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ISSN 1028334X, Doklady Earth Sciences, 2011, Vol. 440, Part 2, pp. 1391–1395. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.S. Antipin, A.M. Fedorov, S.I. Dril’, V.I. Voronin, 2011, published in Doklady Akademii Nauk, 2011, Vol. 440, No. 6, pp. 786–790.
1391
The Patom Crater in the Bodaibo district of Irkutsk
oblast (East Siberia) was discovered by V.V. Kolpakov
during a geological survey in 1949; the discoverer sug
gested a meteoritic hypothesis of its origin [1]. Later,
this hypothesis was supported by A.M. Portnov [2, 3],
who estimated the depth of meteorite bedding at about
180–200 m from the surface. He also believed that
Patom Crater had formed resulting from the fall of
Tunguska meteorite’s fragment in this part of the
Patom Highland in 1908. However, there were no con
vincing arguments for meteorite origin of the Patom
Crater in any of the publications. In 2006 and 2008,
the Patom Crater was complexly investigated by
geochemical geologists (Institute of Geochemistry,
Siberian Branch, Russian Academy of Sciences), geo
physicists (Irkutsk State Technical University), biolo
gists (Siberian Institute of Plant Physiology and Bio
chemistry, Siberian Branch, Russian Academy of Sci
ences), and astronomers (Astronomical Observatory
of Irkutsk State University); then, a geological map
was made and detailed geological–geochemical infor
mation on the rocks comprising the crater was
acquired for the first time [4, 5]. Now, on the basis of
these materials, th new data on Patom Crater age have
been obtained [6]; additionally, the substantial com
position of the composing rocks and their isotopic
geochemical peculiarities have been analyzed and this
has given ground for the endogenous hypothesis of the
crater origin.
The heterogeneous structure of Patom Crater is
expressed in a clearly seen zoning—alternation of its
principal structural elements: (1) outer slope of the
cone, (2) annular swell, (3) annular trench, and
(4) central rath (Fig. 1). The crater is surrounded by
terrigenous–carbonate rocks of the Mariinsk Forma
tion (Proterozoic) and is seen as an ejecta cone com
posed mainly of limestones and silicate rocks (sand
stones, metamorphized schists, quartz veins, some
times with muscovite). It has been found that the most
elevated part of the crater—the annular swell—is
divided by a shallow depression into two parts that
formed at different times. In the early stage, the inter
nal annular swell formed; it is composed of platelike
highly mouldy gray limestones with veins of white
quartz. It is a zone of gray limestones, where individual
blocks of metamorphized schists and sandstones are
found, and the landwaste of these carbonate and ter
rigenous rocks is often covered by moss. Additionally,
The New Data on the Origin
of the Patom Crater (East Siberia)
V. S. Antipin
a
, A. M. Fedorov
a
, S. I. Dril’
a
, and V. I. Voronin
b
Presented by Academician M.I. Kuz’min March 9, 2011
Received May 20, 2011
Abstract
—It has been found that the origin of the Patom Crater is related to endogenous processes with the
main role played by deep flow of fluid components, which determine formation of the ejecta cone at about
500 years ago or more. This is evidenced by the zonal structure of the crater and geochemical peculiarities of
rocks, caused by the long formation time for particular zones. Sandstone and schist blocks that were included
into eruptive breccia within the crater were affected by gaseous or fluid components and intensively carbon
ized. During carbonatization, these rocks within the crater were being enriched in Ca and Sr, but the shares
of the
87
Sr and, consequently,
87
Sr/
86
Sr ratio in them abruptly decrease. This is explained by the influence of
deep fluids on terrigenous rocks, which were initially depleted in the radiogenic strontium isotope and might
flow from a magmatic source with a low
87
Sr/
86
Sr ratio. However, these fluids were enriched in CO2 and
transported significant quantities of Sr, which led to enrichment of all terrigenous rocks in the crater in this
element. The discovery of individual sandstone blocks with high concentrations of summarized rare earth ele
ments (up to 557 g/t) and higher Sr and Ba contents among the fragments of host stratum within the Patom
Crater allows us to suppose that there is a magmatic source enriched in fluid components at depths. The effect
of the active fluid phase with low strontium isotopic ratios on rocks during the Patom Crater formation might
lead to an abrupt decrease in values of the initial
87
Sr/
86
Sr ratio in carbonized sandstones and schists.
