused by the pre- existing CPO and the systematic misorientation relationship between (martensitic) transformation. An alternative mechanism the reidite and zircon. Ries Clast 2 does not show an obvious system- for the formation of granular reidite, supported by the atic CPO crystallographic relationships outlined above, is that of a reconstructive transformation, whereby newly formed reidite nucleated mostly (but not strictly) with a topotax- Table 4 Zircon–reidite crystallographic orientation relationship ial relationship to the host zircon. This interpretation is variants from Ries Clasts 1 and 2. Each cell shows number of occur- supported by ab initio dynamical simulations (Marqués rences of reidite transformation with relationship relating to each et al. 2008). of the two {100} in zircon, here shown arbitrarily as {100}A and {100}B. Color coding of the cells indicates dominance of one {100} The granular reidite from Zircon 37 (Ries Clast 2) relationship over the other occurs exclusively within a domain of the zircon that has poor indexing of the EBSPs (Fig. 9). This domain is inter- {100}A {100}B 0 1234 preted to be of lower crystallinity, which could have been 0 14 9 9 1 1 caused by either metamictization of the lattice following 1 5 2 2 2 3 crystallization of the grain (Geisler and Pidgeon 2001), or 3 4 localized conversion of zircon to diaplectic ZrSiO4 during impact shock (Wittmann et al. 2006), while in Rock Elm Symmetric –no preference for any parcular {100} relaonship Zircon 9 granular reidite occurs within grain boundaries Weak preference for one {100} relaonship over the other Dominated by one {100} relaonship over the other and on the walls of vugs, suggesting the reidite nucleated Strongly dominated by one {100} relaonship over the other on more crystalline domains of the primary zircon (Cavosie et al. 2015a). In either scenario, at lower shock pressures than those required for lamellar reidite formation, stored the nucleation energy barrier to be overcome, resulting in strain energy associated with damaged or amorphized zir- reidite formation with a predominantly epitaxial relation- con lattice in these domains could be sufficient to enable ships with the host zircon.

1 3 6 Page 22 of 26 Contrib Mineral Petrol (2017) 172:6

Effect of zircon crystallinity on the transformation of their crystal structure from radiation damage prior to to reidite impact shock are not favorable for transformation to rei- dite. This is likely due to the damage of the crystal lattice This is the first study that combines both EBSD mapping by α-particle fluence, which inhibits the shear transfor- and laser Raman spectroscopy of shock-metamorphosed mation of zircon to reidite, and increases the stability of zircon grains. Zircon 21 (Fig. 4) contains reidite lamellae zircon relative to reidite in impact environments (Lang that are distinguishable in both EBSD and laser Raman et al. 2008). Furthermore, reidite-bearing zircon grains maps. The reidite lamellae are best developed in the rim of from the Stac Fada ejecta deposit show similar hetero- this grain, and are absent in the CL-dark core (Figs. 3, 4). geneous reidite development truncated by dark CL core The CL response of zircon is controlled by its trace element domains, which workers also speculated was due to the composition and its crystalline state (Geisler and Pidg- inhibition of reidite formation caused by metamictization eon 2001; Hanchar and Miller 1993; Nasdala et al. 2001). of the grain’s core prior to shock deformation (Reddy Radiation damage produced by the radioactive decay of et al. 2015, 2016). Although moderately metamict zir- radioisotopes such as 238U, 235U, and 232Th (and their inter- con will hinder the development of lamellar reidite dur- mediate daughter isotopes) leads to non-luminescence in ing shock metamorphism, granular reidite will prefer- zircon; therefore, CL-dark domains commonly correspond entially nucleate in zircon domains with high levels of to regions with high initial