Meteoritics & Planetary Science 1–19 (2020) doi: 10.1111/maps.13541
High-resolution microstructural and compositional analyses of shock deformed apatite from the peak ring of the Chicxulub Impact Crater
Morgan A. COX *1,2, Timmons M. ERICKSON 1,3, Martin SCHMIEDER 2, Roy CHRISTOFFERSEN3, Daniel K. ROSS3, Aaron J. CAVOSIE 1, Phil A. BLAND 1, David A. KRING 2, and IODP–ICDP Expedition 364 Scientists
1Space Science and Technology Centre (SSTC), School of Earth and Planetary Science, Curtin University, Perth, Western Australia 6102, Australia 2Lunar and Planetary Institute (LPI)—USRA, 3600 Bay Area Boulevard, Houston, Texas 77058, USA 3Jacobs-JETS, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, Texas 77058, USA *Correspondence. E-mail: [email protected] (Received 01 December 2019; revision accepted 09 June 2020)
Abstract–The mineral apatite, Ca5(PO4)3(F,Cl,OH), is a ubiquitous accessory mineral, with its volatile content and isotopic compositions used to interpret the evolution of H2Oon planetary bodies. During hypervelocity impact, extreme pressures shock target rocks resulting in deformation of minerals; however, relatively few microstructural studies of apatite have been undertaken. Given its widespread distribution in the solar system, it is important to understand how apatite responds to progressive shock metamorphism. Here, we present detailed microstructural analyses of shock deformation in ~560 apatite grains throughout ~550 m of shocked granitoid rock from the peak ring of the Chicxulub impact structure, Mexico. A combination of high-resolution backscattered electron (BSE) imaging, electron backscatter diffraction mapping, transmission Kikuchi diffraction mapping, and transmission electron microscopy is used to characterize deformation within apatite grains. Systematic, crystallographically controlled deformation bands are present within apatite, consistent with tilt boundaries that contain the
INTRODUCTION high-pressure/-temperature polymorphs must be identified and documented (e.g., French 1998; French and Impact cratering has played a major role in shaping Koeberl 2010). Shock deformation microstructures and reworking planetary bodies within our solar system within minerals are, in many cases, a reliable indicator of (e.g., Baldwin 1963; Shoemaker 1983; Melosh 1989). In pressure conditions experienced by target rocks during an order to confirm an impact structure on Earth, the impact event. Shock-produced microstructures in presence of shatter cones, meteoritic components, shock common crustal minerals such as quartz, feldspar, and deformation microstructures within minerals, and/or zircon have been studied extensively (e.g., Stoffler¨ and
1 © The Meteoritical Society, 2020. 2 M. A. Cox et al.
Langenhorst 1994; French 1998; Timms et al. 2017), clasts largely retain their pre-impact basement ages while the response of other accessory minerals such as (McGregor et al. 2018). Cernokˇ et al. (2019) correlated titanite, apatite, monazite, and xenotime has received less phosphate microstructures with different shock stages attention (e.g., Cavosie et al. 2016; Erickson et al. 2016; using coexisting feldspar and electron backscatter McGregor et al. 2018; Cernokˇ et al. 2019; Timms et al. diffraction (EBSD) mapping of apatite. They showed 2019; Kenny et al. 2020). Here, we present a detailed that as shock pressure increased, deformation in apatite study of shock deformation in apatite from granitoid and transitioned from a brittle deformation regime to the impact melt lithologies in the recently drilled peak ring of crystal–plastic regime with low-angle boundaries, the Chicxulub impact structure. followed by subgrain formation and the loss of crystallinity (Cernokˇ et al. 2019). Similarly, Kenny et al. Shock Deformation in Apatite (2020) showed that apatite grains from a clast-rich impact melt rock (with lithic and mineral clasts that Shock deformation microstructures in apatite experienced >35 GPa; Schmieder et al. 2008) show described previously include planar fractures (PFs) evidence for shock recrystallization and intragrain (Cavosie and Centeno 2014; Sløby et al. 2017; crystal–plastic deformation. McGregor et al. 2018; see discussion in Montalvo et al. 2019), recrystallization (Alwmark et al. 2017; McGregor Chicxulub Impact Structure et al. 2018, 2020; Cernokˇ et al. 2019; Kenny et al. 2020), microvesicles (Wittmann et al. 2013; McGregor The Chicxulub impact structure, located on the et al. 2018), crystal–plastic deformation (Cernokˇ et al. Yucatan´ Peninsula of Mexico, is ~180 km in diameter 2019; Kenny et al. 2020), and cataclastically deformed and exhibits a well-preserved peak ring (Fig. 1) (e.g., zones (Birski et al. 2019; Cernokˇ et al. 2019). PFs Hildebrand et al. 1991; Kring 1995, 2005; Morgan et al. consist of multiple sets of parallel, planar features that 1997, 2016; Gulick et al. 2008; Kring et al. 2004; Riller cut across the host apatite grain and are typically et al. 2018; Rae et al. 2019). The peak ring of the spaced 5–10 µm apart (Cavosie and Centeno 2014; Li structure is ~80 to 90 km in diameter and rises ~400 m and Hsu 2018; McGregor et al. 2018; Montalvo et al. above the structural crater floor (Fig. 1) (Gulick et al. 2019). PFs identified in apatite grains through 2013). The impact occurred ~66 Ma ago, produced backscattered electron imaging appear similar to those global ejecta deposits, and is causatively related to the identified in shock-deformed zircon and xenotime (e.g., K-T mass extinction event (e.g., Alvarez et al. 1980; Kamo et al. 1996; Cavosie et al. 2010, 2016; Erickson Kring and Boynton 1991; Swisher et al. 1992; Smit et al. 2013; Cavosie et al. 2016). PFs in apatite have 1999; Kring et al. 2017; Schulte et al. 2010; Renne et al. been interpreted to form in the { 1011} orientation 2013, 2018; Sprain et al. 2018). Based on the presence (Cavosie and Centeno 2014), which is different from of impact melt rock and shock metamorphic features natural cleavage directions, {0001} and {hki0}, of identified in early drill core materials (samples from the apatite (Deer et al. 2013). Dislocations and PFs in Yucatan-6´ borehole), Chicxulub was confirmed to have apatite have been produced experimentally within formed from a hypervelocity impact event (e.g., apatite shock-loaded to ~25 GPa using a plate-wave Hilderbrand et al. 1991; Kring and Boynton 1991; generator (Sclar and Morzenti 1972). In natural Sharpton et al. 1992, 1996). samples, PFs in apatite have been identified in rocks In 2016, the International Ocean Discovery that have experienced ~10 to 20 GPa at the Santa Fe Program (IODP) and International Continental impact structure (New Mexico, USA; Cavosie and Scientific Drilling Program (ICDP) drilled 829 m of core Centeno 2014; Montalvo et al. 2019), as well as in clasts from the peak ring of the Chicxulub crater during within impact breccia from the Nicholson Lake impact Expedition 364 (e.g., Morgan et al. 2016; Riller et al. structure (Canada; McGregor et al. 2018) that 2018). Borehole M0077A (21.45°N, 89.95°W) experienced ~10 GPa. encountered ~112 m of postimpact deposits, ~130 m of Shock-induced recrystallization has been reported reworked suevite and underlying impact melt rock, and within apatite from multiple terrestrial impact structures ~587 m of coarse-grained granitoid rocks of the such as Carswell (Canada; Alwmark et al. 2017), crystalline crater basement (predominantly ~340 Ma) Nicholson Lake (McGregor et al. 2018), and Paasselka¨ that also host pre-impact mafic and felsic volcanic (Finland; Kenny et al. 2020), as well as in phosphate dykes, veins and dykes of impact melt, and lithic minerals in lunar samples (Cernokˇ et al. 2019). Apatite (cataclastic) breccia dykes (Fig. 1) (e.g., Morgan et al. grains in contact with impact melt from the Nicholson 2016; Riller et al. 2018). Lake impact structure were shown to have partially Previously indexed orientations of planar reset U-Pb ages, whereas apatite grains with PFs within deformation features (PDFs) and PFs in quartz Shock deformation in apatite 3
Fig. 1. Location and geophysical images of the Chicxulub impact structure. A) Bouguer gravity anomaly of the crater modified from Rae et al. (2019). B) Seismic profile of the peak ring after Gulick et al. (2013). C) Schematic log of the peak-ring drill core showing sample locations, modified from Morgan et al. (2016). constrain shock pressures between ~15 and 18 GPa 1132.79; 1240.62; 1250.19; 1278.47; 1320.5; 1333.6; see throughout the basement portion of the core (e.g., data repository for sampling core box numbers) consist Feignon et al. 2020). Shock deformation features have of plagioclase, quartz, alkali feldspar, biotite, minor also been described within titanite grains (Timms et al. muscovite, apatite, zircon, titanite, epidote, garnet, 2019), along with the occurrence of the high-pressure ilmenite, and magnetite. The green–black impact melt polymorph TiO2–II (Schmieder et al. 2019). Here, we rocks (728.515 mbsf; see also Schulte et al. 2017; complement previous studies of shock deformation Wittmann 2018a, 2018b; Slivicki et al. 2019) and melt within IODP-ICDP Expedition 364 core M0077A with veins (917.295 mbsf, 1039.23 mbsf) are aphanitic and new observations of shock deformation in apatite from are andesitic in composition with quartz and feldspar the peak-ring lithologies and xenocrysts within the clasts, and secondary calcite. The melt veins are found impact melt rock unit that immediately overlies the within brecciated granitoid lithologies and contain clasts peak ring (Morgan et al. 2016; Gulick et al. 2017). of granite bedrock. A total of 560 apatite grains were identified and SAMPLES AND METHODS imaged using optical microscopy at the Lunar and Planetary Institute (LPI), Houston. Backscattered Seventeen samples from the core were selected from electron (BSE) imaging using a JEOL-5910 scanning within the interval between 728.5 and 1333.6 m below electron microscope (SEM), operated at an accelerating sea floor (Fig. 1). The granitoid rock samples (sample voltage of 15 kV, was then conducted at the NASA numbers are meters below sea floor (mbsf): 745.7; Johnson Space Center (JSC) in order to characterize 749.58; 791.64; 828.7; 886.665; 896.56; 932.79; 1050.1; microtextures within select apatite grains. 4 M. A. Cox et al.
