Abstract and Figures

The state of substances under ultrahigh pressures and temperatures (UHPHT) now raises a special interest as a matter existing under extreme conditions and as potential new material. Under laboratory conditions only small amounts of micrometer-sized matter are produced at a pressure up to 100 GPa and at room temperature. Simultaneous combination of ultrahigh pressures and temperatures in a lab still requires serious technological effort. Here we describe the composition and structure of the UHPHT vein-like impact glass discovered by us in 2015 on the territory of the Kara astrobleme (Russia) and compare its properties with impact glass from the Ries crater (Germany). A complex of structural and spectroscopic methods presents unusual high pressure marks of structural elements in 8-fold co-ordination that had been described earlier neither in synthetic nor natural glasses. The Kara natural UHPHT glasses being about 70 Ma old have well preserved initial structure, presenting some heterogeneity as a result of partial liquation and crystallization differentiation where an amorphous component is proposed to originate from low level polymerization. Homogeneous parts of the UHPHT glasses can be used to deepened fundamental investigation of a substance under extreme PT conditions and to technological studies for novel material creations. The full paper text is available by the link https://rdcu.be/Nbgr
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Scientific RepoRTS | (2018) 8:6923 | DOI:10.1038/s41598-018-25037-z
Spectroscopic features of ultrahigh-
pressure impact glasses of the Kara
T. G. Shumilova1,2, V. P. Lutoev1, S. I. Isaenko1, N. S. Kovalchuk1, B. A. Makeev1, A. Yu. Lysiuk1,
A. A. Zubov1 & K. Ernstson3
The state of substances under ultrahigh pressures and temperatures (UHPHT) now raises a special
interest as a matter existing under extreme conditions and as potential new material. Under laboratory
conditions only small amounts of micrometer-sized matter are produced at a pressure up to 100 GPa
and at room temperature. Simultaneous combination of ultrahigh pressures and temperatures in
a lab still requires serious technological eort. Here we describe the composition and structure of
the UHPHT vein-like impact glass discovered by us in 2015 on the territory of the Kara astrobleme
(Russia) and compare its properties with impact glass from the Ries crater (Germany). A complex of
structural and spectroscopic methods presents unusual high pressure marks of structural elements in
8-fold co-ordination that had been described earlier neither in synthetic nor natural glasses. The Kara
natural UHPHT glasses being about 70 Ma old have well preserved initial structure, presenting some
heterogeneity as a result of partial liquation and crystallization dierentiation where an amorphous
component is proposed to originate from low level polymerization. Homogeneous parts of the UHPHT
glasses can be used to deepened fundamental investigation of a substance under extreme PT conditions
and to technological studies for novel material creations.
e state of substances under ultrahigh temperatures and pressures now raises a special interest both from the
point of view of fundamental questions of the existence of matter under extreme conditions17, and from the
point of view of practical interest with the aim of evaluating them as possible potential new types of materials811.
Under laboratory conditions, at extremely high pressures, only small amounts of matter are produced, which
are limited to particles of micrometer size at a pressure up to 100 GPa, where the synthesis is carried out preferably
at room temperature15. Simultaneous combination of ultrahigh temperatures and pressures can theoretically be
accompanied by the formation of specic materials7, which still requires a serious study. Among the objects of
natural origin, impact glasses represent interest1216, and UHPHT melt-type varieties are of particular interest,
since their formation is caused by high pressures (35–90 GPa, up to hundreds of GPa) with fast subsynchronous
high-temperature impact (up to 3000 °C and higher)1719. Within the considered problem, the advantage of nat-
ural impact glasses is also their much larger volume and preservation of their structure over millions of years.
During our studies of diamond-bearing impactites of the 70 Ma old Kara astrobleme (Russia), we for the rst
time discovered high pressure post-impact liquation glasses with coesite20, which may be interesting for deepened
research of their phase state and evaluation of physical properties.
In the context of a large interest in high-pressure glasses as novel promising materials and with regard to
strongly limited experimentally produced matter we suggest that the recent nd of natural vein-like UHPHT
glasses at the Kara astrobleme20 could be pioneering. e glasses, which were formed under extreme PT condi-
tions as essentially macroscopic bodies, can be perspective as possible UHPHT materials and/or valuable sub-
stance for fundamental study of matter under extreme conditions. With a complex of spectroscopic methods, we
examined the natural UHPHT impact glasses to understand specics of their composition, structure and char-
acter of UHPHT memory through 70 Ma age and level of post impact alteration. For the latter we compare the
Kara UHPHT glasses characteristics with substantially younger diamond-bearing glasses from the about 15 Ma
old Ries impact crater (Germany).
1Institute of Geology, Komi Scientic Center of Ural Division of Russian Academy of Sciences, Pervomayskaya st. 54,
Syktyvkar, 167982, Russia. 2Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, 1680
East-West Road, Honolulu, HI, 96822, USA. 3Faculty of Philosophy I, University of Würzburg, Würzburg, Germany.
Correspondence and requests for materials should be addressed to T.G.S. (email: tg_shumilova@mail.ru)
Received: 3 November 2017
Accepted: 13 April 2018
Published: xx xx xxxx
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Geological position and sampling regions. Two impact craters, Kara (ca. 60 km) and Ust`-Kara
(ca. 25 km, predicted), are located in the north-east of the European part of Russia, and they belong to the
North-Eastern part of the Pay-Khoy Ridge structure (SM 1). e Kara astrobleme is completely set on land sur-
face, while Ust`-Kara is generally at seawater depth. At present the Kara astrobleme is observed as depression in
landscape and well expressed in the gravity and magnetic elds21,22.
It is proposed that these two astroblemes were formed about 70 Ma past2123 by one bolide, which had been
destructed before its contact with the target. e geological structure of the Kara astrobleme is presented by a tar-
get consisting of Ordovician-Permian units of black shales, sandstones, limestones and other sedimentary rocks
with a total thickness more than 5 km, and by impactites – tagamites (massive melt rocks) and suevites21,22. Just
this year a complex of vein-like impact melt bodies with coesite has been discovered20 (Figs1 and 2). A unique
Figure 1. Massive impactite with vein-like ultrahigh pressure melt glasses in contact with black shales of the
Kara astrobleme target. (A) Outcrop on the right bank of the Kara river, (B) magnied part (red square in (A)),
red lines tracing the vein-like bodies of UHPHT melt glasses. (CE) thin sections in transparent light, (C,E)
parallel polarizers, (D,F) crossed polarizers; (C,D) UHPHT glass (Gl) in suevite (Sv) transporting lithoclasts
(Lc). (E,F) crystallized impact melt (CIM) clast, CIM clast within suevite. Photos and microimages were made
by T.G.Shumilova.
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feature of the Kara astrobleme are abundant aercoal diamonds20,24,25 formed aer bitumen coal-like carbona-
ceous matter, widely spread within the sedimentary rock target.