actinide concentrations (Geisler amorphization. and Pidgeon 2001). Within the rim of Zircon 21, the Raman spectra (spot 1 Reidite in the geologic record: an impact barometer? in Fig. 4c, e) have a narrow, high-amplitude v3(SiO4) peak 1 (wave number 1000 cm− ), indicative of highly crystal- In this study of Ries zircon grains, reidite was found in ≈ line zircon (Nasdala et al. 2001), while in the reidite-absent shock stage II and III clasts, consistent with other results core of the grain (spot 2 in Fig. 4c, e) the v3(SiO4) peak is from Ries (Gucsik et al. 2004a; Wittmann et al. 2006), and shifted relative to that of the crystalline zircon to a lower the Chesapeake Bay (Wittmann et al. 2009) impact struc- wave number, has a lower amplitude, and the spectrum tures. Within the Xiuyan Crater, reidite was only found in contains peaks in addition to zircon. Using Eq. 6 of Nas- zircon grains from a shock stage II gneiss and not in shock dala et al. (2001), the α-dose within the core of Zircon 21 is stage III (Chen et al. 2013). In our study, 70% of zircon calculated to be ~0.9 1016 decay events per mg, which is grains from Clasts 1 and 2 (shock stage II–III) contained × consistent with moderately metamict zircon. While shock reidite, similar to the results of Wittmann et al. (2006). deformation can cause amorphization of zircon crystal lat- These results are consistent with the experimental shock tice (Wittmann et al. 2006), the observed domain of lower studies of Kusaba et al. (1985), Leroux et al. (1999), and crystallinity (Fig. 4) closely follows the chemical growth van Westrenen et al. (2004), which found the phase trans- zonation of the zircon grain visible in CL (Figs. 3e, 4d), formation from zircon to reidite began above 20 GPa. This and therefore, supports the hypothesis that the amorphi- is further supported by the coexistence of zircon {112} zation is a result of α-recoil damage prior to shock defor- shock twins and reidite from both Ries Clasts 1 (zircon mation. In addition, while some of the extra Raman peaks 14) and 2 (zircon 42) of this study. Shock twins in zircon from the core of the metamict zircon are similar to those are ubiquitous in impact environments (Moser et al. 2011; of reidite (spots 2 and 3, Fig. 4e), no reidite was identi- Timms et al. 2012; Erickson et al. 2013b; Thomson et al. fied by EBSD mapping in this region (Fig. 4a). Because 2014; Cavosie et al. 2015b) and have also been produced EBSD mapping with a 200 nm step size did not identify experimentally at 20 GPa (Morozova 2015). While the con- reidite within the metamict core of this grain zircon, two ditions for the production of shock twins and reidite over- explanations can be attributed to the observed Raman sig- lap, it is uncommon (2/32 of reidite-bearing grains from nal (Fig. 4e); (1) the reidite peaks are caused by a large- this study, 6%, Figs. 6 and 8) to have both microstructures volume interaction of the laser with the sample, whereby in one grain, suggesting that there are different conditions reidite from outside of the metamict zircon core contrib- for their formation. uted to the Raman signal, or (2) short order transforma- These results also suggest that the conditions under tion of the zircon structure occurred at a scale that was not which granular and lamellar reidite form differ, as granular resolved by EBSD (<200 nm). While option (2) is possible, reidite was only found within one grain in Clast 2 (shock it is unlikely because the EBSPs from within the core of the stage III) and none in Clast 1 (shock stage II), while lamel- grain do not show any significant decrease in their quality lar reidite was prevalent in both Clasts 1 and 2. However, as (i.e., band contrast; Fig. 4a). noted for lamellar reidite, other factors may also control the Therefore, based on these results, we posit that zir- formation of granular reidite, such as the crystalline state con grains that have experienced moderate degradation (e.g., metamictization) of the parent zircon.