EBSD Mapping, Transmission Kikuchi Diffraction program Stereonet (Allmendinger et al. 2011; Cardozo Mapping, and Transmission Electron Microscopy and Allmendinger 2013), so that they could be rotated about the absolute crystallographic orientation by the Microstructural analyses of a subset of 108 apatite average Euler angles φ1, Φ, φ2 as determined by EBSD grains as well as nine zircon grains were conducted using (see data repository). This rotation allowed the c-axis of an Oxford Symmetry EBSD detector on a JEOL 7600f the grains to be centered in stereoplots and, therefore, field emission gun SEM at NASA-JSC. Acquisition the fracture sets of all grains could be compared in the parameters included a 20 kV accelerating voltage, 18 nA same crystal reference frame to help elucidate any beam current, 20.5 mm working distance, and 70° sample systematic patterns in order to determine the tilt. The Oxford Instruments AZtec 4.1 software was used crystallographic orientation (hkil) of the PFs. to collect the data and Channel5 Tango and Mambo modules were used for post-acquisition processing of the Electron Microprobe data to create EBSD maps and pole figures. EBSD maps of apatite grains were collected at spatial resolutions Apatite grains from impact melt domains in between 50 and 500 nm. samples 728.515 mbsf and 917.295 mbsf were analyzed An apatite grain from sample 917.295 mbsf using a JEOL 8530F field emission gun microprobe at containing a representative planar deformation band NASA-JSC. Working conditions employed an (PDB) was prepared by focused ion beam (FIB) cross- accelerating voltage of 15 kV, a beam current of 20 nA, sectioning using an FEI Quanta dual electron/FIB and a spot size of 3 µm. Microprobe results from 53 instrument at NASA JSC (see data repository for FIB spots in 14 apatite grains were collected in order to cross section methods). determine the local F, Cl, Na, Mg, Al, Si, Ca, S, La, The FIB section was then analyzed by high- Ce, P, Sr, Y, Fe, Mn, Sm, and Nd abundances. resolution transmission Kikuchi diffraction (TKD) in An additional analytical protocol followed for order to characterize the degree of misorientation apatite analyses included the following conditions: F Kα observed across the PDB. TKD maps were run at (LD1, 30s), Cl Kα (PETL, 30s), Na Kα (TAP, 30s), Mg 12 nm step size, with the apatite section yielding EBSD Kα (TAP, 30s), Al Kα (TAP, 30s), Si Kα (TAP, 30s), Ca patterns of high quality. The mapping used a 25 kV Kα (PET, 30s), S Kα (PET, 30s), La Lα (PET, 30s), Ce accelerating voltage, a 10 nA beam current, 20.5 mm Lα (PET, 30s), P Kα (PETL, 30s), Sr Lα (PETL, 30s), Y working distance, and −20° sample tilt. Lα (LPET, 30s), Fe Kα (LIFH, 30s), Mn Kα (LIFH, 30s), After TKD characterization, transmission electron Sm Lα (LIFH, 30s), and Nd Lα (LIFH, 30s). All elements microscopy (TEM) imaging and analysis of the apatite were counted for 30 s at their peak positions, and 15 s at FIB section utilized a JEOL JEM-2500SE 200 KV field- each background position. Standardization of F was emission scanning transmission electron microscope performed using a Wilberforce (Ontario, Canada) (FE-STEM) at NASA-JSC. The 2500SE FE-STEM has fluorapatite crystal, and Cl using a tugtupite crystal (see analytical energy dispersive X-ray spectroscopy (EDS) data repository for additional list of standards used). capabilities for spot analysis and submicrometer scale Reanalysis of the Wilberforce fluorapatite standards as element mapping provided by a JEOL DrySD 60 mm2 unknowns yielded an average K-raw of 105.54 indicating silicon drift EDS detector interfaced to a Thermo NSS that fluorine X-ray yield drifted up compared to the System Seven spectral analyzer system. original calibration. An empirical correction of 0.9475 The characterization of the apatite FIB sample with was therefore applied to all fluorine data from apatite FE-STEM utilized the full range of instrument unknowns. Analyses on apatite that yielded fluorine capabilities for bright-field (BF)/dark-field (DF) concentrations greater than that which is stoichiometri- conventional TEM and STEM imaging, with particular cally possible (i.e., >3.76 wt%) were categorized as a emphasis on characterization of dislocations, subgrains, misanalysis and removed; only two such analyses were and low-angle/high-angle boundaries by conventional found. The Cl standards yielded reproducible values TEM BF/DF diffraction contrast imaging. across the analyses and, therefore no correction was applied to the data. Orientation of PFs in Apatite RESULTS Crystallographic orientations of PFs within apatite grains were measured using the program Image-J from Optical and BSE Imaging of Apatite forescatter images collected during EBSD mapping of apatite grains. The lineations collected by measuring the Apatite grains range in length from 30 to 900 µm PFs in forescatter images were then plotted within the and exhibit euhedral to subhedral basal and prismatic Shock deformation in apatite 5 sections. Optical and BSE imaging of 560 apatite grains EBSD Mapping revealed either PFs, sub-PFs, cataclastically deformed zones, and granular textures, or a combination Microstructural EBSD analyses of 120 apatite thereof (Fig. 2; see data repository). All samples contain grains in granitoid rocks indicate plastic deformation grains with PFs; a total of ~250 apatite grains contain affected apatite throughout the core (Figs. 2 and 3). PFs in up to three orientations within individual grains Grains with PFs exhibit a higher degree of intragrain (Figs. 2 and 3). Offsets along PFs also occur in heavily plastic strain than other apatite grains analyzed (Fig. 2). fractured grains, with up to ~5 µm of apparent PDBs are observed in five grains, with PDBs displacement. Sub-PFs are common within apatite. systematically misorientated up to 20° from the host Cataclastic deformation is evident in 60 grains, with about (0001) (Fig. 3). Cataclastically deformed grains some grains displaced along fractures. Sample 1333.6 exhibit >40° of misorientation between rotated mbsf contains the best example of cataclastic fragments (see data repository), with adjacent quartz microstructures, with 22 apatite grains containing also showing >10° of crystal–plastic deformation. complex brittle deformation microstructures. Seven High-resolution EBSD mapping of partially apatite grains containing granular microstructures were recrystallized grains from the impact melt unit shows identified from impact melt rock and melt veins in that orientation data from host apatite grains are highly samples 728.515 mbsf and 917.295 mbsf (Fig. 4). dispersed in pole figures, which is attributed to impact- Granules are ~10 to 100 µm in size and contain a related deformation. In contrast, newly recrystallized mixture of rounded neoblastic granules and larger domains show little to no dispersion in pole figures of euhedral laths (e.g., Fig. 4). Apatite grains hosted by individual recrystallized granules indicating that they pre-impact biotite exhibit minimal fracturing, with curvi- are virtually strain-free (Fig. 5). Fully recrystallized planar fractures being the predominant microstructure apatite grains show differences in crystallinity (Fig. 4), observed, whereas grains in direct contact with quartz, with one grain containing a newly crystallized rim of feldspar, and/or zircon contain multiple sets of PFs that apatite, while the interior of the grain does not index by crosscut the grains. EBSD and is not visible in band contrast. Neither zircon grains included within apatite, nor Apatite included in sheet silicates that exhibit kink those that are in contact with quartz and feldspar bands within the shocked granitoid rocks shows very display evidence of planar microstructures, except for low levels of crystal–plastic deformation, with <5° of two grains that contain one set of planar cumulative misorientation observed, while grains in microstructures each (Fig. 7). Zircon grains within the contact with zircon and/or quartz show up to 20° impact melt rock samples exhibit granular misorientation across the grain, with a particularly high microstructures, with evidence of BSE-bright degree of deformation close to the contact between inclusions of ZrO2, presumably baddeleyite (see data apatite and zircon or quartz (Fig. 6). repository). A single zircon grain within shocked granitoid sample 1050.1 mbsf contains {112} deformation twins Orientation of PFs in Apatite (Fig. 7). The single orientation of twin lamellae is ~50 to 100 nm in width and is locally developed within Planar fractures observed within the apatite grains subdomains of the zircon grain. The grain contains <5° are crosscutting features that extend across polished of crystal–plastic deformation across the crystal grain interiors. Fractures are typically spaced ~5to structure and exhibits planar and non-planar fractures. 