# Orientations of planar cataclasite zones in the Chicxulub peak ring as a ground truth for peak ring formation models

Naoma Mccall, Sean P. S. Gulick, Brendon Hall, Auriol S. P. Rae, Michael H. Poelchau, Ulrich Riller, Johanna Lofi, Joanna V. Morgan

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## To cite this version:

Naoma Mccall, Sean P. S. Gulick, Brendon Hall, Auriol S. P. Rae, Michael H. Poelchau, et al. Orientations of planar cataclasite zones in the Chicxulub peak ring as a ground truth for peak ring formation models. Earth and Planetary Science Letters, 2021, 576, 10.1016/j.epsl.2021.117236. insu-03661279

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1 Orientations of planar cataclasite zones in the Chicxulub peak ring as a ground truth for peak

2 ring formation models

3

4 N. McCall¹, S.P.S. Gulick¹,², B. Hall³, A.S.P. Rae⁴,⁵, M. H. Poelchau⁴, U. Riller⁶, J. Lofi⁷, J.V. Morgan⁸

5 ¹University of Texas at Austin, Jackson School of Geosciences, Institute for Geophysics &

6 Department of Geological Sciences, J.J. Pickle Research Campus, Austin, Texas 78758, USA

7 (nmccall@utexas.edu). ²Center for Planetary Systems Habitability, University of Texas at Austin,

8 Austin, Texas USA ³Enthought, Inc., Austin, Texas USA, ⁴Institute of Earth and Environmental

9 Sciences—Geology, Albert-Ludwigs Universität Freiburg, Albertstrasse 23b, Freiburg 79110,

10 Germany, ⁵Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge

11 CB2 3EQ, UK, ⁶Institut für Geologie, Universität Hamburg, Bundesstrasse 55, Hamburg, 20146,

12 Germany, ⁷Géosciences Montpellier, Université de Montpellier, CNRS, France, ⁸Department of

13 Earth Science and Engineering, Imperial College London, SW7 2AZ, UK.

14

15 Corresponding author: N. McCall, University of Texas at Austin, Jackson School of Geosciences,

16 Institute for Geophysics, J.J. Pickle Research Campus, Austin, Texas 78758, USA

17 (nmccall@utexas.edu)

18

19 Address: University of Texas Institute for Geophysics, 10100 Burnet Rd. Bldg 196 Austin, Texas

20 78758-4445

21

22
23 Abstract

24 Hypervelocity impact cratering is an important geologic process but the rarity of large

25 terrestrial impact craters on Earth and the limited technical options to study cratering

26 processes in the laboratory hinders our understanding of large-scale impact processes. Drill

27 core recovered from the peak ring of the Chicxulub impact crater during International Ocean

28 Discovery Program (IODP)/International Continental scientific Drilling Program (ICDP)

29 Expedition 364 provides an opportunity to examine target rock deformation and thus, to assess

30 cratering models in this regard. Using oriented computer tomography (CT) scans and line scan

31 images of the core, we present the orientations of mm-to-cm-scale planar cataclasite and

32 ultracataclasite zones in the deformed granitoid target rock of the peak ring. In the upper 470

33 m of the target rock, the cataclasite zones dip towards the crater center, whereas the dip

34 directions for the ultracataclasite zones are approximately tangential to the peak ring. These

35 two orientations are consistent with deformation expected from hydrocode-modeled principal

36 stress directions for the outward movement of rocks as the transient crater develops, and the

37 inward movement of rocks associated with collapse of the transient crater. Near the base of the

38 core is a 96 m-thick interval of highly-deformed target rock with impact melt rock and rock

39 fragments not observed elsewhere in the core; this interval has previously been interpreted as

40 an imbricate thrust zone within the peak ring. The cataclasite zones below this thrust zone have

41 different orientations than those in the 470-m-thick block above. This observation implies a

42 differential rotation from the overlying block during the final stages of peak-ring formation. Our

43 results support an acoustic fluidization process, wherein blocks that vibrate or slide relative to

44 each other allow the target rock to flow during transient crater collapse, and that the size of
coherent rock blocks increases over the course of crater modification as the target rock regains its cohesive strength and acoustic fluidization decreases.

Keywords: Impact cratering, peak ring formation, computer tomography, structural geology, planetary evolution

Abbreviations:

CCSF-a: core composite depth below sea floor

CT: computer tomography

ICDP: International Continental Scientific Drilling Program

IODP: International Ocean Discovery Program

mbsf: meters below sea floor

## 1. Introduction

The cratering process for large hypervelocity impacts on Earth has not been observed firsthand, and so our understanding of crater formation is reliant on limited observational data, theoretical calculations and numerical simulations (e.g., Grieve, 1987; Collins et al., 2002; Morgan et al., 2011; Rae et al., 2019). Terrestrial outcrop, well and geophysical data, as well as observations from remote sensing on other planetary bodies, have all been used to reconstruct crater morphologies, and determine how they change with increasing crater size (Grieve, 1987; Melosh, 1989). Such data, in turn, are useful for ground-truthing numerical simulations of crater formation. Baker et al. (2016) presented two end-member models for the formation of
peak ring impact craters: the dynamic collapse model (Murray, 1980; Grieve, 1987; Collins et al., 2002) and the nested melt-cavity model (Cintala and Grieve, 1998; Head, 2010). These two models predict different depths of origin and degrees of shock deformation within the peak-ring rocks. In 2016, IODP/ICDP Expedition 364 drilled into the Chicxulub peak ring; one of the principal objectives of the drilling was to distinguish between these two models of peak-ring formation. A peak ring is an interior discontinuous ring of hills rising from the crater floor present in large complex basins. The finding that peak ring rocks are primarily composed of moderately shocked granitoid rocks supported the dynamic collapse model of impact crater formation (Morgan et al., 2016).

Core recovered during IODP/ICDP Expedition 364 has provided us with unprecedented structural data that helps us further improve our understanding of large-crater formation. In this paper, we adopt the terminology presented by Rae et al. (2019) for the phases of crater modification during peak-ring formation. During the *Contact and Compression and Excavation* stages, pervasive grain-scale micro-fractures form during shock wave propagation and the growth of the transient crater (Riller et al., 2018; Rae et al., 2019). Next, the transient crater begins to collapse at the center while net displacement of rocks at the margin is outwards during the *Rim Growth* phase. During the *Inward Transport* phase of peak-ring formation, the material that forms the peak ring collapses inwards and downwards, moving towards the emerging central uplift. Riller et al. (2018) conclude that planar ultracataclasite and cataclasite zones formed early in the cratering process, at proposed times that correspond primarily to the *Rim Growth* and *Inward Transport* crater modification phases (Rae et al., 2019). Core observations show a small number of cataclasite zones truncated by ultracataclasites (Riller et
al., 2018). The central uplift reaches its maximum height and begins to collapse during the *Central Peak Entrainment* phase. During the *Outward Transport* phase, the peak-ring material is emplaced on top of sedimentary rocks slumped inward from the crater rim. Deformation following ultracataclasite formation is characterized by shear faults (Riller et al., 2018), interpreted to form during *Central Peak Entrainment* and *Outward Transport* phases.

Emplacement of melt into dilatant fractures occurs during and after shear faulting, during the *Outward Transport* phase. Finally, formation of ductile band structures with a normal shear sense occur during the *Relaxation* phase (Riller et al., 2018; Rae et al., 2019).

In this paper, we use our measurements of the orientations of mm-to-cm-scale planar cataclasite and ultracataclasite zones to test the predictions of principal stresses and deformation based on the dynamic collapse model as presented by hydrocode modeling. We measured the cataclasite and ultracataclasite zones using X-ray computer tomography (CT) scans of the core, line-scan photographs of the split core, and acoustic borehole images acquired as part of Expedition 364. We present orientations of planar cataclasite and ultracataclasite zones from the granitoid target rocks within the Expedition 364 core. We hypothesize that the modeled orientations of principal stresses are portrayed in the strain present in the peak-ring rocks.