1 3 Contrib Mineral Petrol (2017) 172:6 Page 23 of 26 6

It is possible that the habit plane orientations of the there is significant alteration of the major minerals in Clast reidite lamellae within the parent zircon are controlled 2 (Fig. 2). While Clast 2 experienced higher peak shock by shock conditions and, similarly to PDFs in shocked temperature and pressure than Clast 1, both clasts are sig- quartz, the specific orientations could be used to estimate nificantly altered, probably due to post-impact hydrother- shock levels (Stöffler and Langenhorst 1994). The habit mal processes. However, both clasts preserve reidite that plane orientations of the reidite lamellae are inconsistently has resisted alteration and exhibit sharp boundaries with developed, in Clast 1 29% of lamellae are oriented along the host zircon grains, which is consistent with other locali-

{512}zircon, while no dominant orientation is observed in ties of reidite-bearing zircon. At the Chesapeake Bay, crater Clast 2 (Fig. 12). These results suggest that varying shock reidite was found in heavily altered gneissic clasts, which conditions may develop different reidite habit orientations included smectite, chlorite, and opal-like microcrystalline within the parent zircon; however, further work is required SiO2 (Wittmann et al. 2009). Likewise, reidite from the to determine whether other controlling factors may be Mesoproterozoic Stac Fada ejecta deposit survived post- important, such as if the intrinsic elasticity of zircon has an impact prehnite–pumpellyite facies metamorphism (Reddy effect on the development of specific habit planes. et al. 2015). Therefore, reidite is a geologically robust high- Reidite-bearing zircon grains have not been reported in pressure phase and likely to be extant through deep geo- impactites that have experienced shock stage IV or above, logic time, preserving evidence of shock metamorphism. likely due to increased post-shock temperatures. Gener- ally, shock pressures and temperatures are coupled (i.e., temperatures increase with shock pressure); however, the Conclusions shock temperature dissipates at a much slower rate than shock pressure (Melosh 1989). Reidite has been shown to The results of this study offer insights into the conditions revert to zircon at temperatures above 1200 °C in labora- and mechanisms for the transformation of zircon to the tory experiments (Kusaba et al. 1985; Fiske et al. 1999). high-pressure polymorph reidite during shock metamor- Therefore, while reidite will be produced in shock stage phism. Reidite forms in two distinct habits, as lamellae and IV, it may revert to zircon when the shock wave has passed as submicrometer granules, which are interpreted to form and is thus erased from the geologic record. Evidence for by deviatoric and reconstructive transformations, respec- this reversion is observed in Zircon 37 from Clast 2, which tively. All lamellar reidite strictly preserve a consistent contains both lamellar and granular reidite. The granular alignment of {100}zircon to {112}reidite and {112}zircon to a reidite is associated with the amorphous domain of the conjugate {112}reidite; however, reidite lamellae are found grain, which also contains numerous submicrometer zircon in a large range of habit plane orientations within the par- granules that share the crystallographic orientation of the ent grains. The formation of reidite lamellae is consistent granular reidite (Fig. 9d). The misoriented submicrometer with a rapid, displacive transformation during the passage granules of zircon likely either nucleated on reidite gran- of an impact shock wave and record conditions of >20 GPa. ules or reverted from reidite granules