10 µm apart and occur in up to three orientations Other zircon grains throughout the shocked granitoid within individual grains. A total of 24 fracture sets were rocks show varying levels of crystal–plastic deformation; measured from forescatter images of apatite grains in one zircon inclusion within apatite contains PDBs that order to determine their crystallographic orientation. are misoriented up to 20° from the host zircon grain Criteria for measured sets were that fractures must (see data repository). occur as multiple sets, they are evenly spaced, planar, Within impact melt rock sample 728.515 mbsf, four and crosscut the grain. Of the 24 fracture sets measured, zircon grains have a granular microstructure (e.g., two distinct conjugate fracture sets are identified when Fig. 8). EBSD mapping of the granular grains shows the lineations are plotted on stereonets in the crystal they are composed of individual neoblastic subdomains reference frame (see data repository). The two conjugate that are misoriented in a systematic way, 90° fracture sets coincide with known crystallographic misorientation relationships about {110} and (001), orientations within the hexagonal crystal system, with indicating evidence of the former presence of the high- the fractures oriented within either the {2110g,{2110g, pressure ZrSiO polymorph reidite (Fig. 8) (Cavosie 4 {1120g, or {1120g planes. et al. 2018). 6 M. A. Cox et al.
Fig. 2. Images of apatite grains from shock-deformed granitoid rock of the Chicxulub peak ring. A) Apatite grain with three orientations of planar fractures (PFs) from sample 896.56 mbsf. B) Apatite grain with three orientations of PFs from sample 932.79 mbsf. C) Apatite grain with three orientations of PFs from sample 749.58 mbsf. D) Apatite grain with up to two orientations of PFs from sample 1050.1 mbsf. PPL = plane polarized light, BSE = backscattered electron image, BC = band contrast, IPF = inverse pole figure
TKD Mapping TEM Analysis
An FIB section was prepared from an apatite grain in TEM imaging (both conventional TEM bright-field sample 917.295 mbsf (Fig. 9). The grain was selected and STEM) of an apatite grain from sample 917.295 based on EBSD analyses which revealed systematic PDBs mbsf reveals a complex subgrain microstructure with with <0001> disorientation axes; the vertical section the subgrains showing varying degrees of misorientation extracted is orthogonal to one of the PDBs (Fig. 9). (but mostly low-angle) across boundaries made up of High-resolution TKD mapping reveals that within the complex dislocation networks (Fig. 10). Lower density section, there are two individual deformation bands that dislocation substructures are also present inside the are misoriented up to 10° from the host apatite grain. The subgrains themselves (Fig. 10). In bright-field STEM deformation bands are oriented parallel to the c-axis of imaging, the PDB within the central part of the sample the grain and are ~2 µm in width. Pole figures of the is prominent and remains in contrast through a range of TKD map show that there is minimal rotation about tilting orientations (Fig. 10A). The strain contrast width <0001> of the grain while poles to {1120} and {1010} of the dislocation arrays defining the PDB boundaries is show dispersion up to 20° (Fig. 9). at a minimum in imaging normal to the symmetrical c- Shock deformation in apatite 7
condition for dislocations within the subgrains as well as the subgrain walls themselves, suggesting the dislocation Burgers vector b is parallel to <0001>,or has a significant c-axis component. Although the dislocations and dislocation array substructures associated with the PDB regions in the FIB sample are fundamentally shock-generated in their origin, some amount of thermal strain recovery is also indicated by the relatively low dislocation density in the regions between the low-angle grain boundaries (i.e., within the subgrains themselves), and the recovery of intracrystalline strain by dislocation organization into subgrain walls. Based on the characterization of the apatite foil, there was no evidence of PFs being infilled with any material but to fully address this hypothesis, additional grains with planar features should be analyzed by TEM.
Electron Microprobe
Electron microprobe analysis of 14 apatite grains in impact melt rock (728.515 mbsf) and impact melt veins (917.295 mbsf) shows that apatite grains in sample 728.515 mbsf are chlorine-rich (~0.3 to 0.8 wt%), while grains from sample 917.295 mbsf have <0.1 wt% Cl (Table 1, see data repository for microprobe results). Apatite in both samples is fluorine-rich, with F concentrations ranging from 3.71 to 2.8 wt%. Both calcium and phosphorous concentrations are relatively constant throughout apatite grains in both samples, with values ranging from ~52 to 55 wt% for CaO and 39 to 42 wt% P2O5. Apatite in both samples is also relatively sulfur-rich, with as much as 0.34 wt% SO3 (Table 1). A single, partially recrystallized grain (sample 163, grain 7) was analyzed by microprobe with 11 individual spots (Fig. 5, Table 1), targeting both recrystallized and pre-existing host grain domains. Recrystallized domains have higher MgO, with concentrations ranging from ~0.2 to 0.01 wt% MgO, while Mg in the pre-existing apatite grain is typically below detection limit (=0.0 wt%). The recrystallized domains also have higher measured wt% SiO2, with the host apatite ranging from Fig. 3. Texture component map showing misorientation within 0.1 to 0.17 wt% and the recrystallized domains ranging apatite grains in shocked granitoid rock. A) Apatite grain that contains PDBs which are up to ~10° misoriented from the from 0.33 to 1.86 wt% SiO2 (Tables 1 and DR1 in host grain. Texture component map shows up to 18° of supporting information). However, FeO is highly cumulative misorientation across the grain from sample 932.79 variable within both the host apatite and recrystallized mbsf. Dotted box = FIB section location. B) Apatite grain domains. Phosphorous and chlorine concentrations in that contains planar fractures and PDBs. Texture component both recrystallized domains and host apatite grain are map shows up to 17° misorientation across the grain from sample 932.79 mbsf. Qz = quartz. constant throughout all spots, but CaO values are slightly higher in the host apatite, reaching up to 55.3 wt% while the recrystallized domains are all <54.3 wt% (Table 1). The recrystallized apatite grains axis zone orientation, suggesting the boundaries tend to within the uppermost impact melt rock (728.515 mbsf) be oriented parallel to <0001> (e.g., f1120g). The c-axis also have elevated MgO values ranging from ~0.2 to zone orientation also results in a near-extinction 0.05 wt% MgO. 8 M. A. Cox et al.