## 2. Background

The Chicxulub impact crater (Figure 1 A) was formed 66 Ma, after a ~12-km asteroid collided into what is now the Yucatán peninsula (Hildebrand et al., 1991). The crater is approximately 200 km wide (Gulick et al., 2008) and is unique in that it has been preserved due to its relatively young age, tectonic inactivity and burial beneath 100s of meters of sedimentary
<figure><img src="image_3.png" /></figure>

Figure 1: A) Bouguer gravity anomaly map of the Chicxulub impact crater. The Yucatan coastline is outlined in white, black dots are cenotes that outline the outer crater onshore. Location of exterior ring, crater rim, and peak-ring shown as defined by seismic interpretation (Gulick et al., 2008). Image from Gulick et al., (2013). B) Schematic illustration showing lithology of core recovered in Expedition 364. Image from Morgan et al., (2016).

rock (Brittan et al., 1999). Seismic reflection surveys have resolved much of the structure of the Chicxulub crater (Morgan et al., 1997; Gulick et al., 2008). Chicxulub is a complex crater with an inner ring, outer

122 ring and exterior ring (Figure 1 A), and is the only impact structure on Earth with an unambiguous, morphologically intact peak ring (Morgan et al., 1997). The 80-90 km diameter peak ring at Chicxulub is a discontinuous ring of hills 400-500 m above the crater floor that overlies Cretaceous sedimentary strata collapsed inward during crater modification (Gulick et al., 2013).

127 IODP/ICDP Expedition 364 drilled into the peak ring of the crater in April and May 2016 at Site M0077, 45.6 km WNW of the crater center (Figure 1 A). Expedition 364 recovered 829 m of core from 505.7 to 1334.7 meters below seafloor (mbsf). The core is composed, from top to bottom, of 112 m of Paleogene sedimentary rocks, 104 m of suevite, a melt-bearing impact breccia, 25 m of impact melt rock, and 588 m of shocked granitoid rocks with a small number of cm to meter-scale pre-impact magmatic sheet intrusions and impact-related intrusions
composed of melt rock and breccia (Figure 1 B) (Gulick et al., 2017a). Towards the base of the core is a proposed imbricate thrust zone composed of a 96 m thick interval of strongly fractured and cataclastically deformed granitoid rocks along with impact melt rock, not observed elsewhere in the core (Riller et al., 2018). The Site M0077 cores are important due to the rarity of undisturbed complex craters on Earth and lack of consensus regarding peak-ring formation mechanisms.

## 3. Methods

### 3.1. Data sources

The drilling of IODP/ICDP Expedition 364 resulted in near 100% recovery for the granitoid

section of the core (Gulick et al.,

2017a). To orient the core, we

used wireline-acquired acoustic

images from the borehole, which

provides a 360-degree image of

the wall of the drilled borehole.

The slimline tool used for acoustic

imaging is coupled with a 3-

component magnetometer that

gives the magnetic north

orientation in the acoustic image

(Lofi et al., 2018). Although the

downhole acoustic image is lower

<figure><img src="image_4.png" /></figure>

Figure 2: A) Example of cataclasite zones presented in the cylinder unwrap view of the CT scan, the cataclasite zones are dark gray sinusoids, the black sinusoid is an open fracture. B) The CT scan of the same core section displaying the x-z slice. C) Line-scan photograph of the same core section of the split core (core 300-2 1324.00-1324.25 mbsf). D) Example of an ultracataclasite zone presented in the cylinder unwrap CT scan. E) CT scan of the same core sections displaying the x-z slice. F) Line-scan photograph of the same core section of the split core (core 193-2 1001.40-1001.55 mbsf).
resolution than CT images, prominent features such as lithological contacts and inclined beds that are present in both the borehole image and CT scans served as a reference to restore the depth and orientation of the recovered core relative to the borehole wall. For an outlined orientation methodology see IODP Expedition 364 data report 201 (McCall et al., 2020).

All cores have been imaged using three-dimensional dual energy X-ray CT at 0.3 mm³ resolution. CT scanning was carried out at the Weatherford Laboratories in Houston, Texas and the raw data were processed by Enthought in Austin, Texas. CT scans produce a 3D model of the core, allowing for observation and analysis of the internal structure of the core without alteration or damage to the core. Structures such as fractures and faults can be accentuated using Enthought's Virtual Core visualization software and algorithms (Hall and Govert, 2016).

CT images were acquired in two runs; first using a high-energy beam (135 kV) and secondly, using a low-energy beam (80 kV) (Gulick et al., 2017b). Together, along with calibration, these scans can be used to determine the CT number, where low CT numbers correspond to low densities and/or low atomic numbers of the sample (Amos, 1996; Duliu, 1999). The images are in grayscale with low CT number areas displayed as dark and black, and high value areas shown as light and white (Figure 2). After CT scanning was complete, the core was split in half at IODP facilities of the MARUM in Bremen, Germany, to preserve an archive half and a working half. The archive half of the split core was then imaged with a line-scan camera at a resolution of 150 pixels/cm (Gulick et al., 2017b).

## 3.2. Characterization of cataclasite and ultracataclasite zones

Cataclasis is the fracturing and crushing of grains, coupled with frictional sliding along grain contacts and grain rotation (Engelder, 1974; Sibson, 1977). Cataclasite zones, the product of
cataclasis, can be subdivided based on their proportion of fine-grained matrix, a cataclasite is composed of 50-90% matrix, whereas an ultracataclasite has >90% matrix (Sibson, 1977; Woodcock and Mort, 2008). The cataclasite zones have low CT numbers and appear gray to dark gray in CT images (Figure 2 A, B), in the line-scan photographs they are beige colored and have a thickness of several mm to cm (Figure 2 C). In the line-scan photographs cataclasites may appear to occur over a wide interval, but in CT images discrete planes can be identified (Figure 2 A, B). Ultracataclasite zones also have low CT numbers and are gray to dark gray in CT

<figure><img src="image_5.png" /></figure>

Figure 3: Line-scan photographs of the split core showing texture and morphology of cataclasite zones and ultracataclasite zones. A) Thin ultracataclasite zone showing offset with displaced pegmatite, direction of displacement indicated by white half arrows (core 216-1, 1067.09-1067.36mbsf). B) Ultracataclasite with internal foliation, granites on opposite sides of ultracataclasite zone have noticeably different amounts of potassium feldspar. (core 164-1, 918.66-918.80 mbsf). C) Ultracataclasite with foliation (core 125-2, 828.61-828.66 mbsf). D) Banded deformation zone with ultracataclasite and cataclasite (core 109-1, 784.17-784.33 mbsf). E) Cataclasite grading into ultracataclasite (core 194-2, 1004.73-1004.78mbsf). F) Cataclasite (pink-beige) cross-cut by ultracataclasite (gray). G) Cataclasite zone lacking internal foliation or banding (core 184-1, 972.99-973.06 mbsf). H) Cataclasite with minimal internal foliation (core 183-3, 972.47-972.53 mbsf). I) Thin cataclasite showing possible offset with displaced mineral grains, proposed direction of displacement indicated by white arrows (core 145-2, 869.82-869.86 mbsf). A black and white version of this figure with cataclasite and ultracataclasite zones highlighted is Appendix Figure A.1.
184

images but appear gray, green-gray, or dark gray in line-scan photographs, in contrast to the beige color of cataclasite zones (Figure 2 D, E, F).

