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Evolution of the Kurile-Kamchatkan Volcanic Arcs and Dynamics of the Kamchatka-Aleutian Junction


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The Cenozoic tectonic evolution of the Kurile-Kamchatkan arc system has been reconstructed based on the spatial-tectonic setting of the volcanic-rock formations and their petrologic-geochemical characteristics, using gravity and seismic data. Three volcanic arc trench systems of different ages that become successively younger toward the Pacific have been recognized in the region: the West Kamchatka (Eocene), Mid-Kamchatka-Kurile (Late Oligocene-Quaternary), and Recent Kurile-Kamchatka systems. The Kamchatka volcanic belts are viewed as the products of these systems, which originated above the subduction zones. The geometry of the present-day Kurile-Kamchatka subduction zone and dynamics of contemporary volcanism can be defined from seismic data. The contemporary Kurile-Kamchatka arc can be subdivided into individual segments in accord with its tectonic evolution and geodynamics. The East Kamchatka segment represents the initial subduction stage (7-10 Ma ago) of the Pacific Plate. The Petropavlovsk segment (the Malka-Petropavlovsk zone of transverse faults) is a zone of discordant superposition of the contemporary Kurile-Kamchatka arc over the older Mid-Kamchatka arc. Within the South Kamchatka segment subduction remained practically unchanged since the Late Oligocene, i.e., since the origin of the Mid-Kamchatka-Kurile arc system, as well as within the three Kurile segments. Geodynamics controlled magma generation and is imprinted in the petrochemical properties of the volcanic rocks. Typical arc magmas are generated at the steady-state geodynamic regime of subduction. Lavas of an intraplate geochemical type are generated at initial and final stages of subduction, and also at the Kamchatka-Aleutian junction.
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Evolution of the Kurile-Kamchatkan Volcanic Arcs and
Dynamics of the Kamchatka-Aleutian Junction
G. P. Avdeiko, D. P. Savelyev, A.A. Palueva, and S. V. Popruzhenko
Institute of Volcanology and Seismology, East Division of Russian Academy of Science,
Petropavlovsk-Kamchatsky, Russia
The Cenozoic tectonic evolution of the Kurile-Kamchatkan arc system has been
reconstructed based on the spatial-tectonic setting of the volcanic-rock forma-
tions and their petrologic-geochemical characteristics, using gravity and seismic
data. Three volcanic arc trench systems of different ages that become successively
younger toward the Pacific have been recognized in the region: the West Kamchatka
(Eocene), Mid-Kamchatka-Kurile (Late OligoceneQuaternary), and Recent
Kurile-Kamchatka systems. The Kamchatka volcanic belts are viewed as the prod-
ucts of these systems, which originated above the subduction zones. The geometry of
the present-day Kurile-Kamchatka subduction zone and dynamics of contemporary
volcanism can be defined from seismic data. The contemporary Kurile-Kamchatka
arc can be subdivided into individual segments in accord with its tectonic evolution
and geodynamics. The East Kamchatka segment represents the initial subduction
stage (7–10 Ma ago) of the Pacific Plate. The Petropavlovsk segment (the Malka-
Petropavlovsk zone of transverse faults) is a zone of discordant superposition of the
contemporary Kurile-Kamchatka arc over the older Mid-Kamchatka arc. Within the
South Kamchatka segment subduction remained practically unchanged since the
Late Oligocene, i.e., since the origin of the Mid-Kamchatka-Kurile arc system, as
well as within the three Kurile segments. Geodynamics controlled magma genera-
tion and is imprinted in the petrochemical properties of the volcanic rocks. Typical
arc magmas are generated at the steady-state geodynamic regime of subduction.
Lavas of an intraplate geochemical type are generated at initial and final stages of
subduction, and also at the Kamchatka-Aleutian junction.
The Kur ile-Kamchatkan subduction system is a very
appropriate region for the reconstruction of volcanic arc
(VA) evolution and of the geodynamic conditions of VA
volcanism and magma generation for a number of reasons.
First, the Kurile segment of this system is a typical island arc
with a steady-state regime of subduction, but Kamchatka is
an active continental margin with three VA of different ages.
Second, within Kamchatka there are VA temporally posi-
tioned at the initial stage of subduction (Eastern Kamchatka)
and at the final stage of subduction (the Sredinny Range).
Third, typical VA rocks are distributed on the Kuriles and in
South Kamchatka, whereas some volcanic rocks with intra-
plate geochemical characteristics coexist with predominant
VA rocks in East Kamchatka and in the Sredinny Range
[Volynets, 1994]. And finally, a transition from arc to oce-
anic volcanic rocks takes place at the Kamchatka-Aleutian
Volcanism and Subduction: The Kamchatka Region
Geophysical Monograph Series 172
Copyright 2007 by the American Geophysical Union.
junction [Portnyagin et al., 2005]. Additionally, high mag-
nesian basalts and adakites occur in this region [Volynets et
al., 1999; Yogodzinsky et al., 2002].
This paper is an attempt to synthesize moder n spatial-
str uctural, petrological and geochemical data in relation
to the tectonic evolution and volcanism of the Ku rile-
Kamchatkan VA system, with the aim of reconstruction of
geodynamic conditions of different types of VA volcanism
and establishing criteria for paleotectonic reconstructions of
volcanism of ancient subduction zones.
2.1 Geology Framework of Kamchatka
The Kamchatka peninsula has been developing as an ocean-
continent transition zone for a long time. Allochthonous and
autochthonous geological formations comprise its structure
(Plate 1). Autochthonous terrigenous and volcanogenic com-
plexes were formed during island arc stages of development
beginning from the Paleogene. Allochthonous complexes
were formed in different geological and geodynamic condi-
tions and were accreted to Kamchatka in the Late Mesozoic-
Early Cenozoic time. Now the majority of them, excluding
geological complexes of the eastern peninsulas, form a base-
ment for the Kamchatka volcanic arcs (Plate 1). The most
ancient rocks of the basement obviously are metamorphic
complexes of the Sredinny and Ganalsky Ranges, but their
age has been a subject of debate for almost a half century.
At first geologists assumed that the metamorphic rocks were
Precambrian. Later, it was determined that allochthonous-
folded structure of Sredinny and Ganalsky massifs and meta-
morphism of separate allochthonous units were related to
collision processes in Mesozoic and Cenozoic time [Rikhter,
1991, 1995; Konstantinovskaya, 2001].
Sredinny metamorphic massif (Plate 1) is composed of
several main units that differ in structure and degree of meta-
morphism. The lower unit (Kamchatskaya Unit) contains a
high-grade metamorphic core composed of granulite facies
rocks [Rikhter, 1995]. Amphibolite-facies rocks (Malkinskaya
Unit) are thrust over the rocks of Kamchatskaya Unit in peri-
clinal zones, and along the eastern margin of the metamor-
phic core. Terrigenous, volcanic-siliceous and volcaniclastic
rocks were protoliths for the rocks of Kamchatskaya and
Malkinskaya Units. Originally these rocks were formed as
a result of transportation of terrigenous material to a back-
arc basin and volcanic arc. During collision, the continental
margin and arc rocks were metamorphosed and intruded by
plagiogranites, Rb/Sr dated as 127 Ma [Vinogradov et al.,
1991]. Along the eastern margin, the Sredinny metamorphic
massif is tectonically covered by Upper Cretaceous terrig-
enous and volcanic-siliceous deposits of Khosgonskaya and
Iruneyskaya Units.
The Ganalsky metamorphic massif (Plate 1) consists of
three allochthonous units. The uppermost contains phyllite
and chlorite-biotite facies rocks, the middle one includes
greenshists and epidote amphibolites, and the lower unit is
made of garnet amphibolites [Rikhter, 1991]. In contrast to
the Sredinny massif, the protoliths for these metamorphic
rocks were oceanic basalts, pelagic siliceous rocks, lime-
stones and also VA rocks. Tectonic slices are often separated
by metamorphized ultramafics and serpentinite melange. The
metamorphism is related to arc-continent collision. 39Ar/40Ar
age from garnet amphibolites (50.6–47 Ma) indicate that the
amphibole-grade metamorphism occurred before the end of
Early Eocene [Konstantinovskaya, 2001].
Me t a m or p h ic ro c k s also o c c u r i n t he structure
Khavyvenskaya Rise (Plate 1) and comprise blocks in ser-
pentinite melanges on the Ozernoy Peninsula, Kamchatsky
Mys Peninsula and northern part of Kumroch Range. These
units consist of amphibolites, green slates, and rare quartz-
ites. The metamorphism is related with subduction of an
oceanic plate, fragments of which were thrust to the surface
in the process of the tectonic reorganization [Osipenko et
al., 2005].
Besides metamorphic rocks, the basement of Cenozoic
volcanic arcs includes Late Cretaceous Paleocene units,
the composition of which varies for different tectonic zones
(Plate 1). The basement of West Kamchatka and of the Mid-
Kamchatka arcs (Sredinny Range) is Upper Cretaceous ter-
rigenous deposits (Khosgonskaya and Lesnovskaya Units),
volcanic-siliceous rocks of Iruneyskaya Unit, and volcanic
formations of VA-type of the Upper-Cretaceous-Paleocene
Kirganikskaya Unit. Terrigenous deposits were formed by
transpor tation of material from a continental margin to a
back-arc basin, often as turbidites. Volcanic-siliceous depos-
its of the Iruneyskaya Unit were clearly formed in back-arc
spreading conditions.
Wit hin Eastern Kamch atka (in t he Valag insky and
Kumroch Ranges, on the Ozernoy Peninsula), the basement is
represent by Upper Cretaceous volcanic, volcano-terrigenous
and siliceous rocks (Khapitskaya and Kitilginskaya Units),
which were formed in the conditions of an ensimatic island
arc. Paleocene-Lower Eocene complexes consist of conti-
nental-derived turbidites. Deposits of different arc facies
were tectonically combined and formed the accretion struc-
ture of basement of the moder n volcanic arc of Eastern
Kamchatka. The east part of Kumroch Ridge and southern
par t of Valaginsk y Ridge are character ized by series of
tectonic slices, which comprise the accretionary complex of
Paleocene-Early Eocene age (Vetlovka Unit). This unit con-
tains volcaniclastic rocks, pelagic radiolarites, limestones,
Plate 1Plate 1
Plate 1. Generalized tectonic map and geologic formation complexes of Kamchatka.
MORB-like basalts, and diabases formed in the Vetlovka
oceanic basin [Konstantinovskaya, 2001].
