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Chicxulub impact structure, IODP‐ICDP Expedition 364 drill core: Geochemistry of the granite basement

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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, major and trace element contents, and Sr–Nd isotopic ratios are presented here, providing a broad overview of the composition of the granitic crystalline basement. Mainly granite but also granite clasts (in impact melt rock), granite breccias, and aplite were analyzed, yielding relatively homogeneous compositions between all samples. The granite is part of the high-K, calc-alkaline metaluminous series. Additionally, they are characterized by high Sr/Y and (La/Yb)N ratios, and low Y and Yb contents, which are typical for adakitic rocks. However, other criteria (such as Al2O3 and MgO contents, Mg#, K2O/Na2O ratio, Ni concentrations, etc.) do not match the adakite definition. Rubidium–Sr errorchron and initial ⁸⁷Sr/⁸⁶Srt=326Ma suggest that a hydrothermal fluid metasomatic event occurred shortly after the granite formation, in addition to the postimpact alteration, which mainly affected samples crosscut by shear fractures or in contact with aplite, where the fluid circulation was enhanced, and would have preferentially affected fluid-mobile element concentrations. The initial (ɛNd)t=326Ma values range from −4.0 to 3.2 and indicate that a minor Grenville basement component may have been involved in the granite genesis. Our results are consistent with previous studies, further supporting that the cored granite unit intruded the Maya block during the Carboniferous, in an arc setting with crustal melting related to the closure of the Rheic Ocean associated with the assembly of Pangea. The granite was likely affected by two distinct hydrothermal alteration events, both influencing the granite chemistry: (1) a hydrothermal metasomatic event, possibly related to the first stages of Pangea breakup, which occurred approximately 50 Myr after the granite crystallization, and (2) the postimpact hydrothermal alteration linked to a long-lived hydrothermal system within the Chicxulub structure. Importantly, the granites sampled in Hole M0077A are unique in composition when compared to granite or gneiss clasts from other drill cores recovered from the Chicxulub impact structure. This marks them as valuable lithologies that provide new insights into the Yucatán basement.
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Chicxulub impact structure, IODP-ICDP Expedition 364 drill core: Geochemistry of
the granite basement
Jean-Guillaume FEIGNON
1
*, Sietze J. DE GRAAFF
2,3
, Ludovic FERRI
ERE
4
,
Pim KASKES
2,3
, Thomas D
EHAIS
2,3
, Steven GODERIS
2
, Philippe CLAEYS
2
, and
Christian KOEBERL
1
1
Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna A-1090, Austria
2
Research Unit: Analytical, Environmental & Geo-Chemistry, Department of Chemistry, Vrije Universiteit Brussel,
AMGC-WE-VUB, Pleinlaan 2, Brussels 1050, Belgium
3
Laboratoire G-Time, Universit
e Libre de Bruxelles, Av. F.D. Roosevelt 50, Brussels 1050, Belgium
4
Natural History Museum, Burgring 7, Vienna A-1010, Austria
*Corresponding author. E-mail: jean-guillaume.feignon@univie.ac.at
(Received 24 November 2020; revision accepted 28 May 2021)
Abstract–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, major and trace element contents, and SrNd isotopic ratios are presented here,
providing a broad overview of the composition of the granitic crystalline basement. Mainly
granite but also granite clasts (in impact melt rock), granite breccias, and aplite were
analyzed, yielding relatively homogeneous compositions between all samples. The granite is
part of the high-K, calc-alkaline metaluminous series. Additionally, they are characterized
by high Sr/Y and (La/Yb)
N
ratios, and low Y and Yb contents, which are typical for
adakitic rocks. However, other criteria (such as Al
2
O
3
and MgO contents, Mg#, K
2
O/Na
2
O
ratio, Ni concentrations, etc.) do not match the adakite definition. RubidiumSr errorchron
and initial
87
Sr/
86
Sr
t=326Ma
suggest that a hydrothermal fluid metasomatic event occurred
shortly after the granite formation, in addition to the postimpact alteration, which mainly
affected samples crosscut by shear fractures or in contact with aplite, where the fluid
circulation was enhanced, and would have preferentially affected fluid-mobile element
concentrations. The initial (e
Nd
)
t=326Ma
values range from 4.0 to 3.2 and indicate that a
minor Grenville basement component may have been involved in the granite genesis. Our
results are consistent with previous studies, further supporting that the cored granite unit
intruded the Maya block during the Carboniferous, in an arc setting with crustal melting
related to the closure of the Rheic Ocean associated with the assembly of Pangea. The
granite was likely affected by two distinct hydrothermal alteration events, both influencing
the granite chemistry: (1) a hydrothermal metasomatic event, possibly related to the first
stages of Pangea breakup, which occurred approximately 50 Myr after the granite
crystallization, and (2) the postimpact hydrothermal alteration linked to a long-lived
hydrothermal system within the Chicxulub structure. Importantly, the granites sampled in
Hole M0077A are unique in composition when compared to granite or gneiss clasts from
other drill cores recovered from the Chicxulub impact structure. This marks them as
valuable lithologies that provide new insights into the Yucat
an basement.
Meteoritics & Planetary Science 56, Nr 7, 1243–1273 (2021)
doi: 10.1111/maps.13705
1243 ©2021 The Authors. Meteoritics & Planetary Science
published by Wiley Periodicals LLC on behalf of The Meteoritical Society (MET)
This is an open access article under the terms of the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the original work is properly cited.
INTRODUCTION
The ~200 km diameter (e.g., Gulick et al. 2013) and
66.05 Myr old (Sprain et al. 2018) Chicxulub impact
structure is located in the northwestern part of the
Yucat
an peninsula (Mexico, Fig. 1). The
characterization of shocked quartz grains in samples
derived from within the structure confirmed its impact
origin (Penfield and Camargo 1981; Hildebrand et al.
1991). Chicxulub is the only known terrestrial impact
structure with a nearly intact, well-preserved peak ring
(e.g., Morgan et al. 1997, 2016) and it is related to the
CretaceousPaleogene boundary and the non-avian
dinosaur extinction (Swisher et al. 1992; Smit 1999;
Schulte et al. 2010; Chiarenza et al. 2020; Goderis et al.
2021). The structure was formed by the impact of an
~12 km diameter carbonaceous chondrite-like body
(Shukolyukov and Lugmair 1998; Quitt
e et al. 2007;
Goderis et al. 2013; Collins et al. 2020) on an ~3km
thick Mesozoic carbonate and evaporite platform
overlying crystalline basement rock (e.g., Morgan et al.
[2016] and references therein).
Today, the impact structure is buried under ~1kmof
Cenozoic limestones, with its only surface expression
being a ring of cenotes (i.e., water-filled sinkholes).
Consequently, the direct study of the different lithologies
occurring in the impact structure (i.e., a variety of impact
breccias, impact melt rocks, and (shocked) pre-impact
basement rocks) is only possible either by investigating
ejecta material (Belza et al. 2015) or by using samples
recovered by scientific drilling programs (e.g., Koeberl
and Sigurdsson 1992; Koeberl 1993a; Belza et al. 2012) or
petroleum exploration campaigns (e.g., Lopez Ramos
1975; Hildebrand et al. 1991; Swisher et al. 1992; Urrutia-
Fucugauchi et al. 1996; Claeys et al. 2003; Tuchscherer
et al. [2004a] and references therein). Drilling campaigns
were conducted within the impact structure by Petr
oleos
M
exicanos (PEMEX), recovering the Chicxulub1(C1)
and Yucatan6 (Y6) cores, which sampled melt-bearing
impact breccia (suevite) and impact melt rock (e.g.,
Hildebrand et al. 1991; Kring and Boynton 1992; Swisher
et al. 1992; Schuraytz et al. 1994; Ward et al. 1995; Claeys
et al. 2003; Kettrup and Deutsch 2003); and by the
International Continental Scientific Drilling Program
(ICDP), recovering the Yaxcopoil1 (Yax1) core (e.g.,
Tuchscherer et al. 2004a, 2004b, 2005, 2006).
Pre-impact basement material was generally found as
clasts in the suevite units recovered in previous drill core
campaigns, with a wide variety of target lithologies being
reported, including Cretaceous sedimentary platform
rocks (a 616 m thick megablock of limestones, dolomites,
and anhydrites was identified in the Yax1 drill core, e.g.,
Dressler et al. 2003; Wittmann et al. 2004; Belza et al.
2012), granites, orthogneisses, amphibolites, quartzites,
quartz-mica schists, and dolerites (e.g., Sharpton et al.
1992; Kettrup et al. 2000; Claeys et al. 2003; Kettrup and
Deutsch 2003; Schmitt et al. 2004; Tuchscherer et al.
2005). Importantly, no large unit of the underlying
crystalline basement material was ever recovered in any
of the previous drill core campaigns.
A large crystalline basement unit composed mainly
of granite was recovered for the first time in the
Chicxulub peak ring drilled during the joint
International Ocean Discovery Program (IODP) and
ICDP Expedition 364 (see the IODP-ICDP Expedition
364 Drill Core section and Morgan et al. 2017). This
unit represents the main focus of this study. In order to
better characterize the granite basement, we present the
results of the major and trace element analyses of 41
granitoid samples, including SrNd isotopic analyses for
16 samples, from the “lower peak ring” section. A
comparison with chemical data for granites and granitic
gneisses from previous studies is also presented. Our
investigations of a large set of granite samples offer a
unique opportunity to constrain the chemistry and
sources of the granite, a major component to the
impactites recovered in the drill core; how it was
affected by the impact event; and, more generally, refine
the Yucat
an basement geology.
THE CHICXULUB IMPACT STRUCTURE
Geological Setting
The crystalline basement rocks forming the Yucat
an
platform belong to the Maya block (Fig. 1), which is
generally described as encompassing the Yucat
an
peninsula, the northeast of Mexico, the coastal plains of
the western and northern Gulf of Mexico, and the
Chiapas massif complex (Keppie et al. 2011; Weber
et al. 2012, 2018), with its north and northeastern
boundaries bordered by continental shelves and oceanic
lithosphere (Alaniz-
Alvarez et al. 1996; Keppie et al.
2011). The Maya block was thought to be bordered in
the northwest by the Oaxaquia block (Grenvillian-aged);
in the southwest by the Cuicateco complex; and in the
south by the Polochic, Motagua, and Jocotl
an-
Chamale
on fault systems (Fig. 1), making the
separation with the Caribbean plate (Dengo 1969;
Donnelly et al. 1990; Weber et al. 2012, 2018).
However, the exact geographical area covered by the
Maya block remains a topic of discussion. Indeed,
the work by Ortega-Guti
errez et al. (2018) suggests that
the Chiapas massif (or Southern Maya) forms a distinct
lithotectonic domain (Fig. 1), characterized by the
presence of medium- to high-grade metamorphic rock
outcrops that were not observed in the Maya block
(Weber et al. 2008; Ortega-Guti
errez et al. 2018). The
1244 J.-G. Feignon et al.
Chiapas massif would be separated from the Maya
block by the Paleozoic-aged Huastecan orogenic belt.
This orogenic system is mostly buried and extends from
the Ouachita suture belt in Northwest Mexico to the
Polochic, Motagua, and Jocotl
an-Chamale
on fault
systems in Guatemala. Consequently, the Huastecan
orogenic belt separates the Maya block from the
Oaxaquia and Cuicateco terranes in the west and
southwest, respectively (Fig. 1).
The material composing the Maya block is mainly
Pan-Africanaged, such as tholeiitic dolerite intruded in
Grenvillian Novillo gneiss in the Cd. Victoria area,
yielding an Ar/Ar age of 546 5 Ma (Keppie et al.
2011). In addition, the age of zircon grains found in
ejected material at various KPg boundary locations
and from boreholes inside the Chicxulub impact
structure range mainly between 550 and 545 Ma, just
after the CambrianPrecambrian boundary (Krogh
et al. 1993; Kettrup and Deutsch [2003] and references
therein; Kamo et al. 2011; Keppie et al. 2011),
suggesting that a predominantly late Ediacaran
crystalline basement constitutes the northern part of the
Yucat
an peninsula (Ortega-Guti
errez et al. 2018). The
SmNd T
DM
model ages reported from orthogneisses,
impact melt rock, impact glass, and amphibolites
display a wide range between 1.4 and 0.7 Ga, suggesting
the involvement of a Grenvillian component during the
formation of Yucat
an crystalline basement (Kettrup and
Deutsch 2003; Keppie et al. 2011). Granites and zircon
grains with younger ages (late Paleozoic, ~320345 Ma)
are also reported, but are comparatively rare (Kamo
and Krogh 1995; Kamo et al. 2011; Keppie et al. 2011).