as the grain regressed Reidite lamellae orientations appear to be controlled by the from peak shock conditions. Therefore, we propose that local crystal structure of the grain (i.e., the most energeti- granular zircon (systematically misoriented 90° about cally favorable planes) and less so by the orientation of the 110) is indicative of shock-produced reidite, which has passing shock wave. Granular reidite preserves a general 110 110 been obscured by post-shock temperatures. These results alignment of [001]zircon to reidite and zircon to the are consistent with previously published data from granu- conjugate 110reidite, but are less well defined than the reid- lar shocked zircon from lechatelierite-bearing sandstone ite lamellae–zircon relationship. Formation of granular rei- at Meteor Crater, which do not contain reidite, but contain dite is consistent with a reconstructive transformation from submicrometer zircon granules that are misorientated 90° amorphous ZrSiO4. Finally, these results show a strong about 110 that were interpreted to represent reversion control of the primary crystallinity (or metamict state) of from reidite (Cavosie et al. 2016). the zircon on the transformation to reidite. While moder- The results of this study show that reidite, especially as ate metamictization of the zircon crystal lattice inhibits the lamellae crosscutting parent zircon grains, are well devel- growth of reidite lamellae, granular reidite may transform oped in shock stage II and III conditions. Coupled with the from diaplectic ZrSiO4, formed through either mechanical perseverance of reidite in deep time (Cavosie et al. 2015a; breakdown of the zircon lattice or breakdown caused by Reddy et al. 2015), this suggests that reidite should be high α-doses from the actinide content of the host zircon preserved in the geologic record. Due to the proximity of grains. Clast 1 and Clast 2 (<1 cm), it can be assumed that they Our results suggest that relatively crystalline zircon can experienced similar post-shock thermal histories. Quartz (1) partially transform to reidite at and above shock stage in Clast 1 is distinctly toasted (Whitehead et al. 2002), and II, (2) survive post-shock alteration, and (3) is a suitable

1 3 6 Page 24 of 26 Contrib Mineral Petrol (2017) 172:6 shock indicator at many impact structures. Reidite in zircon El Goresy A, Dubrovinsky L, Gillet P, Graup G, Chen M (2010) Aka- grains that experience shock stage IV is destroyed by post- ogiite: an ultra-dense polymorph of TiO2 with the baddeleyite- type structure, in shocked garnet gneiss from the Ries Crater, shock temperatures, but systematic misorientation of ~90° Germany. Am Mineral 95:892–895. doi:10.2138/am.2010.3425 about 110 within the zircon, likely preserves evidence of Engelhardt WV, Bertsch W (1969) Shock induced planar deforma- passage through the reidite stability field. tion structures in quartz from the Ries crater, Germany. Contrib Miner Petrol 20:203–234. doi:10.1007/BF00377477 Acknowledgements We would like to thank Gisele Pösges, Deputy Erickson TM, Cavosie AJ, Moser DE, Barker IR, Radovan HA Director of the Ries Crater Museum, for supplying the samples. TME (2013a) Correlating planar microstructures in shocked zircon acknowledges financial support from a Curtin International Postgrad- from the Vredefort Dome at multiple scales: crystallographic uate Research Scholarship from Curtin University Office of Research modeling, external and internal imaging, and EBSD structural and Development. AJC acknowledges support from the US National analysis. Am Mineral 98:53–65. doi:10.2138/am.2013.4165 Science Foundation (EAR-1145118) and the NASA Astrobiology Erickson TM, Cavosie AJ, Moser