Terranes of easter n penin sul as (Kamchatsky Mys,
Kronotsky and Shipunsky) form a frontal (tectonic) arc in
the modern structure of Kamchatka (Plate 1). They are parts
of the K ronotskaya paleoarc for med in the central part of
Pacific and accreted to the Kamchatka [Khubunaya, 1987;
Levashova et al., 2000]. Upper Cretaceous-Eocene marine
volcanogenic-sedimentary rocks are characteristic for this
arc. The peninsulas are separated from the rest of Kamchatka
by a long trough, the Tyushevskiy paleobasin, filled with
Upper Eocene-Miocene terrigenous sediments. The western
border of the Tyushevskiy trough is a large zone of east-
trending thrust (Grechishkin Suture) formed as a result of
accretion of the Kronotskaya paleoarc. There are two points
of view on the time of collision of the Kronotskaya paleoarc
with Kamchatka. According to one of them [Tsukanov, 1991],
it took place in the Middle Eocene phase of compression
simultaneously with the main structural reorganization of
the entire region. According to other authors [Avdeiko et
al., 1999; Konstantinovskaya, 2001], tectonic accretion of
the Kronotskaya paleoarc took place in the Late Miocene
(7–10 Ma ago), and resulted in closing of the Tyushevskoy
basin and jump of the subduction zone to the present-day
Much interest is focused on the structure of Kamchatsky
Mys Peninsula where there are ophiolites and volcanic rocks
of the OIB and IAB types. This terrane occupies a key posi-
tion at the Kamchatka-Aleutian junction. The geological
structure of this area consists of intrusive, volcanic and sedi-
mentary complexes from the Cretaceous to Quaternary that
were formed in a variety of geodynamic conditions (Plate 1).
Data on rock composition and age allow us to reconstruct the
history of development of this area.
The southern part of the Kamchatsky Mys Peninsula is
composed of components of an ophiolite assotiation ultra-
basic rocks, gabbro, dikes and lavas of the basalts, as well
as Cretaceous silicic-volcanic and terrigenous sedimentary
rocks. Some amphibolites occur as blocks in a serpentinite
melange. Volcanoclastic tuff and chert deposits with pillow-
basalt, jasper and limestone are melded with in the Smagin
Unit. The age of this sequence was estimated to be Albian-
Cenomanian by the radiolarian assemblage from jasper in
the limestones. This complex contains a suite of MORB-like
tholeiites and high-K2O alkali basalts [Fedorchuk, 1992;
Savelyev, 2003; Portnyagin et al., 2005b]. Alkali basalts
constitute about 5–7% of the volcanic rocks in the Smagin
Unit and their geochemical characteristics cor respond to
those of ocean island basalts (OIB). The high content of K,
P, Nb and LREE in these rocks is similar to alkali basalts of
the Emperor Seamount Chain. Thus, composition and age
connects the formation of Kamchatsky Mys alkali basalts
to activity of the Hawaiian mantle plume [Avdeiko and
Savelyev, 2005]. Deposits of the Smagin Unit are overlain by
Turonian-Campanian sandstones and siltstones of the Pikezh
Unit. The northern part of Kamchatsky Mys Peninsula is
composed of Cretaceous – Middle Eocenian terrigenous-vol-
canogenic deposits of the Stolbovskaya Unit similar to those
of K ronotsky and Shipunsky Peninsulas of the same age.
Primitive tholeiites and high-Al basalts, typical for ensimatic
island arcs, predominate in it [Khubunaya, 1987; Tsukanov,
1991]. During the Early Eocene, ophiolite complexes were
eroded from this arc, as evidenced by abundant serpentinite
fragments in sandstones of the Stolbovskaya Unit.
A model of geological development was constructed con-
sistent with these data. Early Cretaceous: oceanic crust was
formed in the axial zone of a mid-oceanic ridge (ultrabasic
rocks, gabbro, basalts MORB-type). Albian-Cenomanian: an
intra-oceanic rise was formed on the flanks of an anomalous
segment of this mid-oceanic r idge, affected by the adja-
cent Hawaiian mantle plume (i.e., the Smagin Seamount
composed of tuffaceous sediments, tuffs, limestones with
jasper, MORB-like tholeiites, and high-K2O alkali basalts).
Turonian-Campanian: the Smagin Seamount migrated into
a continental margin into a zone of terrigenous sedimenta-
tion (sandstones and siltstones of Pikezh Unit). Campanian-
Maastrichtian: Kronotskaya arc began to form on oceanic
crust. Active volcanism in this arc continued up to Eocene
and volcanogenic-sedimentary deposits accumulated. Middle
Eocene: a large tectonic reconstruct ion occurred as the
Pacific plate changed its direction. Collision of Achaivayam-
Valaginskaya arc with Kamchatk a [Konstantinovskaya,
2000 ]: Th is is a stage of folding and metamor phism.
Possibly at the same time, the Smagin Seamount collided
with the Kronotskaya arc. Late Eocene: Volcanism stopped
in the Kronotskaya arc. Oligocene and Early Miocene: the
Kronotskaya arc continued its passive motion on the Pacific
oceanic plate. The Tyushevskiy basin (with accumulated
terrigenous deposits) was situated between Kamchatka and
the inactive Kronotskaya arc . Kamchatka collided with the
Kronotskaya inactive arc and Smagin Seamount in Late
Miocene (7–10 Ma ago). This collision caused the latest
tectonic reconstruction of East Kamchatka and a jump of the
subduction zone to their present-day position. The Smagin
Sea mount was separated f rom the rest of the Emperor
Seamount Chain.
2.2. Distribution of VA Formations
Three VA complexes of different age were formed within
the Kurile-Kamchatka VA system (Fig. 1). The Eocene
volcanic and subvolcanic rock complexes from basalts to
Fig. 1Fig. 1
rhyolites (Kinkil unit) stretch out along the western coast and
depression of the Parapolsky Dol [Filatova, 1988; Bogdanov,
Khain, 2000].
The associations of Neogene-Quater nary volcanic and
intrusive rocks from basalts to dacites and lipar ites are
widespread within the Sredinny ridge of Kamchatka and
Southern Kamchatka. Rocks of both normal and alkalic series,
i.e. trachybasalts, trachyandesites, etc., occur among them.
Some data indicate that the oldest are of Late Oligocene age
[Litvinov, Patoka, 1999], but other data indicate that they are
Miocene [Sheimovich, Patoka, 2000]. Detailed geological and
petrographic descriptions of these rocks are reported in a num-
ber of publications [Ogorodov et al., 1972; Volynets, 1994].
Sheimovitch and Patoka [2000] distinguish six volcanoplu-
tonic formations in Southern Kamchatka and the Sredinny
Range: Miocene andesite, Miocene-Pliocene liparite-dacite,
Pliocene basic andesites, Early Pleistocene basalt, Pleistocene-
Holocene basaltic andesites (to which all active volcanoes
belong), and Holocene basalts (distributed, monogenic vol-
canism). It should be noted that the name of the formations
is the predominant rock type. Two basic features distinguish
VA formation complexes of the Sredinny Range from ones
of Southern Kamchatka: (1) only typical VA volcanic forma-
tions are distributed on Southern Kamchatka, whereas some
volcanic rocks of the intraplate non-VA geochemical type
occur in the Sredinny Range among the predominant typical
VA lavas [Volynets, 1994], (2) only two potentially active
volcanoes, Ichinsky and Khangar, are in the Sredinny Range
[Melekestsev et al., 2001], whereas active volcanism is well-
spread within South Kamchatka.
VA volcanic rocks of the Great Kurile Islands have a simi-
lar composition. “Green tuff”, volcanogenic-siliceous–diato-
mite, andesite– basaltic andesite, and andesite formation
complexes have been described there [Sergeev, Krasny, 1987;
Piscunov, 1987]. The oldest of these is the Oligocene–Middle
Miocene green-tuff complex, whose volcanic rocks are rep-
resented by basalt, basaltic andesite, andesite, and dacite
lavas along with volcanic breccias of the same compositions.
Quartz diorite is the only representative of intrusive rocks.
The Middle Miocene–Pliocene volcanogenic-siliceous–diat-
omite complex contains large amounts of andesite and dacite
pumice and may be comparable to the rhyolite–dacite rock
association of Southern Kamchatka. The andesite–basaltic
andesite complex of the Kurile Islands is close both in age
and composition to the basaltic andesite rock association of
South Kamchatka. Pillow lavas, detrital–pillow breccias, and
aquagene tuff are characteristic of this complex. All three
pre-Quaternary volcanic-rock complexes occur only at the
flanks of the Greater Kurile Islands: on the Shumshu and
Paramushir islands (North Kuriles) and on the Urup, Iturup
and Kunashir (South Kuriles). Volcanic rocks of the Kurile
Islands display evident features of submarine eruption, in
cont rast to those of the South Kamchatka and Sredinny
Range of Kamchatka. The andesite complex of the Kurile
Islands is represented by basalt, basaltic andesites, andes-
ites, and dacites of Quaternary volcanoes, many of which
are active. The Quaternary submarine volcanoes located on
the back-arc part of the Great Kurile Islands were studied
in detail during 9 cruises of R/V “Vulkanolog”. They also
are represented by basalts, basaltic andesites and andesites
[Avdeiko et al., 1991].
In East Kamchatka, including the Central Kamchatka
Depression, Oligocene–Miocene volcanic rocks of the VA
type are absent, i n contrast to the Kamchatka Sredinny
Range, Southern Kamchatka, and the Kurile Islands. Here,
a large group of Pliocene and Pliocene–Early Pleistocene
volcanic complexes composed of basalt, andesite, and dacite
Fig ure 1. Spatial distr ibution of Cenozoic subduct ion-related
volcanic formations in the Kurile-Kamchatka island-arc system.
I-I location of model cross-section on Fig. 4. On the incut: EA
– Eurasian, NA – North American, P – Pacific plates, K – Kom-
andorskaya microplate.
lavas in variable proportions and of subvolcanic facies of the
same rocks have been recognized [Litvinov, Patoka, 1999].
There are also modern volcanoes (Fig. 1). In addition, there
are some small volcanic bodies of alkaline and subalkaline
basalts with intraplate geochemical characteristics [Volynets
et al., 1990; Volynets, 1994]. These are Late Miocene rocks
and are the oldest volcanic products withi n the Eastern
Kamchatka VA belt.
On the whole, Pliocene–Quater nar y VA rocks are most
common within the Kurile-Kamchatka system. Their com-
positions range from basalts to dacites and rhyolites and vary
across different regions. Basaltic andesites and andesites are
predominant rocks on the Kurile Islands, while basalts and
basic basaltic andesite are predominant in Kamchatka.
2.3. Chemical Characteristics of VA Formations
The chemical composition of lavas is most completely
studied for the Pliocene-Quaternary association of volcanic
rocks [Avdeiko et al., 1991; 1992; Volynets, 1994)] Within
the Kuriles and Kamchatka lavas there can be distinguished
low-K, moderate-K, high-K, and shoshonite-latite series
and normal and subalkalic series. Following the criteria of
Miyashiro [1974], tholeiitic and calc-alkaline differences are
distinguished within every series. Calc-alkali, moderate-K
series predominate in both Kamchatka and Kuriles and are
usually found within frontal zones of the volcanic arcs: on
the Kuriles and on east Kamchatka, where they are wide
spread, on the Central Kamchatka Depression and on the
Sredinny Range, where they appear only sporadically along
the eastern margins of these structures [Volynets, 1994].