While the exact extent of the lithotectonic domains
remains up for debate, paleomagnetic reconstructions
indicate that the Maya block, and more precisely the
Yucat
an-Chiapas block, separated from Texas (southern
Chicxulub
impact
structure
Drilling site
M0077A
Maya
Maya
Huastecan
Oaxaquia
Greater
Guerrero
Xolapa
Acatlán
Morelos
Cuicateco
Chiapas
Polochic fault
Motagua fault
Jocotlán - Chamaleon fault
Teh uantepec fault
Y6
Yax-1
C-1
Merida
Belmopan
Guatemala City
San Salvador
Tegucigalpa
Villahermosa
Tux t la
Gutiérrez
Oaxaca
Mexico
100°W 84°W
88°W92°W96°W
100°W 84°W
88°W92°W96°W
Fault
Borehole
Major city
16°N
20°N
24°N
16°N
20°N
24°N
Fig. 1. Map of southeast Mexico with the main tectonostratigraphic domains proposed by Ortega-Guti
errez et al. (2018), major
faults, and the Chicxulub impact structure (dashed circle; 200 km in diameter) with the IODP-ICDP Expedition 364 (M0077A)
and previous drilling (Y6, Yax1, and C1) locations reported (modified from Weber et al. 2012, 2018; Ortega-Guti
errez et al.
2018). SRTM data can be found online at: https://www2.jpl.nasa.gov/srtm/cbanddataproducts.html. (Color figure can be viewed
at wileyonlinelibrary.com.)
Chicxulub peak ring granite chemistry 1245
margin of Laurentia) during the breakup of Pangea
during the Late Triassic (~230 Ma). The Yucat
an-
Chiapas block then rotated ~40°(up to 60°for the
Yucat
an basement, independently from the Chiapas
block) anticlockwise as the Gulf of Mexico opened. The
rotation was accommodated by the presence of a
transform fault marking the boundary between
continental and oceanic crust offshore the east coast of
Mexico (Dickinson and Lawton 2001; Steiner 2005). The
seafloor spreading began during the Callovian
(~164 Ma). The rotation ceased by the Berriasian
(~139 Ma), and, since then, the Yucat
an block has
remained geologically stable (see detailed geotectonic
reconstructions in Dickinson and Lawton 2001; Steiner
[2005] and references therein). At the time of the
Chicxulub impact event, at ~66.05 Ma (Sprain et al.
2018), the Yucat
an basement was covered by an
approximately 3 km thick carbonate platform composed
of limestone, dolomite, marl, and anhydrite (Lopez
Ramos 1975; Kring 2005). Additionally, the platform was
covered by seawater, deepening to the north and
northeast with an average water depth of ~600 m (Gulick
et al. 2008).
During the impact event, the target rocks
(sedimentary rocks and the underlying basement rocks)
were either vaporized, melted, shocked, ejected from the
crater, uplifted, injected as melt into the structure, and/or
incorporated into gravity flows during crater modification
(Morgan et al. 2016; Gulick et al. 2019; de Graaff et al.
2021). Rock fluidization rapidly led to the formation of a
central peak ring inside the structure (Riller et al. 2018;
Rae et al. 2019). Afterward, the peak ring was intensively
altered by a long-lived, by more than one million years,
hydrothermal system (Kring et al. 2020).
The impact structure site was finally covered by
carbonates and evaporites from the Cretaceous to the
Quaternary, forming the current subsurface geology of
the Yucat
an peninsula (Lopez Ramos 1975; Hildebrand
et al. 1991), and preserving the impact structure and its
peak ring from erosion.
IODP-ICDP Expedition 364 Drill Core
Investigating the rocks that make up the peak ring
in order to understand its nature, chemistry, and origin,
as well as its formation mechanism, was one of the
primary goals of the IODP-ICDP Expedition 364 (e.g.,
Morgan et al. 2017). A continuous core from Hole
M0077A (see Fig. 2) was recovered between 505.7 and
1334.7 mbsf (meters below sea floor). Four main
lithological units were identified, including (1) a
“postimpact” Cenozoic sedimentary rock section (from
505.7 to 617.3 mbsf); (2) a melt-bearing, polymict,
impact breccia (suevite) section (from 617.3 to
721.6 mbsf); overlaying (3) an impact melt rock and
green schlieren unit (from 721.6 to 747.0 mbsf), or
“upper impact melt rock” unit (Morgan et al. 2017; de
Graaff et al. 2021). The lower and thicker recovered
unit (4), the so-called “lower peak ring” section (from
747.0 to 1334.7 mbsf), consists of granitoid (coarse-
grained granite with centimeter to decimeter aplite and
pegmatite facies areas) intruded by several pre-impact
subvolcanic dikes and intercalations of millimeter to
decameter suevite-like breccia and impact melt rocks
(Morgan et al. 2017). The latter has been discussed in
detail, and referred to as the “lower impact melt-bearing
unit” (LIMB), by de Graaff et al. (2021).
The “lower peak ring” section represents a large,
nearly uninterrupted crystalline basement rock unit, and
is the main focus of this study. The occurrence of
crystalline basement rocks at such relatively shallow
depths suggests that they were uplifted from a pre-impact
depth of 810 km (Morgan et al. 2016; Riller et al. 2018).
The basement rocks are shocked, with most of the
minerals showing signs of shock metamorphism. Shock
pressures experienced by the granite were estimated
between ~16 and 18 GPa (Feignon et al. 2020).
Zhao et al. (2020) reported on the investigation of
nine granite samples and suggested that these late
Paleozoic granites are K-rich adakitic rocks that formed
following the melting of a thickened crust with a residue
of garnet-bearing amphibolite or garnet-bearing
granulite. However, the term “adakitic” should be used
with care in this context, as a full set of criteria should
be used in addition to the used Sr/Y and La/Yb ratios
to define an adakitic rock (see Moyen 2009). The long-
lasting hydrothermal system, which occurred within
Chicxulub (e.g., Kring et al. 2020), may also have had a
significant effect on the bulk granite geochemistry as
also suggested by de Graaff et al. (2021).
Granite Ages
Dating on the Hole M0077A granites was performed
on zircon and yield late Paleozoic (Carboniferous) UPb
ages of 326 5 Ma (Rasmussen et al. 2019; Zhao et al.
2020) and 334 2.3 Ma (Ross et al. 2021). More recent
ages (215 28 to 260 9 Ma) were obtained for
allanite and probably recorded allanite growth during
alteration events, while zircon ages represent the igneous
crystallization (Wittmann et al. 2018). A similar late
Paleozoic age, albeit with large uncertainty, of
478 110 Ma, was obtained in zircons from Yax1
impact breccia (Schmieder et al. 2017). These ages
contrast the mostly dominant Pan-Africanaged zircon
population recovered from KPg boundary sites and
previous drill cores (e.g., Krogh et al. 1993; Kamo et al.
2011; Keppie et al. 2011).
1246 J.-G. Feignon et al.
Using the ages presented in both Zhao et al. (2020)
and Ross et al. (2021), we can assume that these
granites were probably emplaced during the
Carboniferous. During this period, the Yucat
an block
was located at the edge of the Gondwana craton and
recorded arc magmatism originating from the
subduction of oceanic crust of the Rheic ocean beneath
the northern edge of Gondwana before its collision with
Laurentia (Pangean assembly) according to the
geotectonic reconstructions of Dickinson and Lawton
(2001).
MATERIALS AND METHODS
Sample Selection
Forty-one samples ranging from 20 to 50 g in mass
were prepared from a selected number of granitoid
samples taken at regular intervals between 745.1 and
1334.7 mbsf. Sample nomenclature used in this study
corresponds to Core#Section#_Top(cm)Bottom(cm)
and indicates the exact sampling interval as defined in
Morgan et al. (2017), while the centimeters indicate the
700
750
800
850
Depth (mbsf)
900
950
1000
1050
1100
1150
1200
1250
1300
M0077A
Lower peak ring
Impact melt-bearing breccia Impact melt rock Crystalline pre-impact granite
Subvolcanic pre-impact dike
Granite (main unit) Granite clast Granite breccia Aplite
SiO2
(wt.%)
Al2O3
(wt.%)
CaO
(wt.%)
K2O
(wt.%)
Rb
(ppm)
Sr
(ppm)
Zr
(ppm)
87Sr/86Srt=0 Nd)t=0
Fig. 2. Lithostratigraphy of the “lower peak ring” section (747.01334.7 mbsf) of the Hole M0077A core (from de Graaff et al.
2021), comparing the concentration variations of selected major (SiO
2
,Al
2
O
3
, CaO, K
2
O), trace elements (Rb, Sr, Zr), and Sr
Nd isotopic compositions with depth in the investigated samples. (Color figure can be viewed at wileyonlinelibrary.com.)
Chicxulub peak ring granite chemistry 1247
distance in a core section from the top. The uppermost
sample consists of a granite clast located in the upper
impact melt rock (Unit 3), whereas the other samples
were taken from the “lower peak ring” section. Due to
the size of core samples (8 cm diameter), special care was
taken to select representative equigranular granite
samples to assess any compositional variation with core
depth; texture change; and the effects of shock,
fracturing, and other types of chemical alteration as well
as the fluid circulation following the onset of the
hydrothermal system. As such, three samples exhibiting a
porphyritic texture (with large K-feldspar crystals up to
7 cm in size) were excluded from the scope of this study,
as their chemistry would be biased by K-feldspar
accumulation rather than representing whole rock
composition.
The majority of the selected samples (n=33) were
taken from the main granite unit (i.e., granites sampled
from the continuous granite interval of at least 1 m in
thickness). In addition, samples of granite clasts in
impact melt rock (n=4), one from the “upper impact
melt rock” and the remaining three from the LIMB,
were selected. A granite clast was considered in this
study as having a size smaller than one meter
throughout the drill core. Additionally, two granite
breccias as well as two aplites were selected to assess
any chemical variation related to petrographic textures.
Sample locations and their relative depths within the
core are shown in Fig. 2 and Table 1.
Petrographic Investigations
Polished thin sections of the samples were prepared
and investigated for their mineralogy, textures, and
shock metamorphic features in minerals using optical
microscopy at the University of Vienna and a JEOL
JSM-6610 variable pressure (VP) scanning electron
microscope (SEM) at the Natural History Museum
(Vienna, Austria). Additionally, detailed investigations
on shocked quartz grains were made on 11 thin sections
using a universal stage (see Feignon et al. 2020).
Major Element Mapping
Energy-dispersive micro X-ray fluorescence (µXRF)
was performed on 20 granite samples at the Vrije
Universiteit Brussels (VUB) using a Bruker M4 Tornado
benchtop µXRF surface scanner equipped with an Rh
tube as X-ray source and two XFlash 430 Silicon Drift
detectors. This technique produced high-resolution
elemental distribution maps by scanning flat sample
surfaces (i.e., polished thin and thick sections), in a rapid,
nondestructive, and cost-efficient way (e.g., de Winter
and Claeys 2016; Kaskes et al. 2021). The µXRF
mapping was performed with two detectors and
maximized X-ray source energy settings (50 kV and
600 µA, without any filter). The measurements were
carried out under near vacuum conditions (20 mbar) with
a spatial resolution of 25 lm and an integration time of
1 ms per 25 lm. This approach resulted in qualitative
multi-element maps and semiquantitative single-element
heat maps, in which the highest spectral peak for one
element (i.e., the largest number of counts below thein
generalKapeak) corresponds to the pixel in the sample
with the highest possible RGB value (i.e., 255).
Geochemical Analysis
The samples were crushed in polyethylene wrappers
and then powdered in an agate bowl using a Retsch
RS200 vibratory disk mill. The obtained sample
powders were then stored in clean, hermetically sealed,
polyethylene vials.
Major Element Analysis
Samples were measured by means of glass bead-
based X-ray fluorescence (XRF). The analyses were
performed using an X-ray spectrometer PHILIPS
PW2404 at the Department of Lithospheric Research
(University of Vienna, Austria) with a super sharp end
window tube and an Rh-anode. The element
concentrations were determined using calibration curves
established using international reference materials.
Accuracy and precision values (in wt%) are about 0.6 for
SiO
2
and Fe
2
O
3
, 0.3 for Al
2
O
3
, 0.2 for Na
2
O, 0.07 for
MgO and CaO, 0.03 for TiO
2
and K
2
O, 0.02 for P
2
O
5
,
and 0.01 for MnO.
Approximately 3 g of homogenized rock powder
was weighed in a porcelain crucible that was previously
heated at 1050 °C for at least 3 h and cooled down to
room temperature in a desiccator. For LOI
determination, the crucible with rock powder was
placed into an oven at 110 °C overnight, and weighed
again. Next, the crucible with rock powder was placed
into a muffle furnace at 850 °C for 3 h, and weighed
one final time. The LOI was then calculated.
Fused beads were prepared by adding 0.8 g of the
calcined sample powder to 8.0 g of a di-lithium
tetraborate and di-lithium metaborate (Fluxana FX-
X65-2) mixture (2:1 ratio). This mixture was then
poured into a crucible of platinum and gold and fused
using a PANalytical EAGON 2 furnace.
Trace Element Analysis
Trace element concentrations were both measured
using bulk XRF and instrumental neutron activation
analysis (INAA). The bulk XRF measurement for trace
element concentrations was done on pressed powder
1248 J.-G. Feignon et al.
Table 1. Major element concentrations (in wt%) of all the investigated samples from the Expedition 364 Chicxulub drill core, namely granites
(from the main unit), granite clasts, granite breccias, and aplites, as determined using bulk XRF.