For the study we collected samples from natural outcrops at banks of the rivers: Kara (suevite, melt rock,
vein-like UHPHT glass), Anaroga (clast-poor melt rock) and Sopchau (suevite) at the southern part of the Kara
astrobleme close to the outer rim of the impact structure (SM 1).
e about 15 Ma old 26 km-diameter Ries crater in Bavaria (Germany) (also named Nördlinger Ries or Ries
Basin) is one of the most studied impact craters on the Earth26, which is accepted as a classic middle-size impact
structure in a mixed, sedimentary-crystalline target. e geology of the crater and impact glasses have been
described elsewhere2630. In this work we used suevites sampled in the Altenbürg and disused Polsingen quarries.
Chemical and phase composition of impact glasses. e solidied impact melts of the Kara astrob-
leme and the Ries crater are in various degree crystallized melts (Fig.2, SM 2, 3) represented by massive bodies
of tagamites; lenses, bombs and ashes in suevites, and also by vein-like formations in massive complexes, recently
discovered by us.
e analysis of the geochemical specicity of impact glasses (IG) and crystallized impact melts (CIM) of the
Kara astrobleme and the Ries crater generally showed aluminosilicate compositions (SM 4), which occupy a wide
eld, covering the regions from basic to ultra-acid composition and a wide range of contents of alkaline com-
ponents (Fig.3, SM 5). Such a diversity of impact glass compositions can be explained rst of all by the impact
melting process having aected a complex lithological interbedding of heterogeneous sedimentary rocks.
X-ray diraction of the impact glasses material from the Kara astrobleme shows an amorphous component of
quartz-feldspar glass (Fig.4). e X-ray patterns show reexes indicating the presence of feldspar, variously disor-
dered due to the degree of crystallization of the impact melt, as well as of quartz. A weak and strongly broadened
reex corresponds to interplanar spacing 1.4 nm of clay minerals, while a small narrow reex, corresponding to
0.309 nm be referred to the coesite lattice planes 040.
e diraction patterns of the glasses from the Ries crater (Fig.4) are characterized by a similar amorphous
halo reecting the presence of a signicant fraction of an amorphous component, and they also have reexes of
feldspar, quartz and weak broadened reections 0.253 and 0.171 nm, which possibly refer to the reections from
the magnetite lattice planes 311 and 422 (SM 6).
Local analysis by Raman spectroscopy. Raman spectroscopy of the Kara impact glasses was carried
out to identify in detail the components of solidied impact melts from UHPHT vein-like bodies from the Kara
astrobleme and the impact glasses of the Altenburg suevites (Ries crater) for comparison. e diagnostics was
performed in locally homogeneous areas, where the analysis points were focused on optically visible crystallites
and amorphous regions. In both cases the impact glasses proved to be relatively inhomogeneous, characterized
by dierent amounts of microcrystallites of pyroxene and coesite (for the Kara astrobleme) and magnetite (for
both astroblemes) (Fig.5, SM 7, 8). UHPHT impact glasses of the Kara astrobleme are also characterized by the
presence of a carbon matter in the graphite-like (glass-like) state or in the state of amorphous carbon - sputtered
a-C carbon31. At that in a number of cases we determined the co-occurrence of UHPHT silica glass, coesite and
carbon matter in a conned volume of only about 1 μm3 (Fig.5, spectrum KR-115-p19, SM 7, 8).
Figure 2. SEM images of dierent regions in UHPHT impact glass from a vein-like body in the Kara
astrobleme, Kr-12–115, Kara river. (A) aluminosilicate glass with some pyroxene crystallites, (B) coesite-
bearing silica glass drop within aluminosilicate glass surrounding matter. Black rounded regions in (B) are
pores, produced probably at vacuum probe preparing by recovering of liquid (water-rich) inclusions in glass.
GlFsp and GlSiO2 – feldspar and quartz melting glasses, Coe – coesite, Px – pyroxene, Py – pyrite.
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Feldspar glasses (Fig.5, spectrum KR-117-p6, KR-118a-p10, SM 7, 8) are characterized by dierent position
and structure of the general glass band pointing to variety in polymerization level toward to very small structural
elements and their heterogenity. In some cases the maximum band position can be downshied up to 80 cm1
compare to glass produced at the ambient pressure.
According to the obtained spectra, the UHPHT impact glasses of the Kara astrobleme are characterized by a
wide general band, oen asymmetric with a broad non-structured or structured shoulder toward a red shi in the
Figure 3. e feldspar ternary diagram of compositions of clastogenic impact glasses from suevites and
UHPHT vein-like glasses of the Kara and Ries astroblemes: 1 – Anaroga river; 2 – Kara river; 3 – Sopchau river;
4 – Ries astrobleme, Altenbürg quarry. Points belonging to UHPHT vein-like glasses from the Kara river are
encircled in green.
Figure 4. Diraction patterns of solidied impact melts with dierent level of crystallinity. Fls – feldspar, Qtz –
quarts, Coe – coesite, Clc – calcite, Anc – analcim, Mgt – magnetite, Mc – mica, Chl – chlorite, Smt – smectite.
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spectrum. e general structural band of the impact silica glasses has a full width at half maximum (FWHM) of
about 200 cm1 and corresponds to δ(Si-O-Si) bonds of the polymerized structure with a maximum position at
416 cm1, which is substantially shied from the usual position32 at 440 cm1. Unlike glasses, produced at normal
pressure, the Raman spectra of UHPHT silica impact glasses are also characterized by the absence of D1 and D2
bands (490 and 603 cm1 respectively) that refer to the three- and four-membered rings of SiO4 tetrahedra in sil-
ica glass32. ese features probably characterize the substantially smaller sizes of the structured regions as a result
of the lower degree of polymerization caused by a rapid cooling of UHPHT impact melt.
e feldspar glasses are characterized by dierently positioned general Raman bands with similar FWHM to
low pressure glasses (about 250–300 cm1). Sometimes the UHPHT feldspar glasses have a complicated general
band consisting of several sub-bands with a single FWHM about 100 cm1 in total getting up to 400–500 cm1
(Fig.5, SM 5, spectrum KR12-118-p10).
e presence of a glass-like carbon matter within the UPH silica glasses is determined by the presence of the
bands D = 1347 cm1 and G = 1606 cm1, as well as by a broad band of the second order - 2937 cm1. Sputtered
a-C carbon (Fig.5, spectrum KR12–118-p10, SM 5) is diagnosed according to31 by broad bands of 1424, 1608,
2912 cm1, corresponding respectively to D, G and second order bands.
e presence of a large amount of water with a dierent structural state in glass is noteworthy for UHPHT
impact glasses from the Kara astrobleme. e water is predominant in the molecular (absorbed) form, but can
partly be chemically bonded to structural radicals in the glass (Fig.5, spectrum Kr-2-15-p4, SM 7, 8). e Raman
spectroscopy allowed us to estimate to some extent the relative water content in UHPHT impact glasses according
to the ratio of the integrated intensities of the structural band of the glass-forming component and water. is
ratio in the studied material ranges from 0 to 4.5, which indicates a signicant inhomogeneity of the uid in the
solidied impact melts. According to experimental data33, the water content in UHPHT glasses can make several
percent, which conforms with our previous studies using gas chromatography and thermogravimetric analysis20.
