Chicx-03A drilling report
Source: ESO - Chicxulub K-Pg Impact Crater Expedition 364
Norbert Brügge Germany
What can we say:
The Chicxulub crater is smaller than predicted (see above). It is more like
a huge volcanic vent with about 70 km diameter. The expected peak or peak
ring in the "impact-crater" does not exist.
The indifferent seismic profiles were unfortunately misinterpreted because
they were accompanied by a wishful thinking. The ever-used gravity anomaly
map shows neither a crater nor a paek ring, but is only the reflection of
a former magma chamber.
The "Chicxulub-impact" is a great error. The
compact crystalline basement is encountered here in an exceptionally high
postion (similar as in the
Chesapeake Bay structure).
Enclosed mafic dykes are intrusions from the dioritic magma chamber. There
are even indications that the so-called "impact melt" in the cores is partly
a pure andesite rock. But that must be verified. It should also be verified
whether all the granites have the same age.
The Lamprophyre dykes are the oldest
hypabyssal intrusions and were created long times before the event.
Paper "Science" vol. 354, issue 6314, pp. 878-882 (2016, Nov.16)
"The uppermost peak ring is composed of ~130 m of breccia, with
impactmelt fragments that overlie clastpoor impact melt rock.We encountered
felsic basement rocks between 748 and 1334.7 mbsf that were intruded by preimpact
mafic and felsic igneous dikes as well as impact-generated dikes.
We recovered one particularly thick impact breccia and impact melt rock sequence
between 1250 and 1316 mbsf. The entire section of felsic basement exhibits
impact-induced deformation on multiple scales. There aremany fractures (Fig.
3A), foliated shear zones (Fig. 3B), and cataclasites (Fig. 3C), as well as
signs of localized hydrothermal alteration (Fig. 3D). The felsic basement
is predominantly a coarse-grained, roughly equigranular granitic rock (Fig.
3E) that is locally aplitic or pegmatitic and, in a few cases, syenitic.
The basement rocks in the peak ring differ from basement in nearby drill holes
encountered immediately below the Mesozoic sedimentary rocks, suggesting a
source of origin that was deeper than 3 km (???).
Evidence of shock metamorphism is pervasive throughout the entire basement,
with quartz crystals displaying up to four sets of decorated planar deformation
features. We observed shatter cone fragments in pre-impact dikes between
1129 and 1162 mbsf, as well as within the breccia. Jointly, the observed shock
metamorphic features suggest that the peak ring rocks were subjected to shock
pressures of ~10 to 35 GPa (?) . No clear systematic
variation in shock metamorphism was observed with depth. Impact-melt, which
is formed at shock pressures of >60 GPa (?),
is also a component of the peak ring.
The formation of the Chicxulub peak ring from felsic basement confirms that
crustal rocks lie directly above Mesozoic sedimentary rocks, which is consistent
with the dynamic collapse model of peak-ring formation
The drilling data confirm that the peak-ring rocks have low densities and
seismic velocities, as suggested by geophysical models. The density of the
felsic basement varies between 2.10 and 2.55 g cm−3, with a mean of 2.41 g
cm−3, and P wave velocities vary between 3.5 and 4.5 km s−1, with a mean of
4.1 km s−1. These values are unusually low for felsic basement, which typically
has densities of >2.6 g cm−3 (correct is: 2.5 to 2.7
!) and seismic velocities of >5.5 km s−1 (correct
is: 4.0 to 6.0)."
It is claimed that
the condition of the drilled felsic basement rocks provide the evidence for
the existent of a "peak ring" in the Chicxulub crater. These parts of this
crystalline basement were shifted several kilometers towards the surface during
impact and lie directly above Mesozoic sedimentary rocks. These rocks are
cross-cut by dikes and shear zones and have an unusually (?) low density and
seismic velocity. Analysis shows
that impact generated vertical fluxes and increased porosity.
Again only wishful thinking ! Model simulations are for the trash.
Nothing was uplifted and the shear zones etc. can have emerged during
the explosion of the supervolcano, or of times long before the event.
"Shatter cone fragments in pre-impact dikes" in amphibolite facies are even
a clear indication that they were created by shock waves
in the magma-chamber long time before the event. But, no of the existing
hypotheses for the formation of shatter-cones currently is able satisfactory
explain the characteristics of this fracturing phenomenon.
I refer in this context to
angular sandstone columns
in Jebel Uweinat (Egypt), and Israel, Scotland, Germany, Australia and Paraguay,
which were clearly created by subvolcanic shock waves.