DOI:
10.1134/S1028334X11100187
a
Vinogradov Institute of Geochemistry, Siberian Branch,
Russian Academy of Sciences, Irkutsk, Russia
b
Siberian Institute of Plant Physiology and Biochemistry,
Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia
email: antipin@igc.irk.ru (Antipin), sashaf@igc.irk.ru
(Fedorov)
GEOLOGY
1392
DOKLADY EARTH SCIENCES Vol. 440 Part 2 2011
ANTIPIN
et al.
individual larch trees grow upon these rocks. The
external swell is younger in age and does not contain
blocks of terrigenous rocks; it is composed of dark
gray massive crystalline limestones nearly intact by
weathering. The formation of Patom Crater had fin
ished before the appearance of the central hill, which
has on its top by massive crystalline limestones slightly
affected by weathering.
The quartz sandstones that bed northeast of the
crater, dipping beneath the limestones, are fine
grained rocks that contain quartz grains and cement
ing aggregate (chlorite, muscovite, carbonate, rare
plagioclase fragments, and sphene grains). The indi
vidual blocks of these sandstones within the ejecta
cone contain the same mineral association, but with a
sharply higher content of calcite that fills gaps between
isometric quartz and feldspar grains and often replaces
plagioclase precipitation products. This indicates late
formation of carbonate (i.e., a substantial carbonati
zation of silicate rocks). Along with fine and mid
grained sandstones, their more coarsegrained
polymicte types are found; these types contain, in
addition to isometric quartz grains, feldspars, mica,
sphene, magnetite, and rarely orthite and apatite. In
the interstitions between grains of these minerals, one
can also find calcite, which sometimes replaced by
feldspars. The content of carbonate material—and, in
particular blocks, schists—sharply increases in com
parison to the host stratum schists (Dzhebaldo
Mount), which consist of plagioclase, chlorite, mus
covite, and magnetite.
Since the age of the crater is of fundamental signif
icance, in 2008 V.I. Voronin performed a mass sam
pling of the most aged larch trees, which grew at a dis
tance of several meters from the internal scree of the
crater and in the crater proper. Dendrochronological
analysis indicated that about 500 years ago, during the
ejecta cone formation and active ground motion, a
mass tree felling occurred and the new generation of
larch trees originated (400–480 years in age). Thus,
the period of the crater formation can be assessed at
the late 15th–early 16th century. In the external scree
and in the earlier annular swell of the crater, the oldest
trees appeared 250–300 years ago. The studied trees
contained a catastrophic event in the rings of 1841–
1842 that caused various damage to trees. The time of
later annular swell formation may be around these
years. The conclusion that an earlier annular swell had
already been formed by this time is well grounded
since on the rocks of this swell a tree was found with
the age of 236 years [7]. In the central hill, trees are
significantly younger (from 101 to 71 years); i.e., it was
the last formed structure of the ejecta cone. Thus, the
age of the crater is about 500 years or more. The con
clusion proceeding from the geological data about the
crater’s formation over a long time has been proved;
particular catastrophic events related to different
stages of endogenous activity and the crater’s forma
tion have been recorded in dendrochronology.
The carbonate rocks, which are predominant in the
crater, correspond to an intermediate composition of
typical limestones with a CaO content of more than
Fig. 1.
Ph oto gra ph o f Pato m Cr ate r (m ade b y M. V. Anti pin , vi ew from Dzhebaldo Mount). The diameter of the basement is 125 ×
155 m, and the diameter of the annular swell is 80 m. The inset shows the geographical position of Patom Crater (asterisk).