Lavas of high-K series are localized within the rear zones
of the Kuriles, south and east Kamchatka and the Sredinny
Range. Lavas of shoshonite-latite series occur in the rear
zones of the northern Kuriles (and only among basalts),
south Kamchatka and Central Kamchatka Depression, but
are more common in the Sredinny Range where they are
found in the central and rear zones of the volcanic belt.
The distribution of rocks of different series is interrupted
by large transverse fault structures, where lavas of the high-
K ser ies are found even in the f rontal zones of volcanic
belts, for example, at the bend of the Kurile arc in the area
of Bussole strait [Avdeiko et al., 1992], and in the area of
the Malko-Petropavlovsk zone of transverse dislocations in
Kamchatka [Baluev et al., 1979].
Among the VA associations of the Kuriles, south and
east Kamchatka, a transverse mineralogical and geochemi-
cal zonation is well manifested while a longitudinal zona-
tion is less distinct [Avdeiko et al., 1991; Volynets, 1994].
Lavas of the frontal volcanic zones are characterized mainly
by two-pyroxene phenocrysts, whereas in basalts of the
rear zones phenocr ysts of orthopyroxene are seldom seen.
Phenocrysts of amphibole and biotite are wide spread in
andesites and acid rocks and sometimes even in basalts of
rear zones while they are absent in analogous rocks of the
frontal zone. Similar minerals from different zones also vary
in chemical composition [Volynets et al., 1990 b; Volynets,
1994; Osipenko, 2000].
Transverse geochemical zoning is expressed in increasing
concentrations of many incompatible trace elements (K, Rb,
Li, Be, Ba, Sr, U, Th, La, Ce, Nb, Ta, Zr, W, Mo) in lavas
from front to rear. K/Na, Rb/Sr, La/Yb, Sr/Ca, Th/U, and
Mg/(Mg+Fe) (Mg#) ratios, as well as contents of volatile
components (H2O, F, Cl, S), also increase in the same direc-
tion. In contrast, contents of Fe, V, and Fe2+/Fe3+ decrease
in lavas in the same direction. A well pronounced isotope
zonation has been defined in the Kurile lavas: 87Sr/86Sr and
143Nd/144Nd values decrease notably from the front to the rear
[Volynets et al., 1988; Avdeiko et al., 1991].
Similar transverse zoning is manifested in the Quaternary
VA-type volcanic products of the Sred in ny Range, with
higher general alkalinity and higher level of the incompatible
trace elements concentrations [Volynets et al., 1987; 1990].
Two volcanic zones, front and rear, parallel to the deep-
sea trench with a zone of weak volcanic activity between
them, are distinctly displayed in the Kuriles and in southern
Kamchatka [Avdeiko et al., 1991; 1992]. The volcanic belt of
the Central Kamchatka Depression can also be interpreted as
a rear zone relative to the frontal one of Eastern Kamchatka
(Fig. 1). In any event, the same regularities of geochemical
zoning as in the Kuriles and south Kamchatka are character-
istic of these zones [Volynets et al., 1990; Volynets, 1994].
In addition, lavas of an intraplate geochemical type were
discovered and described by Volynets [1994] among the Late
Cenozoic volcanic rocks of Kamchatka. In contrast to typical
VA lavas, these are characterized by high concentrations of
Ta, Nb, and Ti, with a Ta-Nb minimum in the rock/primi-
tive mantle spider-diagram that is small or absent [Volynets,
1994; Avdeiko and Savelyev, 2005]. In addition, they are also
characterized by modestly high concentrations of incompat-
ible elements like volcanic rocks of the rear zones (Fig. 2).
“Intraplate” lavas of Kamchatka include the following vol-
canic series: K–Na alkaline basalts (of Late Miocene age in
eastern Kamchatka); K–Na alkaline olivine basalts (Pliocene
in eastern Kamchatka and Late Pliocene–Holocene in the
Sredinny Range, where they comprise a zone of flood-basalt
volcanism); K–Na basalt– comendite (of Pliocene–Early
Pleistocene age in the Sredinny Range); and K-basalt and
associated shoshonite–latite series (Late Miocene–Pliocene
in between the Western Kamchatka and Sredinny Range).
No systematic transverse geochemical zonation was found
among lavas of the intraplate geochemical type.
Fig. 2Fig. 2
There are some unusual characteristics of subduction-
related volcanic rocks in the Kamchatka-Aleutian junction
area. One is the wide distribution here of high-magnesian
basalts, basaltic andesites and andesites, including adakites
[Volynets et al., 1998; 1999 a]. The volume of magnesian
rocks of this area is approximately 10 times more than in all
other areas of Kamchatka. Within the magnesian rocks there
are certain regularities. Magnesian basalts (Mg# 80–88) of
the northern volcanoes (Shiveluch, Kharchinsky, Zarechny)
have lower Ca, higher Sc, Y, Yb concentrations and higher
K/Ti, La/Yb, Ni/Sc, and La/Ta ratios compared to the similar
ones from the Kluchevskaya group of volcanoes. Most of the
volcanic rocks of this region are characterized by high alka-
linity and high LILE and LREE concentrations. Volcanoes
of the Kluchevskaya group are characterized by a very high
productivity, supplying about 1/3 of volume of the volcanic
material erupted by all Kamchatka volcanoes and two times
more than east Kamchatka volcanoes during Holocene time
[Volynets et al., 1998; Kozhemyaka, 2000]. These unusual
features of volcanism reflect the unique geodynamic condi-
tions of the Kamchatka-Aleutian junction.
The data on the distribution , age and chemical com-
position of VA rocks testify that the volcanic belt of the
Sredinny Range is different from the Eastern Kamchatka
belt. The origin of the Late Oligocene–Quaternary volcanic
belt in the Sredinny Range is still a matter of debate. Some
authors interpret it as an independent volcanic arc located
above a separate subduction zone u nder t he Sr edinny
Range. This belt has now completed its development as the
result of a blockade of its subduction zone by accretion of
the eastern peninsulas to Kamchatka [Legler, 1977; Avdeiko
et al., 1999; Trubizin et al., 1998]. Other authors believe
that the volcanic belt of the Sred inny Range is relat ed
to the present- day Kurile–Kamchatka subduction zone,
being a third volcanic zone, a back-arc one relative to the
Eastern volcanic zone and the volcanic zone of the Central
Kamchatka depression [Tatsumi et al., 1994; Seliverstov,
1998]. The origin of the Sredinny Range volcanic belt will
be discussed below.
2.4. Gravity Data
The gravity field of the present-day Kurile–Kamchatka
arc-trench system has principal gravity features character-
istic of such systems, i.e., the presence of conjugate positive
and negative free-air gravity anomalies [Watts et al., 1975;
1978]. The positive anomaly extends along the tectonic
(frontal) arc, which encompasses the Lesser Kurile Islands
and their submarine extension in the Kuriles, as well as the
eastern peninsulas in Kamchatka. The positive anomaly is
complicated by transverse lower-intensity gravity anomalies
along large transverse fault zones in the areas of the Gulf of
Avacha in Kamchatka and of the Bussol Strait in the Kuriles
[Watts et al., 1978].
Figure 2. Primitive mantle-normalized trace element for intraplate-type volcanic rocks of Kamchatka. OIB and primitive
mantle composition after Sun and McDonough (1989), typical arc lavas of Central Kamchatka Depression (35 samples)
after Churikova et al. (2001)
The volcan ic b elts of East Kamchat ka, t he Cent ral
Kamch atka Depression, a nd the Sred inny Range show
a mosaic of alternating Bouguer gravity fields (Plate 2)
[Popruzenko et al., 1987]. The character of the anomalies
in the areas of volcanic cones is controlled by the structure
and composition of the basement rocks, the genetic type and
maturity of volcanic centers, the state of isostatic equilib-
rium, and other factors. For example, local gravity maxima,
complicated by gravity ring minima at their margins, mark
basalt and some andesite volcanoes. Volcanic calderas pro-
duce, depending on their origin, gravity lows (explosive
calderas) or highs (collapse calderas).
A characteristic feature of the gravity field in Kamchatka,
as compared to other VA systems is the presence of two addi-
tional, although less intense, zones of positive gravity anoma-
lies in the area between the Malka–Petropavlovsk zone of
transverse faults and the Kamchatka-Aleutian junction. These
additional zones are roughly parallel to the principal zone of
positive gravity anomalies confined to the eastern peninsulas
(Plate 2). One of them, located in the Central Kamchatka
Depression, has been delineated rather reliably, while the posi-
tive anomaly zone in western Kamchatka is less distinct. The
positive anomaly zone in the Central Kamchatka Depression
occupies the same position relative to the volcanic belt of the
Sredinny Range as does the zone of the eastern peninsulas
relative to the volcanic belt of eastern Kamchatka. It coincides
nearly completely with the buried part of Khavyvenskaya
Rise. The maximum gravity values within this uplift occur
on the Khavyvenskaya Rise, which is composed of crystal-
line schists, serpentinized ultrabasic rock, Late Cretaceous–
Paleocene pillow basalt, and tuff, and intruded by a gabbro
body with a density of 3.05 g/cm3. Elsewhere, the anomalous
zone of the Khavyvenka highland is covered by a mantle of
Cenozoic volcanoclastic rocks, which lowers the value of the
positive gravity anomaly. However, the high gravity effect
cannot be explained only by the presence of the high-den-
sity rocks [Aprelkov et al., 1985]. In our opinion, the buried
Khavyvenskaya Rise was the frontal (tectonic) arc of the
subduction zone beneath the Sredinny Range. In this case, the
positive gravity anomaly is partly a residual anomaly produced
by disturbance of isostasy during subduction. We note too that
ophiolite complexes are often distributed in frontal arcs.
The presence of a buried paleotrench, indicated by a nega-
tive free-air gravity anomaly along the continental rise east
of Karaginsky Is. (Watts et al., 1975), suggests the separate
nature of the subduction zone under the Sredinny Range. The
Tyushevskiy trough and the Grechishkin overthrust zone in
the Kamchatka correspond to this subduction zone, the latter
to the western slope of the paleotrench (Fig. 1).
A model vertical gravity section, showing two subduction
zones, is presented in Fig. 3. Our gravity modeling across
Kamchatka (profile A – B in Plate 2) indicated that the shape
and intensity of the calculated gravity anomaly is close to
the measured one if two higher gravity subducting layers
with an effective density of +0.08 to +0.1 g/cm3 and two
lower density zones (–0.08 to 0.1 g/cm3), corresponding
to the inferred sites of magma generation, are used into the
A third zone of positive gravity anomalies in western
Kamchatka seems to mark a Paleogene arc (Plate 2).
2.5. Seismological Data
The spatial distribution of earthquake epicenters recorded
during 1962–2005 are shown in Plate 3. A belt of shallow-
focus earthquakes (less than 50 km deep) extends along on
the continental slope of the deep-sea trench. It is character-
istic that all large earthquakes with magnitude more than
7.5 are located within the tectonic arc, above and within
the sharp downward bend of the Pacific plate, where the
angle of subduction changes from 10–12° to about 50° (Plate
3B). North of the Kamchatka-Aleutian junction, the seismic
belt is offset westward, occupying a position relative to the
Plate 2Plate 2
Fig. 3Fig. 3
Plate 3Plate 3
Figure 3. Density model for the mantle at the cross-section along
line A B (Plate 2). Earth’s crust density heterogeneities were
included into calculations.