Sample Depth (mbsf) SiO
2
TiO
2
Al
2
O
3
Fe
2
O
3
*MnO MgO CaO Na
2
OK
2
OP
2
O
5
LOI Total K
2
O/Na
2
O A/CNK Mg#
Granites (from the main unit)
97R3_1012.5 752.5 74.3 0.16 13.0 1.07 0.02 0.46 1.31 3.71 4.82 0.05 1.06 99.90 1.30 0.94 40
110R2_1416 788.1 72.3 0.21 14.9 1.09 0.02 0.47 1.41 4.82 4.56 0.05 b.d.l. 99.76 0.95 0.96 40
116R2_5862 806.7 69.7 0.21 16.1 1.28 0.02 0.61 1.68 4.75 4.88 0.07 1.34 100.63 1.03 0.99 42
125R1_4042.5 826.7 74.7 0.14 13.7 0.90 0.01 0.36 1.36 4.36 4.27 0.04 0.52 100.31 0.98 0.96 38
134R3_7579 846.9 70.4 0.26 12.6 1.60 0.04 1.32 3.04 4.52 2.91 0.08 2.28 99.10 0.64 0.78 56
136R2_2025 851.4 74.5 0.12 13.5 0.67 0.01 0.33 1.53 4.67 3.38 0.03 1.08 99.85 0.72 0.96 43
142R2_105109 861.9 71.4 0.20 15.1 1.50 0.02 0.62 1.73 5.05 3.64 0.07 0.01 99.32 0.72 0.98 39
142R3_4850 862.6 72.2 0.38 13.2 2.55 0.04 0.94 1.73 4.23 3.48 0.20 0.70 99.60 0.82 0.95 36
153R1_4750.5 890.8 75.9 0.24 13.0 1.04 0.01 0.56 1.21 5.38 2.27 0.10 1.04 100.81 0.42 0.96 45
156R3_1115 902.1 66.7 0.48 15.0 3.76 0.06 1.35 2.19 4.93 4.04 0.34 0.49 99.32 0.82 0.91 36
163R1_7677.5 915.5 70.4 0.22 15.6 1.47 0.02 0.61 1.72 5.41 3.37 0.09 0.62 99.47 0.62 0.99 39
172R1_118121 942.9 75.5 0.15 12.6 0.83 0.02 0.36 1.45 4.41 3.24 0.04 1.10 99.64 0.73 0.94 40
176R2_112116 953.6 69.7 0.26 14.9 1.50 0.02 0.55 2.09 4.04 4.10 0.09 2.64 99.89 1.01 1.00 36
188R2_1113.5 986.2 71.3 0.27 14.6 1.82 0.03 0.74 1.68 5.22 3.09 0.13 0.67 99.48 0.59 0.97 38
200R3_12.515 1021.0 73.9 0.24 13.6 1.23 0.02 0.49 1.27 4.28 3.89 0.05 1.05 100.10 0.91 1.01 38
212R1_129131.5 1056.0 72.2 0.19 13.9 1.28 0.02 0.57 1.64 4.90 3.03 0.04 1.21 98.95 0.62 0.97 41
219R1_105.5108 1077.0 72.2 0.21 14.2 1.48 0.04 0.62 1.43 5.24 3.17 0.06 0.64 99.34 0.60 0.97 39
229R2_6267 1107.2 75.8 0.21 12.3 1.32 0.03 0.59 1.58 4.30 2.55 0.07 1.15 99.87 0.59 0.97 41
236R1_9092.5 1128.8 73.7 0.20 13.8 1.29 0.02 0.56 1.38 3.89 4.55 0.06 0.60 100.05 1.17 1.00 40
256R1_7072.5 1188.6 73.1 0.20 14.5 1.57 0.02 0.66 1.71 5.08 3.06 0.07 0.60 100.51 0.60 0.98 39
266R2_95.598.5 1220.5 72.9 0.29 14.6 1.74 0.02 0.61 1.72 5.01 3.05 0.11 0.47 100.55 0.61 1.00 35
272R1_2830.5 1237.2 74.8 0.26 13.5 1.58 0.02 0.56 1.58 5.01 2.94 0.09 0.77 101.10 0.59 0.95 35
276R2_6264.5 1250.9 74.0 0.18 14.0 1.26 0.01 0.55 1.13 5.03 3.64 0.06 0.69 100.55 0.72 0.98 40
280R1_4749 1262.2 74.5 0.13 13.9 0.96 0.03 0.36 0.78 4.52 4.30 0.04 0.57 100.04 0.95 1.03 37
280R2_51.553.5 1263.5 75.7 0.13 12.2 0.87 0.01 0.33 0.70 3.80 4.91 0.06 0.46 99.15 1.29 0.95 37
288R1_6164 1287.2 73.0 0.19 13.7 1.14 0.02 0.51 1.09 5.42 3.22 0.07 0.44 98.80 0.59 0.95 41
296R1_116118 1311.1 73.0 0.16 13.7 1.28 0.03 0.30 1.51 4.50 4.00 0.07 1.29 99.78 0.89 0.94 26
297R1_3638 1313.4 72.8 0.14 14.1 1.23 0.01 0.29 1.35 4.22 5.16 0.05 1.25 100.62 1.22 0.94 27
298R1_4143 1316.5 72.6 0.23 13.7 1.25 0.02 0.48 1.23 4.66 4.29 0.09 1.04 99.56 0.92 0.94 37
298R3_1.53.5 1318.7 76.5 0.13 12.3 0.71 0.01 0.28 1.05 4.38 3.46 0.04 0.83 99.63 0.79 0.95 38
299R1_52.555 1319.7 77.5 0.16 11.6 1.22 0.02 0.56 0.88 4.01 2.92 0.08 1.04 99.89 0.73 1.02 41
300R1_7879.5 1323.1 73.0 0.17 14.1 0.91 0.02 0.25 1.43 4.46 4.67 0.06 1.33 100.35 1.05 0.94 30
303R2_8284.5 1333.7 73.3 0.16 12.7 0.59 0.01 0.14 2.37 4.11 4.13 0.08 1.93 99.49 1.00 0.82 27
Granite clasts
95R2_1922 745.1 75.8 0.19 12.7 0.94 b.d.l. 0.63 1.57 3.82 3.95 0.09 0.53 100.23 1.03 0.95 51
163R3_5257 917.3 74.8 0.19 13.7 0.94 0.01 0.61 0.81 4.11 4.73 0.06 0.71 100.70 1.15 1.03 50
Chicxulub peak ring granite chemistry 1249
pellets. The latter were prepared by mixing 0.5 mL of
an aqueous polyvinyl alcohol solution (MERCK
Mowiol) and approximately 10 g of non-ignited rock
powder. The mixture was then placed in a hydraulic
press, applying a pressure of approximately 16 tons per
square centimeter. The pressed powder pellets were then
dried in an oven at 70 °C overnight. Tool cleaning was
done using acetone. The trace element concentrations
were then obtained by using the intensities at peak and
background positions, which were measured on blank
specimens for interpolating background intensity at the
peak position (Nisbet et al. 1979).
For bulk INAA analysis, between 100 and 150 mg
of dried rock powder was placed in small polyethylene
vials that were sealed to avoid any leaking of material
and/or radioactive contamination after irradiation. The
same was done for international reference materials
(standards ACE granite, ALL Allende carbonaceous
chondrite meteorite, and SDO-1 shale) but using less
material (6090 mg). Samples were then packed in
groups of 17, to which three standard samples were
added.
Samples and standards were irradiated together for
8 h in the 250 kW Triga reactor of the Atomic Institute
of the Austrian Universities at a neutron flux of
2910
12
ncm
2
s
1
. Samples and standards were then
measured with coaxial Canberra HpGe detectors in
three cycles (L1, L2, and L3). The cycle L1 was
measured ~5 days after irradiation. Each sample is
measured for at least 60 min. Cycle L2 was done
~10 days after irradiation, with ~34 h measuring time
for each sample. Finally, the Cycle L3 was performed
34 weeks after irradiation and the samples were
measured for at least 12 h (generally 24 h in this study).
Data obtained were then processed automatically by
computer, and neutron flux correction was applied.
Finally, the data were checked manually. Replicate
analysis of international reference materials ACE, ALL,
and SDO-1 (n=8) yielded reproducibilities for trace
element contents on the order of ~2 to 15 rel%. More
details on instrumentation, accuracy, and precision of
this method can be found in, for example, Koeberl
(1993b), Son and Koeberl (2005), and Mader and
Koeberl (2009).
SrNd Isotopic Analysis
The Sr and Nd isotopic analytical work was
performed at the Department of Lithospheric Research
(University of Vienna, Austria). Sixteen of the 41
aforementioned samples were selected, including granite
(n=14) and granite clasts (n=2).
Rock powders (approximately 50100 mg) were
digested in tightly screwed Savillex beakers using an
ultra-pure mixture of HF:HNO
3
(4:1 ratio) for 2
Table 1. Continued. Major element concentrations (in wt%) of all the investigated samples from the Expedition 364 Chicxulub drill core, namely
granites (from the main unit), granite clasts, granite breccias, and aplites, as determined using bulk XRF.
Sample Depth (mbsf) SiO
2
TiO
2
Al
2
O
3
Fe
2
O
3
*MnO MgO CaO Na
2
OK
2
OP
2
O
5
LOI Total K
2
O/Na
2
O A/CNK Mg#
285R2_2628.5 1278.7 72.9 0.24 13.3 1.69 0.02 0.64 1.32 5.13 3.20 0.11 0.45 99.00 0.62 0.93 37
295R2_5153 1308.5 74.3 0.13 13.5 1.01 0.01 0.26 0.95 4.36 4.32 0.05 0.80 99.61 0.99 0.99 28
Granite breccias
96R2_5052 748.7 70.5 0.23 13.2 1.62 0.04 1.10 2.32 4.39 3.61 0.08 2.14 99.15 0.82 0.86 51
1278R1_4345 1256.0 71.8 0.22 14.1 1.69 0.02 0.67 1.17 4.90 4.21 0.10 0.53 99.43 0.86 0.96 38
Aplites
147R2_03 875.7 74.4 0.05 14.3 0.55 0.01 0.07 0.96 5.12 4.17 0.02 0.54 100.17 0.81 0.97 16
242R3_2326 1149.0 75.0 0.09 13.2 0.59 0.02 0.15 1.03 4.37 4.48 0.03 0.66 99.60 1.03 0.95 28
b.d.l. =below detection limit; LOI =loss on ignition.
*Iron oxide reported as total ferrous Fe.
1250 J.-G. Feignon et al.
4 weeks at 100120 °C on a hot plate, in order to make
sure the insoluble phases, such as zircon, were fully
digested. After acid evaporation, repeated treatment of
the residue using 6 M HCl resulted in clear solutions.
Element isolation for Sr and rare earth elements (REE)
was performed using AG 50W-X8 (200400 mesh, Bio-
Rad) resin and 2.5 and 4.0 M HCl as eluants.
Neodymium was separated from the REE group using
Teflon-coated HDEHP and 0.22 M HCl as eluant.
Maximum total procedural blanks were <1 ng for Sr
and 40 pg for Nd, which can be considered negligible
for the purpose of this work. The isolated element
fractions were loaded on an Re double filament
assembly and run in static mode on a Thermo-Finnigan
Triton thermal ionization mass spectrometer (TIMS)
instrument. Mass fractionation was corrected for
88
Sr/
86
Sr =8.3752 and
146
Nd/
144
Nd =0.7219,
respectively. Samples were measured in two successive
batches. Mean
87
Sr/
86
Sr of 0.710260 0.000004 (batch
1, n=5) and 0.710257 0.000006 (batch 2, n=5) were
determined for the NBS987 (Sr) and mean
143
Nd/
144
Nd
ratios of 0.511846 0.000003 (batch 1, n=5) and
0.511841 0.000002 (batch 2, n=5) for the La Jolla
(Nd) international standards during the period of
investigation. Uncertainties quoted represent 2rerrors
of the mean. The isotopic ratios
87
Rb/
86
Sr and
147
Sm/
144
Nd were derived from Rb/Sr and Sm/Nd
ratios obtained following RbSr and SmNd
concentration measurements performed by XRF and
INAA, respectively. The assigned uncertainties to
87
Rb/
86
Sr and
147
Sm/
144
Nd are 1 and 7%, respectively,
with an uncertainty on Rb, Sr, Sm, and Nd
measurements of 1, 0.4, 2, and 5%, respectively (Son
and Koeberl 2005; Mader and Koeberl 2009; Nagl and
Mader 2019).
RESULTS
Petrography
Granites and Granite Clasts
The investigated samples mainly consist of
equigranular coarse-grained, holocrystalline and
phaneritic leucogranite. The bulk mineral assemblage is
mainly composed of orange to brownish K-feldspar
(orthoclase, ~2550 vol%); plagioclase (~1535 vol%);
quartz (~1535 vol%); and, to a lesser extent, biotite
(generally 15 vol%). Two samples (156R3_1115 and
272R1_2830.5) display a higher biotite content of
~10 vol%. The grain size varies from ~0.5 to 4 cm for
K-feldspar, plagioclase, and quartz, and from ~0.1 to
1 cm for biotite (Figs. 3 and 4). Textural and
compositional variations are common throughout the
granite unit. The main accessory minerals are
muscovite, (fluor)apatite, titanite, secondary epidote
(piemontite) located in cataclasite areas or associated
with calcite veins, zircon, (titano)magnetite, and allanite.
Other accessory minerals, including monazite, ilmenite,
rutile, chalcopyrite, cobaltoan pyrite, stolzite/raspite,
galena, uranothorite, and uranothorianite, were also
detected during an SEM survey (Fig. 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
fractures.