FTIR spectroscopy characteristics. e main features of the FTIR spectra of the samples from the Kara
crater and the Ries relate to vibrational modes of framework aluminosilicate melt glasses (Fig.6). e most
intense IR absorption bands are due to the stretching asymmetric (1000–1200 cm1) and bending (470 cm1)
vibrations of the bridge oxygen of the glass Si-O-Si bonds. In addition a weak broad band at 800 cm1 refers
to the symmetric stretching vibration of SiO4 units of this matrix. Against the background of the last band, very
weak traces of the characteristic doublet (779, 798 cm1) of crystalline quartz are noticeable. In the spectra of all
glass samples, the high-frequency shoulder of the 470 cm1 band is complicated by weak bands in the region of
540–640 cm1 that relate to the bending vibration O-Si (Al) -O and O-Si-O bands in the plagioclase lattice. e
presence of weak bands at 1430 and 880 cm1 in the FTIR spectra indicates an insignicant amount of carbonate
and pyroxene in the glass samples.
Iron state in UHPHT impact glasses by Mössbauer spectroscopy data. e obtained Mössbauer
spectra of the impact glasses of both astroblemes contain only paramagnetic doublets (Fig.7). A sextet structure
from magnetic phases is not detected against noise background, although X-ray phase analysis and Raman spec-
troscopy revealed traces of magnetite in the sample of the glass from the Ries crater (Fig.4). Analogous spectra
Figure 5. Raman spectra of impact glasses from the Kara astrobleme (KR) and the Ries crater (R). e color
marked elds correspond to spectral ranges of glass, carbon and water. Color marked elds – regions of glass
(Glass), carbon substance (CS) and H2O bands.
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were observed in basaltic and meteorite glasses, as well as in tektites3438. e main feature of the obtained spectra
is an asymmetric doublet with quadrupole splitting (QS) of about 2 mm/s and isomer shi (IS) of 1 mm/s, typical
for Fe2+ ions in 4–6 fold oxygen polyhedron sites. e high velocity peak is slightly wider and less intense than
the low velocity peak.
As shown by the simulation, the spectra of the Ries crater glass are satisfactorily approximated by a pair of
Fe2+ doublets (D1, D2) with dierent values of IS, QS and weak broadened Fe3+ doublet (D3). In similar spectra
of glass from the Kara crater against the background of the low velocity peak of Fe2+ doublets (D1, D2), a broad
component with a typically for Fe3+ ions small quadrupole splitting is clearly observed. It is a superposition of
at least two Fe3+ doublets (D3, D4) with dierent QS values. Besides these broadened doublets related to the
glass-like matrix, an additional doublet with narrow peaks (D), sharpening the main doublets of Fe2+, is observed
in the spectrum of the glass from the Ries crater. And in the spectrum of the glass from the Kara crater there is a
high velocity peak at 3 mm/s (D). e result of decomposition of the spectra in this model and parameters of
doublets, obtained in the tting, are shown in the Fig.7.
ESR of impact glasses. e obtained spectra of glasses in the range of the polarizing magnetic eld 0–0.7 T
are shown in Fig.8. ey contain a wide band with g = 2.2–2.3 (line widths at extremum points ΔBpp = 210 mT),
on which narrow lines with g-factors 4.3 and 2.02 (ΔBpp 8 and 20 mT, respectively) are superimposed, and also
a low-intense sextet of Mn2+ ions in the lattice of calcite impurities. e ESR spectrum of the Ries crater glass
is dominated by narrow lines 4.3 and 2.02 contrasting with a broad band 2.2–2.3 in the Kara crater glass. With
a ratio of 10:7 the integral intensity of a signal 4.3 (IΔBpp2, where I – peak intensity, ΔBpp - width at extremum
points) in the spectra of the glasses from the Ries and Kara craters does not dier signicantly. In both glasses
the wide band is weakly anisotropic, since the shape of its low-eld part slightly changes when the tube with the
sample rotates in the resonator. Lines 4.3 and 2.02 are isotropic. When the sample is grinded, the anisotropy of the
broad band decreases. is signal can be attributed to Fe3+ ions in ferrous mineral inclusions (pyroxenes) in glass
or clusters of iron ions in the glass framework.
A narrow signal of free radicals with g = 2.00 is also present in the spectra of the Kara samples, the detailed
structure of which is shown in the Fig.8B. e free radical line is formed by a singlet with g = 2.0025–2.0028
(ΔBpp 0.3–0.5 mT) and a quartet of approximately equidistant lines with dierent intensities and widths. e
singlet line refers to carbon radicals (C) in the carbon matter. e quartet is characterized by a medium g-factor
2.0035 and a hyperne splitting 2.44 mT. Structure-analogous signals are oen observed in the EPR powder spec-
tra of alkali feldspars and silica with impurities of organic matter. In feldspar spectra, this signal is usually attrib-
uted to the ammonia radical39 NH3+, and in the spectra of silica to the methyl radical40CH3. e value of g-factor
and hyperne splitting of the radicals in the Kara glass spectrum allows attributing them to the NH3+ radical41.
e character of the geochemical specicity of the studied impact glasses, determined by overlapping with the
most part of volcanic rock elds on the TAS diagram (SM 5), as well as a signicant coverage of “forbidden eld”
Figure 6. FTIR absorption spectra of impact glasses and standard samples: Fls – plagioclase (labrador An50–70),
Gl – aluminosilicate glass, Qtz – quartz, Aug – pyroxene (augite), Clc– calcite.
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for feldspars (Fig.3) indicates a signicant geochemical dierence between the impact glasses and CIM glasses
of the Kara astrobleme and glasses of volcanic origin4245, characterized by a more homogeneous composition for
individual volcanic structures and batch eruptions.
During structural studies we established that the massive bodies of melt impactites, as well as numerous inclu-
sions of bombs, lens-like bodies, and ash material in suevites, are largely represented by substantially crystallized
impact melts (Fig.2A). erefore, in the context of the study, the embedded real vein-like glass bodies including
UHPHT glass with a signicant share of coesite are the most interesting features for further detailed study.
e water found by Raman spectroscopy in the impact glass could greatly aect impact melt solidication
temperature, lowering it signicantly, thereby intensively decreasing the viscosity of the impact melt and, hence,
substantially increasing its mobility. Besides, the presence of water can also aect the preservation of impact dia-
monds. It should also be noted that the water inclusions nding within the UHPHT impact glasses support the
hypothesis of the Kara impactites formation at aquagenic conditions21. e studied samples of impact glass from
the Ries crater generally do not contain water, and the analyzed optically homogeneous glass regions are charac-
terized by almost complete absence of a crystalline component. e position and structure of the general Raman
bands are close to ordinary low-pressure aluminosilicate glasses (Fig.5, spectrum R13-5-1-p3).
Comparing the obtained Raman spectra of impact glasses, it should be noted that unlike the glasses from the
Ries crater, the Kara vein-like UHPHT impact glasses are characterized by a signicantly greater heterogeneity
with respect to the degree of polymerization, which is signicantly lower compared to conventional glasses32. is
heterogeneity of the UHPHT aluminosilicate glass matrix is attributed to drops of pure silica glasses with coesite
(Fig.2B) and carboniferous matter (Fig.5, spectrum KR12-115-p19).
