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Thin section photomicrographs (all in cross-polarized light except C in natural transmitted light). A) Typical granite sample with K-feldspar (Kfs) and quartz (Qz) crystals. Quartz is shocked with at least two sets of PF (with FFs) and several sets of PDF, not all shown for image clarity. No obvious shock features are visible on the K-feldspar in this case. B) Granite sample with a finer mean grain size, near aplitic texture. Plagioclase (Pl) is sericitized. Ttn = titanite. C) Cataclasite vein, characterized by brecciated quartz and feldspars, crossing the field of view. Epidote crystals (Ep, piemontite) are localized at the contact between cataclasite and the host rock (i.e., in this case mainly quartz and feldspars). D) Shocked quartz grain with two prominent decorated PDF sets. A third set of PDFs and a set of PFs, barely visible on this photograph, are also indicated with white marks. E) A titanite crystal with well-developed shock-induced planar microstructures (at least two sets visible) next to a sericitized (Ser) plagioclase. F) Large well-developed kinkbands in biotite (Bt). (Color figure can be viewed at wileyonlinelibrary.com.)

Thin section photomicrographs (all in cross-polarized light except C in natural transmitted light). A) Typical granite sample with K-feldspar (Kfs) and quartz (Qz) crystals. Quartz is shocked with at least two sets of PF (with FFs) and several sets of PDF, not all shown for image clarity. No obvious shock features are visible on the K-feldspar in this case. B) Granite sample with a finer mean grain size, near aplitic texture. Plagioclase (Pl) is sericitized. Ttn = titanite. C) Cataclasite vein, characterized by brecciated quartz and feldspars, crossing the field of view. Epidote crystals (Ep, piemontite) are localized at the contact between cataclasite and the host rock (i.e., in this case mainly quartz and feldspars). D) Shocked quartz grain with two prominent decorated PDF sets. A third set of PDFs and a set of PFs, barely visible on this photograph, are also indicated with white marks. E) A titanite crystal with well-developed shock-induced planar microstructures (at least two sets visible) next to a sericitized (Ser) plagioclase. F) Large well-developed kinkbands in biotite (Bt). (Color figure can be viewed at wileyonlinelibrary.com.)

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Article
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The IODP-ICDP Expedition 364 drilling recovered a 829 m core from Hole M0077A, sampling ˜600 m of near continuous crystalline basement within the peak ring of the Chicxulub impact structure. The bulk of the basement consists of pervasively deformed, fractured, and shocked granite. Detailed geochemical investigations of 41 granitoid samples, that is...

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Context 1
... 5). These accessory phases represent <1 vol% of the mineral assemblage and grain size is never more than 0.5 mm. Alteration is pervasive, as evidenced by epidote mineralization; sericitization of plagioclases; common chloritization of biotite; and the presence, to some extent, of secondary albite/K-feldspar veins crosscutting the granite unit (Fig. 4) (see also Kring et al. 2020). Granite alteration appears to be more pronounced in close proximity to impact melt rock dikes and along ...
Context 2
... and plagioclase (i.e., PFs filled with opaque minerals and also some possible PDFs; see Pittarello et al. 2020), titanite, and apatite (with different types of planar microstructures; Timms et al. 2019;Cox et al. 2020). Kinkbanding is common in biotite, muscovite, and chlorite and also observed, to a lesser extent, in plagioclase and in quartz (Figs. ...