The granite unit is pervasively deformed to different
degrees from one sample to another, ranging from not
or slightly deformed to displaying strong mineral
deformation associated with foliation, this ductile
deformation is thought to be pre-impact, providing
evidence for local shear zones cutting the granite (see
Fig. 3B). In addition, fracturing and shearing that
occurred during the impact are abundant, as well as the
presence of cataclasite veins made of microbrecciated
material (mainly submillimeter-sized feldspars and
quartz grains, as well as calcite) cross-cutting the granite
(from millimeter to several centimeters in thickness, see
Figs. 3C, 3D, and 4). In some cases, the cataclasites
exhibit a greenish color associated with the presence of
secondary epidote (piemontite), likely due to
hydrothermal alteration (Kring et al. 2020). Postimpact
calcite veinlets commonly cut through the granite
samples. These veinlets are clearly indicated by µXRF
mapping (Fig. 6). In addition, calcite fillings are
observed in some planar fractures (PFs) within quartz
grains (see also Ferri
ere et al. 2017; Feignon et al.
2020).
Impact-induced shock metamorphic features are
apparent in most rock-forming minerals, that is,
multiple sets of PFs, feather features (FFs), in average
2.8 sets of planar deformation features (PDFs),
undulose extinction, and occasional kinkbanding in
quartz grains (for details, see Feignon et al. 2020); in
alkali-feldspar 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. 4DF).
Chicxulub peak ring granite chemistry 1251
Granite Breccias
Two of the investigated samples consist of
monomict granite breccia. The upper sample (96R2_50
52, 748.7 mbsf) is made of subrounded, ~0.5 mm
mineral clasts (mainly quartz and K-feldspar) with rare
occurrence (<2 vol%) of biotite (Figs. 3F and 6E). The
matrix (~45 vol%) is made of brecciated quartz; K-
feldspar; and, to a lesser extent, calcite. The clastic
breccia shows no signs of melting.
The second sample (278R1_4345, 1256.0 mbsf) is
similarly brecciated (with ~50 vol% of matrix), but
more strongly deformed than 96R2_5052, with a clear
mylonitic-like texture. In addition, the breccia is in
contact with a large, 7 cm sized, coarse-grained granite.
Aplites
Samples 147R2_03 and 242R3_2326 (875.7 and
1149.0 mbsf, respectively) are aplites with a fine-grained
(average mineral size is <1 mm), homogeneous,
equigranular texture (Fig. 3E). The main mineral phases
are K-feldspar, quartz, and plagioclase whereas biotite
is nearly absent (<1 vol%). Plagioclase exhibits
sericitization and some calcite veins crosscut the
samples. Shock features in the form of PFs and up to
1 cm
1 cm
Qz
Kfs
Pl
Bt/Chl
142R2_105–109 (861.9 mbsf)
153R1_47–50.5 (890.8 mbsf)
297R1_36–38 (1313.4 mbsf)
147R2_0–3 (875.7 mbsf)
96R2_50–52 (748.7 mbsf)
276R2_62–64.5 (1250.9 mbsf)
1 cm
1 cm
Cataclasite
1 cm
Cataclasite
1 cm
(A) (B)
(C) (D)
(E) (F)
Fig. 3. Macrophotographs of the different sample types from the “lower peak ring” section of the Hole M0077A core
investigated in this study. A) Coarse-grained granite, relatively undeformed with limited fracturing, exhibiting the typical
paragenesis: K-feldspar (Kfs), quartz (Qz), plagioclase (Pl), biotite (Bt), and chlorite (Chl). B) Highly deformed granite sample
with foliated minerals. C and D) Granite samples cross-cut by centimeter-sized cataclasite veins made up of microbrecciated
material. The alteration is occurring mainly at the contact between the granite and cataclasite in (D), with greenish
mineralization. E) Typical aplite sample with a fine-grained mineralogy and a low-biotite content. F) One of the two investigated
granite breccia samples comprises a greenish-gray matrix with mainly K-feldspar and quartz as mineral clasts. (Color figure can
be viewed at wileyonlinelibrary.com.)
1252 J.-G. Feignon et al.
three sets of PDFs are observed in quartz grains, while
shock microstructures are in some cases also observed
in plagioclase.
Geochemistry
Major element contents of all investigated granitoid
samples are presented in Table 1 and averaged trace
element compositions for each type of sample (i.e.,
granite from the main unit, granite clast, granite
breccia, and aplite) are presented in Table 2. Trace
element compositions for all 41 investigated samples are
reported in Data S1 in supporting information.
Strontium and Nd isotopic data are reported in
Table 3. In order to allow a discussion of the
geochemical patterns of the investigated samples, the
contents of selected major (SiO
2
,Al
2
O
3
, CaO, and K
2
O)
and trace (Ba, Sr, Zr) elements,
87
Sr/
86
Sr and (e
Nd
)
t=0
400 μm
500 μm
Qz
Kfs
PF
142R2_105–109 (861.9 mbsf)
140R2_102–105 (855.6 mbsf)
201R1_70–74 (1022.2 mbsf)
164R2_110–115 (920.2 mbsf)
183R1_20–23 (969.9 mbsf)
229R2_62–67.5 (1107.2 mbsf) 1 mm
500 μm
Cataclasite
FFs
PF
PDF
PDF
PDF
Pl Qz
Ser
Kfs
Ttn
Qz
Ep
Pl
200 µm
PDF
PDF
PDF
PF
Ttn
Pl + Ser
Bt
200 μm
400 μm
(A) (B)
(C) (D)
(E) (F)
Fig. 4. 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.)
Chicxulub peak ring granite chemistry 1253
have been plotted against depth from 745.1 to
1333.7 mbsf (Fig. 2). The LOI recorded for all the
samples is relatively low (<2.6%, average of
0.91 0.55%, n=41); thus, the data were not
recalculated on an LOI-free basis, as this would not
change the major element contents significantly.
Interestingly, the highest LOI values (>1.5%) are
observed for samples located in proximity (<0.5 m) of
fractures, shearing areas, and/or dikes (both pre- and
postimpact in origin), supporting more pronounced
granite alteration near these features, as observed in the
petrographic investigations.
Major Elements
Major elements show broadly similar patterns with
few exceptions (see Fig. 7), independently of the sample
type (granite, granite clast, granite breccia, or aplite) or
the depth in the drill core (Fig. 2), and represent the
most evolved lithology compared to pre-impact dikes,
suevites, and impact melt rocks (Morgan et al. 2017).
Nearly all the samples show a granitic composition,
with the SiO
2
and total alkali (Na
2
O+K
2
O) contents
ranging from 69.68 to 77.45 wt% and from 6.85 and
9.38 wt%, respectively. Two samples plot outside the
granite field and display a monzo-granitic composition
with 156R3_1115 having the lowest SiO
2
content
(66.66 wt%) and 8.97 wt% total alkalis, whereas
116R2_5862 shows the highest total alkali content
(9.63 wt%) and 69.73 wt% SiO
2
. The investigated
granitoid sample suite spreads between the calc-alkaline
and the high-K calc-alkaline series (Ewart 1982), with
K
2
O contents ranging from 2.27 to 5.16 wt%. The
Al
2
O
3
contents show a continuous, decreasing trend
from 16.06 to 11.55 wt% and are accompanied by
increasing SiO
2
concentrations. A less pronounced
decreasing trend can be noticed for CaO concentration
(0.703.04 wt%), while other major elements in the
investigated samples do not show a clear trend with
increasing SiO
2
concentrations but exhibit rather
relatively low and homogeneous compositions with
limited variations in the Fe
2
O
3
*(0.552.55 wt%), TiO
2
(0.050.38 wt%), and MgO (0.071.32 wt%) contents,
highlighting the evolved nature of these samples relative
to the other lithologies present in the drill core (i.e.,
suevites, impact melt rocks, and pre-impact dikes, such
as dolerite and dacite; see e.g., Morgan et al. 2017; de
Graaff et al. 2021). Additionally, the very high SiO
2
contents of all granite samples characterized here
indicate a higher degree of fractionation.
The main outlier is sample 156R3_1115, the least
evolved sample with a quartz-monzonite composition,
having the highest contents in Fe
2
O
3
(3.76 wt%), MgO
(1.35 wt%), TiO
2
(0.48 wt%), and P
2
O
5
(0.34 wt%) of
the investigated sample suite. These relatively high
contents can be explained petrographically, as this
sample contains ~10% of biotite; additionally, apatite
Qz
Or
142R2_105–109 (861.9 mbsf)
200 μm
QzTtn
Ttn Ttn
Ilm
Ap
Zrn
Aln
Fig. 5. SEM backscattered electron (BSE) image of an
assemblage of the most commonly encountered accessory
minerals in the investigated granite samples. Qz =quartz;
Or =orthoclase; Ttn =titanite; Ap =apatite; Zrn =zircon;
Aln =allanite; Ilm =ilmenite. (Color figure can be viewed at
wileyonlinelibrary.com.)
Fig. 6. Micro-XRF overview of representative investigated granitoid samples thick sections. A) Multi-element (FeSiCaK)
maps of eight samples. The upper row displays four granites from the main unit, highlighting some of the textural differences.
The granite sample 134R3_7579 is in contact with a dolerite dike and crosscut by several calcite veins. A large cataclasite vein
occurs in sample 153R1_4750.5. Iron is more abundant at the contact between cataclasite and granite while the matrix is
relatively enriched in K, thus dominated by brecciated K-feldspar; then quartz; and, to a lesser extent, calcite (Ca-rich area
within the cataclasite). The lower row shows two granite clasts, one aplite, and one granite breccia samples. The bulk
geochemistry of all these samples is fairly similar; however, the main differences are textural (i.e., deformation; alteration
features; or, to a lesser extent, interaction with impact melt rock or dike). B) Strontium distribution map (heatmap) of the same
samples shown in (A). The plus and minus on the color scale indicate a high or a low abundance of Sr, respectively. These eight
granitoid samples were mapped simultaneously, resulting in a semiquantitative distribution of Sr. Strontium contents display
variations from one sample to another. While it is mostly concentrated in plagioclase, a relatively higher Sr content is observed
in the Ca-rich area of the cataclasite. The lower Sr content in granite clast 295R2_5153 is also confirmed by INAA and isotopic
analysis (Table 3). Scanned images of thick sections are available in Fig. S1 in supporting information. IMR =impact melt rock.
(Color figure can be viewed at wileyonlinelibrary.com.)
1254 J.-G. Feignon et al.
134R3_75–79 (846.9 mbsf)
Granite (main unit)
+ Dolerite
Granite
Dolerite
Granite (main unit)
+ Cataclasite
Granite (main unit)
highly deformed
Granite (main unit)
+ Impact melt rock zones
Cataclasite
IMR
Granite clast
in impact melt rock
Granite clast in impact
melt-bearing breccia
Granite
IMR
Aplite Granite breccia
153R1_47–50.5 (890.8 mbsf) 276R2_62–64 (1251.0 mbsf) 298R1_4.5–6.5 (1316.1 mbsf)
95R1_84–87 (744.8 mbsf) 295R2_51–53 (1308.5 mbsf) 147R2_4–6 (875.8 mbsf) 96R2_50–52 (748.7 mbsf)
2 cm
(A)
Fe
Si
K
Ca
Calcite vein
(B)
2 cm
134R3_75–79 (846.9 mbsf) 153R1_47–50.5 (890.8 mbsf) 276R2_62–64 (1251.0 mbsf) 298R1_4.5–6.5 (1316.1 mbsf)
95R1_84–87 (744.8 mbsf) 295R2_51–53 (1308.5 mbsf) 147R2_4–6 (875.8 mbsf) 96R2_50–52 (748.7 mbsf)
Sr
-
+
Chicxulub peak ring granite chemistry 1255
and titanite grains are also relatively more abundant
than in the other investigated samples.
The relatively high CaO content (2.093.04 wt%)
observed in four granite and in one granite breccia
samples can be explained by (1) the presence of calcite-
filled fractures, evidenced by the µXRF mapping of
sample 134R3_7579 (Fig. 6A), the sample with the
highest measured CaO contents (3.04 wt%), and the
significant presence of calcite in the matrix of the
granite breccia sample (see Fig. 6A), respectively, and/
or (2) a higher proportion of plagioclase as is the case
for sample 156R3_1115, which displays ~35 vol%
plagioclase and a lower abundance of calcite veins
relative to the other CaO-rich granites.
Based on the Al
2
O
3
/(Na
2
O+K
2
O) versus Al
2
O
3
/
(CaO +Na
2
O+K
2
O) diagram (see Fig. 10), the
investigated samples are metaluminous to weakly
peraluminous. The K
2
O/Na
2
O ratios of the granitoids
range from 0.42 to 1.30, with an average of 0.84 0.21.