Figure 7. Mössbauer spectra of the impact glasses of the Ries (A) and Kara (B) craters. Indicated components
are the results of the best ts. Residual spectra are shown below. Mössbauer parameters of the best ts
components, where IS (mm/s), QS (mm/s),  (mm/s), A (%) – isomer shi, quadrupole splitting, half-width
of doublet peaks, relative area of the doublet. Fe3+/ΣFe = ΣAFe3+/(ΣAFe2+. + kΣAFe3+), where k is the ratio of
probabilities of Mössbauer transition of octahedral complexes Fe3+ and Fe2+, k is taken equal to 1.232,33.
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e FTIR data of bulk specimens do not allow revealing the specic atomic-level structure of the UHPHT
impact glasses, including its ne structure. For a more informative analysis local methods of IR spectroscopy with
reference to various homogeneous parts of the vein-like type impact glass are required.
From local detailed Raman spectroscopy it is evident that the crystalline quartz and feldspar X-ray reections
and characteristic IR absorption bands rather originate from a certain quantity of relict quartz crystal-clasts and
lithoclasts of polymictic sandstones from the target rocks. Raman studies at microlevel do not reveal any newly
formed inclusions of quartz and feldspars directly in the UHPHT impact glasses.
e presence of iron in UHPHT impact glasses allows studying some ne features of the glasses structure
under the study, since it significantly expands the possibilities of applying sensitive methods, in particular
Mössbauer spectroscopy and electron spin resonance. Wide asymmetric peaks from iron sites in the glass and
relatively narrow peaks from iron sites of included crystalline phases are characteristic of Mössbauer spectra.
In the Mössbauer spectra of glasses from Kara and Ries craters (Fig.7), the most intense doublet D1 with
nearly equally large widths (0.5–0.6 mm/s) and the contribution to the total area of the spectral contour is char-
acterized by IS, characteristic of 6-fold oxygen polyhedra with Fe2+, that is, the octahedral type of sites in the
aluminosilicate glass4649. e QS parameter in the glass from the Kara crater is thus signicantly higher than in
the glass from the Ries crater. Taking into account the dependence of QS on the degree of distortion of octahedral
polyhedra48, it can be concluded that the Fe2+ octahedral sites in the glass from the Kara crater is characterized by
relatively low distortion. e second doublet Fe2+ (D2) has a smaller QS value (1.8–1.9 mm/s) and a much smaller
isomer shi (0.9–1.0 mm/s). A decrease of IS parameter indicates a decrease of the coordination number of oxy-
gen polyhedron Fe2+ to 4, that corresponds to the tetrahedral type of the position. For the glass from the Ries cra-
ter, the representativeness of the Fe2+ tetrahedral sites is three times higher than in the glass from the Kara crater.
e additional low-intense doublet D Fe2+ in the spectrum of the glass from the Ries crater has a small width
of peaks, which is a characteristic of a crystalline phase, and possibly relates to one of the Fe2+ octahedral sites
of the pyroxene lattice49. In the spectrum of the glass from the Kara crater, the doublet D with a relatively small
peak width has high values of IS and QS (1.35 and 3.5 mm/s). Note that the doublets with the IS and QS large
values in our data were observed earlier neither in synthetic nor natural aluminosilicate glasses nor in impact
meteorite and tektites glasses3438. Similar values of these parameters were observed for Fe2+ ions in 8-fold sites
of garnets48,49, which lack an independent conrmation among the crystalline inclusions within the Kara glass.
Perhaps 8-fold sites of Fe2+ in the Kara UHPHT glass directly evolved at the glass network formation under
UHPHT conditions.
Isomer shis of Fe3+ doublets (0.35–0.38 mm/s) correspond to octahedral sites of iron within dierent sil-
ica glass and mineral substances46,49. A doublet D3 with the same values of IS, QS also presents in the Kara
sample spectrum, but it is supplemented by a strongly broadened doublet D4 with a large quadrupole splitting
(1.14 mm/s). e areas of the spectral contours of D3, D4 doublets are approximately equal (Fig.7C). In the case
of Fe3+ ions, the rising of the QS value indicates increased distortion of octahedral sites for the D4 doublet. For
Ries crater glass spectra only one low-intense doublet D3 with a large peak width and QS 0.7 mm/s is deter-
mined. It is known that the Fe3+ doublets can be explained by iron both in aluminosilicate glass framework and
mineral inclusions, for example, pyroxene. In contrast with the glass from the Ries crater, pyroxene a Fe2+ doublet
in octahedral sites was not detected in the spectrum of the glass from the Kara crater. For the latter the Mössbauer
data show the degree of iron oxidation (Fe3+/ΣFe in Fig.7C) 3 times higher than in the Ries impact glass. It is
possible that Fe-ions in pyroxene of the Kara crater glass were oxidized to Fe3+ state.
Figure 8. ESR spectra of impact glasses from the Kara astrobleme (upper spectrum) and Ries crater (bottom
spectrum): A – the full range spectra; B – magnied part region of g = 2.00. Power of the microwave eld is 35
and 7 mW for A and B). e spectra of samples are reduced to the same registration conditions.
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e ESR method detects only the signals from Fe3+ ions in iron-containing glass matrix at room temperature.
e lines of bivalent iron, due to a very strong spin-phonon interaction, were resolved in EPR spectra only for
the specimens cooled to liquid helium temperature. e isotropic lines with g = 4.3 and 2.02 are the characteris-
tics of ESR spectra of various glasses with an impurity of isolated Fe3+ ions, including aluminosilicate ones5053.
It is considered that these signals are associated with two types of Fe3+ ions isolated in the glass framework:
(1) g = 4.3 ions in purely rhombic strong crystal eld, E/D = 1/3, D >> hν (D, E parameters of axial and
rhombic component of crystalline elds, hν 10 GHz); (2) g = 2.0 - ions in a strong axial eld E/D = 0). Fe3+
ions in the rhombic eld relate to strongly rhombic distorted tetrahedral positions and iron ions in the axial eld
(g = 2.0) to axially distorted octahedral positions. In the Mössbauer spectra (Fig.7) the doublet of the tetrahe-
dral positions of ferric iron (IS = 0.2–0.32 mm/s) may have been masked by the intense components of the other
iron positions.
e unusual feature of the UHPHT glass from the Kara crater is the tiny presence of carbon and ammonia rad-
icals (NH3+) described in the ESR data (Fig.8B). In mineral matrixes, such as K-feldspars, the ammonia radicals
are formed usually from NH4+ cations under ionizing radiation being stable below 200 °C3941. Precursors (NH4+)
of the analyzed ammonia radicals in the Kara crater glasses perhaps were formed by the interaction of nitrogen
oxides with organic matter during heating of the target rocks. Following the high temperature impact conditions
the carbon radicals were formed during thermal carbonization of the organic matter. As for the paramagnetic
NH3+ radicals, they could have originated under natural radiation aer cooling of the vein-like glasses.
Our studies show that the UHPHT glasses generally consist of an amorphous matter of feldspar composition.