Plate 2. Bouguer gravity anomalies on Kamchatka. A – B – location of model cross-section show in Fig. 3.
Plate 3. Map of earthquakes epicenters (A) and transverse cross-sections (B) of the Kurile-Kamchatkan Island Arc System. A: Eurasian (EA), North
American (NA), Pacific (P) plates, and Komandorskaya microplate (K). B: VA – volcanic arc, T – deep-sea trench.
paleotrench as the seismic belt southward the Kamchatka-
Aleutian junction relative to the Kurile-Kamchatka trench.
This provides additional evidence in favor of a jump of the
subduction zone south of the Kamchatka-Aleutian junction to
the present day position. In addition, a great number of shal-
low-focus earthquakes are recorded in eastern Kamchatka
between the Malka-Petropavlovsk zone of transverse faults
and a prolongation of the Kamchatka-Aleutian junction on
Kamchatka, the segment where we assume the subduction
jump took place, whereas few isolated weak earthquakes
were recorded in South Kamchatka. This indicates that weak
motion still continues along the previous subduction zone,
although no longer recorded at greater depths.
2.6. Geodynamic Characteristics of Volcanic Activity
Earlier, Avdeiko [1994] discussed the principal geody-
namic parameters of volcanism in the Kurile segment of the
Kurile-Kamchatka island-arc system based on a subduction
model. Benioff seismic zone parameters are known to control
aspects of volcanic activity. They exert an effect upon the
temperature, pressure, and composition of the melting sub-
stratum, the quantity and composition of volatile components
participating in the melting process, and the conditions of
magma ascent and eruption. Principal parameters include
the depth of the subduction zone (to the Benioff zone’s upper
surface) under the frontal and back-arc volcanoes, the dis-
tance bet ween the deep-sea trench axis and the volcanic
front, the subduction zone inclination angle, etc.
Recently, in cooperation with V.A. Shirokov, we refined
the geometry of the Benioff zone using the data available
for the earthquakes in the Kurile –Kamchatka region dur-
ing the whole period of detailed instrumental observations
(1962–20 05) . The isodepths to the upper su rface of the
Benioff zone, based on these data, are shown in Fig. 1, and
the refined parameters of the structure as it occurs in various
portions of the East Kamchatka and Kurile segments of the
island-arc system are summarized in Table 1.
The depth of the Benioff focal plane below the volca-
nic front is nearly constant, at about 110 ± 5 km, and the
maximum depth below the back-arc volcanoes farthest from
the volcanic front does not exceed 220 km. Avdeiko [1994]
arg ued that melting conditions in the mantle wedge are
confined to this depth interval of the Benioff plane because
of release of volatiles, in general water, from the subducted
Pacific plate.
The rate of the Pacific Plate subduction varies from 7.5
cm/year under the Kronotsky Peninsula to 8.3 cm/year at
the latitude of Kunashir Is. [Gorbatov, Kostoglodov, 1997].
This rate and the distance between the deep-sea trench axis
and the volcanic-arc front were used to calculate the time
for subduction to 110 km depth where melting of the mantle
wedge begins as a result of volatile flux. This time varies
from 2.8 m.y. in eastern Kamchatka to 3.2–3.5 m.y. in the
southern Kurile Islands.
It should be emphasized that the geodynamic parameters
of magma generation and volcanic activity are approximately
the same in all VA systems throughout the Circum-Pacific
Belt. The principal parameters are as follows: the Benioff-
zone depth below the volcanic arc varies from 110±10 km
beneath a volcanic front up to 220 k m beneath the most
distant from volcanic front volcanoes; the volcanic-arc width
usually is not more then 100 km; and the distance between
the deep-sea trench axis, i.e., the subduction starting line and
the volcanic front line is not more that 250 km. The position
of the volcanic belt in the Kamchatka Sredinny Range does
not agree with these parameters. The depth to the present-
day Benioff zone in the south of the belt varies from 300
km below the frontal volcanoes to 450 km under the rear-
arc volcanoes. As for the area nor th of Ichinsky volcano,
subduction, if present, does not reveal itself in the form of
a seismic zone. The width of the Sredinny Range volcanic
belt exceeds 100 km, which is comparable with the width
of a large volcanic arc. If the volcanic belt of the Sredinny
Range is considered as a third volcanic belt connected with
present-day subduction zone, then the volcanic arc is as wide
as 400 km within this segment of the Kurile–Kamchatka
island-arc system.
Table 1Table 1
Table 1. Geodynamic parameters of the Quaternary of Kurile
Kamchatka VA system
Easther n
Lmin, km 190–200 205 200–205
Ldir, km 190–200 205 200–205
Lb, km 130–140 145 140–145
V, cm/y 7.6 7.6 7.7–7.8
a° 80–90 90 85–90
b° 35–51 51 50–51
Hf, km 105–115 115 110
Hmax, km 195 180 205
t, m.y. 2.8–2.9 3 2.9–3.0
d, km 50–70 70 40– 60
T, km ~40 42–47 40–45
Notes: Lmi n and Ldir the distance between the t rench axes and
volcanic front: minimal (Lmin) and along the direction of the Pacific
plate motion (Ldir). Lb – the distance between the trench axis and
the bend in the Pacif ic plate (a change of subduction angle from
10–12º to about 50º, V – the convergence rate [Gorbatov et al.,
1097], α - angle bet ween a direction of the Pacif ic plate motion
and the arc strike, β - a subduction angle between 40 – 500 km, the
depth beneath the volcanic front (Hf) and the rear volcanoes (Hmax),
t – the time of the Pacif ic plate to pass from the trench axis down
to Hf, d –width of the volcanic arc, T –crustal thickness.
3.1. Nature of the Volcanic Belt of the Sredinny Range,
The above geological and geophysical data enable assess-
ment of the conditions of formation of the volcanic belt of
the Sredinny Range in Kamchatka. On the one hand, this
question is key to reconstr ucting the histor y of tectonic
development of the Kurile-Kamchatka VA system. On the
other hand, it is important for understanding the processes
of magma generation related to the subduction.
Connecting the formation of this belt with the present day
Kurile-Kamchatka subduction zone is well-described in by
Tatsumi et al. [1994; 1995]. In their opinion, the unusual
position of this belt and the atypical composition of the volca-
nic rocks are accounted for by melting of K-amphibole-bear-
ing peridotite at the base of the mantle wedge at anomalously
high temperatures. Such high temperature is explained by the
unusual tectonic setting of the belt at the edge of the Pacific
plate having a transfor m-ty pe boundary with the Nor th
American plate. Calculations made by these authors predict a
temperature rise of 200–300°C in the boundary of the mantle
wedge in comparison with the usual situation.
This explanation could be plausible if the aerial distribution
of volcanoes in the Sredinny Range were restricted to the zone
of the Kamchatka-Aleutian junction. However, the volcanic
belt of the Sredinny Range represented by subduction-related
Late Oligocene-Quaternary volcanic formations extends more
than 700 km from latitude 54.8°N at Khangar volcano in the
south to latitude 60.3° in the north. It should be emphasized,
however, that a zone of anomalously increased temperature
does exist, and, in our view, causes formation of high-mag-
nesian basalts and lavas of the intraplate geochemical type
along with the typical VA lavas [Volynets, 1994; Volynets et al.,
1999; Portnyagin et al., 2005; Avdeiko and Savelyev, 2005].
Seliverstov [1998] believes also that the Sredinny Range
volcanic belt formation is connected with the modern Kurile-
Kamchatka subduction zone. In his opinion, inclination of
the subduction zone in Miocene was more gentle due to
subduction of hotter lithosphere. In Pliocene time, the angle
of the subducted plate increased and VA belt shifted from
the Sredinny Range to the present-day position. This view is
unlikely to be the true for the following reasons:
1. It is not clear why subducting Pacific lithosphere should
have been hotter in the Miocene. A single cause may be
intraplate volcanism, but the age of the nearest volcanoes
of the Obruchev rise (Detroit and Meiji Seamounts) is
more than 85 m.y. [Regelous et al., 2003].
2. The dip angle of subduction of the young Nasca plate exceeds
23°, whereas the subduction angle zone at the distance of
320–350 km between the Kurile-Kamchatka trench axis and
the Sredinny Range volcanic belt must be less than 20°.
3. According to Seliverstov [1998], a change of the sub-
duction angle is a continuous process resulting from an
increase in the sinking rate due to subduction of a heavier
lithosphere. Therefore, the question arises as to why the
volcanic zone was offset east ward over a distance of 150
km (distance between paleovolcanic front of the Sredinny
Range and volcanic front of eastern Kamchatka), during a
continuous process without leaving any trace in the form
of volcanoes.
The data discussed in the previous sections suggest that
the volcanic belt of the Sredinny Range was an indepen-
dent volcanic arc, which was formed above its subduction
zone, which jumped to its present-day position in the end of
Miocene, as incoming positive-buoyancy lithospheric blocks
locked subduction. According to Trubitsyn et al. [1998],
these blocks are represented now by the eastern Kamchatka
peninsulas. The location of the volcanic arcs and the axes
of the deep-sea trenches that mark the subduction zones,
are shown in Fig. 1. The principal lines of evidence for this
interpretation are summarized below.
1. Spatial distribution and tectonic setting of the volcanic
belts and the absence of Miocene island-arc volcanic
rocks in eastern Kamchatka, except Late Miocene intra-
plate lavas (Fig. 1), indicate that the volcanic belts of the
Sredinny Range and eastern Kamchatka (along with the
belts of the Central Kamchatka Depression) are indepen-
dent volcanic arcs. Moreover, frontal and rear-arc volcanic
zones separated by a zone of weaker volcanic activity
have been recognized within the Sredinny Range volcanic
arc, as well as in Southern Kamchatka and in the Kurile
2. The t ransverse petrochemical zoning of the Sredinny
Range volcanic belt is similar to that of other volcanic
arcs, though with higher contents of alkali and incompat-
ible trace elements.
3. Gravity data indicate the doubling, and possibly trebling,
of crustal thickness of the Sredinny frontal (tectonic) arc
(delineated by a belt of positive anomalies) –volcanic arc
systems (Plate 2 and Fig. 3).
4. The seismological data (Plate 3) suggest that some resid-
ual movements still occur in the subduction zone of the
Sredinny Range. It is also possible that these movements
continue in the segment between the Malka–Petropavlovsk
and Kamchatka-Aleutian junction of transverse faults.
These are transform faults that limit the region (segment)
of the subduction zone jump (Fig. 1).
5. A paleotrench corresponding to the Sredinny Range sub-
duction zone has been outlined by gravity and seismic
reflection and refraction data east of Karaginsky Island.