185

186

Pre-impact dolerite sheet intrusions and impact melt rock intrusions can also appear dark grey in line-scan images. However discerning between thin impact melt rock or dolerite intrusions and ultracataclasite zones is possible. Both Impact melt rock and dolerite intrusions have a higher CT number than ultracataclasite zones, additionally impact melt rock contains breccia clasts; dolerite intrusions commonly contain plagioclase laths, whereas ultracataclasite zones lack either of these clasts and have lower CT numbers.

187

188

189

190

191

192

Recognizable offsets along planar cataclasite zones are difficult to identify in crystalline rock; however, we do observe rare examples of offset in the ultracataclasite zones in the form of displaced pegmatite granite contacts (Figure 3 A) and different colored granite on opposite sides of the ultracataclasite (Figure 3 B). Foliation is prevalent in the ultracataclasite zones, with planar to undulating bands of light and dark minerals present (Figure 3 C, D, E). Rare instances of cross cutting relationships between cataclasite and ultracataclasite show ultracataclasite

193

194

195

196

197

<figure><img src="image_6.png" /><figcaption>Figure 4: Schematic drawing of planar structure intersecting a core and in cylinder unwrap view. Parameters used to calculate dip and dip direction in equations 1 and 2 are indicated in red, blue dashed box is representative of rectangular selection made in ImageJ. Diagram modified from Paillet (1994).</figcaption></figure>

truncating cataclasite (Figure 3 F). Cataclasite fabrics range from massive (Figure 3 G) to exhibiting minimal foliation (Figure 3 H). Unambiguous offsets were not commonly observed macroscopically in the cataclasite zones. Generally, cataclasite zones are thicker than ultracataclasite zones; thus distinguishing offsets along mineral boundaries on opposite sides of cm- to mm-scale cataclasite zones is unclear, although possible
206 displacement of mineral grains can be observed along thin planar cataclasite zones (Figure 3 I).

207 Due to the rarity of unambiguous offset for both ultracataclasite and cataclasite zones we do
208 not attempt a kinematic analysis, instead we focus on orientation of these zones, which can be
209 measured with confidence.

210 3.3. Orientation measurement of planar cataclasite and ultracataclasite zones

211 CT images of the oriented core in the cylinder unwrap view were imported into the
212 ImageJ software package (Schindelin et al., 2012) for analysis. In the cylinder unwrap view,
213 traces of fractures and planar deformation zones appear as sinusoids (Figures 2 A, D, and 4). To
214 measure the orientation of the planar cataclasite zones, a rectangular selection was made with
215 the peak and trough of the sinusoid in opposite corners of the rectangle using ImageJ (Figure 4).

216 This selection records the height, width and position of the structure, which can then be used
217 to calculate the dip and dip direction. Equations (1) and (2) can be computed for dip and dip
direction, respectively:

219 (1) dip (φ) = tan⁻¹(fracture amplitude (a)/radius (r))

220 (2) dipdirection (θ) = 360° × Lateral distance of trough (x)/circumference of the core (c)

221 The location of the trough was noted for each measurement to ensure proper calculation of
222 dip direction. Not every cataclasite and ultracataclasite zone is included in our measurements:
223 we excluded non-planar cataclasite and ultracataclasite zones which present as asymmetric
224 sinusoids and areas of cataclastic deformation where individual planes were difficult to identify
225 with confidence. The highest concentration of data points was determined by calculating the
226 maximum eigenvector of the orientation tensor, which we refer to as the mean orientation (see
227 Appendix).
## 228 4. Results

<table><caption>Table 1: Mean orientations of measured cataclasite zones and ultracataclasite zones</caption><thead><tr><th>Deformation type</th><th>Depth range (mbsf)</th><th>n</th><th>Dip direction/Dip</th></tr></thead><tbody><tr><td rowspan="4">Cataclasite zones</td><td>All</td><td>158</td><td>094°/36°</td></tr><tr><td>750-910</td><td>27</td><td>113°/43°</td></tr><tr><td>910-1050</td><td>70</td><td>113°/34°</td></tr><tr><td>1050-1220</td><td>26</td><td>136°/34°</td></tr><tr><td>1220-1335</td><td>35</td><td>043°/55°</td></tr><tr><td rowspan="4">Ultracataclasite zones</td><td>All</td><td>135</td><td>233°/59°</td></tr><tr><td>750-910</td><td>29</td><td>049°/89°</td></tr><tr><td>910-1050</td><td>51</td><td>228°/51°</td></tr><tr><td>1050-1220</td><td>40</td><td>240°/62°</td></tr><tr><td>1220-1335</td><td>15</td><td>057°/35°</td></tr></tbody></table>

We identified and measured the depth and orientations of 158 planar cataclasite zones and 135 planar ultracataclasite zones (Table 1, Supplemental Tables 1 and 2). Thirteen zones had both the beige cataclastic material and the gray finer grained material found in ultracataclasite zones (Figure 3 D, E). These structures were interpreted as cataclasites that grade into ultracataclasites and were included in both data sets and are denoted with an asterisk in Supplemental Tables 1 and 2. The average spacing between structures is 2.60 m for cataclasite zones and 3.66 m for ultracataclasite zones. Continuous change in orientation with depth is shown on the tadpole plots in Figure 5. To assess variation in orientation trends with depth, we divide the data into 4 subsets by depth range: 750-910 mbsf, 910-1050 mbsf, 1050-1220 mbsf and 1220-1335 mbsf (Figure 5, Table 1). These subset boundaries were based on
241 visual assessment of the groupings in the tadpole plots (figure 5) and lithological contrasts.

242 Poles to planes are presented on equal-area projections for the full granitoid section and the
243 four depth intervals (Figure 6).

244 The mean dip direction of cataclasite zones from all depths of the core is 094° (Figure 6).

245 The cataclasite zones in the top three depth subsets have similar ESE and SE mean orientations,
246 whereas the basal subset dips toward NE (Figure 6). Dip directions of 113° and 136° are
247 directed towards the crater center.

248 The mean orientation of ultracataclasite zones from all depths dips towards 233°. The
249 subset of the ultracataclasite zones from 750-910 mbsf significantly differs from this direction,

the mean orientation dips to the NE.

The mean orientation for the intervals of cataclasite zones from 910-1050 mbsf and 1050-1220 mbsf is similar to that of the whole set and dips to the SW. Similar to the cataclasite zones, the orientation for ultracataclasite zones in the basal section dip to the NE. The NE and SW dip directions are approximately 30° from tangential to the peak ring.

While the SW-dipping mean
orientation of ultracataclasite zones for

<figure><img src="image_7.png" /></figure>

Figure 5: Tadpole plots for planar cataclasite zones and ultra-cataclasite zones. The dip direction is shown by a line projected outwards from the plotted point with north aligned with the y-axis. Dashed black lines separate depth intervals for plotted data. Background colors show simplified core lithology modified from Gulick et al. (2017), with granitoid in light pink, pre-impact sheet intrusions in brown, and impact melt rock and/or breccia in purple.
263 depth subsets from 910-1050 mbsf and 1050-
264 1220 mbsf are well defined, the orientation data
265 for the subset of ultracataclasite zones from 750-
266 910 mbsf has a large cone of confidence (Figure
267 6), a small maximum eigenvalue, and does not
268 pass the uniformity test (Mardia, 1972).
269 Additionally, the interval from 1220-1335 mbsf
270 with NE dip direction has a small maximum
271 eigenvalue and does not have enough
272 measurements to compute the confidence cone
273 (Appendix Table A.1, Figure 6).