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Citations

... The concentration profile for Cr at the top of the transitional unit shows around 100 µg/g Cr (see figure 2 from Goderis et al. 2021). The authors report that the top of the transitional unit reflects the deposition of meteoritic matter. ...
... This statement is based on figure S9A. However, the Ni/Co ratios of sulfide minerals from the top TU (616.54-616.60 meter below sea floor) of the study by Goderis et al. (2021) fall outside the range measured in chondritic meteorites. The line in figure S9A showing a Ni/Co ratio of 10 is incorrectly marked by "Chondritic ratios". ...
... Nickel contents in the range of 1.8 to 10.2 μg/g (table 1) were determind in granites (n = 33) from the Chicxulub Hole M0077 (Feignon et al. 2021). Subtraction of Ni values between ~10 to 30 µg/g (approximately crustal concentration, table 1 and figure 2) from upper transitional unit samples would match the Mundrabilla Ni/Ir element ratio of ~82000. ...
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Comment on the interpretation of geochemical data by Goderis et al. (2021) from Core 40R-1, located offshore of the Yucatán Peninsula of Mexico above the Chicxulub peak ring. Notes and corrections are highly appreciated. The peak ring sequence of the Chicxulub impact structure in the drill core was recovered by International Ocean Discovery Program – International Continental Scientific Drilling Program Expedition 364 in April-Mai 2016. The Cretaceous-Paleogene mass extinction is marked globally by elevated concentrations of the platinum group elements (PGE), emplaced by an impact event 66.051 ± 0.031 Ma ago (Alvarez et al. 1980; Renne et al. 2018). The 180- to 200-km-wide Chicxulub impact structure on the Yucatán Peninsula in Mexico is being considered as a possible impact crater that led to the global enrichment of PGE and may have caused the Cretaceous-Paleogene extinctions (Hildebrand et al. 1991). However, the PGE signature in the gray-green marlstone interval (deposition of meteoritic matter and at the top of the transitional unit) of Core 40R-1 recovered at Site M0077 is clearly distinct from a meteoritic component consistent with a chondritic impactor. The signature of the upper transitional unit from the drill core is rather similar to the PGE pattern of the Mundrabilla iron meteorite (see Mundrabilla data from Weinke 1977; Pernicka & Wasson 1987; Wasson & Kallemeyn 2002; Petaev & Jacobsen 2004). The compositional evidence calls into question the Chicxulub impact structure as a source crater for the near-chondritic PGE abundance patterns in Europe and worldwide. The PGE signature is distinct from the European Cretaceous-Paleogene boundary sites of Caravaca in Spain and Stevns Klint in Denmark (see data from Lee, Wasserburg & Kyte 2003). It appears to have been different projectiles and different events in time (see also Keller et al. 2003, Keller 2005, Szopa et al. 2017) that produced the PGE pattern in Europe and the Chicxulub impact structure. When talking about single events or synchronicity in geoscience, it is easily overlooked that enormous time spans of at least ±31 ka (uncertainties) are meant for events that took place e.g. 66 Ma ago. However, relative dating of individual events and their correlation is possible with stratigraphic methods (examination of rock layers and stratification, lithological and biological stratigraphy) and can be supplemented, but not replaced, by radioisotope dating. A recent article by Holm-Alwmark et al. (2021) published in Geochimica et Cosmochimica Acta states, "We would also like to emphasize that proving synchronicity between an impact event and a biotic event is only the first step and is not the same as proving causality." That is also my opinion on this subject.
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Constraining the degree of preservation of a meteoritic signature within an impact structure provides vital insights in the complex pathways and processes that occur during and after an impact cratering event, providing information on the fate of the projectile. The IODP-ICDP Expedition 364 drilling recovered a ∼829 m continuous core (M0077A) of impactites and basement rocks within the ∼200-km diameter Chicxulub impact structure peak ring. No highly siderophile element (HSE) data have been reported for any of the impact melt rocks of this drill core to date. Previous work has shown that most Chicxulub impactites contain less than 0.1% of a chondritic component. Only few impact melt rock samples in previous drill cores recovered from the Chicxulub might contain such a signal. Therefore, we analyzed impact melt rock and suevite samples, as well as pre-impact lithologies of the Chicxulub peak ring, with a focus on the HSE concentrations and Re–Os isotopic compositions. Similar to the concentrations of the other major and trace elements, those of the moderately siderophile elements (Cr, Co, Ni) of impact melt rock samples primarily reflect mixing between a mafic (dolerite) and felsic (granite) components, with the incorporation of carbonate material in the upper impact melt rock unit (from 715.60 to 747.02 meters below seafloor). The HSE concentrations of the impact melt rocks and suevites are generally low (<39 ppt Ir, <96 ppt Os, <149 ppt Pt), comparable to the values of the average upper continental crust, yet three impact melt rock samples exhibit an enrichment in Os (125–410 ppt) and two of them also in Ir (250–324 ppt) by one order of magnitude relative to the other investigated samples. The ¹⁸⁷Os/¹⁸⁸Os ratios of the impact melt rocks are highly variable, ranging from 0.18 to 2.09, probably reflecting heterogenous target rock contributions to the impact melt rocks. The significant amount of mafic dolerite (mainly ∼20–60% and up to 80–90%) , which is less radiogenic (¹⁸⁷Os/¹⁸⁸Os ratio of 0.17), within the impact melt rocks makes an unambiguous identification of an extraterrestrial admixture challenging. Granite samples have unusually low ¹⁸⁷Os/¹⁸⁸Os ratios (0.16 on average), while impact melt rocks and suevites broadly follow a mixing trend between upper continental crust and chondritic/mantle material. Only one of the investigated samples of the upper impact melt rock unit could also be interpreted in terms of a highly diluted (∼0.01–0.05%) meteoritic component. Importantly, the impact melt rocks and pre-impact lithologies were affected by post-impact hydrothermal alteration processes, probably remobilizing Re and Os. The mafic contribution, explaining the least radiogenic ¹⁸⁷Os/¹⁸⁸Os values, is rather likely. The low amount of meteoritic material preserved within impactites of the Chicxulub impact structure may result from a combination of the assumed steeply-inclined trajectory of the Chicxulub impactor (enhanced vaporization, and incorporation of projectile material within the expansion plume), the impact velocity, and the volatile-rich target lithologies.