Fig. 4. Electron backscatter diffraction (EBSD) and BSE maps of recrystallized apatite grains. A) BSE image of granular apatite grain from sample 728.515 mbsf. B) Inverse pole figure showing misorientation of individual granules within the apatite grain from (A). C) Pole figure of granular apatite grain from (B), showing random orientations of granules indexed by EBSD. D) BSE image of granular apatite grain from sample 917.295 mbsf. E) Inverse pole figure showing misorientation of individual granules and domains within the apatite grain from (D). F) Pole figure of granular apatite grain from B, showing both random and preferred orientations of granules indexed by EBSD. Shock deformation in apatite 9
Fig. 5. Partially recrystallized apatite grain from sample 917.295 mbsf (sample 163, grain 7). A) BSE image of apatite grain. Dotted line = recrystallized domains, white circles = electron microprobe spots with labels (see Table 1 for results), inlay shows a close-up of microprobe spots within the recrystallized domain. B) EBSD inverse pole figure (IPF) of misorientation within grain. C) Pole figure for host apatite grain showing dispersed poles. D) Pole figure for undeformed recrystallized domains showing little misorientation within individual recrystallized domains. Ap = apatite, Bt = biotite.
DISCUSSION recrystallization. The orientations of PFs observed within apatite from this study are consistent with being Microstructures in Apatite oriented in either the {2110g,{2110g,{1120g, or {1120g crystallographic planes. Previous studies have Apatite grains throughout the samples surveyed documented conjugate sets of PFs in apatite that appear show shock deformation microstructures, ranging from to be oriented parallel to the {1011g prism plane of the PFs to crystal–plastic deformation and complete grain (Cavosie and Centeno 2014). However, it is 10 M. A. Cox et al.
Fig. 6. BSE and EBSD maps of apatite grains exhibiting impedance mismatching with neighboring phases from sample 1050.1 mbsf. A) BSE image of virtually undeformed apatite grain found within sheet silicates (chloritized biotite). B) Texture component map showing that apatite grain from A contains <3° misorientation. C) BSE image of deformed apatite grain found within sheet silicates and in contact with zircon. Parts of the grain in contact with zircon contain planar fractures while other regions of the grain that are only in contact with sheet silicates contain few planar fractures. D) Texture component map showing that apatite grain from B contains up to 12° misorientation, with a higher degree of strain toward the contact with adjacent apatite and zircon grains. Ap = apatite, Bt = biotite, Chl = chlorite, Zrn = zircon.
difficult to distinguish between prismatic orientations and monazite (Erickson et al. 2016). Deformation bands using solely BSE or optical light images. Therefore, our in zircon have been suggested to be a product of results confirm the presence of conjugate sets of PFs in impact-related deformation but are not considered shocked apatite and further build on the suggested diagnostic evidence of impact as they have also been orientations of PFs formed within the mineral resulting documented in tectonically deformed rocks (e.g., from shock deformation. Kovaleva et al. 2015). Combining EBSD, TKD, and Crystal–plastic deformation observed within apatite TEM analyses of the PDB within apatite shows that the from the Chicxulub impact structure is similar to that band is consistent with tilt boundaries that contain the described in apatite from the Paasselka¨ impact structure c-axis and results from slip in <1010> on f1120g as (Kenny et al. 2020) as well as in phosphate minerals determined using high-resolution EBSD and TKD, as from the Moon (Cernokˇ et al. 2019). PDBs observed well as the alignment of dislocations when the FIB within apatite from our samples represent the first section is rotated to the c-axis during TEM imaging. documented occurrence of this microstructure in apatite. With our new results from Chicxulub, impact- The deformation bands observed in the apatite grains induced recrystallization of apatite has now been are texturally similar to those observed in zircon (e.g., described from five terrestrial impact structures with Erickson et al. 2013), xenotime (Cavosie et al. 2016), similar microstructures of lath-like grains and rounded Shock deformation in apatite 11
Fig. 7. EBSD and BSE maps of shock-deformed zircon grain from granitoid rock sample 1050.1 mbsf. A) BSE image of zircon grain showing subplanar microstructures. B) Inverse pole figure (IPF) showing misorientation of the grain and {112} deformation twins identified within the grain. C) Pole figure from inset for shock-deformed zircon grain showing the relationship of the {112} deformation twins with the host zircon (Zrn). neoblasts observed in recrystallized grains from the PDFs within quartz grains. These features have been Carswell (Canada; Alwmark et al. 2017), Lac La traditionally used to determine (peak) shock pressures Moinerie (Canada; McGregor et al. 2019), Paasselka¨ because they have been extensively studied in nature and (Finland; Kenny et al. 2020), and Steen River (Canada; reproduced in controlled experiments (e.g., Stoffler¨ and McGregor et al. 2020) impact structures. Langenhorst 1994). Based on experimental replication, different specific orientations of PDFs in quartz indicate Shock Barometry of Peak-Ring Samples different pressure ranges, with {10 1 3} and {10 14} suggesting >10 to <20 GPa, while the presence of {10 1 To evaluate shock pressures in peak-ring granitoid 2} PDFs indicates slightly higher pressures around rocks and impact melt within them, we begin by utilizing ~20 GPa (according to the shock barometry calibrated 12 M. A. Cox et al.
Fig. 8. EBSD maps of granular zircon grain that contains misorientation relationships indicating former reidite in granular neoblastic zircon (FRIGN zircon) from sample 728.515 mbsf. A) BSE image of granular zircon grain. B) Band contrast (BC) image of zircon grain showing subgranular microstructures as well as intact host grain domains. C) Inverse pole figure (IPF) showing misorientation of the grain. D) Stereonet of shock-deformed zircon grain showing the 90° relationships of the granules and host indicating the former presence of the high-pressure polymorph reidite (Cavosie et al. 2018).
for non-porous quartzofeldspathic rocks; Stoffler¨ and The presence of {112} twins within a zircon grain Langenhorst 1994; Stoffler¨ et al. 2018). In the case of the from granitoid rock sample 1050.1 mbsf supports our PDFs in shocked quartz grains within granitoid rocks, interpretation of the pressure estimates derived from the relatively high abundance of {10 1 3} and {10 14} quartz PDF indexing, as empirical studies indicate that along with subordinate {10 1 2}, {11 2 1}, and {51 61} zircon requires shock pressures of ~20 GPa to form orientations suggests the granitoid target rocks of the {112} deformation twins (e.g., Moser et al. 2011; Timms Chicxulub peak ring experienced shock pressures of ~15 et al. 2017; Cox et al. 2018). Due to the low abundance to 18 GPa (Feignon et al. 2020). of shock-twinned zircon (one grain) identified within the Shock deformation in apatite 13
Fig. 9. High-resolution transmission Kikuchi diffraction (TKD) mapping of focused ion beam (FIB) section removed from apatite grain in sample 917.295 mbsf (shown in Fig. 3A). A) Texture component map showing up to 10° misorientation across section. One distinct orientation of planar deformation bands is observed. B) Pole figure showing misorientation within the apatite grain, as well as little dispersion of poles about the c-axis, suggesting PDBs are parallel to the c-axis. samples, as well as only one orientation of extremely required to form granular microstructures in apatite fine twins (~50 nm in width) therein, it appears that the grains within the impact melt, but are suggestive of a non-melted granitoid rocks of the peak ring did not minimum shock pressure of ~30 GPa that affected experience shock pressures much higher than ~20 GPa, target rock clasts and mineral grains incorporated into and/or that the shock twins may have resulted from the Chicxulub impact melt. localized amplification of peak shock pressure (e.g., along grain boundaries that may have served as zones Impedance Mismatching of enhanced shock impedance [e.g., Stoffler¨ 1971; El Goresy et al. 2001]. The estimated pressure range Impedance mismatching refers to variations in the (≤20 GPa) is consistent with the absence within the velocity of the shock wave through different, coexisting granitoid rocks of reidite, the high-pressure polymorph minerals due to differences in physical properties and of ZrSiO4, which requires shock pressures of ~30 GPa crystal structure, such as density, hardness, and to form in granitoid rocks (e.g., Kusaba et al. 1985; orientation of the phase relative to the shock wave Leroux et al. 1999; Glass et al. 2002; Erickson et al. (e.g., Stoffler¨ 1972; Kusaba et al. 1988). Impedance 2017; Cox et al. 2018). mismatching is inferred in all granitoid samples, with More variable and potentially higher shock apatite grains that are enclosed within (chloritized) pressures are reasonably expected in the impact melt biotite showing <5° of crystal plastic deformation. In rock within the peak ring. The identification of the contrast, apatite grains fully surrounded by quartz or former presence of reidite in granular zircon (FRIGN in contact with zircon and coexisting apatite contain zircon) within the impact melt rock samples (Fig. 8) >10° crystal–plastic deformation, PDBs, and PFs suggests that individual zircon grains experienced (Fig. 6). Biotite and chloritized biotite within the pressures >30 GPa (e.g., Cavosie et al. 2018). Previous granitoid samples appear to have compressed during work on target rock components of the impact melt in shock wave propagation, forming typical kink bands the Chicxulub structure suggested pressures of ~60 GPa and, therefore, may have accommodated most of the (e.g., Morgan et al. 2016), while other rock and mineral strain, allowing it to largely bypass enclosed apatite clasts underwent complete melting. However, because grains (e.g., HOrz¨ and Ahrens 1969). Shock-induced shock metamorphism is an inherently heterogeneous compression of sheet silicates has been documented process and because shock pressure isobars crosscut within grains from multiple impact structures (e.g., excavation flow lines during the impact cratering Santa Fe; Montalvo et al. 2019), as well as in process (e.g., French 1998), impact melt rocks and experimentally shocked mica (e.g., Lambert and breccias typically contain a mix of variably (weakly to Mackinnon 1984). The inferred impedance severely) shocked target rock and mineral fragments mismatching suggests that apatite responds to the same (e.g., Stoffler¨ 1971; Schmieder et al. 2015). The zircon shock pressures (from the same shock wave front) in microstructures alone cannot constrain the pressures different ways, depending on the mineralogy of the 14 M. A. Cox et al.