274 5. Interpretation

275 5.1. Orientation of cataclasite and
276 ultracataclasite zones in context of
277 modeled principal stress directions
278 Here, we evaluate the orientations of
279 cataclasite and ultracataclasite zones based on
280 the assumption that the observed strain can be
281 used to evaluate the hydrocode modeled stress
282 states for crater modification. If the suggested
283 timing of the generation of the cataclasite zones
284 (Riller et al., 2018) and the modeled principal

<figure><img src="image_8.png" /><figcaption>Figure 6: Lower-hemisphere equal-area projections of poles to cataclasite and ultracataclasite zones. Kamb contours at multiples of uniform density, represents deviation from a uniform distribution. White dot denotes the mean orientation (maximum eigenvector), white ellipse is 95% confidence cone. Equal-area projections were plotted using Orient Software (Vollmer, 1995, 2015).</figcaption></figure>
stress axis orientations (Rae et al., 2019) are correct, the orientation of planar cataclasite and ultracataclasite zones are expected to correspond with modelled stress states. Our interpretation assumes that the strain portrayed by the cataclasite and ultracataclasite zones is a result of Andersonian faulting. According to Andersonian fault theory, shear fractures form at angles approximately 30° to the direction of maximum principal stress, σ₁, and 60° to the direction of the minimum principal stress, σ₃ (Anderson, 1905). Polymodal faulting is a possibility but beyond the scope of this paper (Healy et al., 2015).

Idealized fracture orientations are based on modeling results from Rae et al. (2019). Idealized fracture orientations are planes 30° from σ₁, rotated about the σ₂ axis. During the *Rim Growth* phase σ₂ remains constant in orientation and is tangential to the peak ring (202°/0°), and σ₁ and σ₃ rotate clockwise by 45.2°: at the start of rim growth σ₁ is oriented at 292°/16.2° and rotates to 292°/61.4°, σ₃ is oriented at 112°/73.8° in the beginning of *Rim Growth* and 112°/28.6° at the end of the phase (Rae et al., 2019).

During the *Inward Transport* phase, the orientation of principal stress axes changes: for most of this phase, σ₁ remains constant in orientation and is tangential to the peak ring (202°/0°), and σ₂ and σ₃ rotate 91.3° clockwise: at the start of the *Inward Transport* phase σ₂ is oriented at 292°/67.6° and at 112°/23.7° at the end of the *Inward Transport* phase, and σ₃ rotates from 112°/22.4° to 292°/66.3° (Rae et al., 2019). In addition to the principal stresses rotating, the target rock rotates as well, 23.8° and 23.7° clockwise during the *Rim Growth* and *Inward Transport* phases, respectively. Considering the rotation of the material, there is a smaller interval over which fractures can form, 21.7° for the *Rim Growth* phase and 67.6° for the *Inward Transport* phase.
After calculating the position of idealized fractures formed during both the *Rim Growth* and *Inward Transport* phases, the idealized fractures are then rotated based on the amount of solid body rotation that occurs from the end of the *Rim Growth* or *Inward Transport* phases to the end of the cratering process, an additional 78.4° for *Rim Growth* idealized fractures and an additional 49° for *Inward Transport* idealized fractures (Rae et al., 2019). Idealized fracture planes formed during the *Rim Growth* phase dip towards or away from the crater center (292° or 112° degrees), poles to idealized fracture planes formed during the *Inward Transport* phase plot along a small circle 60° from σ₁ on an equal-area projection (Figure 7 D, H, Supplemental Table 3).

The orientations of planar cataclasite zones above the proposed thrust at 1220 mbsf are consistent with the deformation expected from the modeled orientations of principal stress axes for the different phases of crater formation, and support cataclastic deformation during

<figure><img src="image_9.png" /></figure>

Figure 7: A, B) Profile view from center of the crater to beyond the crater wall for the beginning (A) and end (B) crater morphology for Rim Growth. C) Orientation of modeled principal stress directions and idealized Andersonian fracture orientation for mid-Rim Growth, direction of target rock rotation shown by dashed arrow. r, h (hoop) and z direction shown in corner. D) Poles to idealized fracture locations for Rim Growth considering rotation of material and principal stress directions, arrows show locations of poles from start to end of Rim Growth. E, F, G, H) Same as above for the Inward Transport phase. Modified from Rae et al. (2019).
the Rim Growth phase, and ultracataclasite formation during the Inward Transport phase (Riller et al., 2018; Rae et al., 2019).

During the Rim Growth phase, which is the proposed onset of cataclastic deformation, $σ_1$- and $σ_3$-directions are radially oriented and the direction of $σ_2$ is oriented in the hoop direction (Figure 7 C) (Rae et al., 2019). Because the directions of $σ_1$ and $σ_3$ rotate about the hoop direction during this cratering phase, the inclinations of $σ_1$- and $σ_3$-directions change, but their azimuths do not (Rae et al., 2019). The idealized planar structures produced from this arrangement of principal stresses would display radial dip directions (Figure 7 D, Supplemental Table 3). The orientations of planar cataclasite zones above 1220 mbsf have a directional preference of nearly radially oriented dip directions (Figure 6).

Once rocks begin to converge towards the crater center during the Inward Transport phase, the orientations of principal stress directions change: the $σ_1$-direction is oriented in the hoop direction, and the $σ_2$- and $σ_3$-directions are radially oriented and rotate about the hoop direction (Figure 7 G) (Rae et al., 2019). With this configuration of principal stress directions, we would expect to observe shear fractures with a range of SW dip directions and a conjugate set with NE dip directions. In this case, the poles of these planes will plot on a small circle 60° from the $σ_1$-direction on an equal-area projection (Figure 7 H). The mean orientation for measured ultracataclasite zones is 233°/59°. The inclination is steeper than the range of expected fractures in figure 7 H, but the dip direction is consistent with predictions for the end of the Inward Transport phase (Supplemental Table 3). We are uncertain why the dip angles are higher in our data than for the predicted idealized fractures during Inward Transport; possibilities for this deviation include existing rock anisotropy or preexisting zones of weakness
341 in the target rock. Our orientation results therefore suggest that planar cataclasite zones

342 occurred during the *Rim Growth* and possibly early *Inward Transport* phases, and planar

343 ultracataclasite zones formed during the mid-to-late *Inward Transport* phase.

344 5.2. Change in cataclasite orientation with depth

345 The mean orientations of cataclasite zones in the upper 3 sections of the granitoid rocks

346 (750-1220 mbsf) dip towards the ESE and SE, whereas in the basal section (1220-1335 mbsf)

347 cataclasite zones dip on average to the NE. The similar orientations for cataclasite zones above

348 1220 mbsf and the different orientation for cataclasite zones below 1220 mbsf suggests that

349 the granitoid target rocks above this depth behaved as a quasi-coherent block during late

350 stages of cratering.

351 The cataclasite zones have similar orientations for the upper 3 sections of the granitoid

352 rocks (750-1220 mbsf), whereas ultracataclasite zones share similar mean orientations for only

353 the middle 2 sections of the granitoids (910-1220 mbsf). The orientation of ultracataclasite

354 zones at the top section of the granite (750-910 mbsf) is dissimilar to mean orientations of the

355 middle 2 sections. From 750-910 mbsf, there is considerable scatter in the orientation of

356 ultracataclasite zones (Figures 4 and 5) and the data do not pass the uniformity test (Appendix

357 Table A.1). It is unclear why the orientations are scattered here. Using analysis of feather

358 features Ebert et al. (2020) proposes a fold at the top of the granitoid section. However, we do

359 not see a girdle distribution for the orientation of ultracataclasite or cataclasite zones that

360 would suggest a fold.