The idea of the jump of tectonic zones in Kamchatka,
which are regarded as the paleoanalogues of modern VA–
trench systems, was put forward by one of the present writers
independent of the subduction model [Avdeiko, 1971]. Later,
Legler [1977] elaborated the concept as a subduction-zone
offset. However, the mechanism of subduction north of the
Kamchatka Peninsula, i.e., to the north of the junction with
the Aleutian arc, remained unclear. Based on computer mod-
eling, Trubitsyn et al. (1998) showed that subduction and,
consequently, volcanism in the northern segment of the
Sredinny Range arc had been caused by mantle convection
under the Komandorskaya Basin induced by the Pacific Plate
motion. A system of back-arc spreading rifts, which corre-
sponds to this interpretation, had previously been discovered
within the Komandorskaya Basin [Baranov et al., 1991].
3.2. Tectonic History
The data presented above allow us to interpret Cenozoic tec-
tonic history of the Kurile–Kamchatka region as the develop-
ment of VA subduction systems of different ages, which were
offset discretely and consecutively grew younger toward the
Pacific Ocean (Fig. 1 and 4). Obviously, a system of volcanic
complexes existed in western Kamchatka in the Paleogene
(Fig. 1), of which only isolated outcrops of volcanic sheets and
subvolcanic bodies remain [Bogdanov, Khain, 2000]. A belt of
positive gravity anomalies seems to mark a frontal (tectonic)
arc (Plate 2). The intensity of the anomalies has been reduced
by partial recovery of isostatic equilibrium.
Beginning from the end of the Oligocene (Fig 4, cross-sec-
tion 1), a system of two arcs existed within Kamchatka and
the Kurile Islands, i.e., the Mid Kamchatka and the South
Kamchatka–Kurile arcs. The formation of this system south
of the Kamchatka-Aleutian junction was caused by the sub-
duction of the Pacific Plate, while to the north, it was caused
by subduction of a young small plate of the Komandorskaya
basin. These arcs are marked in the present-day structure by
their own volcanic-rock associations (Fig. 1). A frontal (tec-
tonic) arc of this subduction system shown (Fig. 4) now is bur-
ied beneath sediments of the Central Kamchatka Depression
excluding Havyvenskaya Rise. A positive gravity anomaly
marks its position. A paleotrench of this system shown on
Fig. 1 is reconstructed as a prolongation of buried trench of
Komandorskaya basin and on the basis of geodynamic param-
eters of modern Kurile-Kamchatka subduction system (Table
1). A portion of sediments deposited on this trench continental
slope was eroded, a portion is shown on the generalized map
as Oligocene-Miocene deposits of Eastern Kamchatka, and a
portion was covered by volcanic rocks of East Kamchatka VA.
Fragments of these deposits were carried upward as xenolites
during Large Tolbachik eruption (Fedotov et al., 1984).
In the end of the Miocene, the subduction zone of the Pacific
Plate within the segment from the Shipunsky Peninsula to the
Kamchatka-Aleutian junction was blocked by the accretion of
the eastern Kamchatka peninsulas and, probably, some other
structural elements of eastern Kamchatka. As a result, the
subduction zone jumped to its present-day position, and the
Kurile–Kamchatka island-arc system acquired its present-day
shape (Fig. 1). Geodynamic conditions changed. The area of
the Miocene trench, where a negative isostatic anomaly was
present, began to elevate as isostatic equilibrium was restored.
In contrast, the Miocene frontal arc began to subside, forming
the Central Kamchatka Depression. Opposite movements led
to formation of a fault zone probably with a thrust component
due to compression.
We postulate the for ming of a plate gap, and conse-
quently opening of mantle windows, after cessation of
subduction (Fig. 4, cross-section 2). This breakage is pos-
sible as a result of increase of plate sink ing after eclogi-
tization. P-wave seismic tomog raphy appears to show a
gap in the slab at a dept h of 450–600 k m [Gorbatov et
al., 2000, Fig. 7, cross-section E–E’]. This cross-section
is located in the centr al part of Kamchatka , where the
jump of subduction zone took place. We suggest that the
high velocity body in this cross-section at the depth about
600 –1000 km was torn away f rom the Pacif ic plate after
subduction stopped beneath the Sredinny Range. There
is no such gap in the cross-section D–D’ located beneath
southern Kamchatka, where no jump of the subduction
zone occu r red, i.e. i n the segment of the s teady-state
regime of subduction.
An inter-arc trough formed between frontal and volcanic
arcs. It is suture zone, were sediments of the lower slope
of the Miocene trench were accumulated. They are shown
as Oligocene-Miocene inter-arc deposits including terrig-
enous mélange on Plate 1. Later some of them were covered
Quaternary unconsolidated deposits.
3.3. Volcanic–Tectonic Zonation
Our interpretation of volcanic–tectonic zonation is based
on the principle of classifying volcanic arcs by the ages of
the subduction zones and the episodes of volcanic activity.
The present-day Kurile–Kamchatka VA system can be sub-
divided into segments based upon variations in geodynamic
parameters of the subduction zone, which are also ref lected
in the spatial distribution and tectonic setting of the volca-
noes and by the composition of the volcanic rocks. Since we
did not find any effects of the age or the composition of the
basement rocks upon the composition of the volcanics in the
Kurile–Kamchatka VA system, we do not use this parameter
in defining the volcanic–tectonic zonation.
Fig. 4Fig. 4
Figure 4. Model cross-sections of evolution of the Kurile-Kamchatka island arc system (after Avdeiko et al., 2001 with
correction). See Fig. 1 for location of cross-sections.
Three volcanic arc–deep-sea trench systems of differ-
ent ages that become successively younger toward the
Pacific Ocean have been recogn ized in the region: the
West Kamchatka (Eocene), Mid Kamchatka–Kurile (Late
Oligocene-Miocene), and Recent Kurile–Kamchatka sys-
tems. These volcanic arcs form the rigid framework of the
present-day tectonic struct ure of the Kurile–Kamchatka
island-arc system. Sedimentary troughs separating these arcs
are either forearc or back-arc basins.
We recognize the following segments within the Kurile–
Kamchatka VA system based on the tectonic evolution and
geodynamics of the present-day volcanic activities above the
zone of the Pacific Plate subduction under the Eurasian Plate.
The East Kamchatka segment represents the initial stage
(7–10 Ma) of an orthogonal subduction process. The sub-
sidence of the Pacific Plate margin to a depth of approxi-
mately 110 km, where the separation of initial magmatic
melts becomes possible and over which the volcanic front
is located, lasted 2.8–2.9 m.y. This implies that subduction
must have commenced before the extrusion of the associ-
ated oldest volcanic rocks, i.e., in the latest Miocene. This
segment consists of various components, with an area where
the lithospheric plate carrying normal oceanic crust is under-
thrust at an angle of 50°, and an area where the oceanic crust,
thickened owing to the presence of the Obruchev Rise, is
subducted at an angle of about 30°–35°. This segment also
includes the Kamchatka-Aleutian junction.
The Pet ropavlovsk segment (the Malka–Petropavlovsk
transverse-fault zone) is a zone of discordant superposition of
the present-day Kurile–Kamchatka arc of NE trend upon the
Malka–Petropavlovsk segment of the Middle Kamchatka
Kurile VA system, having a NW trend there. In the south
Kamchatka segment, as well as in the three Kurile segments,
subduction began at the end of the Oligocene. A virtually
stationary subduction zone persisted there for about 25-m.y.
We postulate that westward shift of the volcanic front was
caused by the cooling effect of the subducted Pacific Plate
and a consequent shift of the magma-generation zone in the
mantle wedge in the same direction as slab motion. We have
subdivided the Kurile segment of the Kurile –Kamchatka
arc into the North, Middle and South Kurile segments, with
different geodynamic characteristics of the subduction zone
and subduction-related volcanism (Table 1). Both the fron-
tal and back volcanic zones, separated by a zone of weaker
volcanic activity, are distinctly displayed in each segment
of the volcanic arcs.
3.4. Geodynamics of the Kamchatka-Aleutian Junction
Geodynamical conditions of this area have evolved over
the last 40 Myr due to interaction of the Pacif ic, North
American, Eurasian and Kula plates and Komandorskaya
microplate. The junction assumed its present shape during
the last 7–10 Myr, after blockage of the Pacific plate subduc-
tion under the Sredinny Range of Kamchatka and its jump
to the present-day position (Fig. 1 and 4). Both the jump and
the arrow-like shape of the Kamchatka-Aleutian junction are
in large measure caused by the Hawaiian-Emperor volcanic
chain. The proposed geodynamic model of the Kamchatka-
Aleutian junction (Fig. 5) assumes gradual westward transfer
of motion from oblique subduction of the Aleutian arc to
the transform fault near Kamchatka. The braking effect of
the motionless North American plate upon the moving and
subducting Pacific plate results in a tension and sometimes
rupture of the latter (slab-windows) and intrusion of hotter
below-slab material into the mantle wedge. One such slab-
window probably occurs under the Kluchevskaya group of
volcanoes and is the reason for their high productivity and
the magnesian composition of their rocks. Additionally,
separation of the Pacific slab-edge blocks, their sinking
into the mantle, and subsequent heating can lead to gen-
eration of small mantle plumes (Fig. 5). One such plume
is confirmed by seismic tomography data [Gorbatov et al.,
2000; Levin et al., 2002] and by the presence of the OIB-like
rocks [Portnyagin et al., 2005]. The large variety of volcanic
rocks from usual VA-type up to the intraplate type is caused
by varying contributions of mantle materials from the hot
below-slab zone, mantle wedge and also by the fluid and/or
melt separated from the slab. The role of fluids in magma
generation decreases, while the role of slab melt increases in
the direction from the Kluchevskaya group of volcanoes to
the northern volcanoes Hailula and Nachikinsky [Portnyagin
et al., 2005a].
The br a k i ng effe ct also wa s a cau s e of for ming
Komandorskaya microplate, which separated from North
American plate. Northwestward motion of this microplate at
3.7 cm/y was determined from GPS data (Fig. 1 and 5) after
the Kronotsky 1997 earthquake (Levin et al., 2002).
3.5. Geodynamic Conditions of Magma Generation
Magma generation is one of the most important problems
in volcanology and petrology. The Ku rile VA system is
an appropriate object to solve this problem, because geo-
dynamics conditions varied in space and time du ring its
evolution. Geodynamics controlled the magma generation
and geochemical characteristics of volcanic rocks. Magma
generation beneath the Kurile Island Arc [Avdeiko, 1999]
corresponding to a steady-state regime of subduction takes
place in the mantle wedge under the influence of f luids
derived from the subducted slab. Frontal and rear volcanic
zones are formed above two zones of magma generation,
Fig. 5Fig. 5
controlled by two levels of dehydration of water-bearing
minerals in the slab. Varying composition of the fluids result
from differences in compositions of the dehydrating of water-
bearing minerals. Amphiboles (including tremolite) and
chlorites from the layers 1 and 2 of the oceanic crust are
dehydrated beneath the frontal arc zone, and serpentine and
talc from the 3B layer are dehydrated beneath the rear one.
