Geology and Geophysics, 2004, V 45, N 11, November.
TECTONICS AND GEODYNAMICS
Mechanisms of sea-depth changes in Silurian epeiric basins
of East Siberia.
E.B. Artyushkov and P.A. Chekhovich
1219
Formation of the East Kamchatkan accretionary prism based on
fission-track dating of detrital zircons from terrigene rocks.
A.V. Solov'ev, M.N. Shapiro, J.E. Garver, and A.V. Lander
1237
Neotectonic type structures of contraction, shear, and extension of
the northern part of Great Altai (Gorny Altai and Southern Altai).
I.S. Novikov, E.M. Vysotsky, and A.R. Agatova
1248
PETROLOGY, GEOCHEMISTRY, AND MINERALOGY
Relationship between Al-bearing phases NAL and CF in the lower
mantle.
K.D. Litasov and E. Ohtani
1259
Initial magmas of Proterozoic troctolite-anorthosite massifs of
North America and evolutionary trend of time-dependent
variability of composition of peridotite-gabbro massifs.
P.A. Balykin and T.E. Petrova.
1274
Distribution of noble metals in ophiolite associations of the
Altai-Sayan folded area.
A.S. Lapukhov, V.A. Simonov, R.D. Mel'nikova,
and G.A. Tret'yakov
1286
Carbon isotope composition of the Hesen and
Chulaktau formations (Hovsgol and Karatau
phosphorite basins).
A.V. Il'in, Yu.A. Kiperman, and A.A. Poyarel’
1297
GEOPHYSICS
Seismic exploration by refracted waves in
petroleum prospecting.
N.N. Puzyrev
1304
Estimating parameters of a ferromagnetic
cylindrical conductor by inversion of TEM field
M.I. Epov, G.M. Morozova, E.Yu. Antonov, and S.V. Shatrov
1306
Assessment of a large earthquake risk in the zone
of Main Sayan Fault using GPS geodesy and paleoseismology.
V.A. San'kov, A.V. Chipizubov, A.V. Lukhnev, O.P. Smekalin,
A.I. Miroshnichenko, E. Calais, and J. Deverchere.
1317
MECHANISMS OF SEA-DEPTH CHANGESIN
SILURIAN EPEIRIC BASINS OF EAST SIBERIA
E.V. Artyushkov and P.A. Chekhovich*
United Institute of the Physics of the Earth, Russian Academy of
Sciences, 10 ul. B. Gruzinskaya, Moscow, 123810, Russia
* Lomonosov Moskow State University, Vorob'yovy Gory, Moscow,
119899, Russia
It is commonly recognized that sea level experienced strong
global-scale systematic changes in the geologic past. Its 20-100 m
fluctuations in 1-10 Myr (third-order) cycles are most often
detected using Fischer plots based on thicknesses of meter-scale
cycles in sections of shallow-marine carbonate facies. However, the
classical Fischer plots constructed for different regions of East
Siberia show considerable mismatch though eustatic changes are
supposed to be globally synchronous. This mismatch is caused by
time-dependent variations in durations of elementary cycles
asynchronous in different sections. Therefore, a great number of
earlier inferred global eustatic events apparently never existed in
reality. We obtained more reliable accommodation plots with
thicknesses of 0.5 Myr synchronous chronozones as elementary units
in the Silurian sections of East Siberia. According to these plots,
eustatic fluctuations never exceeded ±5-7 m throughout the Silurian,
which is far below the accepted magnitude of 30-130 m. The Silurian
stratigraphic subunits and intervals between tectonic events were
constrained due to stable durations of the chronozones. Our plots
reveal strong lateral variations of crustal subsidence rates over
East Siberia. These variations were controlled neither by the
flexural response of lithosphere to changes in horizontal stresses
nor by the mantle topography dynamics, but rather by metamorphic
phase change and related consolidation of the mafic lower crust.
Subsidence rates occasionally became times faster or slower within
~0.5 Myr intervals, the contrasts surprisingly great for platforms.