Fig. 10. TEM images of planar deformation bands and other shock-related defects in an apatite grain from sample 917.295 mbsf, prepared by FIB sectioning (Figs. 3A and 9). A) Bright-field STEM image of entire FIB section showing locations of most prominent PDBs. B) Conventional TEM symmetrical zone axis bright-field image showing detail of subgrains and low-angle subgrain walls associated with a PDB. The PDB contains internal subgrain domains as well as isolated dislocations outside of the PDB. C) Conventional TEM bright-field image of a PDB in a slightly off-axis orientation relative to the [0001] (c-axis). Narrow width of the strain contrast across the PDBs in this diffraction orientation are consistent with minimal inclination of the boundary planes relative to the c-axis (i.e., boundaries are likely along f1120g). D) Conventional bright-field TEM image of PDB in non-systematic diffraction orientation highlighting the dislocation array along the PDB boundary. surrounding host lithology. While local shock pressure Shock-Induced Recrystallization amplification can occur at grain boundaries causing localized pressure excursions (e.g., El Goresy et al. The partially recrystallized apatite grains from this 2001), shock pressures can also be notably reduced in study (Fig. 5) show that recrystallized domains strain-accommodating “shock-buffer” zones such as identified in both EBSD and BSE imaging have higher mica flakes and other sheet silicates. MgO compared to the host grain, while the latter has Shock deformation in apatite 15
Table 1. Representative microprobe analyses of recrystallized apatite grains (728.515 mbsf—sample 89) and a partially recrystallized grain (917.295 mbsf—sample 163) from impact melt domains, core M0077A. Grain spot 89 23-1 89 6-5 89 7-2 89 7-3 163 7-2 163 7-3 163 7-4 163 7-5 163 7-8 163 7-9 163 7-11 CaO 54.9 53.9 53.6 53.8 55.1 55.0 55.1 54.3 54.2 53.6 55.3 P2O5 42.7 41.9 41.7 41.7 42.0 41.8 42.0 41.4 41.1 40.2 42.4 F 3.36 3.26 3.51 3.49 3.42 3.57 3.52 3.46 3.33 3.54 3.26 Cl 0.31 0.63 0.62 0.62 0.01 0.01 b.d.l. 0.02 0.01 0.02 0.01 SiO2 0.18 0.22 0.31 0.27 0.15 0.17 0.12 0.61 0.68 0.66 0.10 Al2O3 b.d.l. b.d.l. b.d.l. 0.02 0.01 0.01 0.01 0.18 0.25 0.10 0.01 Y2O3 b.d.l. b.d.l. 0.10 0.14 0.04 0.03 0.04 0.04 b.d.l. 0.02 0.01 La2O3 b.d.l. 0.02 0.02 b.d.l. b.d.l. 0.02 b.d.l. 0.05 b.d.l. 0.02 0.03 Ce2O3 0.14 0.08 0.04 0.10 0.08 0.07 0.05 0.16 0.03 0.15 0.07 Nd2O3 0.07 0.01 0.08 0.08 0.01 0.03 b.d.l. 0.04 0.03 b.d.l. 0.06 Sm2O3 0.03 0.02 b.d.l. 0.04 b.d.l. b.d.l. b.d.l. 0.02 0.02 b.d.l. b.d.l. FeO 0.09 0.38 0.39 0.33 0.36 0.45 0.34 0.59 0.63 0.37 0.33 MnO 0.07 0.14 0.14 0.16 0.10 0.10 0.12 0.09 0.10 0.10 0.07 MgO 0.01 0.20 0.19 0.16 b.d.l. b.d.l. b.d.l. 0.13 0.20 0.04 b.d.l. SrO b.d.l. 0.01 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. Na2O 0.05 0.04 0.07 0.07 0.05 0.08 0.06 0.07 0.05 0.10 0.04 SO3 0.17 0.08 0.11 0.15 0.10 0.22 0.17 0.19 0.13 0.20 0.06 O = F + Cl −1.56 −1.59 −1.70 −1.69 −1.52 −1.59 −1.57 −1.54 −1.58 −1.45 −1.40 Total 100.64 99.44 99.42 99.62 100.09 100.19 100.24 100.03 99.66 97.53 100.41 Units in table are in wt%. XX XX-X = sample, grain spot no. b.d.l. = below detection limit. slightly higher CaO. This indicates that during the of dolomite in the sedimentary portion of the target partial recrystallization of apatite within the impact rock and mafic (dolerite) veins and amphibolite units melt, Mg2+ may have been substituted for Ca2+ and, within the deeper, crystalline portion of the target therefore, the composition of apatite was locally altered rock (e.g., Sharpton et al. 1996; Kring 2005; in response to shock-induced or post-shock Schmieder et al. 2017, 2018). Therefore, elevated Mg temperature-induced recrystallization. There is also within the apatite could be due to impact-induced elevated SiO2 within the recrystallized domains of the alkali and Mg-/Ca-metasomatism (e.g., Rowe et al. apatite grain suggesting that the granitic bedrock may 2004; Tuchscherer et al. 2004; Zurcher¨ and Kring potentially be a source of fluids during impact-induced 2004; Trepmann et al. 2005), but further chemical melting. However, variability in FeO concentrations characterization of variably shocked apatite in both that is uncorrelated with recrystallized apatite textures fresh and hydrothermally altered target rock and domains is evidence for pre-impact heterogeneity within impactite samples from the Chicxulub crater is the grains. Partial recrystallization created an open required to test this hypothesis. network within the grain and, therefore, these areas Observations within our sample suite indicate that were able to thermally interact with the hot impact impact-induced recrystallization of apatite can change melt, as supported by elevated MgO and SiO2 values the chemical composition of the mineral. A recent study within fully recrystallized grains within the upper most by Kenny et al. (2020) showed that partially impact melt unit (e.g., Fig. 4, Table 1). recrystallized apatite grains from the Paasselka¨ impact The differences in both the Cl concentrations in structure in Finland also have observed changes in recrystallized apatite grains from the upper impact chemistry, with recrystallized domains being depleted in melt unit and deeper melt veins could all be due to Mg and Fe relative to the host grain. Therefore, a postimpact hydrothermal alteration or pre-impact combination of microstructural and geochemical variations in magmatic fluids. The differences in MgO characterization of any potential apatite targets, concentrations within the partially recrystallized grain especially from meteorites and lunar samples where the could potentially be due to a long-lived hydrothermal petrographic context is often poorly characterized or system triggered by the Chicxulub impact (Zurcher¨ unknown, is necessary before determining meaningful and Kring 2004; Abramov and Kring 2007; Kring geochronologic ages or potentially measuring apatite et al. 2017). Magnesium was originally present within OH, Cl, and F concentrations to assess planetary the target rocks at the Chicxulub structure in the form volatile abundances. 16 M. A. Cox et al.