361 Similar to the cataclasite zones, the ultracataclasite zones below 1220 mbsf show a

362 different preferred orientation than the sections above this depth (Figure 6). The mean dip
direction for ultracataclasite zones is to the SW in the sections above 1220 mbsf and to the NE in sections below 1220 mbsf, although there is a statistically small number of ultracataclasite zones from 1220 - 1335 mbsf. The granite interval below the melt rock and breccia at 1220 mbsf is less than 20 m long, and the base of the core is composed of impact melt rock and breccia. Therefore, it is unclear if the granite below 1220 mbsf is the top of another 100-meter scale block or a short interruption to the impact melt and breccia interval near the base of the core that may continue at depth.

Diaw et al. (2017) measured the orientations of pre-impact magmatic sheet intrusions using the acoustic borehole image acquired during Expedition 364. Above 1220 mbsf, all but 4 of the pre-impact sheet intrusions cluster in orientation through the core, suggesting that the relative orientation of the pre-impact sheet intrusions was largely preserved during cratering (Diaw et al., 2017; Riller et al., 2018). Microstructural feather features have uniform orientations from ~880 – 1200 mbsf (Ebert et al., 2020). The consistent orientations of pre-impact magmatic sheet intrusions, feather features, and planar cataclasite zones supports our interpretation that the granitoid target rock above 1220 mbsf behaved as a quasi-coherent block during cratering.

## 6. Discussion

Our results are the first quantitative structural measurements from an oriented core from a peak ring of an impact crater. By comparing our results to deformation expected from modeled principal stress axis directions we can further confirm the chronology of cataclastic and ultracataclastic deformation and the transition from acoustic fluidization to shear faulting. These measurements portray the deformation history of a quasi-coherent block during peak
385 ring formation, a process we cannot observe first-hand. Prior crater drilling efforts did not have
386 the data sources needed to acquire these measurements, as core drilled from other craters and
387 prior Chicxulub drilling expeditions were not re-oriented relative to the borehole wall. Our
388 structural measurements were made possible from borehole imaging collected with a
389 magnetometer, CT scans of the core, and high resolution core photographs.

390 While there are very few terrestrial craters that approach the size of Chicxulub, there
391 are numerous central peak craters to compare our results to. These smaller craters can be
392 analogues for the deformation that occurs up to the *Inward Transport* phase, when the central
393 uplift builds, but does not collapse (Riller et al., 2018). Many of these central peak craters
394 contain radially striking faults, which can be expected during the inward movement of rocks.
395 Wilshire (1972) describes the deformation as the central uplift builds by analogy to the
396 formation of folds in fabric that result when pulling a napkin through a ring. Radial faults have
397 been observed at several structures including Siljan (~65 km diameter), Decaturville (6 km),
398 Carswell (39 km; Kenkmann and von Dalwigk, 2000), Upheaval Dome (5 km; Kriens, 1999;
399 Kenkmann and von Dalwigk, 2000), and Sierra Madera (15 km; Wilshire, 1972). The geometry of
400 radially striking faults and folds in these complex craters and the tangentially dipping (i.e.,
401 radially striking) ultracataclasite zones are indicative of the same deformation flow field during
402 cratering.

403 Acoustic fluidization is a leading potential mechanism to allow rocks to move large
404 distances rapidly during transient crater collapse (Melosh, 1979). An acoustically fluidized rock
405 mass behaves as a fluid due to oscillating pressure waves from the impact and subsequent
406 deformation periodically relieves overburden pressure, facilitating shear failure of the rock
mass at low shear stresses (Melosh, 1996). Several characteristics of the cataclasite and ultracataclasite zones observed in Site M0077 suggest a decrease in acoustic fluidization with time in the cratering process. The ultracataclasite zones commonly exhibit foliation (Figure 3 A-E), whereas the earlier formed cataclasite fabric is weakly foliated to featureless, suggesting that shear stress increases with the formation of ultracataclasites (Figure 3 G, H). Additionally, ultracataclasite zones are usually thinner than cataclasite zones (Figure 3 A, B, G, H). We interpret this progressive localization to potentially indicate that the ultracataclasite zones undergo more shear strain than the cataclasite zones. As acoustic fluidization decreases, rock strength and shear strain increase (Melosh, 1979). Based on these physical conditions, we propose that acoustic fluidization has diminished by the time cataclasite zones are formed and stops at or just after formation of the ultracataclasite zones, specifically after the *Inward Transport* phase according to our interpretation of deformation as a result of modeled orientation of principal stress directions from Rae et al. (2019).

The block model of acoustic fluidization is a simplification of the original model of acoustic fluidization commonly used in numerical impact simulations (Melosh and Ivanov, 1999). Its original conception was based on observations of coherent rock blocks, 100s of meters in size, separated by inter-block breccia at the Puchezh-Katunki impact structure (Ivanov and Kostuchenko, 1997; Melosh and Ivanov, 1999). The block model of acoustic fluidization produces a time-varying Bingham fluid, with a constant effective viscosity. Riller et al. (2018) found that the spacing between cataclasite zones in the Site M0077 core is approximately 3.5 m, suggesting that block sizes are far smaller than originally suggested in the block model and that block size may increase with time during the cratering process. The average spacing of
planar cataclasite (2.60 m) and ultracataclasite zones (3.66 m) presented here is similar to the
results of Riller et al. (2018).

The contrast in orientations of cataclasite and ultracataclasite zones above and below
the proposed thrust zone suggests there was no differential rotation from ~750 mbsf to 1220
mbsf and that the change in orientation below this depth defines a quasi-coherent block size of
~470 m that must have developed after acoustic fluidization ceased where late-stage
deformation was more similar to tectonic-scale faulting (e.g., shear zone in Riller et al., 2018).
Our results support the hypothesis that block size increases over time from finely spaced to
meter-scale blocks during acoustic fluidization to larger effective block sizes as the rocks regain
effective cohesion after acoustic fluidization wanes. This evolution implies that the effective
viscosity of rocks in impact cratering increases with time (Riller et al., 2018). To further assess
this change in block size, future explorations should focus on remotely sensed, field and core
evidence for representative cross-cutting relationships and fracture spacing, orientation and
effective block sizes at a range of crater sizes and locations within complex craters.

7. Conclusions

We measured the orientations of planar cataclasite zones and ultracataclasite zones in
the lower 580 m of core from the Chicxulub peak ring using oriented CT scans and line scan
images of the shocked granitoid. We divided the data into four depth intervals, with the basal
interval containing a proposed imbricate thrust zone and the granite below this zone.
Cataclasite zones within the upper three depth intervals dip towards the crater, whereas the
dip direction is approximately tangential to the peak ring for cataclasite zones below 1220
mbsf. The mean dip direction for ultracataclasite zones is also approximately tangential to the
peak ring. The orientations of ultracataclasite zones and cataclasite zones above the proposed thrust zone are broadly consistent with the hydrocode-modeled orientation of principal stress directions for the *Rim Growth* and *Inward Transport* phases of crater formation. The marked change in orientations between the upper 470 m and the material beneath supports the imbricate thrust zone hypothesis and implies that the upper 470 m of granite was emplaced as a single but internally faulted block.