Phase change rates may have been controlled by deviatoric stresses
in addition to temperature and fluid migration. This mechanism can
be responsible for subsidence rate variations reported for many
intracratonic basins.
Siberian craton, Silurian, epeiric seas, subsidence rate,
metamorphism in lower crust, eustasy, sedimentary cycles
FORMATION OF THE EAST KAMCHATKAN ACCRETIONARY PRISMBASED
ON FISSION-TRACK DATING OF DETRITAL ZIRCONSFROM TERRIGENE ROCKS
A.V. Solov'ev, M.N. Shapiro*, J.I. Garver**, and A.V. Lander***
Institute of Lithosphere of Marginal and Inner Seas of the RAS, 22
Staromonetny per., Moscow, 119180, Russia
* United Institute of Physics of the Earth, 10 ul. Bol'shaya
Gruzinskaya, Moscow, 123810, Russia
** Geological Department, Union College, Schenectady, New York, USA
*** International Institute of Earthquake Prediction Theory and
Mathematical Geophysics of the RAS,
79 Varshavskoe Shosse, Bldg. 2, Moscow, 113566, Russia
Fission-track ages were determined from detrital zircons from
sandstones of the Drozdov and Stanislavskaya Formations and Tyushev
Series of the Kumroch Range, eastern Kamchatka. The age of the young
zircon population in the sandstones of the Drozdov Formation
(Kumroch Range) is late Late Paleocene (from 55.9 ± 4.4 to 57.7 ±
3.5 Ma). The Drozdov Formation was deposited in the late Paleocene
and continued to accumulate in the Early Eocene. The age of young
zircon populations in the coarse-clastic sequence of the
Stanislavskaya Formation (40.7 ± 3.1; 40.9 ± 3.9; 42.4 ± 1.9 Ma)
indicates that it accumulated as late as middle Bartonian. The age
of young zircon populations in the sandstones of the Tyushev Series
(from 50.0 ± 2.9 to 38.1 ± 3.4 Ma) is much older than the age of the
sandstones themselves (Early-Middle Miocene, 24-11 Ma). Therefore,
in the Early Miocene, the Tyushev Series accumulated a distance from
central Kamchatka, volcanic activity was intense at that time.
There are three tectonic zones within the East Kamchatkan
accretionary prism: Stanislavskaya, Vetlovaya, and Tyushev. The
Stanislavskaya zone, represented by terrigenous units, are
interpreted as deposits of the accretionary prism that originated
after the Ozernoe-Valagin arc collided with the Eurasian margin. The
Vetlovaya zone was formed by offscraping cover strata from the
oceanic crust that separated the Ozernoe-Valagin and Kronotsky arcs
in the middle Paleocene to late Miocene. Deposits of the Tyushev
zone formed the Oligocene-Miocene cover of the «aseismic» Kronotsky
Range, which was active following the demise of the Kronotsky arc.
Units of the Tyushev zone became part of the East Kamchatkan
accretionary prism after the Late Miocene collision of the Kronotsky
block with Kamchatka.
Fission-track dating, zircon, tectonic evolution, East
Kamchatkan accretionary prism
NEOTECTONIC TYPE STRUCTURES OF CONTRACTION, SHEAR,AND EXTENSION
OF THE NORTHERN PART OF GREAT ALTAI(Gorny Altai and Southern Altai)
I.S. Novikov, E.M. Vysotsky, and A.R. Agatova
United Institute of Geology, Geophysics and Mineralogy, Siberian
Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Neotectonics and orography of southern Great Altai are
controlled by a system of dextral shears of northwestern strike,
which are completed in the north by systems of upthrows and
divergent faults. The recentmost structure of the northern part of
Altai is more complicated. It does not result, however, from chaotic
hummocking of the continental lithosphere but follows the same
structural regularities as the shear structure of the southern part
of the Mongolian Altai mountains to which it is spatially and
genetically related. It is more complicated because, unlike the
Mongolian Altai, it formed at the boundary of three rather than two
framing walls which approach each other slipping along the strike.