DE, Barker IR, Radovan HA, program. MAP was supported by a CSIRO Office of the Chief Execu- Wooden J (2013b) Identification and provenance determination tive Postdoctoral Fellowship. Analytical costs were supported by the of distally transported, Vredefort-derived shocked minerals in ARC Core to Crust Fluid System Centre of Excellence. The ARC the Vaal River, South Africa using SEM and SHRIMP-RG tech- (LE130100053), Curtin University, University of Western Australia, niques. Geochim Cosmochim Acta 107:170–188. doi:10.1016/j. and CSIRO are acknowledged for funding the Tescan Mira3 FEG- gca.2012.12.008 SEM housed in the John de Laeter Centre’s Microscopy & Microanal- Ferrière L, Morrow JR, Amgaa T, Koeberl C (2009) Systematic study ysis Facility at Curtin University. The Tescan Lyra3 FIB-SEM is part of universal-stage measurements of planar deformation fea- of the Australian Resource Characterisation Facility (ARCF), under tures in shocked quartz: implications for statistical significance the auspices of the National Resource Sciences Precinct (NRSP)—a and representation of results. Meteorit Planet Sci 44:925–940. collaboration between CSIRO, Curtin University and The University doi:10.1111/j.1945-5100.2009.tb00778.x of Western Australia—and is supported by the Science and Industry Fiske PS, Nellis WJ, Sinha AK (1999) Shock-induced phase transi- Endowment Fund. We would like to thank Gordon Moore for thor- tions of ZrSiO4, reversion kinetics, and implications for impact ough editorial handling and two anonymous reviewers for their sig- heating in terrestrial craters. In: APS, shock compression of con- nificant improvements to the manuscript. densed matter meeting abstract: 501 Flórez M, Contreras-García J, Recio JM, Marqués M (2009) Quan- tum-mechanical calculations of zircon to scheelite transition pathways in ZrSiO4. Phys Rev B 79:104101 References French BM (1998) Traces of catastrophe: a handbook of shock-meta- morphic effects in terrestrial meteorite impact structures. Lunar Bauberger W, Mielke H, Schmeer D, Stettner G (1974) Petrographis- and Planetary Institute che Profildarstellung der Forschungsbohrung Nördlingen 1973 French BM, Koeberl C (2010) The convincing identification of (von Meter 263 an bis zur Endteufe im Maßstab 1:200). Geo- terrestrial meteorite impact structures: what works, what logica Bavarica 72:33–34 doesn’t, and why. Earth Sci Rev 98:123–170. doi:10.1016/j. Bohor BF, Betterton WJ, Krogh TE (1993) Impact-shocked zircons: earscirev.2009.10.009 discovery of shock-induced textures reflecting increasing degrees Geisler T, Pidgeon R (2001) Significance of radiation damage on the of shock metamorphism. Earth Planet Sci Lett 119:419–424. integral SEM cathodoluminescence intensity of zircon: an exper- doi:10.1016/0012-821X(93)90149-4 imental annealing study. N Jhb Mineral Monatsh 10:433–445 Cavosie AJ, Erickson TM, Timms NE (2015a) Nanoscale records Glass BP, Liu S (2001) Discovery of high-pressure ZrSiO4 polymorph in of ancient shock deformation: reidite (ZrSiO4) in sandstone at naturally occurring shock-metamorphosed zircons. Geology 29:371– the Ordovician Rock Elm impact crater. Geology 43:315–318. 