CONCLUSION Planetary Sciences and the Space Science and Technology Center at Curtin University. LPI Developing a better understanding of how apatite Contribution no. 2370. LPI is operated by USRA under responds to shock deformation is crucial in order to a cooperative agreement with the Science Mission understand more about changes in the crystal structure Directorate of the National Aeronautics and Space and composition of the mineral on other planetary Administration. We thank the editor Christian Koeberl materials, in particular, older materials that have and reviewers A. Cernok and an anonymous reviewer experienced complex histories of impact bombardment for constructive comments. over billions of years. Using multiple, correlated techniques to characterize and identify deformation Editorial Handling—Dr.Christian Koeberl microstructures and recrystallization textures within apatite is important, as no single technique alone can REFERENCES identify all changes in the mineral resulting from shock deformation. Recrystallized and partially recrystallized Abramov O. and Kring D. A. 2007. Numerical modeling of impact-induced hydrothermal activity at the Chicxulub apatite grains analyzed in this study show that shock crater. Meteoritics & Planetary Science 42:93–112. recrystallization can cause apparent changes in apatite Allmendinger R. W., Cardozo N., and Fisher D. M. 2011. composition. Structural geology algorithms: Vectors and tensors. The crystallographically controlled PDBs identified Cambridge, UK: Cambridge University Press. within apatite in this study are the first to be reported Alvarez L. W., Alvarez W., Asaro F., and Michel H. V. 1980. Extraterrestrial cause for the cretaceous-tertiary extinction. in this mineral and result from active slip in <1010 > on Science 208:1095–1108. f1120g. The PDBs contain complex subgrain domains Alwmark C., Bleeker W., LeCheminant A., Page L., and and low-angle boundaries with the bands defined by Schersten´ A. 2017. An Early Ordovician 40Ar-39Ar age dislocation arrays, confirming that apatite responds to for the ∼50 km Carswell impact structure, Canada. GSA – shock deformation in a complex way even at the Bulletin 129:1442 1449. Baldwin R. C. 1963. The measure of the Moon. Chicago: The nanometer to micrometer scale. We show that the PFs University of Chicago Press. 488 p. within apatite form conjugate sets and are orientedÈÉBirski Ł., Søaby E., Wirth R., Koch-Muller¨ M., Simon K., within either the {2110g,{2110g,{1120g,or1120 Wudarska A., Gotze¨ J., Lepland A., Hofmann A., and planes, which increase the known orientations of PFs in Kuras A. 2019. Archaean phosphates: A case study of naturally shocked apatite. Additionally, the suspected transformation processes in apatite from the Barberton greenstone belt. Contributions to Mineral and Petrology impedance mismatching observed within the samples 174:25. shows that apatite deforms differently based on its Cardozo N. and Allmendinger R. W. 2013. Spherical petrographic context with coexisting adjacent minerals projections with OSXStereonet. Computers & Geosciences and, therefore, the surrounding mineralogy of the host 51:193–205. rock may significantly influence the behavior of apatite Cavosie A. J. and Centeno C. L. 2014. Shocked apatite from the Santa Fe impact structure, (USA): A new mineral for during shock deformation processes. studies of shock metamorphism (abstract #1691). 45th Lunar and Planetary Science Conference. CD-ROM. Acknowledgments—The IODP-ICDP Expedition 364 Cavosie A. J., Quintero R. R., Radovan H. A., and Moser D. Science Party is composed of S. Gulick (US), J. V. 2010. A record of ancient cataclysm in modern sand: Morgan (UK), G. Carter (UK), E. Chenot (France), G. Shock microstructures in detrital minerals from the Vaal River, Vredefort Dome, South Africa. Geological Society Christeson (US), Ph. Claeys (Belgium), C. Cockell of America Bulletin 112:1968–1980. (UK), M. J. L. Coolen (Australia), L. Ferriere` Cavosie A. J., Montalvo P. E., Timms N. E., and Reddy S. (Austria), C. Gebhardt (Germany), K. Goto (Japan), H. M. 2016. Nanoscale deformation twinning in xenotime, a Jones (US), D. A. Kring (US), J. Lofi (France), C. new shocked mineral, from the Santa Fe impact structure – Lowery (US), R. Ocampo-Torres (France), L. Perez- (New Mexico, USA). Geology 44:803 806. Cavosie A. J., Timms N. E., Ferriere` L., and Rochette R. Cruz (Mexico), A. Pickersgill (UK), M. Poelchau 2018. FRIGN zircon—The only terrestrial mineral (Germany), A. Rae (UK), C. Rasmussen (US), M. diagnostic of high-pressure and high temperature shock Rebolledo-Vieyra (Mexico), U. Riller (Germany), H. deformation. Geology 46:891–894. ˇ Sato (Japan), J. Smit (Netherlands), S. Tikoo (US), N. Cernok A., White L. F., Darling J., Dunlop J., and Anand M. Tomioka (Japan), M. Whalen (US), A. Wittmann (US), 2019. Shock induced microtextures in lunar apatite and merrillite. Meteoritics & Planetary Science 56:1–21. J. Urrutia-Fucugauchi (Mexico), L. Xiao (China), and Cox M. A., Cavosie A. J., Bland P. A., Miljkovic K., and K. E. Yamaguchi (Japan). Work by MAC, MS, and Wingate M. T. D. 2018. Microstructural dynamics of DAK at the LPI was partially supported by National central uplifts revealed: Reidite off-set by zircon twins at Science Foundation (NSF) award 1736826. Support was the Woodleigh impact structure, Australia. Geology – also provided by the LPI Summer Intern Program in 46:983 986. Shock deformation in apatite 17
Deer W. A., Howie R. A., and Zussman J. 2013. Introduction and a first report of shock metamorphosed zircons in to the rock forming minerals, 3rd ed. London: pseudotachylitic breccias and granophyre. Earth and Mineralogical Society of Great Brittan and Ireland. Planetary Science Letters 144:369–387. El Goresy A., Chen M., Gillet P., Dubrovinsky L., Graup G., Kenny G. G., Karlsson A., Schmieder M., Whitehouse M. J., and Ahuja R. 2001. A natural shock-induced dense Nemchin A. A., and Bellucci J. J. 2020. Recrystallization polymorph of rutile with α-PbO2 structure in the suevite and chemical changes in apatite in response to from the Ries crater in Germany. Earth and Planetary hypervelocity impact. Geology 48:19–23. Science Letters 192:485–495. Kovaleva E., Klotzli¨ U., Habler G., and Wheeler J. 2015. Erickson T. M., Cavosie A. J., Moser D. E., Barker I. R., and Planar microstructures in zircon from paleo-seismic zones. Radovan H. A. 2013. Correlating planar microstructures American Mineralogist 100:1834–1847. in shocked zircon from the Vredefort Dome at multiple Kring D. A. 1995. The dimensions of the Chicxulub impact scales: Crystallographic modeling, external and internal crater and impact melt sheet. Journal of Geophysics and imaging, and EBSD structural analysis. American Research Planets 100:16,979–16,986. Mineralogist 98:53–65. Kring D. A. 2005. Hypervelocity collisions into continental Erickson T. M., Cavosie A. J., Pearce M. A., Timms N. E., crust composed of sediments and an underlying crystalline and Reddy S. M. 2016. Empirical constraints on shock basement: comparing the Ries (∼24 km) and Chicxulub features in monazite using shocked zircon inclusions. (∼180 km) impact craters. Chemie d Erde Geochemistry Geology 44:635–638. 