Trace Elements
Concerning trace element contents presented in CI-
chondrite-normalized diagrams (Fig. 8), with
normalization values from McDonough and Sun (1995),
the granites from the main unit (Fig. 8A) show similar
patterns to one another and to literature data (Zhao
et al. 2020; de Graaff et al. 2021), with enriched
compositions relative to CI-chondritic values. Fluid-
mobile elements, such as Ba and U, are highly enriched,
with samples 298R1_4143 and 300R1_7879.5, located
in the lower part of the basement (1316.5 and
1323.1 mbsf, respectively), and highly fractured,
Table 2. Averages and range of trace element contents (all in ppm) for each of the investigated sample types from
the Expedition 364 Chicxulub drill core (i.e., granites from the main unit, granite clasts, granite breccias, and
aplites) as obtained using INAA and bulk XRF. Detailed results for each sample are available in Data S1.
Granites (n=33) Granite clasts (n=4) Granite breccias (n=2) Aplites (n=2)
Average Range Average Range Average Range Average Range
Sc 3.07 1.577.82 3.20 2.724.06 4.16 3.844.49 2.72 1.983.46
V*28.8 12.576.0 26.6 18.430.1 42.6 36.448.7 10.8 6.7014.8
Cr 11.4 7.2721.2 10.8 9.6711.8 20.9 10.930.9 6.26 5.417.10
Co 3.33 1.2210.1 3.45 1.916.45 4.52 3.425.62 0.72 0.520.92
Ni*3.91 1.8010.2 4.45 2.707.10 9.40 4.6014.2 0.70 0.500.90
Cu*18.4 8.40123 13.1 9.9019.0 17.1 12.221.9 13.8 11.016.5
Zn*26.2 4.0089.8 17.4 6.3025.6 20.5 11.929.0 10.6 7.3013.8
As*1.50 b.d.l.3.10 2.27 b.d.l.4.60 2.20 1.403.00 1.75 1.701.80
Rb*126 87.1171 129 101159 122 122122 181 175187
Ba*468 229847 391 211532 343 266420 176 170182
Th*11.4 5.2020.0 15.3 8.9026.3 11.4 9.7013.1 15.1 13.616.5
U*7.50 3.8030.2 6.20 2.909.20 6.10 5.207.00 8.10 5.3010.9
Nb*6.49 3.2012.2 6.13 5.507.00 7.05 5.608.50 12.5 11.813.2
Ta 0.60 0.300.95 0.59 0.460.76 0.65 0.520.79 1.55 1.141.97
La 15.0 2.1030.5 11.3 4.6014.4 16.7 12.720.7 7.50 10.44.50
Ce 29.6 9.7056.2 26.3 10.134.0 27.3 26.328.3 13.6 10.616.5
Pb*25.3 13.498.5 22.6 17.533.3 152 24.1280 32.7 26.239.2
Sr*351 200491 321 195450 311 270352 185 179192
Nd 11.2 4.0023.0 11.3 8.4013.0 15.1 15.015.3 7.10 5.808.30
Zr*103 69.2204 94.9 78.4117 110 97.3123 52.7 52.652.8
Cs 1.51 0.754.87 1.18 0.571.50 1.19 1.101.30 1.52 1.381.67
Hf 3.08 2.035.91 2.74 2.423.38 3.51 3.063.97 2.74 2.632.86
Sm 2.38 1.095.96 2.39 1.743.10 2.80 2.543.10 2.48 2.662.29
Eu 0.45 0.270.85 0.46 0.340.60 0.53 0.460.60 0.40 0.400.40
Gd 2.03 1.034.56 1.87 1.242.52 1.96 1.322.60 2.00 1.542.46
Tb 0.16 0.100.36 0.16 0.130.20 0.21 0.190.20 0.23 0.200.26
Yb 0.60 0.231.04 0.55 0.350.70 0.62 0.480.76 0.75 0.610.90
Y*5.97 3.7010.9 6.45 5.607.50 8.05 6.809.30 7.20 6.208.20
Lu 0.08 0.050.14 0.09 0.060.10 0.11 0.080.14 0.10 0.100.10
K/Rb 256 158319 282 250332 249 234264 193 192194
Sr/Y 62.2 36.6123 49.8 29.659.9 40.4 29.051.8 26.4 21.830.9
(La/Yb)
N
19.0 2.8540.9 15.8 4.6425.9 20.3 11.329.4 7.50 3.4011.6
b.d.l. =below detection limit.
*Measured with XRF.
1256 J.-G. Feignon et al.
Table 3. RbSr and SmNd isotopic compositions of 14 granites and two granite clasts from the Expedition 364 Chicxulub drill core.
Sample
Depth
(mbsf)
Rb
(ppm)
Sr
(ppm)
87
Rb/
86
Sr
a87
Sr/
86
Sr
b
(
87
Sr/
86
Sr)
t=326Ma
Sm
(ppm)
Nd
(ppm)
147
Sm/
144
Nd
a 143
Nd/
144
Nd
c
e
Ndd
(e
Nd
)
t=326Ma
T
NdDM
(326Ma)
(Ga)
e
Granites
97R3_1012.5 752.5 143 333 1.2431 0.709614 0.70385 1.73 10.0 0.1025 0.512410 4.4 0.5 1.1
125R1_4042.5 826.7 132 374 1.0217 0.708963 0.70422 1.70 8.03 0.1285 0.512470 3.3 0.4 1.1
136R2_2025 851.4 114 447 0.7382 0.707975 0.70455 1.09 4.10 0.1607 0.512484 3.0 1.5 1.2
142R3_4850 862.6 124 384 0.9347 0.708807 0.70447 4.09 23.0 0.1075 0.512424 4.2 0.5 1.1
153R1_4750.5 890.8 125 269 1.3452 0.709801 0.70356 2.00 10.0 0.1209 0.512449 3.7 0.5 1.2
156R3_1115 902.1 171 404 1.2254 0.710231 0.70454 1.20 19.0 0.0382 0.512464 3.4 3.2 0.8
176R2_112116 953.6 159 231 1.9933 0.713210 0.70396 1.94 14.0 0.0838 0.512433 4.0 0.7 1.0
200R3_12.515 1021.0 109 368 0.8573 0.708447 0.70447 2.47 13.9 0.1074 0.512439 3.9 0.2 1.1
229R2_6267 1107.2 89 319 0.8075 0.708159 0.70441 2.02 14.0 0.0872 0.512467 3.3 1.2 0.9
266R2_95.598.5 1220.5 106 444 0.6910 0.707981 0.70477 2.16 16.0 0.0816 0.512436 3.9 0.8 1.0
280R2_51.553.5 1263.5 163 220 2.1457 0.713705 0.70375 2.80 10.4 0.1628 0.512477 3.1 1.7 1.2
297R1_3638 1313.4 167 265 1.8248 0.712105 0.70364 1.36 4.00 0.2055 0.512454 3.6 4.0 1.4
299R1_52.555.5 1319.7 118 200 1.7083 0.711652 0.70373 1.39 9.00 0.0934 0.512447 3.7 0.6 1.0
300R1_7879.5 1323.1 162 291 1.6118 0.711322 0.70384 3.25 11.8 0.1659 0.512449 3.7 2.4 1.2
Granite clasts
285R2_2628.5 1278.7 113 317 1.0319 0.709111 0.70432 3.10 12.6 0.1487 0.512447 3.7 1.7 1.2
295R2_5153 1308.5 159 195 2.3614 0.713686 0.70273 1.82 13.0 0.0846 0.512440 3.9 0.8 1.0
a
Uncertainties on
87
Rb/
86
Sr and
147
Sm/
144
Nd are 1.0% and 5.0%, respectively.
b
The uncertainty on
87
Sr/
86
Sr ratio is 2r=0.000004.
c
The uncertainty on
143
Nd/
144
Nd ratio is 2r=0.000004.
d
Calculated using
143
Nd/
144
Nd
CHUR
=0.512638 (DePaolo and Wasserburg 1976). CHUR =chondritic uniform reservoir.
e
Two-stage Nd model age calculated following the method of Liew and Hofmann (1988) with
143
Nd/
144
Nd
DM
=0.513151,
147
Sm/
144
Nd
DM
=0.219, and
147
Sm/
144
Nd
CC
=0.12.
DM =depleted mantle; CC =continental crust.
Chicxulub peak ring granite chemistry 1257
0
2
4
6
8
10
12
14
N
a2
O
+
K
2O (wt.%)
Syenite
Quartz
Monzonite
Quartzolite
Granite
Granodiorite
7
9
11
13
15
17
19
21
Al
2
O
3
(wt.%)
0
1
2
3
4
5
Fe
2
O
3
* (wt.%)
0
0.5
1
1.5
2
Mg
O
(
wt.
%)
0
1
2
3
65 75 85
CaO (wt.%)
SiO
2
(wt. %)
0
0.1
0.2
0.3
0.4
0.5
0.6
65 75 85
TiO
2
(wt.%)
SiO
2
(wt. %)
Granite (main unit) Granite clast Granite breccia Aplite
Granite (main unit, Zhao et al., 2020; de Graaff et al., 2021)
Granite clast (Y6, Kettrup and Deutsch, 2003)
Granite clast (de Graaff et al., 2021)
Gneiss clast (Y6, Kettrup and Deutsch, 2000, 2003)
(A) (B)
(C) (D)
(E) (F)
Fig. 7. A) Total alkalis versus SiO
2
(TAS) diagram (upper left) modified from Middlemost (1994). BF) Harker diagrams of
Al
2
O
3
,Fe
2
O
3
*(total ferrous Fe), MgO, CaO, and TiO
2
versus SiO
2
for the investigated granite, granite clast, granite breccia,
and aplite samples.
1258 J.-G. Feignon et al.
showing values more than 1000 times the CI-chondritic
value for U, whereas a depletion of Pb is observed for
nearly all the samples. In contrast, Nb and Ta show a
relative depletion, while Zr and Hf show a moderate
enrichment, relative to neighboring trace elements, a
pattern typical of arc-type magmatism (Pearce et al.
1984). Otherwise, the granites are mainly characterized
by light rare earth elements (LREE) with concentrations
higher than 10 times CI-chondritic values and lower
contents of heavy rare earth elements (HREE), below
10 times the CI-chondritic values, and displaying a
relatively flat pattern. No pronounced positive or
negative Eu anomalies were recorded. Additionally, Yb
shows a slight negative anomaly relative to Er and Y
(Yb*is 0.81 0.30, Yb*=Yb
N
/[Er
N
9Y
N
]
0.5
,n=33)
in some of the samples. While similar Yb negative
anomalies may previously have been observed, Yb is
more slightly depleted relative to Lu in the samples
investigated by Zhao et al. (2020) and de Graaff et al.
(2021), and thus, an analytical artifact cannot be fully
excluded here. Negative Yb anomalies require highly
reducing conditions to occur and are typically coupled
with clear Eu anomalies (Hsu 2003), which are not
observed in our samples. Finally, some samples show
either a depletion or an enrichment in some elements
relative to the large majority of the granites. Sample
136R2_2025 is depleted in La and Nd (an Nd
depletion is also observed for 297R1_3638), whereas
sample 153R1_4750.5 exhibits no depletion in Pb
compared to the other investigated samples.
The trace element compositions of the granite clasts
are plotted in Fig. 8B. The concentrations for the
plotted elements are within the range of the investigated
granite samples from the main unit, with only sample
95R2_1922 showing a small depletion in La and Ce
and an enriched Sr composition compared to the other
clasts investigated.
The trace element contents of the two investigated
granite breccia samples are shown in Fig. 8C. Sample
278R1_4345 does not exhibit any significant differences
compared to the main granite suite, whereas sample
96R2_5052 shows a clear enrichment in Pb (280 ppm
relative to the <99 ppm in the main granite group),
which may be explained by the presence of a Pb-bearing
phase (e.g., sulfide minerals). These secondary phases
are commonly observed in the impact melt-bearing
breccias (see Kring et al. 2020), making this Pb-
enrichment secondary. The Pb composition of this
specific sample (as for granite 153R1_4750.5) is similar
to that of the “upper impact melt rock” sample
100_2_89.5_91.5 investigated by de Graaff et al. (2021)
and may have a similar secondary Pb-enriched
component.
The two investigated aplites (Fig. 8D) have trace
element composition patterns somewhat similar to those
of the granites, with only a slight enrichment in Ta and
a depletion in Ba and Zr concentrations. Sample
147R2_03 is also slightly depleted in La concentrations
compared to the granites. However, in bivariate
immobile trace element diagrams (Fig. 9), the aplites
plot slightly outside of the main trend as defined by the
granites; the difference is even more striking in the Ta
versus Nb diagram (Fig. 9B).
SrNd Isotopic Ratios
In the 16 investigated granite samples (including
two granite clasts from the lower part of the core;
samples 285R2_2628.5 and 295R2_5153), the element
concentrations range from 89 to 171 ppm Rb, 195 to
447 ppm Sr, 1.1 to 4.1 ppm Sm, and 4.1 to 23 ppm Nd.
The granite clasts do not have distinct RbSr/NdSm
concentrations relative to the main granite group
(Table 3). The Rb/Sr and Sm/Nd ratios vary from 0.24
to 0.82 and from 0.14 to 0.27, respectively. Only granite
156R3_1115 shows a lower Sm/Nd ratio of 0.06.
The present-day
87
Sr/
86
Sr ratios show a clear
variability, ranging from 0.70798 and 0.71371 (Table 3).