373. doi:10.1130/0091-7613(2001)029<0371:dohpzp>2.0 .co;2 doi:10.1130/g36489.1 Glass BP, Liu S, Leavens PB (2002) Reidite: an impact-produced Cavosie AJ, Erickson TM, Timms NE, Reddy SM, Talavara C, Mon- high-pressure polymorph of zircon found in marine sediments. talvo SD, Pincus MR, Gibbon RJ, Moser D (2015b) A terres- Am Mineral 87:562–565 trial perspective on using ex situ shocked zircons to date lunar Goltrant O, Cordier P, Doukhan J-C (1991) Planar deformation impacts. Geology 43:999–1002. doi:10.1130/g37059.1 features in shocked quartz; a transmission electron micros- Cavosie AJ, Timms NE, Erickson TM, Hagerty JJ, Hörz F (2016) copy investigation. Earth Planet Sci Lett 106:103–115. Transformations to granular zircon revealed: twinning, reidite, doi:10.1016/0012-821X(91)90066-Q and ZrO2 in shocked zircon from Meteor Crater (Arizona, USA). Gucsik A, Koeberl C, Brandstätter F, Libowitzky E, Reimold W Geology. doi:10.1130/g38043.1 (2004a) Cathodoluminescence, electron microscopy, and Raman Chen M, Yin F, Li X, Xie X, Xiao W, Tan D (2013) Natural occur- spectroscopy of experimentally shock metamorphosed zircon rence of reidite in the Xiuyan crater of China. Meteorit Planet crystals and naturally shocked zircon from the ries impact crater. Sci 48:796–805. doi:10.1111/maps.12106 In: Dypvik H, Burchell M, Claeys P (eds) Cratering in marine Delaey L (2006) Diffusionless transformations. In: Materials science environments and on ice. Impact studies. Springer, Berlin, pp and technology. Wiley-VCH Verlag GmbH & Co. KGaA, pp 281–322 585–654. doi:10.1002/9783527603978.mst0392 Gucsik A, Zhang M, Koeberl C, Salje EKH, Redfern SAT, Pruneda Di Vincenzo G, Skála R (2009) 40Ar–39Ar laser dating of tektites JM (2004b) Infrared and Raman spectra of ZrSiO4 experi- from the Cheb Basin (Czech Republic): evidence for coeval- mentally shocked at high pressures. Mineral Mag 68:801–811. ity with moldavites and influence of the dating standard on the doi:10.1180/0026461046850220 age of the Ries impact. Geochim Cosmochim Acta 73:493–513. Hanchar J, Miller C (1993) Zircon zonation patterns as revealed by doi:10.1016/j.gca.2008.10.002 cathodoluminescence and backscattered electron images: impli- El Goresy A (1965) Baddeleyite and its significance in impact glasses. cations for interpretation of complex crustal histories. Chem J Geophys Res 70:3453–3456. doi:10.1029/JZ070i014p03453 Geol 110:1–13

1 3 Contrib Mineral Petrol (2017) 172:6 Page 25 of 26 6

Hough RM, Gilmour I, Pillinger CT, Arden JW, Gilkess KWR, Yuan Ono S, Funakoshi K, Nakajima Y, Tange Y, Katsura T (2004) Phase J, Milledge HJ (1995) Diamond and silicon carbide in impact transition of zircon at high P-T conditions. Contrib Miner Petrol melt rock from the Ries impact crater. Nature 378:41–44 147:505–509. doi:10.1007/s00410-004-0570-6 Kaczmarek MA, Reddy SM, Timms NE (2011) Evolution of zircon Poelchau MH, Kenkmann T (2011) Feather features: A low-shock- deformation mechanisms in a shear zone (Lanzo massif, West- pressure indicator in quartz. J Geophys Res 116:B02201. doi:10. ern-Alps). Lithos 127:414–426. doi:10.1016/j.lithos.2011.09.016 1029/2010jb007803 Kamo SL, Krogh T, Glass BP, Liu S (2002) U-Pb Study of Shocked Pohl J, Poschlod K, Reimold WU, Meyer C, Jacob J (2010) Ries Zircons from the North American Microtektite Layer. In: 33rd crater, Germany: the Enkingen magnetic anomaly and associ- Annual LPSC Abstract:1643 ated drill core SUBO 18. Geol Soc Am Spec Pap 465:141–163. Knittle E, Williams Q (1993) High-pressure Raman spectroscopy of doi:10.1130/2010.2465(10) ZrSiOoz observation of the zircon to scheelite transition at 300 Reddy SM, Johnson TE, Fischer S, Rickard WDA, Taylor RJM (2015) K. Am Mineral 78:245–252 Precambrian reidite discovered in shocked zircon from the Stac Krogh T, Davis DW, Corfu F (1984) Precise U-Pb zircon and badde- Fada impactite, Scotland. Geology 43:899–902. doi:10.1130/ leyite ages for the sudbury area. In: Pye EG, Naldrett AJ, Giblin g37066.1 PE (eds) The geology and ore deposits of the Sudbury structure, Reddy SM, van Riessen A, Saxey DW, Johnson TE, Rickard WAD, Ontario. Ontario Geological Survey, London, pp 431–447 Fougerouse D, Fischer S, Prosa TJ, Rice KP, Reinhard DA, Chen Krogh TE, Kamo SL, Bohor BF (1993) Fingerprinting the K/T impact Y, Olson D (2016) Mechanisms of deformation-induced trace site and determining the time of impact by UPb dating of sin- element migration in zircon resolved by atom probe and cor- gle shocked zircons from distal ejecta. Earth Planet Sci Lett relative microscopy. Geochim Cosmochim Acta 195:158–170. 