Compared to the clastic glasses in suevites, the compositions of the vein-like glasses are localized within a small region
in the chemical diagrams having quite stable anorthoclase content and contain small drops of coesite-containing silica
glass. A complex of structural and spectroscopic methods presents unusual high pressure marks of structural elements
in 8-fold co-ordination that had been described earlier neither in synthetic nor natural glasses.
is comprehensive and complex study for the rst time resulted in a rather detailed characterization of the
impact glasses of the Kara astrobleme, including a low degree of polymerization of silicate framework on the basis
of Raman spectroscopy data. By complex spectroscopic and microscopic data we also determined a signicant
structure and composition heterogeneity of the UHPHT glasses probably connected with fast partial liquation
and crystallization dierentiation. In spite of the long post-impact period of about 70 Ma, this type of glasses
preserve mostly the initial structure without essential altering over time and under hydrothermal processes. us,
the Kara UHPHT glasses can be used to deeper fundamental studies by local and high resolution methods for
understanding of a substance state under extreme PT conditions.
For the study we selected monomineral fractions of impact glasses by a binocular from impactites of Kara astrob-
leme and Ries crater, sampled during eldwork in 2013–2017. e analysis of UHPHT glasses of the Kara astrob-
leme was performed in comparison with glasses from the Ries crater. e analytical works were carried out by the
equipment of Center for Collective Usage “Geonauka” of Institute of Geology Komi SC UB RAS.
e preliminary optical observations were performed using POLAM R-312 polarization microscope (LOMO,
Russia) with and without an analyzer.
e elemental composition of the glasses was analyzed by microprobe analysis combined with scanning elec-
tron microscopy20,45,54,55, which is common today and most informative to study natural inhomogeneous sys-
tems, including impactites, where the detrital component introduces signicant distortions during the study by
chemical methods. We used a scanning electron microscope TESCAN VEGA3 (Czech Republic) with Oxford
instruments X-Max energy dispersive device, analyst S.S. Shevchuk.
For a high-quality assessment of the phase mineral composition of the impact glasses in volume we used
X-ray phase analysis (XRD) with a Shimadzu XRD-6000 diractometer. e conditions of the survey – CuKα, 30
m, 30 kV, Ni-lter, scanning step 2θ 0.05°, 1 deg/min. We used pounded specimens placed on a at aluminum
substrate. e local analysis of the structure of the impact glasses and the phase diagnostics of its inclusions were
performed using a high-resolution Raman spectrometer LabRam HR 800 (Horiba Jobin Yvon). e conditions
for recording the spectra were as follows: monochromator grating - 600 g/mm, confocal hole - 300 μm, slit - 100
μm, exposure time 10 sec, number of signal accumulation cycles - 3, power of an excitation Ar + laser (488 nm)
1.2 mW. e size of analyzed regions of the samples was 2.5 μm2. e spectra were recorded at room temperature.
To analyze ne features of the structure of impact glasses we used infrared spectroscopy. Infrared spectra were
obtained by a FTIR spectrometer Lumex FT-02 in the range 400–4000 cm1 at 256 scans and with an instrumental
resolution 2 cm1. e specimens were prepared as pressed pellets of 800 mg KBr and 1.4–1.7 mg of a powder specimen.
Electron spin resonance (ESR) spectra were obtained by a radiospectrometer SE/X-2547 (“RadioPAN”,
Poland) in X-frequency range with 100 kHz HF modulation at room temperature of the samples. We used RX102
rectangular resonator with TE102 mode. g-Factors were calibrated according to the standard Li0:LiF (g0 = 2.00229).
e samples weighed from 30 to 60 mg and were rubbed in a jasper mortar to the state of “powder”. e recorded
spectra were reduced to the same value of the frequency of SHF quantum, amplication and sample weight. In
some cases, the averaging of the spectrum for 3–5 scans was performed to reduce noise.
e Mössbauer 57Fe spectra were recorded on a spectrometer MS-1104Em in the mode of a thin absorber in
the range of 11 to +11 and 4 to +4 mm/s at room temperature of the preparation. Pounded samples (10–
20 mg) were used for spectra accumulation. e accumulation time of spectra was from 100 to 200 hours. e
isomer shi was determined relatively to α-Fe. When processing the spectra, Univem standard soware of the
spectrometer was used.
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e authors kindly thank M.F. Samotolkova and S.S.Shevchuk for help in analytical works with IR spectroscopy
and microprobe analysis, correspondently. e study has been nancially supported by the Russian Scientic
Foundation, project # 17-17-01080.
Author Contributions
T.Sh. introduced the original goal, organized and led the eld work of the Russian team, prepared specimens for
analytical work, participated in analytical studies, provided the data analysis and wrote the paper. V.L. provided
EPR spectroscopy, analyzed Mössbauer and IR spectroscopy, interpretation of X-ray diraction data, wrote the
paper. S.I. took part in eld studies, provided detailed high resolution Raman studies, conducted the analysis of all
Raman data, and contributed to writing the paper. N.K. took part in eld studies, in microprobe studies and data
interpretation, B.M. took part in eld studies, provided X-ray diraction. A.L. realized Mössbauer spectroscopy.
A.Z. took part in optical and Raman spectroscopy studies. K.E. organized sampling at the Ries impact structure
and took part at the paper editing.
Additional Information
Supplementary information accompanies this paper at https://doi.org/10.1038/s41598-018-25037-z.
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... In the focus of the present studies are the unusual natural ultrahigh pressure high temperature (UHPHT) impact glasses which for the first time have been discovered at the Southern part of the Kara astrobleme (Pay-Khoy, Russia) at the right bank of the Kara river in 2015 [4]. The UHPHT glasses are presented with stockwork-like system of thin veins within suevite breccia. ...
... The UHPHT glasses are presented with stockwork-like system of thin veins within suevite breccia. The Kara glasses have many specific features pointing to their UHPHT origin that has been described in our several publications [4][5][6][7]. To understand the geological position of the UHPHT impact glasses we have provided field observations with the detail topographic photoand video-documentation of the outcrops from the «airbird high» with data collecting for 3D modeling. ...
... It is accepted that the Kara astrobleme has about 65 km in diameter [8] which was formed by giant impact event about 70 Ma [9,10] close to the Kara seashore. At present the Kara meteorite crater is set in the basin of the Kara river including its mouth (Figure 1), the crater is slightly seen from air and cosmic observations in the present eroding level but the impactites are very good recognized in natural nicely preserved outcrops in the rivers stream channels and canyons around the astrobleme rim [4,8]. The impactites natural outcrops get hundreds meters (up to first kilometers) in extention and up to tens of meters in visible thickness. ...
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The unusual natural ultrahigh pressure high temperature (UHPHT) impact glasses have been discovered at the Southern part of the Kara astrobleme (Pay-Khoy, Russia) in 2015. The glasses form a complex of stockwork-like system of thin vein bodies set within suevite breccia at the right bank of the Kara river. The Kara glasses have many specific features pointing to UHPHT origin. For better understanding of the geological position of the UHPHT impact glasses we have provided additional field observation with the use of copter facility to observe the outcrops from the «air-bird high» and collecting data for 3D modeling. Here we present natural topological details for the more complete analysis of the discovered UHPHT complex at the Kara River (Pay-Khoy, Russia) and “bottom flow” suevites with UHPHT impact ribbon-like glasses on the Baydarata Bay shore (Kara Sea, Arctic, Russia).