115
°
60
°
N
E
Bodaibo
Irkutsk
DOKLADY EARTH SCIENCES Vol. 440 Part 2 2011
THE NEW DATA ON THE ORIGIN OF THE PATOM CRATER 1393
50% and MgO content no more than 1%. The content
of SiO
2
in them is ordinary for this type of rocks and
only quite increased in limestones of the earlier annu
lar swell (4.45%) due to the appearance of rare quartz
grains in the form of lensshaped schliers with recrys
tallization of carbonate rocks. Limestones of the later
swell contain less SiO
2
on average (2.09%). In general,
we can state that limestones from all the crater zones
and from the host stratum do not differ substantially in
terms of the average chemical composition. We
emphasize that the iron group elements (Ni, Cr, Co,
Cu, Sc), especially Ni, whose contents are usually the
highest in meteoritic material (relative to the terres
trial rocks from the continental crust), keep quite close
and very low concentrations in all the examinations of
carbonate rocks.
Owing to the mentioned process of substantial car
bonatization of sandstones and schists, which were
transported from deeper horizons during formation of
the ejecta cone, the CaO contents sharply increased in
these rocks (6.55–11.63% in sandstones and 17.41–
18.78% in schists) relative to the host stratum (3.01%
and 1.65% on average in sandstones and schists,
respectively). Terrigenous rocks within the crater are
also enriched in Sr: in some particular sandstone
blocks, the Sr content changes from 810 to 1117 g/t, at
an average content of 176 g/t in host sandstones and
680 g/t in schists, whereas the average Sr concentra
tion far from the crater is 406 g/t. However, the highest
Sr concentrations (often exceeding 2000 g/t) have
been identified both in limestones of the crater and in
carbonate rocks of the host stratum. Ba concentra
tions also increase in sandstones of the crater (up to
538 g/t) in comparison to its average concentration in
sandstones of the host stratum (315 g/t). In connec
tion with the analysis of geochemical zoning of the
Patom Crater rocks, the concentration of rare earth
elements (REEs) in them appeared to be quite low
(Fig. 2). It has also been found that the summarized
concentration of lanthanides in sandstones and schists
is lower within the crater (59.6–88.5) relative to the
host terrigenous rocks beyond it (92.0–119.5). The
distribution pattern of light and heavy lantanoids
changes insignificantly; this is seen from the visible
increase in the La/Yb ratio in sandstones and schists
within the crater (17.0–21.6) relative to the same
rocks within the host stratum (9.7–13.6).
Among the rocks of the earlier annular swell, we
found particular samples of polymicte sandstone,
ejected out from deep horizons; this sandstone dem
onstrate an anomalously high summarized REE con
centration (557.4 g/t) and the highest La/Yb ratio
(42.2) (Fig. 2). These sandstones are substantially
metamorphized and carbonatized, and contain
sphene, apathyte, and zircon, in addition to rock
forming minerals. The discovery of such rocks
enriched in REEs and other elements (Sr, Ba; see
table) within the crater is of a special interest, because
their levels of increased concentrations are character
istic for alkaline basalts and for some facies of carbon
atites in Siberia. For example, based on the published
data [8], in particular carbonatites of Siberia, the sum
marized REE+Y contents are from 549 to 566 g/t,
which is close to these concentrations in the studied
sandstones. In terms of normalized REE concentra
tions and of the La/Yb ratio, carbonatized sandstones
of Patom Crater are quite close, for example, to alka
line basalts of Kamar Ridge (CisBaikal Region) and
to the rocks of modern carbonatite volcanoes of the
East African Rift (Oldoinyo Lengai and Kerimasi)
(Fig. 2). The calcites from the studied carbonatized
sandstones of the crater contain substantially higher
quantities of Fe (11750 g/t) and Ba (135 g/t); calcites
of later calcite veins with rare fluorite are sharply
enriched in Sr (4130–6150 g/t), compared to the
Sr content in calcites of sedimentary carbonate rocks
(610 g/t) [9].