Interestingly, the samples located close to the bulk of
the LIMB, in the lower part of the granite unit (at
1263.5 mbsf, n=6), where several impact melt rock and
suevite dikes occur, and where the granite exhibits
higher degrees of deformation relative to the upper
samples, generally display more radiogenic compositions
than in the upper part (n=10), with average
87
Sr/
86
Sr
of 0.711930 and 0.709319, respectively. Only sample
176R2_112116 (953.6 mbsf) has a distinct, more
radiogenic composition in the upper part of the granite
unit, with an
87
Sr/
86
Sr of 0.713210. This particular
sample is characterized by the presence of 23mm
cataclasites and is near a contact with a 10 cm thick,
pervasive, shear zone. The
87
Rb/
86
Sr ratios range from
0.6910 to 2.3614. Samples in close proximity to the
LIMB display a generally higher
87
Rb/
86
Sr ratio
(average of 1.7807) compared to the samples located in
the upper part of the granite unit (average of 1.0857).
The investigated samples form an isochron between
87
Sr/
86
Sr and
87
Rb/
86
Sr (see Fig. 11C). Given the
estimated errors on the
87
Sr/
86
Sr and
87
Rb/
86
Sr ratios,
the isochron has a very high scattering with a mean
square of weighed deviates (MSWD) of 25. The MSWD
of the isochron is well above the value for a statistically
acceptable isochron, defined at <~2.5 by Brooks et al.
(1972), and, thus, should be considered to represent an
errorchron, indicating that the RbSr system has not
been completely reset. The apparent regression age is
calculated to be 273 21 Ma, with an initial
87
Sr/
86
Sr
Chicxulub peak ring granite chemistry 1259
1
10
100
1 000
10,000
Rb Ba Th U Nb Ta La Ce Pb Pr Sr Nd Zr Hf Sm Eu Gd Tb Dy Ho Er Yb Y Lu
Granite (CI-chondrite normalized)
Granite (Zhao et al., 2020;
de Graaff et al., 2021)
Granite
136R2_20-25
153R1_47–50.5
1
10
100
1 000
10,000
RbBaThU NbTaLaCePbPrSrNdZr HfSmEuGdTbDyHoErYbY Lu
Granite breccia (CI-chondrite normalized)
Granite
Granite breccia
96R2_50–52
1
10
100
1 000
10,000
RbBaThU NbTaLaCePbPrSrNdZr HfSmEuGdTbDyHoErYb Y Lu
Granite clast (CI-chondrite normalized)
Granite
Granite clast
95R2_19–22
1
10
100
1 000
10,000
Rb Ba Th U Nb Ta La Ce Pb Pr Sr Nd Zr Hf Sm Eu Gd Tb Dy Ho Er Yb Y Lu
Aplite (CI-chondrite normalized)
Granite
Aplite
242R3_23–26
147R2_0–3
(A)
(B)
(C)
(D)
1260 J.-G. Feignon et al.
of 0.705164 0.0003. However, given the high
uncertainty on age determination and its deviation from
the well-constrained UPb Carboniferous ages obtained
in zircons by Zhao et al. (2020) and Ross et al. (2021),
this apparent age obtained from the errorchron
corresponds to a disturbance of the RbSr system (see
the Discussion section).
In contrast, current
143
Nd/
144
Nd ratios display
limited variations (0.5124100.512484) and (e
Nd
)
t=0
values plot in a narrow range between 4.4 and 3.0
for all the investigated samples. The corresponding
147
Sm/
144
Nd ratios vary from 0.0816 to 0.2055, while
granite sample 156R3_1115 shows a lower
147
Sm/
144
Nd
ratio of 0.0382 (Table 3). There is no significant
difference observed between samples in the upper part
of the granite unit and the samples in the lower part,
next to the LIMB, indicating that Nd remained mostly
unaffected by alteration processes.
Based on the work of Zhao et al. (2020), the initial
87
Sr/
86
Sr and e
Nd
are calculated using t=326 Ma.
Initial (
87
Sr/
86
Sr)
t=326Ma
are 0.702730.70477, while
(e
Nd
)
t=326Ma
vary from 4.0 to 3.2 (see Fig. 11A). The
Nd two-stage model age (DePaolo 1981; Liew and
Hofmann 1988) T
DM2(326Ma)
ranges between 0.8 and
1.4 Ga. The model ages are relatively similar for all
samples (Table 3).
DISCUSSION
Granite Characterization
In general, the granitoids investigated in this study
(i.e., granites, granite clasts, brecciated granites, and
aplites) are relatively homogeneous in terms of their
major element content (i.e., limited variations in
composition or well-defined compositional trends). Only
a single outlier compared to the other granitoids, the
quartz-monzonite sample (156R3_1115), with higher
major element contents other than SiO
2
,aswellas
enrichments in Zr and Hf, is noted. The relatively high
proportion of plagioclase (~35 vol%), biotite (~10 vol%),
and zircon may explain the distinct chemical
composition of this sample. No samples with clearly
distinct compositions were identified, suggesting that the
investigated granite clasts all belong to the main granite
unit, and that the granite breccias did not experience
significant interaction with lithologies other than granite
during their emplacement. Additionally, the textural
variations (i.e., degree of deformation, presence of
cataclasite veins) observed during petrographic
investigations (see the Petrography section 4.1) within
the main granite unit do not significantly affect the
major element contents. As a result, for simplicity, all
the investigated samples are from here onward termed
“granite” (whether they are granite clasts or granite
breccia samples; also including the aplite samples
[except where indicated], which are a fine-grained
equivalent of granite).
The granite samples are characterized by a
decreasing Al
2
O
3
and, to a lesser extent, CaO content,
with increasing degrees of differentiation, as is
commonly associated with fractionation of plagioclase
(Langmuir et al. 1992; Sisson and Grove 1993),
although the variation of modal mineral components
(mainly the K-feldspar content relative to plagioclase)
may contribute, to some extent, to these trends.
However, the Al
2
O
3
contents are relatively high,
indicating a retention of plagioclase in the granite,
albeit to a limited extent as no positive Eu anomaly is
observed in any of the investigated samples. This
observation further supports that the granites represent
intrusions rather than cumulates (see also de Graaff
et al. 2021). None of the samples investigated in this
study display a distinct trace element composition that
would either suggest interaction with other lithologies
within the core (i.e., impact melt rock or pre-impact
volcanic dikes) or a distinct granite type other than arc
derived, implying that the granites sampled in the Hole
M0077A core are related to a single magmatic intrusion
event.
Our petrographic investigations and previous
studies have highlighted the pervasive alteration of the
recovered rocks from IODP-ICDP Expedition 364 drill
core (Morgan et al. 2017; Simpson et al. 2020; de
Graaff et al. 2021), following the onset of a long-living
hydrothermal system (Kring et al. 2020) that could have
affected the whole rock compositions, especially the
mobile elements like Ba, Rb, and U. Immobile
incompatible elements, especially high field strength
elements (HFSE) like Zr, Hf, Nb, and Ta, are less
affected by alteration processes, and can thus be used to
trace the magmatic signatures of the granite samples
Fig. 8. AD) CI-chondrite-normalized trace element compositions, with normalization values from McDonough and Sun (1995).
A) The blue area in the upper diagram represents the compositions from previous work made on granite from the M0077A core
(Zhao et al. 2020; de Graaff et al. 2021). BD) The gray outline represents the main composition of all the granite samples
investigated in this study, to allow a comparison with the granite clast, breccia, and aplite samples. Investigated samples have
highly similar patterns, except one granite breccia with a significant Pb positive anomaly that may due to the presence of a Pb-
bearing phase. (Color figure can be viewed at wileyonlinelibrary.com.)
Chicxulub peak ring granite chemistry 1261
R² = 0.877
0
1
2
3
4
5
6
7
8
9
0 100 200 300 400
Hf (ppm)
Zr (ppm)
R² = 0.742
0
5
10
15
20
25
0 0.5 1 1.5 2 2.5
Nb (ppm)
Ta ( p p m )
R² = 0.011
0
5
10
15
20
25
30
35
0 100 200 300 400
Th (ppm)
Zr (ppm)
R² = 0.011
0
500
1000
1500
2000
2500
0 100 200 300 400
Ba (ppm)
Zr (ppm)
R² = 0.717
0
5
10
15
20
25
0 5 10 15 20 25
Y (ppm)
Nb (ppm)
R² = 0.028
R² = 0.324
0
50
100
150
200
250
0100200300400
Rb (ppm)
Zr (ppm)
Granite (main unit) Granite clast Granite breccia Aplite
Granite (main unit, Zhao et al., 2020; de Graaff et al., 2021)
Granite (main unit) linear regression curve
Granite clast (de Graaff et al., 2021)
Granite (main unit) linear regression curve (excluding sample 156R3_11–15)
156R3_11–15
(A) (B)
(C) (D)
(E) (F)
Fig. 9. AF) Bivariate diagrams on trace element variations in granite samples. The trend line is calculated based on the main
granite unit samples only. Zr versus Hf, Ta versus Nb, and Nb versus Y show strong covariations with R
2
above 0.7. The aplites
plot slightly outside the main trend. Th, Ba, and Rb abundances are more scattered. In the Rb versus Zr diagram, the dashed
trend line is calculated excluding the outlier samples enriched in Zr (i.e., sample 156R3_1115) providing a better, although still
low, covariation (R
2
of 0.324).
1262 J.-G. Feignon et al.
(e.g., Pearce et al. 1984; Pearce 2014). Strong linear
covariations for all sample groups, with the notable
exception of the aplite samples, which plot outside the
main trend, are observed between Zr and Hf, Ta and
Nb, and Nb and Y (Fig. 9). A similar linear correlation
is observed when plotting Zr and V versus TiO
2
content
(see Fig. S2 in supporting information). In contrast, Th,
Ba, and U contents are more scattered when plotted
versus Zr concentrations. A similar scattering is
observed for Rb, but with a slightly lower importance
than for Th, Ba, and U (Fig. 9 and Fig. S2). The
decoupling between immobile and these mobile elements
therefore indicates that they were probably affected by
alteration. Additionally, as already shown in de Graaff
et al. (2021), no covariation is observed between La and
Zr (Fig. S2) in the granites investigated, with the (La/
Yb)
N
ratio displaying strong variation (from ~3to~41)
while Yb
N
has relatively similar contents. This
observation confirms that La must have been
remobilized by alteration processes within the Chicxulub
impact structure (de Graaff et al. 2021).
In order to assess the degree of hydrothermal
alteration of the investigated samples, the K/Rb ratio
was used to discriminate between altered and less
altered granites. According to Helvaci and Griffin
(1983), less altered and unaltered crustal rocks show K/
Rb ratio <300, while in the case of hydrothermally
altered rocks, the K/Rb ratio is typically between 400
and 500. The average K/Rb ratio of the investigated
samples is of 256 for the main granite group, 282 for
the granite clasts, 249 for the granite breccias, and 193
for the aplites (Table 2). Four of the investigated
samples exhibit K/Rb ratios slightly above 300, that is,
granite clast 95R2_1922 with a K/Rb of 332, and
granite samples 110R2_1416, 116R2_5862, and
236R1_9092.5 with K/Rb of 314, 306, and 319,
respectively (Table 2). However, great care should be
taken with the use of this ratio, as, on the one hand, Rb
contents are decoupled relative to immobile elements
like Zr, and on the other hand, postimpact K-
metasomatism was clearly indicated throughout the
Chicxulub impact structure and in the entire drill core
(Hecht et al. 2004; Kring et al. 2020), and, thus, K/Rb
and Na
2
O/K
2
O ratios may not totally reflect the
original, primary magmatic signature of the Chicxulub
granites.
As described in the Trace Elements section, the
trace element contents of the granite indicate a typical
arc-like signature characterized by Ta and Nb
depletions (see also de Graaff et al. 2021) coupled with
slight Lu (HREE) enrichment relative to HREE Yb,
which is compatible with a source melted with garnet in
the residue as also reported by Zhao et al. (2020) and
de Graaff et al. (2021). Using the chemical classification
of Pearce et al. (1984) to decipher the tectonic context
of the granite formation, the Rb content is plotted
versus Y +Nb concentrations (Fig. 10B), as Rb and Nb
are affected in a similar way by mantle heterogeneities,
while Y remains unaffected. Even though some
scattering of the data is noticed, all the samples plot
within the volcanic arc granite field, close to or on the
limit with the syn-collision granite array, which may
suggest a transition between arc magmatism and a
collisional context (Fig. 10B).
Interestingly, the two investigated aplite samples
plot within the enriched-MORB array (Fig. 10C);
together with their immobile element compositions
(Fig. 9), this may suggest that the aplites were emplaced
as dikes during a distinct event, with a more “enriched-
MORB”-like source, or may result from a remelting of
granite material (e.g., through local changes in the
solidus temperature caused by fluid circulation or
during a thermal event), or may be the result of a
different crystallization stage of the granite. Further
investigations are needed in order to confirm their
origin.