65:1–46. Erickson T. M., Pearce M. A., Reddy S. M., Timms N. E., Kring D. A. and Boynton W. V. 1991. Altered spherules of Cavosie A. J., Bourdet J., Rickard W. D. A., and impact melt and associated relic glass from the K/T Nemchin A. A. 2017. Microstructural constraints on the boundary sediments in Haiti. Geochimica et Cosmochimica mechanisms of the transformation to reidite in naturally Acta 55:1737–1742. shocked zircon. Contributions to Mineralogy and Petrology Kring D. A. and Boynton W. V. 1992. Petrogenesis of an 172:1–26. augite-bearing melt rock in the Chicxulub structure and its Feignon J.-G., Ferriere` L., and Koeberl C. 2020). relationship to K/T impact spherules in Haiti. Nature Characterization of shocked quartz grains and shock 358:141–144. pressure estimations in the Chicxulub impact structure Kring D. A., Horz¨ F., Zurcher L., and Fucugauchi J. U. 2004. peak-ring granites from IODP-ICDPicdp expedition 364 Implacement inpact lithologies and their em the Chicxulub drill core (abstract #1388). 51st Lunar and Planetary impact crater: Initial results from the Chicxulub Scientific Science Conference. CD-ROM. Drilling Project, Yaxcopoil, Mexico. Meteoritics & French B. M. 1998. Traces of catastrophe: A handbook of Planetary Science 39:879–897. shock-metamorphic effects in terrestrial meteorite impact Kring D. A., Schmieder M., Shaulis B. J., Riller U., Cockell structures. Houston, Texas: Lunar and Planetary Science C., Coolen M. J. L. & the IODP–ICDP Expedition 364 Institute. Science Party. 2017. Probing the impact-generated French B. M. and Koeberl C. 2010. The convincing hydrothermal system in the peak ring of the Chicxulub identification of terrestrial meteorite impact structures: crater and its potential as a habitat (abstract # 1212). What works, what doesn’t, and why. Earth-Science Lunar and Planetary Science XLVIII, The Woodlands, Reviews 98:123–170. TX. Glass B. P., Liu S., and Leavens P. B. 2002. Reidite: An Kusaba K., Syono Y., Kikuchi M., and Fukuoka K. 1985. impact-produced high-pressure polymorph of zircon found Shock behavior of zircon: phase transition to scheelite in marine sediments. American Mineralogist 87:562–565. structure and decomposition. Earth and Planetary Science Gulick S. P. S., Barton P. J., Christeson G. L., Morgan J. V., Letters 72:433–439. McDonald M., Mendoza-Cervantes K., Pearson Z. F., Kusaba K., Kikuchi M., Fukuoka K., and Syono Y. 1988. Surendra A., Urrutia-Fucugauchi J., Vermeesch P. M., Anisotropic phase transition of rutile under shock and Warner M. R. 2008. Importance of pre-impact crustal compression. Physics and Chemistry of Minerals structure for the asymmetry of the Chicxulub impact 15:238–245. crater. Nature Geoscience 1(2):131–135. Lambert P. and Mackinnon I. E. R. 1984. Micas in Gulick S., Morgan J., Mellett C. L., and the Expedition 364 experimentally shocked gneiss. Journal of Geophysical Scientists 2017. Expedition 364 preliminary report: Research 89:685–699. Chicxulub: Drilling the K-Pg impact crater. International Leroux H., Reimold W. U., Koeberl C., Horneman U., and Ocean Discovery Program. 38 p. Doukha J.-C. 1999. Experimental shock deformation in Gulick S. P. S., Christeson G. L., Barton P. J., Grieve R. A. zircon: a transmission electron microscopic study. Earth F., Morgan J. V., and Urrutia-Fucugauchi J. 2013. and Planetary Science Letters 169:291–301. Geophysical characterization of the Chicxulub impact Li S. and Hsu W. 2018. Dating phosphates of the strongly crater. Reviews of Geophysics 51:31–52. shocked Suizhou chondrite. American Mineralogist Hildebrand A. R., Penfield G. T., Kring D. A., Pilkington M., 103:1789–1799. Camargo Z. A., Jacobsen S. B., and Boynton W. V. 1991. McGregor M., McFarlane C. R. M., and Spray J. G. 2018. In Chicxulub crater: A possible Cretaceous/Tertiary boundary situ LA-ICP-MS apatite and zircon U-Pb geochronology impact crater on the Yucatan Peninsula, Mexico. Geology of the Nicholson Lake impact structure, Canada: shock 19:867–871. and related thermal effects. Earth and Planetary Science Horz¨ F. and Ahrens T. J. 1969. Deformation of experimentally Letters 504:185–197. shocked biotite. American Journal of Science 267:1213–1229. McGregor M., McFarlane C. R. M., and Spray J. G. 2019. In Kamo S. L., Reimold W. U., Krogh T. E., and Colliston W. situ multiphase U-Pb geochronology and shock analysis of P. 1996. A 2.023 Ga age for the Vredefort impact event apatite, titanite and zircon from the Lac La Moinerie 18 M. A. Cox et al.
impact structure, Canada. Contributions to Mineralogy and Schmieder M., Tohver E., Jourdan F., Denyszyn S. W., and Petrology 174:62. Haines P. W. 2015. Zircons from the Acraman impact McGregor M., Walton E. L., McFarlane C. R. M., and Spray melt rock (South Australia): Shock metamorphism, U-Pb J. G. 2020. Multiphase U-Pb geochronology of sintered and 40Ar/39Ar systematics, and implications for the breccias from the Steen River impact structure, Canada: isotopic dating of impact events. Geochimica et Mixed target considerations for a Jurrasic-Cretaceous Cosmochimica Acta 161:71–100. boundary event. Geochimica et Cosmochimica Acta Schmieder M., Shaulis B. J., Lapen T. J., and Kring D. A. 274:136–156. 2018. U-Th–Pb systematics in zircon and apatite from the Melosh H. J. 1989. Impact cratering: A Geologic Process. Chicxulub impact crater, Yucatan,´ Mexico. Geological Oxford Monographs on Geology and Geophysics No. 11. Magazine 155:1330–1350. New York: Oxford University Press. Schmieder M., Erickson T. M., Rahman Z., Keller L. P., and Montalvo P., Cavosie A., Kirkland C., Evans N., McDonald Kring D. A. 2019. Outstanding natural occurrence of B., Talavera C., and Erickson T. 2019. Detrital shocked TiO2–II at the Chicxulub crater—Anatomy of a shock- zircon provides first radiometric age constraint (<1472 produced high-pressure polymorph (abstract #6320). 50th Ma) for the Santa Fe impact structure, New Mexico, Lunar and Planetary Science Conference. CD-ROM. USA. Geological Society of America Bulletin. 131:845–863. Schulte P., Alegret L., Arenillas I., Arz J. A., Barton P. J., Morgan J., Warner M., Brittan J., Bufer R., Camargo A., Bown P. R., Bralower T. J., Christeson G. L., Claeys P. Christeson G., Denton P., Hildebrand A., Hobbs R., H., Cockell C. S., Collins G. S., Deutsch A., Goldin T. J., Macintyre H., and Mackenzie G. 1997. Size and Goto K., Grajales-Nishimura J. M., Grieve R. A. F., morphology of the Chicxulub impact crater. Nature Gulick S. P. S., Johnson K. R., Kiessling W., Koeberl C., 390:472–476. Kring D. A., MacLeod K. G., Matsui T., Melosh J., Morgan J. V., Gulick S. P., Bralower T., Chenot E., Montanari A., Morgan J. V., Neal C. R., Nichols D. J., Christeson G., Claeys P., Cockell C., Collins G. S., Coolen Norris R. D., Pierazzo E., Ravizza G., Rebolledo-Vieyra M. J., Ferriere` L., and Gebhardt C. 2016. The formation M., Reimold W. U., Robin E., Salge T., Speijer R. P., of peak rings in large impact craters. Science 354:878–882. Sweet A. R., Urrutia-Fucugauchi J., Vajda V., Whalen M. Moser D. E., Cupelli C. L., Barker I. R., Flowers R. M., T., and Willumsen P. S. 2010. The Chicxulub asteroid Bowman J. R., Wooden J., and Hart J. R. 2011. New impact and mass extinction the Cretaceous-Paleogene zircon shock phenomena and their use for dating and boundary. Science 327:1214–1218. reconstruction of large impact structures revealed by Schulte F. M., Riller U., Grieve R. A. F., Kring D. A., Claeys electron nanobeam (EBSD, CL, EDS) and isotopic U-Pb P. H. (2017). Structural characteristics of the impact melt and (U–Th)/He analysis of the Vredefort dome. Canadian rock and suevite of the Chicxulub Peak Ring—Initial Journal