Within the Mongolian Altai the strikes of fractures of the Paleozoic
basement and the recentmost fractures generally coincide in space so
that the recentmost disjunctions often renew the lines of old
tectonic contacts, whereas in northern Altai the recentmost ruptures
occur along the Paleozoic faulting zones only at some segments and
more frequently cut them at different angles.
Geomorphology, neotectonics, morphotectonics, structural
geology, recentmost strike-slip faults, upthrows, divergent faults,
Altai
RELATIONSHIP BETWEEN Al-BEARING PHASES NAL AND
CFIN THE LOWER MANTLE
K.D. Litasov and E. Ohtani*
United Institute of Geology, Geophysics and Mineralogy, Siberian
Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Institute of Mineralogy, Petrology and Economic Geology, Tohoku
University, Sendai, Japan
Alumina-bearing phases with orthorhombic (phase CF) and
hexagonal (phase NAL) structures have been identified in average
MORB composition at pressures above 25 GPa. These phases are very
similar in structure and composition and can coexist in a single
experimental sample. In this paper, we report data on the chemical
composition, structure, and stability fields of the CF and NAL
phases and study their relationship in the lower mantle. It is shown
that these phases are stable at a pressure of 20 GPa and
temperatures below 1300 °C as well as at a pressure of 25 GPa and
temperatures below the solidus temperature. We have established that
the stability of NAL and CF phases is determined mainly by the
chemical composition of the system and, especially, the proportion
of Na2O and K2O. Phase NAL appears in the MORB system at a pressure
of 24-25 GPa and contains (wt.%) Al2O3 (55-57), SiO2 (10-13), Na2O
(5-6), and K2O (0.5-1.5). Phase CF appears at 26 GPa and completely
replaces the NAL phase at 28-30 GPa. At 26-27 GPa, these phases have
almost a similar composition (32-38 wt.% Al2O3 and 25-28 wt.% SiO2).
However, the NAL phase contains less Na2O (6-7 wt.%) and more K2O
(up to 1.5 wt.%) than the CF phase, which is free of K2O. We suggest
that the CF phase is more stable in the lower mantle than the NAL
phase. The stability field of the NAL phase can expand to higher
pressures as a result of local K2O-enrichment of the mantle.
Lower mantle, oceanic crust, Al-bearing phases
INITIAL MAGMAS OF PROTEROZOICTROCTOLITE-ANORTHOSITE MASSIFS
OF NORTH AMERICAAND EVOLUTIONARY TREND OF TIME-DEPENDENT VARIABILITY
OF COMPOSITION OF PERIDOTITE-GABBRO MASSIFS
P.A. Balykin and T.E. Petrova
Institute of Geology, Siberian Branch of the RAS, 3 prosp. Akad.
Koptyuga,
Novosibirsk, 630090, Russia
Compositions of initial magmas for some well-explored
troctolite-anorthosite massifs of North America were estimated and
numerically modeled using the COMAGMAT-3.3 program. The objects of
study were the Kiglapait, Michikamau, and Harp Lake massifs of the
Nain plutonic series of the Labrador Peninsula (Canada), the
Adirondack massif of the Grenville orogen of Proterozoic age (New
York, USA), and the Duluth massif of the North American rift
(Minnesota, USA). These massifs have been characterized in short,
with petrochemistry of their rock components estimated
statistically. It has been established that in norm composition the
initial magma corresponded to olivine-orthopyroxene-bearing basalts
for the Harp Lake massif, and to olivine basalts, for the other
massifs. On the basis of the Albarede regression equations, it has
been shown that the magmas were extracted by melting at pressures of
9-13 kbar (Harp Lake, Michikamau, and Kiglapait massifs) to 19-22
kbar (Duluth and Adirondack massifs) and at temperatures of 1200 to
1400 °C. The plutons formed at 1-3 kbar, 1100-1300 °C, and oxygen
activity corresponding to wustite-magnetite buffer. The Harp Lake
massif characterized by orthopyroxene trend of rock composition was
formed at relatively lower temperatures and pressures as compared
with the other massifs. The obtained estimates confirmed and refined
the previously established evolutionary trend according to which the
Archean-Early Proterozoic peridotite-gabbroic massifs with
orthopyroxene composition of differentiates were replaced by
Proterozoic-Phanerozoic massifs with olivine-plagioclase and
olivine-clinopyroxene compositions of rocks.