Additionally, aqueous f luid separating beneath the frontal
zone passes upward to the zone of magma generation only
through the wedge base, whereas f luid separating beneath
the rear zone rises successively through layers 3A, 2 and 1
of oceanic crust as well as a longer way through the mantle
wedge to the zone of magma generation. The fluid separating
from the slab beneath the rear zone has a higher temperature
in comparison with the frontal one. Typical VA magmas are
generated beneath the frontal and the rear zones under the
steady-state regime of subduction.
What are conditions of the occurrence in Kamchatka of vol-
canic rocks of an intraplate geochemical type along with the
considerably more abundant typical VA rocks? In contrast to
the typical VA lavas characterized by the low concentrations of
Ta, Nb, and Ti, the intraplate lavas show higher abundances of
these elements (Fig. 2) [Volynets, 1994; Avdeiko and Savelyev,
2005]. The low Ta, Nb, and Ti concentrations in typical VA
magmas are due to the fact that these elements, that reside
principally in rutile, are poorly soluble in fluids [Tatsumi et
al., 1986]. However, partial melting of oceanic-crust basalt
under water-saturated conditions is possible at temperatures
exceeding 750°C [Peacock et al., 1994], and these melts con-
tain, according to experimental data, higher Ti, Nb, and Ta
concentrations especially at depths below 150 km where rutile
is unstable [Ringwood, 1990]. Thus, appearance of intraplate-
type lavas may be due to par tial melting of oceanic crust
because of higher temperatures that prevail within the slab
in the steady-state regime of subduction. Where can there be
such higher slab temperatures? It should be noted, first of all,
that intraplate-type volcanic rocks are present only within
the segment between the zone of the Malka–Petropavlovsk
transverse faults and the Kamchatka-Aleutian junction (Fig.
1), i.e. in the segment of the subduction zone that jumped
in the Late Miocene. Melting of the frontal edge of the sub-
ducting plate was possible at the contact with the hot mantle
during the initial stage of the subduction, as, for instance, in
eastern Kamchatka during the end of Miocene—beginning
the Pliocene (Fig. 4).
Similar conditions for par tial melting of the subducting
plate seem to have existed at the Kamchatka-Aleutian junc-
tion, at the northern edge of the Pacific plate, where the
Figure 5. 3D-model of the geodynamics of the Kamchatka-Aleutian junction as a view from North West. Black stars-
active volcanoes, white stars – Nachikinsky (N) and Khailula (K) extinct volcanoes located off the edge of Pacific plate,
K – Komandorskaya microplate, which separated from North American plate. Some lithosphere blocks are torn off
the Pacific plate edge as a result of interaction (breaking) with North Amer ican plate. These blocks, having a negative
buoyancy, sink into a mantle, are heated, and can form a small mantle plume.
upper mantle has high temperatures [Tatsumi et al., 1994].
Such conditions can occur beneath fracture zones forming
slab windows at some distance south the plate edge, where
intrusion of hot asthenospheric material through the slab
window takes place (Fig. 5).
The formation of the Sredinny Range intraplate-type rocks
coincided in time with the subduction zone jump and also
connected with a mantle window as we discussed in section
3.2 (Fig. 4). Oceanic cr ust can melt in a contact with hot
under-slab mantle material intruded into slab window.
The termination of subduction under the Sredinny Range
might have caused the detachment of the heavier lower por-
tion of the oceanic crust (with underlying lithosphere), its
sinking below the eclogitization zone depth (deeper than 150
km), and the intrusion of a hot mantle material from under
the slab into the resulting gap (Fig. 4). This might have been
accompanied by the melting of layers 1 and 2 of oceanic
crust upon the contact with this material.
Thus, we explain the occurrence of intraplate-type rocks
in all three instances by the melting the upper portion of the
subducted plate (oceanic crust) at its contact with the hotter
mantle. We must qualify that this hypothesis is advanced
here in the most general form and requires a more thor-
ough evaluation by computing temperature distributions in
anomalous areas, seismic tomography, and more detailed
petrochemical and geochemical data. Studies aimed at test-
ing this hypothesis have already been initiated within the
framework of the Russian– German KALMAR Project.
Another scenario for such lavas is low-percentage melting of
mantle with little slab input (e.g. Abratis and Wörner, 2001).
Such scenario is possible for the Sredinny Range and west
Kamchatka. A hot mantle material rises in plate gap (Fig. 4.
cross-section 2) and higher may give small portion melt as a
result of decompression.
We have distinguished the following segments in the pres-
ent-day Kurile–Kamchatka island-arc system based on the
distinctive features of their geological structure and geo-
dynamic parameters: the East Kamchatka, Petropavlovsk,
South Kamchatka, North Kurile, Central Kurile, and South
Kurile segments. The East Kamchatka segment exemplifies
an early subduction stage, the Petropavlovsk segment is
complicated by a transverse fracture zone, while the South
Kamchatka and Kurile segments have been steady-state for
a long time. In contrast, the Mid Kamchatka volcanic arc
represented by the Sredinny Range is in a waning stage,
because subduction jumped eastward when formation of east
Kamchatka capes blocked subduction. Mid Kamchatka arc
volcanism extended north of the Kamchatka-Aleutian junc-
tion because of subduction of western Komandorsky Basin
crust, driven by back-arc spreading. Intraplate-type magmas
enriched in Ta, Nb, and Ti are generated by the systems at
the onset and cessation of subduction and over slab windows,
apparently by melting of slab oceanic basalt.
Other scenarios for appearance of intraplate-type lavas are
possible, but all must be consistent with their restriction to
the area of the Kurile-Kamchatka system where a jump in
subduction took place.
Acknowledgements. We thank Oxana Evdokimova and Dmitry
Isaev for help in the preparation of this paper. We are very grateful
to John Eichelberger and Pavel Izbekov for discussion and correc-
tion of the manuscript. We also thank two anonymous reviewers for
valuable comments that obliged us to make some improvements.
Abratis, M., and Wörner, G., Ridge collision, slab-window forma-
tion, and the flux of Pacific asthenosphere into the Caribbean
realm. Geology, 29, 127–130, 2001.
Aprelkov, S. E., Smirnov, L. M., and Olshanskaya, O. N., The Origin
of Gravity Anomaly in Central Kamchatka Depression, in: Mod-
eling of Deep Geological Structures from Gravity and Magnetic
Data, Vladivostok: PED RAS, 68–71, (in Russian), 1985.
Avdeiko G. P., Evolution of geosynclines on Kamchatka. Pacific
Geology, 3, 1–13, 1971.
Avdeiko G. P., On possible prolongation of the Hawaiian-Emperor
chain in Kamchatka, in: Jackson, E.D., and Koisumi,I et al.
Initial Reports of Deep Sea Drilling Project. Washington D.C.,
55, 851–854, 1980.
Avdeiko, G. P., Geodynamics of Volcanic Occurrences in the Kurile
Island Arc and Evaluation of Magma Generation Models. Geo-
tectonika, 2, 19–32, (in Russian), 1994.
Avdeiko, G. P., Antonov, A. Ju., Volynets, O. N. et al., Subma-
rine volcanism and zonality of the Kurile Island Arc. Moskow,
Nauka, 528 p., (in Russian), 1992.
Avdeiko, G. P., Pilipenko, G. P., Palueva, A. A., Napylova, O. A.,
Geotectonic settings of modern hydrothermal manifestations in
Kamchatka. Volcanology & Seismology, 20, 695–711, 1999.
Avdeiko, G. P., Popruzhenko, S.V., Palueva, A.A., Modern structure
of the Kurile-Kamchatka region and magma-forming condi-
tions, in: Geodynamics and volcanism of the Kurile-Kamchatka
Island-Arc system, Petropavlovsk-Kamchatsky, 9 –33, (in Rus-
sian), 2001.
Avdeiko, G. P., Popruzhenko, S. V., and Palueva, A. A., The Tectonic
Evolution and Volcano–Tectonic Zonation of the Kuril–Kam-
chatka Island-Arc System. Geotectonics, 36 (4), 312–327, 2002.
Avdeiko, G. P., Volynets, O. N., Antonov, A. Yu., Tsvetkov, A. A.,
Kurile island-arc volcanism:str uctural and petrological aspects.
Tectonophysics, 199, 271–287, 1991.
Avdeiko, G. P., and Savelyev, D. P., Two types of “intra-plate” lavas
on Kamchatka, in Problems of sources of deep magmatism and
plumes, Proceeding of International Workshop, Petropavlovsk-
Kamchatsky – Irkutsk, 229–246, 2005.
Baluev, E. Yu., Perepelov, A. B., Anan’ev, V. V., and Taktaev, V. I.,
Forearc high-potassium andesites (Kamchatka). Dokl. Akad.
Nauk SSSR, 279 (4), 977–981, (in Russian), 1979.
Baranov, B. V., Seliverstov, N. I., Murav’ev, A. V., and Muzurov, E.
L., The Komandorsky Basin as a product of spreading behind a
transform plate boundary. Tectonophysics, 199, 237–270, 1991.
Bogdanov, N. A., Khain, V. E., (Eds), Tectonic map of the Sea of
Okhotsk region, scale 1:2500000 (2 sheets) with explanatory
notes. Moskow, Institute of the Lithosphere of Marginal Seas,
Churikova, T., Dorendorf, F., and Wörner, G., Sources and fluids
in the mantle wedge below Kamchatka: Evidence from across-
arc geochemical variation. Journal of Petrology, 42, 1567–1593,
Fedorchu k, A. V., Oceanic and back-arc basin remnants within
accretionary complexes: geological and geochemical evidence
from Eastern Kamchatka. Ofioliti, 17 (2), 219–242, 1992.
Fedotov S. A. et al. (Eds), The 1975–1976 Large Tolbachik Fissure
Eruption in Kamchatka, Moscow, Nauka, (in Russian), 1984.
Filatova, N. I., Circum-oceanic volcanic belts. Nedra, Moscov, (in
Russian), 1988.
Gorbatov, A., Kostoglodov, V., Maximum depth of seismicity and
thermal parameter of the subducting slab: general empirical rela-
tion and its application. Tectonophysics, 277, 165–187, 1997.
Gorbatov, A., Vidiyantoro, S., Fukao, Y. & Gordeev, E., Signature
of remnant slabs in the North Pacific from P-wave tomography.
Gephys. J. Int., 142, 27–36, 2000.
Harabaglia, P., Doglioni, C., 1998. Topography and gravity across
subduction zones. Geophys. Res. Lett., 25 (5), 703–706.
Honda, S., Uyeda, S., Thermal process in subduction zones – a
review and preliminary approach on the origin of arc volca-
nism. Arc volcanism: physics and tectonics, Tokio: Errapub,
117 – 140, 1983.
Khubunaya, S. A., The High-Al Plagioclase Tholeite Association
of Island Arcs, Moscow: Nauka, 1987.
Konstantinovskaia, E. A., Geodynamics of an Early Eocene arc–
continent collision reconstructed from the Kamchatka Orogenic
Belt, NE Russia. Tectonophysics, 325, 87–105, 2000.