Key implications of these findings are:

* the orientations of cataclasite zones and ultracataclasite zones provide important ground truth for models of peak-ring formation. Our results are consistent with predictions from hydrocode simulations of deformation that occurs during the *Rim Growth* and *Inward Transport* phases of crater modification;

* The ESE and SE dip directions for cataclasite zones above 1220 mbsf and the NE dip directions for cataclasite zones below this depth are consistent with a fault zone at 1220 – 1316 mbsf that separates distinct blocks of rock that experienced different late stage rotations;

* Increasing shear strain as reflected in the transition from cataclasite to ultracataclasite zones indicates that acoustic fluidization has decreased by the onset of *Rim Growth* and likely ceases by the end of *Inward Transport*;

* Meter-scale spacing for cataclasite zones support smaller than previously modeled block sizes for acoustic fluidization, whereas, the similar orientations of cataclasite zones in the ~470 m granitoid interval above the proposed thrust fault suggest that block size has increased by the time acoustic fluidization has ceased.
473 8. Appendix:

474 Appendix Table A.1 Orientations of cataclasite zones and ultracataclasite zones with the associated eigenvalues, maximum and minimum 95% confidence angles, and the uniformity index where a value >11.07 rejects uniformity. * indicates sample size is too small to compute confidence angles

476

<table><thead><tr><th>Deformation type</th><th>Depth Range (mbsf)</th><th>n</th><th>Orientation (Dip/Dip Direction)</th><th>λ1</th><th>λ2</th><th>λ3</th><th>95% elliptical max confidence angle</th><th>95% elliptical min confidence angle</th><th>Uniformity index</th></tr></thead><tbody><tr><td rowspan="5">Cataclasite</td><td>all</td><td>158</td><td>094°/36°</td><td>0.5812</td><td>0.241</td><td>0.1778</td><td>9.39</td><td>7.41</td><td>111.59</td></tr><tr><td>750-910</td><td>27</td><td>113°/43°</td><td>0.6093</td><td>0.2724</td><td>0.1183</td><td>24.27</td><td>13.25</td><td>25.54</td></tr><tr><td>910-1050</td><td>70</td><td>113°/34°</td><td>0.6118</td><td>0.2453</td><td>0.1429</td><td>13.72</td><td>9.26</td><td>63.80</td></tr><tr><td>1050-1220</td><td>26</td><td>136°/34°</td><td>0.7094</td><td>0.1916</td><td>0.0990</td><td>16.73</td><td>11.08</td><td>42.20</td></tr><tr><td>1220-1335</td><td>35</td><td>043°/55°</td><td>0.815</td><td>0.1107</td><td>0.0743</td><td>9.40</td><td>7.51</td><td>91.53</td></tr><tr><td rowspan="5">Ultracataclasite</td><td>all</td><td>135</td><td>233°/59°</td><td>0.6020</td><td>0.2220</td><td>0.1760</td><td>9.23</td><td>7.76</td><td>110.69</td></tr><tr><td>750-910</td><td>29</td><td>049°/89°</td><td>0.4945</td><td>0.3077</td><td>0.1978</td><td>33.43</td><td>21.26</td><td>9.79</td></tr><tr><td>910-1050</td><td>51</td><td>228°/51°</td><td>0.7212</td><td>0.1674</td><td>0.1114</td><td>10.89</td><td>8.39</td><td>86.94</td></tr><tr><td>1050-1220</td><td>40</td><td>240°/62°</td><td>0.7259</td><td>0.1576</td><td>0.1165</td><td>11.68</td><td>9.69</td><td>69.60</td></tr><tr><td>1220-1335</td><td>15</td><td>057°/35°</td><td>0.572</td><td>0.2962</td><td>0.1318</td><td>*</td><td>*</td><td>11.13</td></tr></tbody></table>
<figure><img src="image_10.png" /></figure>

Appendix Figure A.1: Black and white version of Figure 3 with cataclasite and ultracataclasite zones highlighted for identification. Ultracataclasite zones highlighted in purple, cataclasite zones highlighted in green, zones with cataclasite and ultracataclasite highlighted in blue.

## 8.1. Data analysis

Cataclasite orientations are presented on a lower-hemisphere equal-area projection showing poles to planes (Figure 6). Contours are made using the modified Kamb method (Vollmer, 1995). This type of plot can be thought of as a density map, where the contour intervals represent a deviation from a random sample drawn from a uniform distribution (Kamb, 1959; Vollmer, 1995). Contour intervals are drawn at multiples of uniform density (MUD), a value of 1 represents no preferred orientation, whereas densities of points above 1 MUD are interpreted as having preferred orientation (Kamb, 1959; Vollmer, 1995; Ragan,
490 2009). Contouring allows for a visual assessment of the orientation data; one is able to get a
491 sense if data are unimodal or multimodal, and the orientation of the highest contours.

492 To calculate a mean for 3-dimensional data, such as dip and dip direction, the numerical
493 mean is not sufficient. Problems arise with two planes that are nearly parallel but dipping in
494 opposite directions. For example, consider two gently dipping planes with opposite dips, the
495 vector mean will yield a vertical plane. To counter this issue, we calculated eigenvector maxima
496 instead of the vector mean (Allmendinger et al., 2012; Davis, 1986). The maximum eigenvector
497 represents the best fit values of the data. The eigenvectors are calculated using direction
498 cosines where dip direction (θ) and dip (φ) of the planar element are as follows:

499

$$
500 \quad (3) \cos \alpha = \cos \theta \sin \phi
$$

$$
501 \quad (4) \cos \beta = \sin \theta \sin \phi
$$

$$
502 \quad (5) \cos \gamma = \cos \phi
$$

503

504 Next, the orientation tensor is given by the symmetric matrix formed by the tensor products of
505 the sum of direction cosines:

506

$$
507 \quad (6) A = \begin{bmatrix} \Sigma \cos^2 \alpha & \Sigma(\cos \alpha \cos \beta) & \Sigma(\cos \alpha \cos \gamma) \\ \Sigma(\cos \alpha \cos \beta) & \Sigma \cos^2 \beta & \Sigma(\cos \gamma \cos \beta) \\ \Sigma(\cos \alpha \cos \gamma) & \Sigma(\cos \gamma \cos \beta) & \Sigma \cos^2 \gamma \end{bmatrix}
$$

508

509 The eigenvalues are given by values that satisfy the characteristic equation:

$$
510 \quad (7) \det(A - \Lambda I) = 0, \text{ which yields } \Lambda_1, \Lambda_2, \Lambda_3
$$
511

512 The eigenvalues sum to the sample size and the normalized eigenvalues sum to 1:

$$
513 \quad (8) \Lambda_1 + \Lambda_2 + \Lambda_3 = N
$$

$$
514 \quad (9) \quad \lambda_i = \Lambda_i / N, \quad \lambda_1 + \lambda_2 + \lambda_3 = 1
$$

515

516 The eigenvector then is determined by

$$
517 \quad (10) \ (A - AI)x = 0, \text{ each eigenvector is composed of } \cos \alpha, \cos \beta, \cos \gamma
$$

518

519 The maximum eigenvector is the best fit of the data and can be converted from direction
520 cosines into a dip direction and dip in degrees to convey the mean orientation.

521 The significance of the eigenvectors can be evaluated using the eigenvalues, the cone of
522 confidence uncertainty angles, and the uniformity index. The eigenvalues (λ₁, λ₂, λ₃)

523 demonstrate the significance of the eigenvector (Bingham, 1974; Fisher et al., 1987; Morin et
524 al., 1997). In general, λ₁ >> λ₂> λ₃ corresponds to a strongly clustered data set, and λ₁ = λ₂ = λ₃
525 implies the data have uniform distribution (Mardia, 1972).

526

527 Deviation from a uniform sample can be tested using the uniformity index:

$$
528 \quad (11) \quad S_u = n \frac{15}{2} (\lambda_1^2 + \lambda_2^2 + \lambda_3^2 - \frac{1}{3})
$$

529

530 Independent of sample size, the cutoff value for rejecting uniformity is 11.07 at the 95%
531 value, whereas values below 1.15 suggest an extremely uniform, i.e. not a random distribution
532 (Mardia, 1972). Eigenvalues, elliptical 95% confidence cones around the maximum

533 eigenvectors, and the uniformity index are given in Appendix Table A.1.