As was noted, cave sandstones and schists were
simultaneously enriched in Ca and Sr during carbon
atization at Patom Crater, and there is a direct depen
dence between the Sr and CO
2
contents. This gives us
grounds to think that Sr enrichment of the studied
rocks is related to the effect of deep fluids on them and
this effect is especially manifested during carbonatiza
tion of sandstones and schists within the zone of the
earlier swell of the crater.
It can be stated based on the resulting isotopic data
(table) that the modern
87
Sr/
86
Sr ratio in limestones of
Patom Crater and in host carbonate rocks changes in
quite narrow limits (0.707694–0.708777) and is close
to average values of this parameter in limestones of
other provinces of Siberia. For example, based on the
data by I.M. Gorokhov et al. [10], within the limits of
the Ura Rise of the Patom Fold Belt, variations of the
primary
87
Sr/
86
Sr ratio for limestones of the Nikolskii
Fig. 2.
Distribution of rare earth elements in the Patom
Crater rocks.
1
, carbonized sandstone (2);
2
, schist (3);
3
, sandstone (6);
4
, limestone of the earlier swell (8);
5
,carbonate of the East African Rift (O is the Oldoinyo
Lengai Volcano, K is the Kerimasi Volcano);
6
, alkali
basalts (Kamar Ridge, CisBaikal Region). Number of
samples is written in parentheses.
10000
100
1000
10
1La Се Pr Nd Sm Eu Gd Tb Dy Ho Er Yb Lu
123456
Rock/Chondrite
O
K
1394
DOKLADY EARTH SCIENCES Vol. 440 Part 2 2011
ANTIPIN
et al.
and Chenchin Formations (Upper Neoproterozoic)
are in the interval of 0.70811–0.70939.
The opposite pattern of strontium isotope distribu
tion was found for silicate rocks (table, Fig. 3). Host
sandstones and crystalline schists of Mariinka Forma
tion demonstrate a substantially more radiogenic
modern isotopic strontium composition:
87
Sr/
86
Sr =
0.714726–0.715049 and 0.725679, respectively. How
ever, within the limits of Patom Crater, these silicate
rocks have significantly lesser radiogenic marks:
0.708481–0.713517 for sandstones and 0.712014 for
schists. The decrease in the
87
Sr/
86
Sr ratio in terrige
nous rocks (which are represented in the forms of
inclusions, blocks, and bombs in carbonate breccias of
the crater) may be related to the deep carbonatization
of these rocks initiated by the endogenous fluid phase,
which was enriched in CO
2
and had low
87
Sr/
86
Sr ratio
values. The change in isotopic composition of sand
stones and schists during the overlain carbonatization
is shown in Fig. 3, where one can see the mixing lines
for strontium from carbonates and host terrigenous
rocks.
Thus, Patom Crater, by its geological and material
characteristics, is a zonal annular structure of the cen
tral type with the ejecta cone composed of carbonate
and silicate rocks. The crater is located in the north
ernmost part of the CisBaikal area of Late Cenozoic
volcanism. The weak activity of processes of the ejecta
cone formation at the Patom highland may be related
to such a marginal position, at a distance from the cen
ters of more extensive volcanic processes.