Konstantinovskaia, E. A., Arc-continent collision and subduction
reversal in the Cenozoic evolution of the Northwest Pacific: an
example from Kamchatka (NE Russia). Tectonophysics, 333,
75–94, 2001.
Kozhemyaka, N. N., Active volcanoes of Kamchatka: spatial and
temporal dynamics of eruptive intensity and productivity. Vol-
canology & Seismology, 22 (1) 25–34, 2000.
Legler, V. A., Development of Kamchatka in Cenozoic accord-
ing the theor y of lithosphere plate tectonics (energ y sources
of tectonic development and plate dynamics), in: Tectonics of
lithosphere plate, Moskow, Institute of Oceanolog y, 137–169,
1977, (in Russian).
Levashova, N. M., Shapi ro, M. N., Ben’ya movskii, V. N., and
Bazhenov, M. L., Kinematics of the Kronotskii Island Arc (Kam-
chatka) from Paleomagnetic and Geological Data. Geotectonics,
34 (2), 141–159, 2000.
Levin, V. E., Gordeev, E. I., Bakhtiarov, V. F., Kasahara, M., Pre-
liminary Results From GPS Monitoring in Kamchatka and the
Komandorskie Island. Volcanology and Seismology, 1, 3–11,
2002, (in Russian).
Levin, V., Shapiro, N., Park, J., and Ritzwoller, M., Seismic evi-
dence for catast rophic slab loss beneath Kamchatka. Nature,
418, 763–767, 2002.
Litvinov, A. F., Patoka, M. G. & Markovsky, B. A., (Eds), Map ot
the mineral resources of Kamchatka region, scale 1: 500000,
St.-Peterburg, Kamchatprirodresource, 19 sheets, 1999.
Miyashiro, A., Volcanic rock series in island arcs and active conti-
nental margins. Amer. J.Sci., 274 (4), 321–355, 1974.
Melekestsev, I. V., Braitseva, O. A., Ponomareva, V. V., A new
approach to definition of the ter m “active volcano”, in: Geody-
namics and volcanism of the Kurile-Kamchatka Island-Arc sys-
tem, Petropavlovsk-Kamchatsky, 191–203 (in Russian), 2001.
Ogorodov, N. V., Kozhemyaka, N. N., Vazheevskaya, A. A., and
Ogorodova, A. S., Volcanoes and Quaternar y volcanism of
Sredinny Ridge of Kamchatka: Moskow, Nauka, 1972, (in Rus-
Osipenko, A. B., Lateral variations in the chemistry of rock-form-
ing minerals in the backarc zone of the Kurile Island: amphi-
boles. Volcanology & Seismology, 22 (1), 143–160, 2000.
Osipenko, A. B., Konilov, A. N., Savelyev, D. P., Krylov, K. A., and
Anikin, L. P. Geology and Petrology of Amphibolites from Cape
Kamchatskii, Eastern Kamchatka. Petrology, 13 (4), 381–404,
Piscunov, B. N., Geological and petrological specificity of island
arc volcanism, Moscow, Nauka, (in Russian), 1987.
Portnyagin, M., Hoernle, K., Avdeiko, G., Hauff, F., Werner, R.,
Binderman, I., Uspensky, V., Garbe-Schönberg, D., Transition
from arc to oceanic magmatism at t he Ka mchatka-Aleutian
junction. Geology, 33 (1), 25–28, 2005a.
Portnyagin, M. V., Savelyev, D. P., and Hoernle, K. Plume-Related
Association of Cretaceous Oceanic Basalts of Easter n Kam-
chatka: Compositions of Spinel and Parental Magmas. Petrology,
13 (6), 571–588, 2005b.
Peacock, S. M., Rushmer, T., Thompson, A. B., Partial melting of
subducting oceanic cr ust. Earth and Planetary Science Letters,
121, 227–244, 1994.
Popruzhenko, S. V., Aprelkov, A. E., & Olshanskaya, O. N., The
East Kamchatkan volcanic belt as reflected by geophysical data.
Volcanology & seismology, 9 (2), 200 –216, 1990.
Regelous, M., Hofmann, A.W., Abouchami, W., and Galer, S. J. G.,
Geochemistry of Lavas from the Emperor Seamounts, and the
Geochemical Evolution of Hawaiian Magmatism from 85 to 42
Ma. Journal of Petrology, 44 (1), 113–140, 2003.
Rikhter, A. V., Structure of metamorphic complexes of the Ganal-
sky Range (Kamchatka). Geotectonics, 25 (1), 75–83, 1991.
Rikhter, A. V., Structure of metamorphic complexes of the Central
Kamchatka massif. Geotectonics, 29 (1), 65–72, 1995.
Ringwood, A. E., Slab-mantle interactions. 3.Petrogenesis of intra-
plate magmas and struct ure of the upper mantle. Chem.Geol.,
82, 187–207, 1990.
Savelyev, D. P., Intraplate alkali basalts in the Cretaceous accretion-
ary complex of the Kamchatkan Peninsula (Eastern Kamchatka).
Volcanology & Seismology, 1, 14–20 (in Russian), 2003.
Sheimovich, V. S., Patoka, M. G., Geology of areas active Cenozoic
volcanism. Moscow: GEOS, (in Russian), 2000.
Seliverstov, N. I., Geological structure of Near-Kamchatka bottom
and geodynamics of junction zone of Kurile-Kamchatka and
Aleutian island ars, Moskow, Nauchnyi Mir, 1998.
Sergeyev, K. F., Krasny, M. L., (Eds), Geology-geophysical atlas
of the Kurile-Kamchatka island system, Leningrad, VSEGEI,
36 sheets, 1987.
Sun, S. S. & McDonough, W. F., Chemical and isotopic sistemat-
ics of oceanic basalts; implications for mantle composition and
processes. In: Saunders, A. D. & Norry, M. J. (cds) Magmatism
in the Ocean Basins. Geological Society, Landon, Special Pub-
lications 42, 313–345, 1989.
Tatsumi, Y., Migration of fluid phases and genesis of basalt magmas
in subduction zones. J.Geophys. Res., 94 (B4), 4697–4707, 1989.
Tatsumi, Y., Furukawa, Y. Kogiso, T. et al., A third volcanic chain
in Kamchatka: thermal anomaly at transform/convergence plate
boundary. Geophys. Res. Lett., 21 (7), 537–540, 1994.
Tatsumi, Y., Hamilton, D.L., Nesbitt, R.W., Chemical character-
istics of the fluid phase released from a subducted lithosphere
and the origin of arc magmas: evidence from high pressu re
experiments and natural rocks. J. Volcanol. Geotherm. Res., 29
(1–4), 293 – 309, 1986.
Tatsumi, Y., Kogiso, T., Nohda, S., Formation of a third volcanic
chain in Kamchatka: generation of unusual subduction-related
magmas. Contrib Mineral. Petrol. 120, 117 – 128, 1995.
Trubitsin, V. P., Shapiro, M. N., and Rykov, V. V., Numerical mod-
eling of the Prepliocene mantle f low in the junction zone of the
Kuril-Kamchatka and Aleutian Island Arcs. Physics of the Solid
Earth, 4, 10–19 (in Russian), 1998.
Tsukanov, N. V. The Late Mesozoic–Early Cenozoic Tectonic History
of the Pacific Coastal Zone of Kamchatka, Moscow: Nauka, 1991.
Vinogradov, V. I., Grigoriev, V. S., Leites, A. M., Age of metamor-
phism of the rocks from the Sredinny Range of Kamchatka. Izv.
Acad. Nauk SSSR. Ser. Geol. 9, 30–38 (in Russian), 1988.
Volynets, O. N., Geochemical types, petrology and genesis of Late
Cenozoic volcanic rocks from the Kurile-Kamchatka island-arc
system. Intern. Geol. Rev., 36, 373–405, 1994.
Volynets, O. N., Avdeiko, G. P., Tsvetkov, A. A., Antonov, A. Yu.,
Markov, I. A., Filosofova, T. M., Mineral zoning in the Quater-
nary lavas of the Kurile Island Arc. Intern. Geol. Rev., 32 (2),
128–142, 1990.
Volynets, O. N., Melekestsev, I. V., Ponomareva, V. V. & Yogodzin-
sky, J. M., Kharchinskii and Zarechnyi volcanoes-unique centers
of Late Pleistocene magnesian basalts in Kamchatka: structural
setting, morphology, globalic structure and age. Volcanology &
Seismolog y, 20 (4-5), 383–400, 1999a.
Volynets, O. N., Melekestsev, I. V., Ponomareva, V. V. & Yogodz-
insky, J. M., K harchinskii and Zarechnyi volcanoes-unique
centers of Late Pleistocene magnesian basalts in Kamchatka:
composition of er upted rocks, Volcanology & Seismology, 21
(1), 45–66, 1999b.
Volynets, O. N., Puzankov, Ju.M., Anoshin, G. N., Geochemis-
try of Neogene-Quaternqry volcanic series in kamchatka. In:
Geochemical typification of magmatic and metamorphic rocks
in Kamchatka. Proceeding of the Institute of Geology and Geo-
physics, Novosibirsk, 390, 73–114 (in Russian), 1990.
Volynets, O. N., Uspenskiy, V. S., Anoshin, G. N. et al, Geo-
chemistry of Late Cenozoic basalts from East Kamchatka and
implications for geody namic evolution of magma generation.
Volcanology & Seismology, 12 (5), 560–575, 1992.
Watts, A. B., Gravity field of the Nor thwest Pacific Ocean basin
and its margin: Aleutian island-arc trench system: Geological
Society of America Map and Chart Series, MC-10, 1975.
Watts, A. B., Kogan, M. G., Bodine, J. H., Gravit y field of the
Northwest Pacific Ocean basin and its margin: Kuril island arc-
trench system: Geological Societ y of America Map and Chart
Series, MC-27, 1978.
Yogodzinski, G. M., Lees, J. M., Churikova, T. G., Dorendorf, F.,
Wörner, G. & Volynets, O. N., Geochemical evidence for the
melting of subducting oceanic lithosphere at plate edges. Nature,
409, 500–504, 2001.
... Orange lines represent main tectonic-plate boundaries; violet ones were suggested by the article authors. The movement speed of the Pacific Plate is (after Avdeiko et al., 2007 andSteblov et al. 2010). Red triangles show active volcanoes (after Simkin and Siebert, 1994). ...
... Quaternary arc volcanism on the peninsula is presented in three distinguished regions: the oldest and nearly extinct Sredinny Ridge, Central Kamchatka Depression containing very active Northern Group of Volcanoes, and young Eastern Volcanic Front (EVF) (Avdeiko et al., 2007). Both Northern Group and EVF are fed by processes associated with the contemporary subduction of the Pacific plate beneath the northern part (Kamchatka-Okhotsk block) of the Okhotsk microplate (Apel et al., 2006;Kogan et al., 2000). ...