534 8.2. Errors and uncertainty

535 Sources of error include accuracy of the wireline magnetometer (±1.2°), resolution of
536 the acoustic borehole image, level of certainty and precision of core orientation adjustments,
537 and manual fitting of peaks and troughs during orientation measurements.

538 The number of planes measured, especially cataclasite zones with steep and shallow
dips may be underestimated. Our measurements are artificially biased against dips with angles
539 below 15° due to the low amplitude expression of troughs and peaks in low angle sinusoids. An
540 additional bias in this data set is that by nature, vertical drilling will sample more horizontal and
541 moderately dipping planes rather than vertical and high angle features (Terzaghi, 1965). The
542 measured orientations have not been corrected for the inclination of the borehole which
543 ranged between <1° to 4° (Lofi et al., 2018).

545

546 9. References:

547 Allmendinger, R.W., Cardozo, N., and Fisher, D.M., 2012, Structural Geology Algorithms:
548 Cambridge University Press.

549 Amos, C.L., Sutherland, T.F., Radzijewski, B. and Doucette, M., 1996, A rapid technique to
550 determine bulk density of fine-grained sediments by X-ray computed tomography. Journal
551 of Sedimentary Research, v.66, no.5.

552 Anderson, E.M., 1905, The dynamics of faulting. Transactions of the Edinburgh Geological
553 Society, v.8, no.3, pp.387-402.

554 Baker, D.M.H., Head, J.W., Collins, G.S., and Potter, R.W.K., 2016, The formation of peak-ring basins: Working hypotheses and path forward in using observations to constrain models of impact-basin formation: Icarus, v. 273, p. 146-163, doi: 10.1016/j.icarus.2015.11.033.

557 Bingham, C., 1974, An antipodally symmetric distribution on the sphere: The Annals of Statistics, v.2, no.6, doi: 10.2307/2958339.

559 Brittan, J., Morgan, J., and Warner, M., 1999, Near-surface seismic expression of the Chicxulub impact crater: Geological Society of America Special Paper, v.339.

561 Cintala, M.J. and Grieve, R.A., 1998, Scaling impact melting and crater dimensions: Implications for the lunar cratering record. Meteoritics & Planetary Science, v.33, no.4, pp.889-912.

563 Collins, G.S., Melosh, H.J., Morgan, J.V., and Warner, M.R., 2002, Hydrocode Simulations of Chicxulub Crater Collapse and Peak-Ring Formation: Icarus, v.157, no.1, p. 24-33, doi: 10.1006/icar.2002.6822.

566 Davis, J.C. and Sampson, R.J., 1986. Statistics and data analysis in geology v.646 New York:Wiley.

568 Diaw, A., 2017, Structural Analysis of The Chicxulub Impact Crater Using Downhole Imaging.

570 Duliu, O., 1999, Computer axial tomography in geosciences: an overview: Earth Science Reviews, v. 48, no. 4, p. 265-281, doi: 10.1016/S0012-8252(99)00056-2.
572 Ebert, M., Poelchau, M.H., Kenkmann, T. and Schuster, B., 2020. Tracing shock-wave propagation in the Chicxulub crater: Implications for the formation of peak rings. Geology.

574 Engelder, J.T., 1974, Cataclasis and the Generation of Fault Gouge: Geological Society of America Bulletin, v. 85, no. 10, p. 1515–1522, doi: 10.1130/0016-7606(1974)85<1515:CATGOF>2.0.CO;2.

577 Fisher, N.I., Lewis, T., and Embleton, B., 1987, Statistical analysis of spherical data: Cambridge University Press.

579 Grieve, R., and Therriault, A., 2000, Vredefort, Sudbury, Chicxulub: three of a kind?: Annual Review of Earth and Planetary Sciences, v. 28, no. 1, p. 305–338, doi: 10.1146/annurev.earth.28.1.305.

582 Gulick, S.P.S., Barton, P.J., Christeson, G.L., Morgan, J.V., McDonald, M., Mendoza-Cervantes, K., Pearson, Z.F., Surendra, A., Urrutia-Fucugauchi, J., Vermeesch, P.M., and Warner, M.R., 2008, Importance of pre-impact crustal structure for the asymmetry of the Chicxulub impact crater: Nature Geoscience, v. 1, no. 2, p. 131–135, doi: 10.1038/ngeo103.

586 Gulick, S.P.S., Christeson, G.L., Barton, P.J., Grieve, R.A.F., Morgan, J.V., and Urrutia-Fucugauchi, J., 2013, Geophysical Characterization of the Chicxulub Impact Crater: Reviews of Geophysics, v. 51, no. 1, p. 31–52, doi: 10.1002/rog.20007.

589 Gulick, S., Morgan, J., Mellett, C.L., Green, S.L., and Bralower, T., 2017a, International Ocean Discovery Program: publications.iodp.org, doi: 10.14379/iodp.proc.364.101.2017.
591 Gulick, S., Morgan, J., Mellett, C.L., Green, S.L., Bralower, T., Chenot, E., Christeson, G., Claeys, P., Cockell, C., Coolen, M.J.L., Ferriere, L., Gebhardt, C., Goto, K., Jones, H., et al., 2017b, *Expedition 364 methods, Proceedings of the International Ocean Discovery Program*, International Ocean Discovery Program. doi: 10.14379/iodp.proc.364.102.2017

595 Hall, B. and Govert, A., 2016, *Techniques for Using Core CT Data for Facies Identification and Analysis*. URTEC 2434059.

597 Head, J.W., 2010, *Transition from complex craters to multi-ringed basins on terrestrial planetary bodies: Scale-dependent role of the expanding melt cavity and progressive interaction with the displaced zone*. Geophysical Research Letters, v. 37, no. 2, p. n/a–n/a, doi: 10.1029/2009GL041790.

601 Healy, D., Blenkinsop, T.G., Timms, N.E., Meredith, P.G., Mitchell, T.M. and Cooke, M.L., 2015, *Polymodal faulting: Time for a new angle on shear failure*. Journal of Structural Geology, v. 80, pp.57-71, https://doi.org/10.1016/j.jsg.2015.08.013

604 Hildebrand, A.R., Penfield, G.T., Kring, D.A., Pilkington, M., Camargo Z, A., Jacobsen, S.B., and Boynton, W.V., 1991, *Chicxulub Crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucatán Peninsula, Mexico*. Geology, v. 19, no. 9, p. 867–871.

607 Jahn, A. and Riller, U., 2015. *Kinematics of large terrestrial impact crater formation inferred from structural analysis and three-dimensional block modeling of the Vredefort Dome, South Africa*. Geol. Soc. Am. Spec. Pap, 518, p.85.

610 Kamb, W., 1959, *Ice petrofabric observations from Blue Glacier, Washington, in relation to*
611 theory and experiment: Journal of Geophysical Research, v. 64, no. 11, p. 1891–1909.

612 Kenkmann, T. and von Dalwigk, I., 2000. Radial transpression ridges: A new structural feature of

613 complex impact craters. *Meteoritics & Planetary Science*, 35(6), pp.1189-1201.

614 Ivanov, B.A. and Kostuchenko, V.N., 1997. Block oscillation model for impact crater collapse.

615 LPI, p.631.

616 Kriens, B.J., Shoemaker, E.M. and Herkenhoff, K.E., 1999. Geology of the Upheaval Dome

617 impact structure, southeast Utah. *Journal of Geophysical Research: Planets*, 104(E8),

618 pp.18867-18887.

619 Kring, D.A., Kramer, G.Y., Collins, G.S., Potter, R.W. and Chandnani, M., 2016. Peak-ring

620 structure and kinematics from a multi-disciplinary study of the Schrödinger impact

621 basin. *Nature communications*, 7, p.13161.