(1) At present, the origin of Patom Crater from
endogenous processes has been proved. Among these
processes, the main role was played by deep flow of
fluid components that determined formation of the
ejecta cone about 500 years ago. This is evidenced by
the zonal structure of the crater and geochemical
Ba and Sr contents and isotopic composition of strontium in the Patom Crater rocks
Sample Characteristics of rocks Ba Sr
87
Sr/
86
Sr ±2
σ
µ
g/g
PT134 Limestone from the central rath 144 1856 0.707864 0.000009
PT135 Limestone from the central rath 212 1594 0.708048 0.000009
PT148 Limestone from the annular trench 151 1853 0.708151 0.000010
PT138 Limestone from the later swell 109 1320 0.708777 0.000010
PT139 Limestone from the earlier swell 156 1714 0.708120 0.000010
PT152 Limestone from the host stratum 80 2283 0.707694 0.000010
PT141 Sandstone from the crater 334 544 0.708481 0.000011
PT142 Sandstone from the crater 374 811 0.713517 0.000009
PT130 Sandstone from the host stratum 287 235 0.715049 0.000012
PT133 Sandstone from the host stratum 230 170 0.714726 0.000010
PT144 Schist from the crater 1099 601 0.712014 0.000010
PT154 Schist from the host stratum 919 445 0.725679 0.000012
Note: Analysis of strontium isotopic composition was performed in the oneband mode with tantalum activator on the Finnigan MAT262
polycollector mass spectrometer (Center of Collective Use for the Institute of the Earth’s Crust, Institute of Geochemistry, and Buryat
Geological Institute, Siberian Branch, Russian Academy of Sciences, Irkutsk). During measurements by the VNIIM standard, the iso
topic ratio of 87Sr/86Sr = 0.708036 ± 10 was derived (errors correspond to 2σ, n = 12) at the recommended value of 87Sr/86Sr =
0.708028 [11]. The table presents the data normalized to the recommended value of the VNIIM standard.
Fig. 3.
The diagram of the modern
87
Sr/
86
Sr ratio varia
tions depending on the value of inverse strontium content
in rocks of Patom Crater and host strata.
1
, host lime
stones;
2
, carbonate rocks of the crater;
3
, sandstones of
the crater;
4
, crystalline schists of the crater and host stra
tum;
5
, host sandstones;
6
, average composition of the
upper continental crust. Mix line 1 describes the shift pro
cess of strontium contained in host carbonates and host
crystalline schists; Mix line 2, strontium contained in host
carbonates and host sandstones.
0.730
1.0
87
Sr/
86
Sr
0.725
0.720
0.715
0.710
0.705
1
2
3
4
5
6
1
Sr
1000×
Mix
line 1
Mix
line 2
DOKLADY EARTH SCIENCES Vol. 440 Part 2 2011
THE NEW DATA ON THE ORIGIN OF THE PATOM CRATER 1395
peculiarities of rocks, caused by the long formation
time for particular zones. It has been found that sand
stone and schist blocks composing eruptive breccia
were affected by gaseous or fluid components and
intensively carbonatized.
(2) During carbonatization within the crater limits,
sandstones and schists become enriched in Ca and Sr,
but the share of radiogenic isotope
87
Sr (and, conse
quently, the
87
Sr/
86
Sr ratio as well) in them sharply
decreases. This is explained by the effect of deep fluids
initially depleted in the radiogenic strontium isotope
(most likely, they were supplied from a source with a
low
87
Sr/
86
Sr ratio) on terrigenous rocks of the crater.
(3) The discovery of individual sandstone blocks
with high concentrations of summarized rare earth
elements (up to 557 g/t) and higher Sr and Ba contents
among the fragments of host stratum within Patom
Crater allows us to suppose that there is a magmatic
source enriched in fluid components at depths. The
effect of the active fluid phase with low ratios of stron
tium isotopes [12] on rocks during Patom Crater for
mation might lead to a sharp drop in the initial value of
the
87
Sr/
86
Sr ratio in carbonatized sandstones and
schists.
ACKNOWLEDGMENTS
The authors are grateful to all the organizators of
the expeditions to Patom Crater for help and support,
and analysts of the Institute of Geochemistry, Siberian
Branch, Russian Academy of Sciences, for analyses
performed: I.E. Vasil’eva (analysis of minerals),
A.K. Klimova (Xray fluorescence), L.A. Chuvashova,
and E.V. Smirnova (ICP MS).
This work was supported by the Presidium of the
Russian Academy of Sciences (project no. 142).
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