The present-day more radiogenic
87
Sr/
86
Sr and
higher
87
Rb/
86
Sr ratios are observed for samples in
proximity to the LIMB (below 1263.5 mbsf), where the
granites are generally highly deformed and crosscut by
numerous, more or less thick, impact melt rock dikes,
and for sample 176R2_112116, recovered from a much
shallower depth, at 953.6 mbsf, which is in contact with
a34 mm thick cataclasite. While these more radiogenic
granites display slightly higher Rb contents (average
147 ppm) compared to the less radiogenic granites
(average 127 ppm), they display a more pronounced
depletion in Sr, with average concentrations of 357 and
258 ppm for the less radiogenic and the more
radiogenic granites, respectively. These observations
clearly indicate that the granite experienced
hydrothermal alteration, affecting both Rb and Sr
contents (as well as other mobile elements such as Ba,
Th, and U), and that the impact-related features (i.e.,
impact melt rock dikes, cataclasites, shock-induced
fractures at the mineral scale) may have enhanced the
hydrothermal fluid circulation. The mobilization and
slight enrichment in Rb (and also in other mobile trace
elements) could be attributed to hydrothermal fluid
alteration and/or to the supply of crustal material, while
the Sr depletion could be related to the hydrothermal
alteration of plagioclase, evidenced by the high level of
sericitization occurring in plagioclases (Plimer and
Elliott 1979; Cruciani et al. 2017).
However, fluid alteration by seawater alone cannot
fully explain the present-day more radiogenic
87
Sr/
86
Sr
ratios measured, as the present-day
87
Sr/
86
Sr of
seawater is estimated at ~0.709 (Veizer 1989). Thus,
Chicxulub peak ring granite chemistry 1263
hydrothermal alteration following the impact cannot
solely account for the more radiogenic
87
Sr/
86
Sr ratios
measured in 10 of the investigated samples (Table 3).
The apparent age of 273 21 Ma determined by
the whole-rock errorchron (Fig. 11C), younger than the
Carboniferous ages reported in Zhao et al. (2020) and
Ross et al. (2021), indicates that the RbSr system was
likely disrupted (i.e., open system behavior), within
~50 Myr after granite crystallization and, thus, could
account for another, older, metasomatic event that
affected the Chicxulub granite unit. Following this
event, the already altered granite was affected by
postimpact hydrothermal overprint. Moreover, this
apparent age overlaps within uncertainty with the age
0.5
1.0
1.5
2.0
0.5 0.7 0.9 1.1 1.3 1.5
Al2O3/(Na2O+K2O)
Al2O3/(CaO+Na2O+K2O)
Metaluminous Peraluminous
Peralkaline
I-Type S-Type
10
100
1000
110100
Rb (ppm)
Nb + Y
Volcanic arc
granites
Syn-collision
granites
WPG
1
10
100
1000
0.1 1 10 100
Zr/Yb
Nb/Yb
0
50
100
150
05101520
(La/Yb)
N
Archean Tonalite-Trondhjemite-
Granodiorite suites & adakites
Arc andesite, dacite and rhyolite
array
Yb
N
(A)
(C) (D)
(B)
Granite (main unit) Granite clast Granite breccia Aplite
Granite (main unit, Zhao et al., 2020; de Graaff et al., 2021)
Granite clast (Y6, Kettrup and Deutsch, 2003)
Granite clast (de Graaff et al., 2021)
Gneiss clast (Y6, Kettrup and Deutsch, 2000, 2003)
Fig. 10. A) A/NK versus A/CNK discriminating diagram, with A =Al
2
O
3
,C=CaO, N =Na
2
O, and K =K
2
O, all in molar
proportions (modified from Maniar and Picolli 1989). The majority of the investigated granites in M0077A core are
metaluminous with a weakly peraluminous character, associated with I-Type granites. Y6 clasts have a more peraluminous
affinity. None of the investigated samples show a peralkaline character. B) Rb versus Nb +Y diagram, discriminating the granite
tectonic context, as defined by Pearce et al. (1984). WPG =within-plate granite. The M0077A core granites are characterized as
volcanic arc granite, with only one sample plotting in the syn-collision granite array. C) Zr/Yb versus Nb/Yb diagram (modified
from Macdonald et al. 2000). N-MORB =normal mid-oceanic ridge basalt; E-MORB =enriched mid-oceanic ridge basalt. The
granite, granite clast, and breccia samples plot outside the MORB array, indicating that they are derived from a different source,
probably enriched. However, the two aplite samples are located in the E-MORB area, suggesting that they could have formed
from a source with a different chemical composition. D) (La/Yb)
N
versus (Yb)
N
with the typical fields for adakites and normal-
arc volcanic rocks (Martin et al. 2005). A significative number of the granite samples plots in the overlapping area between
adakites and “normal” arc-rocks. Interestingly, two granite clasts recovered by de Graaff et al. (2021) have a distinct
composition with high (Yb)
N
and low (La/Yb)
N
typical for “normal” arc volcanic rocks.
1264 J.-G. Feignon et al.
recorded in allanite, that is, 215 28 to 260 9Ma
(Wittmann et al. 2018), and, thus, probably corresponds
to the same hydrothermal event. Taking into account
these parameters, and given the high uncertainty on the
apparent age, a metamorphic/hydrothermal fluid
metasomatism during the late Triassic, possibly related
to the intracontinental extension, which occurred during
the initial breakup of Pangea (Dickinson and Lawton
2001; Steiner 2005), might be the best candidate to
explain the apparent RbSr errorchron age and allanite
ages.
The age-corrected, initial (
87
Sr/
86
Sr)
t=326Ma
and
(e
Nd
)
t=326Ma
compositions suggest that the granites may
have formed following a mixing between a mantle-
(87Rb/86Sr)t=0
1.0 1.5 2.0 2.5
0.708
0.709
0.710
0.711
0.712
0.713
Age = 273 ± 21 Ma (n=16)
(87Sr/86Sr)i = 0.705164 ± 0.00030
MSWD = 25
(87Sr/86Sr)t=0
(87Sr/86Sr)t=326Ma
0.7025 0.7035 0.7045
0.001
0.002
0.003
0.004
0.005
0.006
1/Sr
Granite samples
below 1263 mbsf
Hydrothermal radiogenic Sr enrichment
Granite (main unit)
Granite clast
Granite (main unit, Zhao et al., 2020)
Novillo orthogneiss (Patchett and Ruiz, 1987)
(87Sr/86Sr)t=326Ma
0.706 0.7080.7040.702
-15
-10
-5
0
5
10
(εNd)t=326Ma
Grenville basement
DM
EM I
Hydrothermal
event ca. 294–252 Ma (?)
Anomalously
unradiogenic
Sr composition
(295R2_51–53)
Mixing
0.2%
0.4%
0.6%
0.8%
1%
2%
10%
(A)
(B) (C)
Fig. 11. StrontiumNd isotopic compositions of 14 granite samples from the main unit and two granite clasts. M0077A granite
SrNd isotopic data from Zhao et al. (2020) are also reported for comparison. A) Initial (e
Nd
)
t=326Ma
and (
87
Sr/
86
Sr)
t=326Ma
ratios. The Grenvillian basement area is drawn from data of Patchett and Ruiz (1987) and Weber and K
ohler (1999). The
Novillo Gneiss composition is from Patchett and Ruiz (1987). The mixing model calculation, DM, and EM I compositions at
t=326 Ma are calculated from Faure and Mensing (2004), with DM =depleted mantle, and EM I =enriched mantle I. B)
Strontium concentration (expressed as 1/Sr) versus initial (
87
Sr/
86
Sr)
t=326Ma
. With increasing Sr concentration, Sr is becoming
more radiogenic and thus may be consistent with addition, a short time after granite crystallization, of radiogenic Sr (and of Rb,
to enhance this difference over time) by hydrothermal enrichment. However, the samples in proximity to the LIMB, in the lower
part of the granite unit (dashed circle) are among the least Sr-rich (and least radiogenic) and perhaps have experienced more
“recent” limited addition of Rb (related with the postimpact hydrothermal system). C)
87
Sr/
86
Sr versus
87
Rb/
86
Sr. Isochron of all
the investigated samples (n=16). A strong scattering is noticed with an MSWD of 25. The uncertainty of age and (
87
Sr/
86
Sr)
i
is
expressed with a 2rinterval.
Chicxulub peak ring granite chemistry 1265
derived component, which could be relatively similar in
composition to the Pan-African Stony Mountain gabbro
(Pollock and Hibbard 2010), as suggested by Zhao et al.
(2020), and a minor contribution of a moderately
enriched, Grenvillian, crustal component, which could
be similar to the Novillo Gneiss (Fig. 11A), located in
the Oaxaquian crust, in northeastern Mexico (Patchett
and Ruiz 1987), even though the data display some
scattering. The presence of a Grenvillian component is
suggested by the T
DM2(t=326Ma)
of 0.81.4 Ga recorded
by the samples. Additionally, the assimilation of the
Oaxaquian crust in the Pan-African granitoids of the
northern Maya block was previously suggested by
Lopez et al. (2001). Three granite samples (156R3_11
15, 229R2_6267, and 266R2_95.598.5) plot in the +ve
area (i.e., displaying positive [e
Nd
]
t=326Ma
and radiogenic
[
87
Sr/
86
Sr]
t=326Ma
, see Fig. 11A). These samples, albeit
not showing strong evidence for mineral deformation,
are cross-cut by shear fractures (however, it cannot be
excluded that these features were formed following the
impact) or, in the case of sample 229R2_6267, are in
contact with aplite, which enhanced fluid circulation.
They infer addition of radiogenic Sr but not evolved
Nd, thus indicating consistent hydrothermal fluid
metasomatism. Given the apparent Rb-Sr errorchron
and allanite ages, the Late Triassic metasomatic event
could explain these three specific compositions, by
possibly adding metasomatic Rb in a relatively short
timescale after granite crystallization. The possibility of
metasomatic
87
Rb enrichment is also indicated by the
(
87
Sr/
86
Sr)
t=326Ma
becoming more radiogenic with
increasing Sr concentration (Faure and Mensing 2004)
(Fig. 11B).
The granite clast sample 295R2_5153 displays a
distinctly lower initial (
87
Sr/
86
Sr)
t=326Ma
of 0.70273 and
not evolved (e
Nd
)
t=326Ma
of 0.8, while having the highest
87
Rb/
86
Sr (2.3614) of all investigated samples.
Petrologically, this sample is highly deformed, with
mineral ductile deformation and pervasive shear
fracture networks throughout, which could be either a
record of the late Triassic metamorphic event, or of
postimpact deformation. Addition of Rb during the
onset of the postimpact hydrothermal system, at
temperatures of ~300400 °C as estimated by Kring
et al. (2020) and Simpson et al. (2020), may explain the
particular composition of this sample, as this “recent”
Rb would not have had the time to decay. Interestingly,
granite samples from the lower part of the granite unit
(below 1263 mbsf, n=4) may also have been affected,
to a lesser extent, by this “recent” Rb enrichment
related to the postimpact hydrothermal system
(Fig. 11B), as they display more radiogenic
87
Sr/
86
Sr
(average 0.712196) and higher
87
Rb/
86
Sr (average
1.82265) compared to the granite samples in the upper
part of the granite unit (average
87
Sr/
86
Sr and
87
Rb/
86
Sr
of 0.709319 and 1.08574, respectively), and thus back-
calculate to unradiogenic (
87
Sr/
86
Sr)
t=326Ma
with an
average of 0.703740. However, the Sr depletion
observed in these granites and possibly related to
hydrothermal alteration of plagioclase (sericitization),
could also explain these compositions and may have
occurred either (or both) during the Late Triassic
metasomatic event or during the postimpact alteration,
although the latter is more probable as the Sr depletion
only occurs in the lower granite samples, in proximity
to the LIMB and cataclastites.
The available data seem to indicate that the
Chicxulub peak ring granites were affected by at least
two hydrothermal alteration/metasomatic events, that is,
a first event taking place approximately 50 Myr after
granite formation (273 21 Ma), and a second event
related to the postimpact hydrothermal alteration (as
the result of a hydrothermal system active for more
than 1 Myr after the impact event at 66.05 Ma).
However, some care should be taken in these
interpretations, as it is not possible to fully disentangle
the specific effects of the Late Triassic metasomatic
event from the postimpact hydrothermal alteration
event. In addition, the granite samples may not have
kept their original magmatic Rb-Sr isotopic signature
due to these alteration events.
Comparison with Granitoid Lithologies from the
Chicxulub Impact Structure
Geochemical data available for granitoid rocks
(clasts) from other drill cores recovered inside the
Chicxulub impact structure were compared to the
obtained results (Figs. 711). The geochemistry of nine
granite samples from the “lower peak-ring” section of
the Hole M0077A drill core was investigated by Zhao
et al. (2020), while six granites from the main unit and
18 granite clasts were investigated by de Graaff et al.
(2021). Major and trace element compositions of the
granite samples from the main unit and the majority of
the clasts in Zhao et al. (2020) and de Graaff et al.
(2021) show no significant differences from the samples
in this study, albeit a minor Eu negative anomaly with
an Eu*of 0.77 0.02 (Eu*=Eu
N
/[Sm
N
9Gd
N
]
0.5
)
was recorded in four granite clasts and one granite from
the main unit in de Graaff et al. (2021). Moreover, de
Graaff et al. (2021) describe a granitic clast with a
syenite composition (13.3 wt% Na
2
O+K
2
O), and two
granitic samples at 730.3 and 1287.8 mbsf with distinct
enrichments in the HREE and LREE contents (Fig. 8).