622 Lofi, J., Smith, D., Delahunty, C., Le Ber, E., Brun, L., Henry, G., Paris, J., Tikoo, S., Zylberman, W.,

623 Pezard, P.A., Célérier, B., Schmitt, D.R., Nixon, C., Expedition 364 Science Party, 2018,

624 Drilling-induced and logging-related features illustrated from IODP-ICDP Expedition 364

625 downhole logs and borehole imaging tools: Scientific Drilling, v. 24, p. 1–13, doi:

626 10.5194/sd-24-1-2018.

627 Mardia, K.V., 1972. Statistics of directional data. Journal of the Royal Statistical Society: Series B

628 (Methodological), 37(3), pp.349-371.

629 McCall, N., Gulick, S., Hall, B., Lofi, J. and Poelchau, M., 2020. Data report: orientation
630 correction of Chicxulub core recovered from IODP/ICDP Expedition 364.

631 Melosh, H.J., 1979. Acoustic fluidization: A new geologic process?. Journal of Geophysical

632 Research: Solid Earth, 84(B13), pp.7513-7520.

633 Melosh, H.J., 1989, Impact cratering: A geologic process: Oxford University Press, New York.

634 Melosh, H.J., 1996. Dynamical weakening of faults by acoustic fluidization. Nature, 379(6566),

635 pp.601-606.

636 Melosh, H.J. and Ivanov, B.A., 1999. Impact crater collapse. Annual Review of Earth and

637 Planetary Sciences, 27(1), pp.385-415.

638 Morgan, J.V., Warner, M., the Chicxulub Working Group, Brittan, J., Buffler, R., Camargo, A.,

639 Christeson, G., Denton, P., Hildebrand, A., Hobbs, R., Macintyre, H., Mackenzie, G., Maguire,

640 P., Marin, L., et al., 1997, Size and morphology of the Chicxulub impact crater: Nature, v.

641 390, no. 6659, p. 472-476, doi: 10.1038/37291.

642 Morgan, J.V., Warner, M.R., Collins, G.S., Grieve, R.A.F., Christeson, G.L., Gulick, S.P.S., and

643 Barton, P.J., 2011, Full waveform tomographic images of the peak ring at the Chicxulub

644 impact crater: Journal of Geophysical Research, v. 116, no. B6, doi: 10.1029/2010jb008015.

645 Morgan, J.V., Gulick, S.P.S., Bralower, T., Chenot, E., Christeson, G., Claeys, P., Cockell, C.,

646 Collins, G.S., Coolen, M.J.L., Ferriere, L., Gebhardt, C., Goto, K., Jones, H., Kring, D.A., et al.,

647 2016, The formation of peak rings in large impact craters: Science, v. 354, no. 6314, p. 878-

648 882, doi: doi: 10.1126/science.aah6561.
649 Morin, R.H., Carleton, G.B., and Poirier, S., 1997, Fractured-Aquifer Hydrogeology From Geophysical Logs; The Passic Formation, New Jersey: Groundwater, v. 35, no. 2, p. 328–338, doi: 10.1111/j.1745-6584.1988.tb00792.x.

652 Murray, J.B., 1980, Oscillating peak model of basin and crater formation: The Moon and the Planets, v. 22, no. 3, p. 239–291.

654 Paillet, F. and Duncanson, R., 1994. Comparison of drilling reports and detailed geophysical analysis of ground-water production in bedrock wells. Ground Water, 32(2), p.200.

656 Rae, A.S.P., Collins, G.S., Poelchau, M., Riller, U., Davison, T.M., Grieve, R.A.F., Osinski, G.R., Morgan, J.V., and IODP-ICDP Expedition Scientists, 2019, Stress-Strain Evolution During Peak-Ring Formation: A Case Study of the Chicxulub Impact Structure: Journal of Geophysical Research: Planets, v. 5, no. 1-4, p. 33–55, doi: 10.1029/2018JE005821.

660 Ragan, D.M., 2009, Structural Geology: An Introduction to Geometrical Techniques: Cambridge University Press.

662 Riller, U., Rae, A.S.P., Schulte, F.M., Collins, G.S., Melosh, H.J., Grieve, R.A.F., Lofi, J., Diaw, A., McCall, N., Kring, D.A., Morgan, J.V., Gulick, S.P.S., and Poelchau, M.H., 2018, Rock fluidization during peak-ring formation of large impact structures: Nature, v. 562, no. 7728, p. 511–518, doi: 10.1038/s41586-018-0607-z.

666 Schindelin, J., Arganda-Carreras, I., Frise, E., Kaynig, V., Longair, M., Pietzsch, T., Preibisch, S., Rueden, C., Saalfeld, S., Schmid, B., Tinevez, J.-Y., White, D.J., Hartenstein, V., Eliceiri, K., et al., 2012, Fiji: an open-source platform for biological-image analysis: Nature Methods, v. 9,
669 no. 7, p. 676–682, doi: 10.1038/nmeth.2019.

670 Sibson, R.H., 1977. Fault rocks and fault mechanisms. Journal of the Geological Society, 133(3),

671 pp.191-213.

672 Terzaghi, R.D., 1965. Sources of error in joint surveys. Geotechnique, v 15, no 3, pp.287-304.

673 Therriault, A. M., Grieve, R. A. F., & Reimold, W. U., 1997. Original size of the Vredefort

674 structure: Implications for the geological evolution of the Witwatersrand Basin. Meteoritics

675 & Planetary Science, 32(1), 71-77.

676 Vollmer, F., 1995, C program for automatic contouring of spherical orientation data using a

677 modified Kamb method: Computers and Geosciences, v. 21, no. 1, p. 31–49.

678 Vollmer, F.W. (2015). Orient 3: a new integrated software program for orientation data

679 analysis, kinematic analysis, spherical projections, and Schmidt plots. Geological Society of

680 America Abstracts with Programs, v. 47, n. 7, p. 49.

681 Wilshire, H. G., Offield, T. W., Howard, K. A., & Cummings, D., 1972. Geology of the Sierra

682 Madera cryptoexplosion structure, Pecos County, Texas: US Geol. Survey Prof. Paper.

683 Woodcock, N.H. and Mort, K., 2008. Classification of fault breccias and related fault rocks.

684 Geological Magazine, 145(3), pp.435-440.

685 Acknowledgements: We thank the captain and crew, drilling team, and technical staff who

686 participated in shipboard and/or shore-based operations. We thank the editor and 2

687 anonymous reviewers. Data and samples can be requested from IODP. The European
688 Consortium for Ocean Research Drilling (ECORD) implemented Expedition 364 with funding

689 from the IODP and the ICDP. N.M. and S.P.S.G. were supported by the US Science Support

690 Program and National Science Foundation Grant OCE 1737351. J.V.M. was funded by Natural

691 Environment Research Council Grant NE/P005217/1. U.R. acknowledges funding from the

692 German Science Foundation (grants Ri 916/16-1, 2). This is University of Texas Institute for

693 Geophysics contribution 3812 and Center for Planetary Systems Habitability contribution 0040.

694

695 CRediT author statement:

696 N. McCall: Conceptualization, Methodology, Investigation, Formal analysis, Writing – Original

697 Draft and Editing

698 S.P.S. Gulick: Conceptualization, Supervision, Funding acquisition, Writing - Review and Editing

699 B. Hall: Software, Methodology, Writing - Review and Editing

700 A.S.P. Rae: Writing- Review and Editing, Validation

701 M. H. Poelchau: Writing - Review and Editing

702 U. Riller: Writing - Review and Editing

703 J. Lofi: Writing - Review and Editing

704 J.V. Morgan: Conceptualization, Writing - Review and Editing