... The synthesis of materials under the influence of both high pressures and high temperatures with the formation of UHP melts and their solidification products is interesting both in terms of the fundamental state of the substance and in anticipation of the specific properties of materials [12]. From this point of view, the discovered natural ultrahighpressure high-temperature (UHPHT) melt impact glasses with monocrystalline coesite [13] formed at pressures of more than 60 GPa and temperature of about 2800 K in the giant Kara impact crater (Pay-Khoy, Russia) [14] are of great interest. Using 57 Fe Mössbauer spectroscopy, a small portion of ferrous iron ions in 8-fold coordination (4%), similar to the structural positions of ions in garnets, was revealed in Kara glasses [14,15]. ...
... From this point of view, the discovered natural ultrahighpressure high-temperature (UHPHT) melt impact glasses with monocrystalline coesite [13] formed at pressures of more than 60 GPa and temperature of about 2800 K in the giant Kara impact crater (Pay-Khoy, Russia) [14] are of great interest. Using 57 Fe Mössbauer spectroscopy, a small portion of ferrous iron ions in 8-fold coordination (4%), similar to the structural positions of ions in garnets, was revealed in Kara glasses [14,15]. Since mineral segregations of crystalline garnet in the glass were not found, an assumption about the densification of the glass framework due to the solidification of the impact melt under high pressure was made. ...
... UHPHT melt impact glasses were sampled in 2015 and 2017 from impactites of the southern sector of the Kara crater from vein bodies cutting suevite massif ( Figure 1) at the Kara River (Pay-Khoy, Russia) and these are samples KP15-12-115 and KP15-12-118. A preliminary analysis of the structural state of these glasses was carried out using a set of standard mineralogical research methods [13,14,16]. The main feature distinguishing UHPHT melts from clast type glasses and massive melt impactites was found to be the multilevel differentiation of impact melt, including liquation of silicate and aluminosilicate melts and partial silica melt crystallization to UHP SiO2 variety-monocrystalline coesite [13,14]. ...
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In this study, we carried out the analysis of the impact melt vein glasses from the Kara impact crater (Russia) in comparison to low-pressure impact melt glasses (tektites) of the Zham-anshin crater (Kazakhstan). 27 Al, 23 Na, and 29 Si MAS NMR spectra of the samples of these glasses were analyzed. The samples of the natural glass contained inclusions of crystalline phases, para-magnetic elements that greatly complicate and distort the NMR signals from the glass phase itself. Taking into account the Mossbauer distribution of Fe in these glasses, the analysis of the spectra of MAS NMR of glass network-former (Si, Al) and potential network-modifiers (Na) of nuclei leads to the conclusion that the Kara impact melt vein glasses are characterized by complete polymerization of (Si,Al)O4 tetrahedral structural units. The NMR features of the glasses are consistent with the vein hypothesis of their formation under conditions of high pressures and temperatures resulting in their fluidity, relatively slow solidification with partial melt differentiation, polymerization, and precipitation of mineral phases as the impact melt cools. The 70 Ma stability of the Kara impact vein glass can be explained by the stabilization of the glass network with primary fine-dispersed pyroxene and coesite precipitates and by the high polymerization level of the impact glass.
... Numerous amorphous substances belong to very valuable types of materials, where glasses have especially important for different applications. The high top interest in the field is connected with the state of matter under extreme conditions [1][2][3][4][5]. In the nature the formation conditions of the glasses arise from magmatic melts (for example volcanic glasses and buchite); under impact (shock) processes (including melt impactites and tektites), and also, by quite rare fulgurite occurrences formed under lightning discharges, additionally in the nature some matter can be formed under nuclear weapon explosions [5]. ...
... The high top interest in the field is connected with the state of matter under extreme conditions [1][2][3][4][5]. In the nature the formation conditions of the glasses arise from magmatic melts (for example volcanic glasses and buchite); under impact (shock) processes (including melt impactites and tektites), and also, by quite rare fulgurite occurrences formed under lightning discharges, additionally in the nature some matter can be formed under nuclear weapon explosions [5]. Analyzing a variety natural glasses it is follow that they are quite widely spread on the Earth, Moon and Venus. ...
... In general, the substances have very wide range of chemical composition, structure and properties. Among the listed glasses the impact matter is especially potentially interesting [5]. According to the technical possibilities of the modern facilities for lab modelling of high pressure high temperature (HPHT) materials only tiny-sized particles can be produced with sizes no more than counting hundreds of micrometers under pressure usually up to 100 GPa and usually at room temperature [1][2][3][4]. ...
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Amorphous substances, including glasses, are very important kind of value materials for numerous applications. Among the glasses the impact matter has especially high fundamental interest and use potential, being formed under extremely high PT conditions-up to hundreds GPa and thousands degrees Celsius. In this direction the detail studies of new natural occurrences with UHPHT impact glasses and their features are very actual fundamentally and probably potentially useful for new ideas for technologies. Our analytical studies of the UHPHT ribbon-like impact glasses of the Ust`-Kara area at the Baydarata Bay (Kara Sea, Arctic Ocean) revealed the presence a number of special features such as multilevel differentiation of impact melt and coesite abundance. The specifics of the Ust`-Kara UHPHT glasses rather point to bottom facies of the suevitic breccia. The observed impactites characteristics allow to see new geological importance of the studied Ust`-Kara suevites, allow to correct geological model of the impact structure.
... Therefore, the study of the impact melt rocks and shock metamorphic materials from the impact craters using various spectroscopic and structural techniques is of interest to extract important information about variations of chemical composition, and structural and physical parameters resulting from impact melt rocks formation. For these reasons, various features of different impact melt rocks (impactites and tektites) were studied by chemical analysis, scanning and transmission electron microscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction (XRD), 57 Fe M€ ossbauer spectroscopy, and some other techniques (see, e.g., Bustamante et al., 2005;Ding & Veblen, 2004;Dunlap et al., 1998;Dunlap & McGraw, 2007;Dunlap & Sibley, 2004;Golubev et al., 2019Golubev et al., , 2020Loayza & Cabrejos, 2014;Ostroumov et al., 2002;Shumilova et al., 2018;Verma et al., 2008). ...
... A hump at the diffraction pattern in the 2Θ range of 20-40°indicates the presence of an amorphous component in the sample. A similar amorphous halo was observed in the XRD patterns of impact melts from Kara astrobleme and Ries crater (Golubev et al., 2020;Shumilova et al., 2018). Reflections of crystalline phases are visible against the background of the amorphous halo. ...
Iron‐bearing phases in the impact melt rock (impactite) from Jänisjärvi astrobleme (Karelia, Russian Federation) were studied by optical microscopy, electron probe microanalysis, Raman spectroscopy, X‐ray diffraction, and 57Fe Mössbauer spectroscopy. The phase composition and the contents of elements were determined in the studied impactite. The Raman spectra of cordierite, chamosite, and ilmenite in the impact melt rock were measured and analyzed. The 57Fe Mössbauer spectrum of Jänisjärvi impactite demonstrated the presence of different iron microenvironments in the iron‐bearing phases in the impact melt rock, which were assigned to cordierite; the M1, M2, M3, and M4 sites in chamosite; ilmenite; and ferrihydrite.