Additionally, these two granite clasts show a distinct Sr/
Y, (La/Yb)
N
, Y, and (Yb)
N
(Fig. 10D), which is most
comparable to “normal” arc-related rocks. The former
1266 J.-G. Feignon et al.
was interpreted to be a textural characteristic related to
it being an alkali-feldspar dominated sample while the
latter two clasts were interpreted to either reflect granite
clasts that were significantly affected by an interaction
with the host impact melt rock or they were derived
from a granitic body distinct from the main granite unit
sampled in the Hole M0077A core (de Graaff et al.
2021).
Based on the investigation of a limited number of
granite samples, Zhao et al. (2020) characterized the
granites as “adakitic rocks” due to their anomalously
high Sr/Y and (La/Yb)
N
ratios and low Y content and
low (Yb)
N
. However, the term “adakite” (or “adakitic”)
is often used to cover a large range of rocks with
different characteristics and/or formation processes
(Moyen 2009). More conservatively applied, the term
adakite is restricted to the type of rock called “high
silica adakite” (HSA), which is formed by the melting
of metabasalts from oceanic crust slab (e.g., Martin
et al. 2005). High Sr/Y and (La/Yb)
N
ratios are not the
only criteria used to define an adakite; thus, in order to
decipher the “adakitic” nature of the Chicxulub
granites, the parameters defined by Defant and
Drummond (1990), Martin et al. (2005), and Moyen
(2009) were used in this work. A comparative table
summarizes the difference between HSA rocks and the
investigated granites (Table 4).
In this study, the investigated granites yield Sr/Y
and (La/Yb)
N
ratios with wide variations, from 22 to
123 and 3 to 41, respectively. Based on (La/Yb)
N
versus
(Yb)
N
, the granites effectively plot in the adakite field as
defined in Martin et al. (2005) (Fig. 10D). However, an
overlap between adakitic compositions and “normal”
arc compositions is noticeable in this diagram, and in
addition, de Graaff et al. (2021) demonstrated that La
was mobilized by alteration processes. It is important to
highlight here that the investigated aplite samples yield
values of Sr/Y and (La/Yb)
N
of 26 and 7.5, below the
adakitic thresholds of 40 and 10, respectively (Table 4).
In addition, with Al
2
O
3
content below 15 wt%,
FeO +MgO +MnO +TiO
2
contents <7 wt%, Mg#
<50, K
2
O/Na
2
O above 0.4 (revealing a more potassic
composition), and low Cr and Ni contents (suggesting a
more evolved source), the investigated granites are
distinctly different from a typical “adakitic rock.” In
addition, in the Zr/Yb versus Nb/Yb diagram
(Fig. 10C), the granites, granite clasts, and granite
breccias plot outside the MORB array, further
supporting a contribution of an enriched (or possibly
crustal) endmember in the granite genesis. Combined
with the Nd isotopic data, this indicates a formation
process distinct from adakites (Moyen 2009). Thus, the
investigated granites should be termed high-K (high-Sr/
Y or high (La/Yb)
N
), calc-alkaline granites.
Granite-like lithologies were also sampled and
investigated in the Y6 core (Kettrup et al. 2000; Kettrup
and Deutsch 2003), that is, one granite and four
granitic gneiss clasts in the suevite. Only major element
and SrNd isotopic data are available for these clast
samples. The Y6 granite clast shows a composition
distinct from the Expedition 364 granite samples and is
highly silicic (81.9 wt% SiO
2
) and subalkaline. The
gneiss clast samples exhibit more variations with 67.9
84.3 wt% SiO
2
and have peraluminous compositions.
These distinct compositions highlight the variety of
evolved lithologies represented in the Yucat
an peninsula
crystalline basement and found as clasts in impact
breccia and impact melt rock samples.
Table 4. Comparison between the average composition of the high silica adakite (HSA) and the investigated
granites samples from the Expedition 364 Chicxulub drill core, using all the criteria defined for adakitic rocks in
addition to Sr/Y and (La/Yb)
N
ratios (Defant and Drummond 1990; Martin et al. 2005; Moyen 2009).
HSA Adakites
average values*
Average
granites
Average
granite clasts
Average
granite breccias
Average
aplites
SiO
2
(wt%) >56 73.1 74.4 71.1 74.7
Al
2
O
3
(wt%) >15 14 13 14 14
MgO (wt%) <3 0.6 0.5 0.9 0.1
FeO +MgO +MnO +TiO
2
(wt
%)
7 2.0 1.8 2.6 0.7
Mg# 50 38 41 44 22
K
2
O/Na
2
O0.4 0.8 0.9 0.8 0.9
Y (ppm) <18 6.0 6.5 8.1 7.2
Yb (ppm) <1.9 0.6 0.6 0.6 0.8
Cr (ppm) 36 19 11 26 13
Ni (ppm) 24 3.9 4.5 9.4 0.7
Sr/Y >40 62 50 40 26
(La/Yb)
N
>10 19 16 20 7.5
*As defined by Defant and Drummond (1990), Martin et al. (2005), and Moyen (2009).
Chicxulub peak ring granite chemistry 1267
While the SrNd isotopic composition recorded by
Zhao et al. (2020) is similar to our “group 1” (i.e., the
least altered granites), the SrNd isotopic ratios of the
Y6 granite and three of the gneiss clasts exhibit distinct,
more enriched crustal signatures (Fig. 11). The fourth
gneiss clast (Y6 N14 p4a) has a high (
87
Sr/
86
Sr)
t=0
of
0.732676 and chondritic (e
Nd
)
t=0
of 0.0, and represents
another, distinct component of the Yucat
an target
(Kettrup and Deutsch 2003).
The Nd model ages (one- or two-stage model ages
termed as T
DM1
and T
DM2
, respectively) calculated for
the most primitive samples (T
DM2(326Ma)
of 0.81.2 Ga)
encompass the calculated model age range of Zhao
et al. (2020), with T
DM2(326Ma)
for the granites between
1.0 and 1.1 Ga. Crystalline basement clasts recovered
within impact breccia and impact melt rocks yield T
DM1
between 0.7 and 1.4 Ga, while impact melt rocks have
T
DM1
of 1.11.2 Ga (Kettrup et al. 2000; Kettrup and
Deutsch 2003; Keppie et al. 2011). This implies that the
northern Maya block and the granite investigated here
involved Grenville-aged material during their formation
(Keppie et al. 2012).
In general, our results are consistent with previous
studies on a more limited set of samples (see Zhao et al.
2020; de Graaff et al. 2021), and further support that
the investigated granite unit could be related with arc
magmatism during the closure of the Rheic ocean and
Pangea assembly in the Carboniferous (Zhao et al.
2020; Ross et al. 2021). Conversely, a similar granite
type was not sampled in any previous drill cores,
including Y6 (Kettrup et al. 2000; Kettrup and Deutsch
2003). However, the Expedition 364 drill core offers
only a limited view of the extension of this granite unit;
thus, care should be taken when discussing geodynamic
implications of the data.
CONCLUSIONS
The granite from the “lower peak-ring” section in
the IODP-ICDP Expedition 364 Hole M0077A drill
core can be defined as coarse-grained, phaneritic with
K-feldspar (orthoclase), plagioclase, quartz, and biotite
as the main mineral phases. In addition to the main
granite unit, granite clasts, granite breccias, and aplites
and pegmatites are observed. Impact-induced
deformations are pervasive with fracturing, shearing,
and the presence of cataclasite veins and shock
metamorphic features in minerals (such as PFs, FFs,
and PDFs in quartz, but also a large set of shock
metamorphic features in all other minerals composing
the granites).
Despite numerous textural changes, the chemical
composition of the granite inside the peak ring is
broadly homogeneous and defines the studied samples
as high-K (high-Sr/Y or high [La/Yb]
N
), calc-alkaline
granites.
The major and trace element patterns suggest a
formation by fractional crystallization with moderate
plagioclase fractionation. However, initial SrNd
isotopic data reveal a more complex origin, with
admixture of a Grenvillian crust component during the
granite genesis, as suggested by the two-stage Nd model
ages T
DM2(326Ma)
of 0.81.2 Ga. Additionally, the
granite experienced a hydrothermal fluid metasomatic/
metamorphic event, indicated by the radiogenic Sr
enrichment and allanite crystallization. An apparent
errorchron age of 273 21 Ma indicates that this may
be related to the intracontinental extension that
occurred at the Yucat
an peninsula during the late
Triassic initial breakup of Pangea. However, the high
uncertainty on the apparent age may also reflect the
effect of postimpact alteration, which is also recorded in
the granites, and thus disturbed the Rb-Sr system even
more, adding complexity to the data interpretation.
Additionally, the granites in the vicinity of impact melt
rock or cataclasite dikes, mainly in the lower part of the
granite unit, seem to have experienced, to some extent,
alteration from the long-lasting, postimpact
hydrothermal system, through addition of more recent
Rb. Strontium depletion, related to the hydrothermal
alteration of plagioclase, is also observed in these
samples, without allowing any conclusion on which
hydrothermal event was the cause of this Sr depletion.
Other fluid mobile elements, such as Ba, Th, and U,
have also been affected, probably by both hydrothermal
events.
Our results are consistent with previous work
conducted on granite samples recovered at site M0077,
supporting that the calc-alkaline to high-K calc-alkaline
granites located in the Chicxulub impact structure peak
ring were formed in an arc tectonic context, intruding
the Maya block during the closure of the Rheic ocean
and assembly of Pangea.
Acknowledgments—This paper is dedicated to the
memory of Herv
e Martin (19512021) who developed
the well-known “adakitic” model, constituting a
reference in the characterization of adakites and related
rocks. The Chicxulub drilling was funded by the IODP
as Expedition 364, with co-funding from ICDP.
Expedition 364 was implemented by ECORD, with
contributions and logistical support from the Yucat
an
state government and Universidad Nacional Aut
onoma
de M
exico. Partial funding was provided by the
University of Vienna doctoral school IK-1045 (P.I.:
C.K.). We thank Peter Nagl and Marianne
Schwarzinger for XRF sample preparation and analysis,
Dieter Mader for INAA and data processing, and
1268 J.-G. Feignon et al.
Monika Horschinegg and Wencke Wegner for sample
preparation and TIMS SrNd isotopic analysis. J.-G. F.
thanks Wencke Wegner for constructive discussions on
SrNd isotopic data interpretation, and Jiawei Zhao for
general discussions. The AMGC team is supported by
Research Foundation Flanders (FWO-Vlaanderen) and
BELSPO; P.K. is an FWO PhD fellow (project
11E6619N; 11E6621N). S.G. and P.C. thank the EoS
project “ET-HoME” for support and the VUB Strategic
Research Program. P.C. thanks the FWOHercules
Program for financing the lXRF instrument at the
VUB. J-G. F. thanks Jean-Franc
ßois Moyen for valuable
comments on adakites and granites in general. We
thank Lutz Hecht and Stephen Prevec for their detailed
and constructive reviews, as well as Jeffrey Plescia for
editorial handling.
The authors declare no conflict of interest.
Data Availability Statement—The data that support the
findings of this study are available in the supplementary
material of this article.
Editorial Handling—Dr. Jeffrey Plescia
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SUPPORTING INFORMATION
Additional supporting information may be found in
the online version of this article.
Data S1. Raw geochemical data for major elements,
trace elements, and SrNd isotopic analyses.
Fig. S1. Thick sections mosaic scan of selected
granite, granite clast granite breccia, and aplite samples
investigated using µXRF Three samples were taken
from a different interval than the samples used for
geochemical investigations; however, they are located
very close within few centimeters from each other and
thus, the chemical variation should be negligible.
Fig. S2. Bivariate diagrams of V and Zr versus
TiO
2
, and La and U versus Zr.
Chicxulub peak ring granite chemistry 1273
... 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.
Article
Impact events that create complex craters excavate mid- to lower-crustal rocks, offering a unique perspective on the interior composition and internal dynamics of planetary bodies. On the Yucatán Peninsula, Mexico, the surface geology mainly consists of ~3 km thick sedimentary rocks, with a lack of exposure of crystalline basement in many areas. Consequently, current understanding of the Yucatán subsurface is largely based on impact ejecta and drill cores recovered from the 180–200-km-diameter Chicxulub impact structure. In this study, we present the first apatite and titanite UPb ages for pre-impact dacitic, doleritic, and felsitic magmatic dikes preserved in Chicxulub's peak ring sampled during the 2016 IODP-ICDP Expedition 364. Dating yielded two age groups, with Carboniferous-aged dacites (327–318 Ma) and a felsite (342 ± 4 Ma) overlapping in age with most of the granitoid basement sampled in the Expedition 364 drill core, as well as Jurassic dolerites (168–159 Ma) and a felsite (152 ± 11 Ma) that represent the first in situ sampling of Jurassic-age magmatic intrusions for the Yucatán Peninsula. Further investigation of the Nd, Sr, and Hf isotopic compositions of these pre-impact lithologies and impact melt rocks from the peak ring structure suggest that dolerites generally contributed up to ~10 vol% of the Chicxulub impact melt rock sampled in the peak ring. This percentage implies that the dolerites comprised a large part of the Yucatán subsurface by volume, representing a hitherto unsampled pervasive Jurassic magmatic phase. We interpret this magmatic phase to be related to the opening of the Gulf of Mexico, representing the first physical sampling of lithologies associated with the southern extension of the opening of the Gulf of Mexico and likely constraining its onset to the Late Middle Jurassic.