of Earth Science 48:117–139. results from IODP-ICDP Expedition 364. IODP-ICDP Rae A. S. P., Collins G. S., Poelchau M. H., Riller U., Kolloquim 126–127. Davison T., and Grieve R. A. F. 2019. Stress-strain Sclar C. B. and Morzenti S. P. 1972. Electron microscopy of evolution during peak-ring formation: A case study of the some experimentally shocked counterparts of lunar Chicxulub impact structure. Journal of Geophysical minerals. Proceedings of the Third Lunar Science Research: Planets 124:396–417. Conference. Geochimica et Cosmochimica Acta Renne P. R., Deino A. L., Hilgen F. J., Kuiper K. F., Mark 3:1121–1132. D. F., Mitchell W. S., Morgan L. E., Mundil R., and Smit Sharpton V. L., Dalrymple G. B., Marı´n L. E., Ryder G., J. 2013. Time scales of critical events around the Schuraytz B. C., and Urrutia-Fucugauchi J. 1992. New Cretaceous-Paleogene boundary. Science 339:684–687. links between the Chicxulub impact structure and the Renne P. R., Arenillas I., Arz J. A., Vajda V., Gilabert V., Cretaceous/Tertiary boundary. Nature 359:819–821. and Bermudez´ H. D. 2018. Multi-proxy record of the Sharpton V. L., Marin L. E., Carney J. L., Lee S., Ryder G., Chicxulub impact at the Cretaceous-Paleogene boundary Schuraytz B. C., Sikora P., and Spudis P. D. 1996. A from Gorgonilla Island, Colombia. Geology 46:547–550. model of the Chicxulub impact basin based on evaluation Riller U., Poelchau M. H., Rae A. S. P., Schulte F. M., of geophysical data, well logs, and drill core samples. In Collins G. S., Melosh H. J., Grieve R. A. F., Morgan J. The Cretaceous-Tertiary event and other catastrophes in V., Gulick S. P. S., Lof J., Diaw A., McCall N., Kring D. Earth history, edited by Ryder G., Fastovsky D., and A., and Party I.-I. E. S. 2018. Rock fluidization during Gartner S. Geological Society of America Special Paper peak-ring formation of large impact structures. Nature 307:55–74. 562:511–518. Shoemaker E. 1983. Asteroid and comet bombardment of the Rowe A. J., Wilkinson J. J., Coles B. J., and Morgan J. V. Earth. Annual Reviews in Earth and Planetary Science 2004. Chicxulub: Testing for post-impact hydrothermal 11:461–494. input into the Tertiary ocean. Meteoritics & Planetary Søaby E., Forster¨ H. J., Wirth R., Giera A., Birski L., and Science 39:1223–1231. Moszumanska´ I. 2017. Validity of the apatite/merrillite Schmieder M. and Kring D. A. and the IODP–ICDP relationship in evaluating the water content in the Martian Expedition 364 Science Party. (2017) Petrology of target mantle: Implications from shergottite Northwest Africa dolerite in the Chicxulub peak ring and a possible source (NWA) 2975. Geosciences 7:99. of K/Pg boundary picotite spinel (abstract #1235). 48th Slivicki S. J., Schmieder M., Kring D. A., the IODP–ICDP Lunar & Planetary Science Conference. CD-ROM. Expedition 364 Science Party. 2019. Petrologic analyses Schmieder M., Moilanen J., and Buchner E. 2008. Impact of green-black impact melt rock with a history of melt rocks from the Paasselka¨ impact structure (SE hydrothermal alteration at Chicxulub (abstract #2132). Finland): Petrography and geochemistry. Meteoritics & 50th Lunar and Planetary Science Conference. CD- Planetary Science 43:1189–1200. ROM. Shock deformation in apatite 19
Smit J. 1999. The global stratigraphy of the Cretaceous- Timms N. E., Pearce M. A., Erickson T. M., Cavosie A. J., Tertiary boundary impact ejecta. Annual Review of Earth Rae A. S. P., Wheeler J., Wittmann A., Ferriere` L., and Planetary Sciences 27:75–113. Poelchau M. H., Tomioka N., Collins G. S., Gulick S. P. Sprain C. J., Renne P. R., Clemens W. A., and Wilson G. P. S., Rasmussen C., Morgan J. V., Expedition I. O. D. P.-I. 2018. Calibration of chron C29r: New high precision C. D. P., and 364 Scientists. 2019. New shock geochronologic and paleomagnetic constraints from the microstructures in titanite (CaTiSiO5) from the peak ring Hell Creek region, Montana. GSA Bulletin 130:1615–1644. of the Chicxulub impact structure, Mexico. Contributions Stoffler¨ D. 1971. Progressive metamorphism and classification to Mineralogy and Petrology 174:38. of shocked and brecciated crystalline rocks at impact Trepmann C. A., Gotte¨ T., and Spray J. G. 2005. Impact- craters. Journal of Geophysical Research 76:5541–5551. related Ca-metasomatism in crystalline target-rocks from Stoffler¨ D. 1972. Deformation and transformation of rock- the Charlevoix structure, Quebec, Canada. The Canadian forming minerals by natural and experimental shock Mineralogist 43:553–567. processes. I. Behavior of minerals under shock Tuchscherer M. G., Reimold W. U., Koeberl C., and Gibson compression. Fortschritte der Mineralogie 49:5477–5488. R. L. 2004. Major and trace element characteristics of Stoffler¨ D., Hamann C., and Metzler K. 2018. Shock impactites from the Yaxcopoil-1 borehole, Chicxulub metamorphism of planetary silicate rocks and sediments: structure, Mexico. Meteoritics & Planetary Science 39 Proposal for an updated classification system. Meteoritics (6):955–978. & Planetary Science 53:5–49. Wittmann A. 2018a. Constraints for emplacement conditions Stoffler¨ D. and Langenhorst F. 1994. Shock metamorphism of of the Chicxulub impact crater’s upper peak ring quartz in nature and experiment: I. Basic observation and Section (747–617 Mbsf) in IODP-ICDP expedition 364 theory. Meteoritics 29:155–181. drill cores (abstract #2994). 49th Lunar and Planetary Swisher C. C., Grajales-Nishimura J. M., Montanari A., Science Conference. CD-ROM. Margolis S. V., Claeys P. H., Alvarez W., Renne P., Wittmann A. 2018b. Chicxulub zircon (and apatite) (abstract Cedillo-Pardo E., Maurrasse F. J.-M. R., Curtis G. H., #6295). 81st Meteoritical Society Meeting. Smit J., and McWilliams M. O. 1992. Coeval 40Ar/39Ar Wittmann A., Goderis S., Claeys P., Vanhaecke F., Deutsch ages of 65.0 million years ago from Chicxulub crater melt A., and Adolph L. 2013. Petrology of impactites from rocks and Cretaceous-Tertiary boundary tektites. Science El’gygytgyn crater: Breccias in ICDP-drill core 1C, glassy 257:954–958. impact melt rocks and spherules. Meteoritics & Planetary Timms N. E., Erickson T. M., Pearce M. A., Cavosie A. J., Science 48:1199–1235. Schmieder M., Tohver E., Reddy S. M., Zanetti M. R., Zurcher¨ L. and Kring D. A. 2004. Hydrothermal alteration in Nemchin A. A., and Wittmann A. 2017. A pressure- the core of the Yaxcopoil-1 borehole, Chicxulub impact temperature phase diagram for zircon at extreme structure, Mexico. Meteoritics & Planetary Science conditions. Earth-Science Reviews 165:185–202. 39:1199–1221.
SUPPORTING INFORMATION Item DR4. Stereonet of the orientation of planar fractures in apatite. Additional supporting information may be found in Item DR5. Electron backscatter diffraction maps of the online version of this article. cataclastically deformed apatite grains. Item DR6. Electron backscatter diffraction map of Item DR1. Sample location in meters below sea apatite with deformed zircon inclusion. floor, preparation, and extended methods. Item DR7. BSE images of apatite (sample 89) with Item DR2. Plane polarized light image of planar spot numbers for microprobe analysis of grains. fractures within apatite grains. Item DR8. BSE images of apatite (sample 163) with Item DR3. Backscattered electron images of planar spot numbers for microprobe analysis of grains. fractures in apatite grains Table Item DR1. Electron backscatter diffraction map of apatite with deformed zircon inclusion.