... Large impacts provide shock ultra-high high pressure conditions resulted in high temperature melted material partly saved as a melt pull at a crater bottom, partly ejected with back-fall material forming breccia impactites with clastic impact glasses named by suevites, some melted material is spread away from the crater and quenched as natural glasses -tectites forming wide strewnfields to the distance up to several thousand kilometres [1][2][3]. The impact glasses have specific features including composition and physical properties compare to volcanic glasses [4][5][6][7]. Among their characteristics the magnetic properties are the most important for geological mapping of the impact structures [8][9][10][11][12][13] and can be interesting for specific magnetic materials from impact glasses especially interesting in the context of the recently discovered unusual UHPHT impact melt glasses [5][6][7]. ...
... The impact glasses have specific features including composition and physical properties compare to volcanic glasses [4][5][6][7]. Among their characteristics the magnetic properties are the most important for geological mapping of the impact structures [8][9][10][11][12][13] and can be interesting for specific magnetic materials from impact glasses especially interesting in the context of the recently discovered unusual UHPHT impact melt glasses [5][6][7]. The Kara astrobleme has been studied by industrial geologists at geological mapping and scientific studies [8, [15][16][17][18][19] and it was found 2 that the impact crater is quite good recognisable by the geophysical data. ...
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The shock waves can strongly change the physical properties of the target rock minerals including their density and magnetism which determine petrochemical properties of impactites finely as a rule are resulted in astroblemes contours on geophysical maps. Following to the aero-magnetic mapping data the non-magnetic sedimentary rocks of the Kara target create a zero and negative magnetic field with an average intensity of -1 nT, against the background the southwestern region of the Kara astrobleme provides the positive magnetic anomalies with an intensity of 1 to 3 nT which are in a good correspondence with the Pay-Khoy ridge structure general orientation. The Kara dome is characterised with an isometric negative anomaly of intensity -5 nT. Here we present the magnetic properties of the different kinds of the Kara impactites including impact ultra-high pressure high temperature (UHPHT) melt glasses, melt rocks and suevitic breccia compare to sedimentary target rocks. The petrophysical measurements presented the specific magnetic susceptibility of the impactites in the range of 8 to 48×10 ⁻⁸ SI units, where the UHPHT glasses have the limits from 9 to 38×10 ⁻⁸ SI units (15×10 ⁻⁸ SI units, in average). The sedimentary target is characterised with essentially lower level of magnetic susceptibility – no higher than 15×10 ⁻⁸ SI units, where limestone has it about zero. Following to the similar level of the iron content within the impactites and target rocks the magnetism of the Kara impact melts is explained rather by changing of magnetic properties by the impact process. One of the possible source of magnetism can be partially an iron-containing matter of the asteroid component in the form of pyrrhotine accompanied with Ni and Co impurities. Also, we cannot exclude partial presence of magnetic iron component directly within the quenched impact glasses including UHPHT variety.
... The scanning electron microscopy data indicate that the fluidity is expressed due to SiO2 segregations. Within the melt rock II the segregations have a more complex structure, reminiscent of the liquation pattern of SiO2 droplets in the UHPHT vein glasses that have been widely studied earlier in general [9][10][11][12] and spectroscopically [13]. However, it is likely that these SiO2 structures have been formed as a result of incomplete melting of mineral fragments of the target rocks. ...
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The Kara astrobleme is one of the largest astroblemes known on land. Its diameter is ~65 km, the age is about 70 million years. The astrobleme is located at the northeastern part of the Pay-Khoy anticlinorium at the Kara River mouth region (Kara Sea coast, Russia). It is a unique object of impact genesis due to the presence of a variety of suevites and melt impactites. Melt rocks are products of the highest degree of impact transformation of target rocks. The diversity of melt rock impactites of the Kara astrobleme and obtaining their complex comparative mineralogical and petrochemical characteristics are important for solving the fundamental problem for studying of the typomorphism of the impactitogenesis products of melt rocks both – the impactites of the Kara astrobleme and other astroblemes in general. In the Kara astrobleme region there are at list two different types of massive melt rocks bodies – a cover melt rock at the Anaroga River (I) studied by previous researchers and an unexplored body of melt rock impactite at the Kara River (II) spatially connected with ultrahigh-pressure high-temperature (UHPHT) glasses just recently discovered. Our preliminary data indicate that the melt rock varieties of the Kara astrobleme have significant differences in texture and structure. The considered melt rocks are mostly composed of a matrix represented by a “mixture” of amorphous and cryptocrystalline masses of predominantly feldspar composition with a subordinate SiO 2 content. According to the data of energy dispersive analysis the compositions of the studied melt rocks are similar and have minor deviations within the first percent. The difference in the shape of silicate segregations in melt rocks may indicate that the impact melt could have a high temperature with a shorter time interval for the solidification of melt rock II on the Kara River, in contrast to the massive melt rock I on the Anaroga River, where the impact melt had large volume and, accordingly, was cooled longer at lower temperatures. The data obtained complement the specificity of the Kara melt impactites, which may play a role in complementing the geological model of the Kara astrobleme. The reported study was funded by RFBR, project number 20-35-90065; the analytical equipment has been used at the Center for Collective Use “Geonauka” (IG Komi FRC SC UB RAS, Syktyvkar, Russia); the author expresses his gratitude to Isaenko S.I. for analytical work using Raman spectroscopy; Tropnikov E.M. for help in performing microprobe studies.
... The dike dolerite material for the study has been sampled at Kara dome from the natural outcrops at the banks of the Sopchau river. The UHPHT impact melt glasses have been sampled at the southern part of the Kara astrobleme from natural outcrop of the UHPHT glasses within the host suevitic breccia at the right bank of the Kara river described earlier in [11][12][13][14]. The petrological study has been performed in standard thin sections by optical microscopy using polarization microscope POLAM R-312 (LOMO, Russia). ...
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Recent find of the ultra-high pressure high-temperature (UHPHT) impact melt glasses among the impactites of the Kara astrobleme has a high interest in nicely preserved 70 Ma glass with potentially unusual structure and properties. By the moment, it is important to understand about the substance source for the UHPHT glasses. The Kara target is characterized with complicated rock material preferably presented with Paleozoic sedimentary units. At the same time, the target has in a sequence Devonian sills and dikes of gabbro-dolerites. The latter appear on the surface at the Kara dome being a material which probably have been affected by the most strong impact. Here we for the first time describe the results of preliminary analysis of petrological and geochemical features of the magmatic dikes of the central uplift with the aim to understand their probable genetic source for the UHPHT impact melt veins matter. The provided studies point to essential difference between the compared materials, that means the UHPHT impact melts do not correspond to the magmatic material of the Khengursky complex of gabbro-dolerites of the Pay-Khoy Ridge (Russia).
The paper presents the results of study of the carbon-containing phase discovered in the impact glass of the Kara astrobleme. We used the following research methods: optical, scanning electron, and atomic force microscopies, as well as Raman spectroscopy. This phase represents carbon-containing inclusions up to several tens of micrometres in size with an amorphous diamond-like structure. At the nanoscale, the studied phase is characterized mainly by a homogeneous structure.