119:425–429. doi:10.1016/0012-821X(93)90150-8 doi:10.1016/j.gca.2016.09.019 Kusaba K, Syono Y, Kikuchi M, Fukuoka K (1985) Shock Reid AF, Ringwood AE (1969) Newly observed high pressure trans- behavior of zircon: phase transition to scheelite struc- formations in Mn3O4, CaAl2O4, and ZrSiO4. Earth Planet Sci ture and decomposition. Earth Planet Sci Lett 72:433–439. Lett 6:205–208 doi:10.1016/0012-821X(85)90064-0 Reimold WU, Hansen BK, Jacob J, Artemieva NA, Wunnemann Kusaba K, Yagi T, Kikuchi M, Syono Y (1986) Structural con- K, Meyer C (2011) Petrography of the impact breccias of the siderations on the mechanism of the shock-induced zircon- Enkingen (SUBO 18) drill core, southern Ries crater, Ger- scheelite transition in ZrSiO4. J Phys Chem Solids 47:675–679. many: new estimate of impact melt volume. Geol Soc Am Bull doi:10.1016/0022-3697(86)90082-X 124:104–132. doi:10.1130/b30470.1 Lang M, Zhang F, Lian J, Trautmann C, Neumann R, Ewing RC Schmidt-Kaler H (2004) Geologische Übersichtskarte des Meteor- (2008) Irradiation-induced stabilization of zircon (ZrSiO4) at itenkraters Nördlinger Ries: mit Kurzerläuterungen. Bayerisches high pressure. Earth Planet Sci Lett 269:291–295. doi:10.1016/j. Geologisches Landesamt epsl.2008.02.027 Schmieder M, Tohver E, Jourdan F, Denyszyn SW, Haines PW (2015) Langenhorst F, Deutsch A (2012) Shock metamorphism of minerals. Zircons from the Acraman impact melt rock (South Australia): Elements 8:31–36. doi:10.2113/gselements.8.1.31 shock metamorphism, U-Pb and 40Ar/39Ar systematics, and Leroux H, Reimold WU, Koeberl C, Hornemann U, Doukhan JC implications for the isotopic dating of impact events. Geochim (1999) Experimental shock deformation in zircon: a transmission Cosmochim Acta 161:71–100. doi:10.1016/j.gca.2015.04.021 electron microscopic study. Earth Planet Sci Lett 169:291–301. Shoemaker EM, Chao ECT (1961) New evidence for the impact doi:10.1016/S0012-821X(99)00082-5 origin of the Ries Basin, Bavaria, Germany. J Geophys Res Malone L (2009) Characterization of shock metamorphosed ZrSiO4 66:3371–3378. doi:10.1029/JZ066i010p03371 in the Chesapeake Bay impact crater. In: AAPG, Atlantic Univer- Singleton AC, Osinski GR, Shieh SR (2015) Microscopic effects sities Geologic conference 45:153 of shock metamorphism in zircons from the Haughton impact Malone L, Boonsue S, Spray J, Wittmann A (2010) Zircon-reidite structure, Canada. Geol Soc Am Spec Pap 518:135–148. relations in breccias from the Chesapeake Bay impact structure. doi:10.1130/2015.2518(09) In: 41st annual LPSC abstract: 2286 Smirnov MB, Mirgorodsky AP, Kazimirov VY, Guinebretière R Marqués M, Contreras-García J, Flórez M, Recio JM (2008) On (2008) Bond-switching mechanism for the zircon-scheelite the mechanism of the zircon-reidite pressure induced trans- phase transition. Phys Rev B 78:094109 formation. J Phys Chem Solids 69:2277–2280. doi:10.1016/j. Stähle V, Altherr R, Koch M, Nasdala L (2007) Shock-induced growth jpcs.2008.04.016 and metastability of stishovite and coesite in lithic clasts from Mashimo T, Nagayama K, Sawaoka A (1983) Shock compression of suevite of the Ries impact crater (Germany). Contrib Miner Pet- zirconia ZrO2 and zircon ZrSiO4 in the pressure range up to 150 rol 155:457–472. doi:10.1007/s00410-007-0252-2 GPa. Phys Chem Minerals 9:237–247. doi:10.1007/BF00309573 Stöffler D (1971a) Coesite and stishovite in shocked