Troctolite-anorthosite massifs, initial magma, numerical
modeling, depth of melting, physicochemical conditions of
crystallization, formational type, evolutionary trend
DISTRIBUTION OF NOBLE METALS IN OPHIOLITE ASSOCIATIONS
OF THE ALTAI-SAYAN FOLDED AREA
A.S. Lapukhov, V.A. Simonov, R.D. Mel'nikova, and G.A. Tret'yakov
Institute of Geology, Siberian Branch of the RAS, 3 prosp. Akad.
Koptyuga, Novosibirsk, 630090, Russia
We carried out a comparative analysis of the distribution of
background contents of PGE and gold in rocks of ophiolite
associations of the Altai-Sayan area (ophiolites of Kuznetsk Alatau,
Gorny Altai, and West Sayan) and the Mid-Atlantic Ridge (MAR). The
sections of ophiolites and modern oceanic lithosphere
(ultrabasites-gabbros-dikes-effusions) have been studied. The
contents of gold, PGE, and accompanying elements in the rocks were
determined by the radiochemical neutron activation, atomic
absorption, and X-ray fluorescence methods, and the contents of
volatiles, by gas chromatography. Modern and ancient structures show
similar PGE and gold patterns. The studied rocks have contents of
low-melting PGE of the palladium association commensurate with those
in primitive mantle and are drastically depleted in high-melting PGE
of the iridium association. In PGE contents ultrabasites of all
studied regions of the Altai-Sayan area are close to primitive
mantle. Modern oceanic basalts (like N-MORB of the MAR) are most
similar to magmatic ophiolite complexes of Gorny Altai and West
Sayan. Island-arc ultrabasites of Kuznetsk Alatau are depleted in Ir
and are enriched in Au. Both in the ancient ophiolite associations
and in the modern oceanic lithosphere of the MAR, the water content
increases with the contents of PGE of the iridium association.
Fractionation of PGE and gold occurs both as a result of magmatic
differentiation of matter and under the effect of fluids at
postmagmatic stages.
Ophiolites, modern oceanic lithosphere, geochemistry, platinum
group elements, gold, volatiles, Altai-Sayan area
CARBON ISOTOPE COMPOSITIONOF THE HESEN AND CHULAKTAU FORMATIONS
(Hovsgol and Karatau phosphorite basins)
A.V. Il'in, Yu.A. Kiperman*, and A.A. Poyarel'**
Institute of Lithosphere of Marginal and Inner Seas, Russian Academy
of Sciences,22 Staromonetny per.,
Moscow, 119180, Russia
* All-Russian Research Institute of Economics of Mineral Raw
Materials and Interior Use,38 ul.