Ultra-high-pressure high-temperature (UHPHT) glass from astroblems is a very promising natural material from the point of view of the fundamental problem of the structure and properties of a substance formed under extreme PT-conditions. Such glasses consist of disordered aluminosilicate and silicate micro-sized phases with a heterogeneous structure with domain from units to tens of nanometers in size. We used AFM to evaluation the mechanical properties distribution at nanoscale in UHPHT glasses from the Kara astrobleme. The results of AFM were supplemented with optical and electron microscopy data. It is shown in the work that the nanomechanical properties of glasses measured using by PeakForce QNM generally correspond to the macroscopic properties of a bulk sample. We measured the Young's modulus for the first time for aluminosilicate and silicate phases of UHPHT glasses. AFM can be an effective tool for studying at the micro- and nanoscale mechanical properties of such rigid materials.
X-ray computed microtomography (CT) of impact rock varieties from the Kara astrobleme is used to test the method’s ability to identify the morphology and distribution of the rock components. Three types of suevitic breccias, clast-poor melt rock, and a melt clast from a suevite were studied with a spatial resolution of 24 µm to assess CT data values of 3D structure and components of the impactites. The purpose is first to reconstruct pore space, morphology, and distribution of all distinguishable crystallized melt, clastic components, and carbon products of impact metamorphism, including the impact glasses, after-coal diamonds, and other carbon phases. Second, the data are applied to analyze the morphology and distribution of aluminosilicate and sulfide components in the melt and suevitic breccias. The technical limitations of the CT measurements applied to the Kara impactites are discussed. Because of the similar chemical composition of the aluminosilicate matrix, glasses, and some lithic and crystal clasts, these components are hard to distinguish in tomograms. The carbonaceous matter has absorption characteristics close to air, so the pores and carbonaceous inclusions appear similar. However, X-ray microtomography could be used to prove the differences between the studied types of suevites from the Kara astrobleme using structural-textural features of the whole rock, porosity, and the distributions of carbonates and sulfides.
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Knowledge of pressure-induced structural changes in glasses is important in various scientific fields as well as in engineering and industry. However, polyamorphism in glasses under high pressure remains poorly understood because of experimental challenges. Here we report new experimental findings of ultrahigh-pressure polyamorphism in GeO2 glass, investigated using a newly developed double-stage large-volume cell. The Ge-O coordination number (CN) is found to remain constant at ∼6 between 22.6 and 37.9 GPa. At higher pressures, CN begins to increase rapidly and reaches 7.4 at 91.7 GPa. This transformation begins when the oxygen-packing fraction in GeO2 glass is close to the maximal dense-packing state (the Kepler conjecture = ∼0.74), which provides new insights into structural changes in network-forming glasses and liquids with CN higher than 6 at ultrahigh-pressure conditions.
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Silica glass has been shown in numerous studies to possess significant capacity for permanent densification under pressure at different temperatures to form high density amorphous (HDA) silica. However, it is unknown to what extent the processes leading to irreversible densification of silica glass in cold-compression at room temperature and in hot-compression (e.g., near glass transition temperature) are common in nature. In this work, a hot-compression technique was used to quench silica glass from high temperature (1100 °C) and high pressure (up to 8 GPa) conditions, which leads to density increase of ~25% and Young's modulus increase of ~71% relative to that of pristine silica glass at ambient conditions. Our experiments and molecular dynamics (MD) simulations provide solid evidences that the intermediate-range order of the hot-compressed HDA silica is distinct from that of the counterpart cold-compressed at room temperature. This explains the much higher thermal and mechanical stability of the former than the latter upon heating and compression as revealed in our in-situ Brillouin light scattering (BLS) experiments. Our studies demonstrate the limitation of the resulting density as a structural indicator of polyamorphism, and point out the importance of temperature during compression in order to fundamentally understand HDA silica.
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Modelling the mechanical response of silica glass is still challenging, due to the lack of knowledge concerning the elastic properties of intermediate states of densification. An extensive Brillouin Light Scattering study on permanently densified silica glasses after cold compression in diamond anvil cell has been carried out, in order to deduce the elastic properties of such glasses and to provide new insights concerning the densification process. From sound velocity measurements, we derive phenomenological laws linking the elastic moduli of silica glass as a function of its densification ratio. The found elastic moduli are in excellent agreement with the sparse data extracted from literature, and we show that they do not depend on the thermodynamic path taken during densification (room temperature or heating). We also demonstrate that the longitudinal sound velocity exhibits an anomalous behavior, displaying a minimum for a densification ratio of 5%, and highlight the fact that this anomaly has to be distinguished from the compressibility anomaly of a-SiO2 in the elastic domain.
Impact diamonds were discovered in the 70s and are usually accepted as being paramorphs after graphite, resulting in grains of extremely high mechanical quality. A diffusion-less mechanism for the graphite-to-diamond transition under huge pressure has been experimentally realized and theoretically explained. Besides, another type of impact product has received much less attention, namely diamonds formed after coal as a result of the impact. Here we describe after-coal impact diamonds from the giant Kara astrobleme (Pay-Khoy, Russia), which resulted from a large asteroid impact about 70 Ma ago. The impact created a large number of unusual impact diamonds, which are described here for the first time using high-resolution techniques including visible and UV Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Two main varieties of after-coal diamonds occur: micrograined (sugar-like, subdivided into coherent and friable) and, as a new type, paramorphs after organic relics. After-coal diamonds differ from after-graphite impact diamonds by the texture, the absence of lonsdaleite, a micro- and nanoporous structure. The sugar-like variety consists of tightly aggregated, well-shaped single nanocrystals. The after-organic diamond paramorphs are characterized by a well-preserved relict organic morphology, sub- nanocrystalline–amorphous sp3-carbon (ta-C) nanocomposites and other specific properties (optical transparence, brown color, very high luminescence, spectral features). Based on the description of after-coal diamonds, we propose a new, polystage formation mechanism: high-velocity coal pyrolysis with hetero-elements removal followed by diffusion-limited crystallization of pure carbon. The similarity of the after-coal diamonds features with carbonado is a strong piece of evidence in support of the impact hypothesis for the origin of carbonado.
The state of FeIII ions doped in sodium silicate glasses of the composition (100 − x)Na2O-xSiO2−y Fe2O3 (x = 75, 81 mol.%; y = 0.05−13 wt.%) was studied by electron spin resonance (ESR). X-band ESR spectra exhibited three resonance signals at g ≈ 2.0, 4.3, and 6. The computer simulation of ESR spectra was performed on the basis of spin-Hamiltonian of rhombic symmetry. The nature of observed signals was interpreted as a combination of five types of FeIII complexes. Three of them were clustered iron ions and two other were isolated paramagnetic ones. The ratio of observed forms was found for different glass compositions and various total amounts of FeIII ions in a matrix containing 0.55, 2.5, 4, 7, and 13 wt.% of Fe2O3.
The intensity of broad quartet signal often identified as methyl radical (·CH3) in alkali feldspars is enhanced by γ-irradiation. The average g factor and hyperfine A of the broad distorted signal are g = 2.0033 and A = 2.45 mT, respectively, and were previously identified as ·CH3 or ·C2H5. The intensity of the quartet signal is enhanced by two orders of the magnitude by hydrothermal experiments of Na-feldspars in NH3 atmosphere and therefore the signal was identified as ·NH3+ where the anisotropic hyperfine due to N (I = 1) is not observed due to broadening in the powdered spectrum.