crystalline rocks. Melosh J (1989) Impact cratering: a geologic process. Oxford Mono- J Geophys Res 76:5474–5488. doi:10.1029/JB076i023p05474 graphs on Geology and Geophysics, Oxford Stöffler D (1971b) Progressive metamorphism and classification Morozova I (2015) Strength study of zircon under high pressure. The- of shocked and brecciated crystalline rocks at impact craters. J sis, The University of Western Ontario Geophys Res 76:5541–5551. doi:10.1029/JB076i023p05541 Moser DE, Cupelli CL, Barker IR, Flowers RM, Bowman JR, Stöffler D (1977) Research drilling Nördlingen 1973: polymict brec- Wooden J, Hart JR (2011) New zircon shock phenomena and cias, crater basement, and cratering model of the Ries imapct their use for dating and reconstruction of large impact structures structure. Geol Bavarica 75:443–458 revealed by electron nanobeam (EBSD, CL, EDS) and isotopic Stöffler D, Langenhorst F (1994) Shock metamorphism of quartz in U-Pb and (U–Th)/He analysis of the Vredefort dome. Can J nature and experiment: I. Basic observation and theory*. Mete- Earth Sci 48:117–139. doi:10.1139/e11-011 oritics 29:155–181. doi:10.1111/j.1945-5100.1994.tb00670.x Nasdala L, Wenzel M, Vavra G, Irmer G, Wenzel T, Kober B (2001) Stöffler D, Artemieva NA, Wünnemann K, Reimold WU, Jacob J, Metamictisation of natural zircon: accumulation versus thermal Hansen BK, Summerson IAT (2013) Ries crater and suevite annealing of radioactivity-induced damage. Contrib Miner Petrol revisited-observations and modeling part I: observations. Mete- 141:125–144. doi:10.1007/s004100000235 orit Planet Sci 48:515–589. doi:10.1111/maps.12086

1 3 6 Page 26 of 26 Contrib Mineral Petrol (2017) 172:6

Sturm S, Wulf G, Jung D, Kenkmann T (2013) The Ries impact, a van Westrenen W, Frank MR, Hanchar JM, Fei Y, Finch RJ, Zha C-S double-layer rampart crater on Earth. Geology 41:531–534. (2004) In situ determination of the compressibility of synthetic doi:10.1130/g33934.1 pure zircon (ZrSiO4) and the onset of the zircon-reidite phase Thomson OA, Cavosie AJ, Moser DE, Barker I, Radovan HA, French transition. Am Mineral 89:197–203 BM (2014) Preservation of detrital shocked minerals derived Whitehead J, Spray JG, Grieve RAF (2002) Origin of “toasted” from the 1.85 Ga Sudbury impact structure in modern alluvium quartz in terrestrial impact structures. Geology 30:431–434. and Holocene glacial deposits. Geol Soc Am Bull 126:720–737. doi:10.1130/0091-7613(2002)030<0431:ootqit>2.0.co;2 doi:10.1130/b30958.1 Wittmann A, Kenkmann T, Schmitt RT, Stöffler D (2006) Shock-met- Timms NE, Erickson TM, Pearce MA, Cavosie AJ, Schmieder M, amorphosed zircon in terrestrial impact craters. Meteorit Planet Tohver E, Reddy SM, Zanetti MR, Nemchin AA, Wittmann Sci 41:433–454. doi:10.1111/j.1945-5100.2006.tb00472.x A (2017) A pressure-temperature phase diagram for zircon at Wittmann A, Reimold WU, Schmitt RT, Hecht L, Kenkmann T extreme conditions. Earth-Sci Rev 165:185–202. doi:10.1016/j. (2009) The record of ground zero in the Chesapeake Bay impact earscirev.2016.12.008 crater—Suevites and related rocks. Geol Soc Am Spec Pap Timms NE, Reddy SM, Healy D, Nemchin AA, Grange ML, Pidgeon 458:349–376. doi:10.1130/2009.2458(16) RT, Hart R (2012) Resolution of impact-related microstructures Yue B, Hong F, Merkel S, Tan D, Yan J, Chen B, Mao H-K (2016) in lunar zircon: a shock-deformation mechanism map. Meteorit Deformation behavior across the zircon-scheelite phase transi- Planet Sci 47:120–141. doi:10.1111/j.1945-5100.2011.01316.x tion. Phys Rev Lett 117:135701 Turner D, Langenhorst F, Pollok K (2014) Martensitic mechanism of the zircon-to-reidite transformation. In: 77th annual meeting of the Meteoritical Society Abstract: 5411

1 3