Tret'ya Magistral'naya, Moscow, 123007, Russia
** Kazfosfat Joint-Stock Company, 126 ul. Abaya, Toraz, 484039,
Kazakhstan
The values of d13C were measured in phosphorites and dolomites
composing productive formations of the Hovsgol and Karatau
phosphorite basins (Hesen and Chulaktau Formations, respectively)
and in dolomites overlying these formations (Hovsgol and Tamdy
series, respectively). The d13C plots of both phosphorites and
dolomites from the Hesen Formation demonstrate a clearly expressed
negative anomaly with d13C of up to -7 ‰ PDB. In the underlying
dolomites, d13C is nearly zero and increases to +2 ‰ downsection. In
the overlying thin-layered dolomites, d13C increases from -2 to 0
and up to +7 ‰ upsection. The Chulaktau Formation shows a similar
d13C behavior, with d13C of about -6 ‰ in phosphorites, dolomites,
and other phosphate and carbonate rocks. The lower dolomite member
and ferromanganese horizon have d13C values close to zero; in the
overlying dolomites of the Tamdy series, d13C increases to +3 ‰. The
d13C plots are similar for rocks of both basins. Negative anomalies
are observed within the Hovsgol basin and are lacking in dolomites
of the Bokson series stratigraphically corresponding to the Hesen
Formation. The anomalies are caused by the decomposition of organic
remains, which served as primary concentrators of phosphorus
dissolved in sea water. The decomposition was accompanied by release
of isotopically light carbon dioxide, which was then mineralized in
dolomites and, as an isomorphous admixture, in phosphates.
Carbon isotope anomaly, phosphorite, dolomite
SEISMIC EXPLORATION BY REFRACTED WAVESIN PETROLEUM PROSPECTING
N.N. Puzyrev
United Institute of Geology, Geophysics and Mineralogy, Siberian
Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
The method of refracted (head) waves rarely used in petroleum
prospecting has a high exploratory potential and can be applied to
regional- and local-scale problems. Special experimental work in
petroleum basins will be useful to investigate the influence of oil
and gas fields on the behavior of refracted waves.
Seismic exploration in petroleum basins, head waves, method of
refracted waves, wide-angle reflections
ESTIMATING PARAMETERS OF A FERROMAGNETIC CYLINDRICAL
CONDUCTOR BY INVERSION OF TEM FIELD
M.I. Epov, G.M. Morozova, E.Yu. Antonov, and S.V. Shatrov*
Institute of Geophysics, Siberian Branch of the RAS, 3 prosp. Akad.
Koptyuga, Novosibirsk, 630090, Russia
* Novosibirsk State University, 2 ul. Pirogova, Novosibirsk, 630090,
Russia
A new approach to estimating the wall thickness and magnetic
permeability of well casing strings for flaw detector designing
implies simulation of the TEM response of a current loop in a
cylindrically layered ferromagnetic conductor using analytical
expressions of emf partial derivatives. Wall thicknesses and
magnetic permeabilities of metal casing found as an iteration
solution to the inverse problem show good agreement with the exact
parameters in theoretical curves and with experimental data.
TEM field, conductivity, ferromagnet, magnetic permeability,
inverse problem
ASSESSMENT OF A LARGE EARTHQUAKE RISKIN THE ZONE OF MAIN SAYAN FAULT
USING GPS GEODESY AND PALEOSEISMOLOGY
V.A. San'kov, A.V. Chipizubov, A.V. Lukhnev, O.P. Smekalin,A.I.
Miroshnichenko,
E. Calais*, and J. Deverchere**
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul.
Lermontova, Irkutsk, 664 033, Russia
* Purdue University, West Lafayette, IN 47907-1397, USA
** Universitede Bretagne Occidentale (UBO), Institut Universitaire
Europeen de la Mer (IUEM),Technopole Brest-Iroise,
Place Nicolas Copernic, F-29280, Plouzane, France
GPS and paleoseismological studies of Holocene and recent slip
rates in the zone of the Main Sayan Fault show that the fault is
currently locked, and the accumulated stress may release in a large
earthquake. The southeastern flank of the fault generated at least
five large earthquakes for the past 10 kyr. For the time elapsed
since the ultimate event, the fault has accumulated pending
displacement of 1.4-3.1 m, given its 3.1 mm/yr average slip, which
can be accommodated in an M = 7.1-7.5 earthquake. Thus the densely
populated industrial areas around the southeastern fault flank in
the southern Baikal region are exposed to high seismic risk.
Faults, GPS measurements, paleoseismology, slip rate,
earthquake, seismic risk