... While magmatism on Kamchatka dates back to the Cretaceous, current plate-tectonic geometry has formed from Late Miocene to Early Pliocene with the following remarkable increase in volcanic activity during Upper Pleistocene and Holocene period (Melekescev et al., 1987). The formation of the Kamchatka volcanic arc is associated with the rotation of the Pacific Plate 45 and 30 million years ago, which led to the restructuring of the back-arc basins and subduction zones in the interval 15-20 million years ago (Avdeiko et al., 2007). It started with a collision of the Ozernovsko-Valaginsky island arc with Kamchatka, which dates back about 55 million years ago (Volynets et al., 1992). ...
Gorely, being one of many active volcanoes in Kamchatka, stands out due to the rich magmatic history reflected in its composite structure and persistent degassing activity. In 2013–2014, a temporary network of 20 seismic stations was installed on the volcano to gather data autonomously for almost a year. During the four months of its high degassing rate, seismic activity was mostly expressed in the form of a long-period seismic tremor. In this study, a workflow based on the combination of back-projection, cluster analysis, and template-matching methods was developed to inspect the observed seismic signature. The processing of continuous seismic records yielded a catalog of individual long-period earthquakes that merges to constitute observed tremor-like signals. A catalog obtained using the back-projection detection algorithm consist of 1741 high-energy events. Cluster analysis revealed that a significant part of earthquakes in this catalog could be grouped into five families, which are sequentially organized in time. Utilizing stacked waveforms for each family in the template-matching detection resulted in the complementary catalog of 80,615 low-energy events. Such long-term occurrence of highly repetitive long-period earthquakes suggests a non-destructive mechanism that may correspond to several physical models. Ultimately, long-period earthquakes on Gorely represent a seismic signature of the magmatic system behaving in response to the high-pressure gases flowing from the decompressed magma chamber up to the volcano's crater.
... A partir de l'Oligocène supérieur, un double arc de subduction s'est mis en place au Kamchatka et dans les îles Kouriles. Au sud de la jonction entre le Kamchatka et les îles Aléoutiennes, la Plaque Pacifique subduit sous la marge Eurasiatique ; au nord de la jonction, la microplaque du Commandeur subduit sous la marge Eurasiatique (Avdeiko et al., 2007). Le volcanisme de la Chaîne Centrale date de cette époque. ...
... Parallèlement, la subduction s'est déplacée à son emplacement actuel, en arrière de la collision Kamchatka-Kronotski. L'ancien front de subduction est devenu inactif et un nouveau s'est formé à l'est de l'emplacement précédent, créant de ce fait le nouvel arc volcanique de la Chaîne Orientale (Lander and Shapiro, 2007). En réponse aux changements de conditions géodynamiques, plusieurs réajustements isostatiques ont eu lieu, tels que la subsidence au niveau de l'actuelle Dépression Centrale du Kamchatka (Avdeiko et al., 2007). ...
... 13 -Carte géologique du Kamchatka(Avdeiko et al., 2007). Geological map of the Kamchatka(Avdeiko et al., 2007). ...
Les éléments halogènes sont caractérisés par une configuration électronique S2P5 qui leur confère une très forte électronégativité leur permettant de former des ions halogénures très réactifs (X-, où X est un élément halogène). De par leur comportement volatil et incompatible dans la plupart des minéraux cristallisant dans les réservoirs magmatiques, leur concentration augmente dans la phase liquide résiduelle lors de la cristallisation fractionnée. Lorsque le magma remonte vers la surface, la solubilité des éléments volatils diminuant (parmi lesquels les éléments halogènes), ils s’exsolvent du magma sous forme de gaz. Les gaz émis lors des éruptions pliniennes sont propulsés à plusieurs kilomètres d’altitude et, selon l’importance de l’éruption, peuvent parvenir dans la stratosphère. Une fois injectés dans la stratosphère, les éléments halogènes ont un temps de résidence qui varie selon l’élément et le composé qu’il forme, et qui peut atteindre plusieurs années. Ils y déstabilisent les équilibres chimiques et provoquent la destruction de l’ozone stratosphérique. La méthode utilisée durant cette thèse consiste en une estimation du volume total d’un élément volatil donné émis lors d’une éruption, par la différence de concentration de l’élément dans le magma avant et après éruption. Le dégazage correspond à la différence de concentration de l’élément avant et après éruption. Cette méthode présente le double intérêt de permettre la mesure de la concentration totale de l’élément dans le magma, de manière non spécifique, et de ne pas requérir d’observation directe au moment de l’éruption.
... According to another concept, the CKD was formed in Eocene-Pliocene as a fore-arc basin when the subduction occurred more to the west, and the Sredinny Range acted as the main volcanic arc (Avdeiko et al., 2007;Pevzner et al., 2017;Portnyagin et al., 2005). The subduction and the volcanic front migrated to the east a few million years ago following the Miocene-Pliocene collision of the Kronotsky arc terrane (Alexeiev et al., 2006;Avdeiko et al., 2007;Lander & Shapiro, 2007;Pedoja et al., 2013). ...
... According to another concept, the CKD was formed in Eocene-Pliocene as a fore-arc basin when the subduction occurred more to the west, and the Sredinny Range acted as the main volcanic arc (Avdeiko et al., 2007;Pevzner et al., 2017;Portnyagin et al., 2005). The subduction and the volcanic front migrated to the east a few million years ago following the Miocene-Pliocene collision of the Kronotsky arc terrane (Alexeiev et al., 2006;Avdeiko et al., 2007;Lander & Shapiro, 2007;Pedoja et al., 2013). ...
... Green et al. (2020) proposed that the CKD subsidence and accumulation of sediments occurred in two stages. The first stage was related to relatively slow formation of the fore-arc basin during Eocene-Pliocene, when Sredinny Range acted as the main volcanic arc (Avdeiko et al., 2007;Portnyagin et al., 2005). The second stage started a few Ma ago, after major reconfiguration of the subduction zones at the vicinity of the Kamchatka-Aleutian junction following the Miocene-Pliocene collisions of the Kronotsky arc terrane (Alexeiev et al., 2006;Avdeiko et al., 2007;Lander & Shapiro, 2007;Pedoja et al., 2013). ...
Full-text available
Klyuchevskoy and surrounding volcanoes in central Kamchatka form the Northern Group of Volcanoes (NGV), which is an area of particularly diverse and intensive Pleistocene‐Holocene volcanism. In this study, we present a new seismic tomographic model of the crust and uppermost mantle beneath NGV based on local earthquake data recorded by several permanent and temporary seismic networks including a large‐scale experiment that was conducted in 2015–2016 by an international scientific consortium. Having an unprecedented resolution for this part of Kamchatka, the new model reveals many features associated with the present and past volcanic activity within the NGV. In the upper crust, we found several prominent high‐velocity anomalies interpreted as traces of large basaltic shield volcanoes, which were hidden by more recent volcanic structures and sediments. We interpret the mantle structure to reflect asthenospheric flow up through a slab window below the Kamchatka‐Aleutian junction that feeds the entire NGV. The interaction of the hot asthenospheric material with fluids released from the slab determines the particular volcanic activity within the NGV. We argue that the eastern branch of the Central Kamchatka Depression, which is associated with a prominent low‐velocity anomaly in the uppermost mantle, was formed as a recent rift zone separating the NGV from the Kamchatka Eastern Ranges.
... The margin is tectonically complex, with along-and across-arc changes in slab dip and Moho depth; evidence for slab-tearing and a relict slab; and intra-arc rifting associated with anomalously high magma production (e.g. Avdeiko et al., 2007;Portnyagin and Manea, 2008;Hayes et al., 2018). Previous studies have identified a melting regime dominated by hydrous flux melting, with contributions from a variably depleted MORB mantle wedge, an OIB-type enriched mantle, slab-derived aqueous fluids, slab-derived melts, and sediment melt (Churikova et al., , 2007Portnyagin et al., 2007a;Simon et al., 2014). ...
... trench to its current location (e.g. Avdeiko et al., 2007). REVF samples in this study include scoria from monogenetic cones related to Bakening stratovolcano. ...
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The chemistry of primitive arc rocks provides a window into compositional variability in the mantle wedge, as well as slab-derived inputs to subduction-related magmatism. However, in the long-term cycling of elements between Earth's internal and external reservoirs, a key unknown is the importance of retaining mobile elements within the subduction system, through subduction-related metasomatism of the mantle. To address these questions, we have analysed olivine-hosted melt inclusions and corresponding bulk rocks from the Kamchatka arc. Suites of melt inclusions record evidence for entrapment along melt mixing arrays during assembly of diverse parental magma compositions. Systematic variations in parental magma B/Zr, Nb/Zr, Ce/B, and δ11B are also apparent among the different eruptive centres studied. These element ratios constrain the nature of subduction-related metasomatism and provide evidence for ambient mantle heterogeneity and variable degrees of mantle melting. High Nb/Zr and low B/Zr in back-arc rocks indicate smaller degree melts, lower slab-derived inputs, but relatively enriched mantle compositions. Similarly, small monogenetic eruptive centres located away from the main stratocones also tend to erupt magmas with relatively lower slab contribution and overall smaller melting degrees. Conversely, arc-front compositions reflect greater slab contributions and larger degree melts of a more depleted ambient mantle. Across-arc variations in δ11B (ranging from ca. −6‰ in the rear-arc and Sredinny Ridge to +7‰ in the Central Kamchatka Depression) are generally consistent with variable addition of an isotopically heavy slab-derived component to a depleted MORB mantle composition. However, individual volcanic centres (e.g. Bakening volcano) show correlations between melt inclusion δ11B and other geochemical indicators (e.g. Cl/K2O, Ce/B) that require mixing between isotopically distinct melt batches that have undergone different extents of crustal evolution and degassing processes. Our results show that while melt inclusion volatile inventories are largely overprinted during shallower melt storage and aggregation, incompatible trace element ratios and B isotope compositions more faithfully trace initial mantle compositions and subduction inputs. Furthermore, we suggest that the signals of compositional heterogeneity generated in the sub-arc mantle by protracted metasomatism during earlier phases of subduction can be preserved during later magma assembly and storage in the crust.
... The geochemistry of the Kamchatka volcanic rocks is typical of global arc volcanism. They contain a high amount of large ion lithophile elements such as Rb, Ba, K, Pb, and Sr in comparison with high field strength elements such as Nb, Zr, and Ti [34][35][36][37]. Mutnovsky and Gorely volcanoes belong to the Mutnovsky geothermal field, which is part of the Mutnovsky geothermal region with an area of about 750 km 2 [38] (Figure 1). ...
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Volcanic activity has a great impact on terrestrial ecosystems, including soil algae in general and diatoms in particular. To understand the influence of volcanoes on the biodiversity of diatoms, it is necessary to explore the flora of these microorganisms in regions with high volcanic activity, which includes the Kamchatka peninsula. During the study on diatoms in the soils of Mutnovsky and Gorely volcanoes of Kamchatka, 38 taxa were found. The Mutnovsky volcano diatom flora was more diverse and accounted for 35 taxa. Eunotia curtagrunowii, Humidophila contenta, and Pinnularia borealis were the dominant species. In the Gorely volcano, only 9 species were identified, with Caloneis bacillum and Pinnularia borealis prevailing in the samples. Overall, the genera Pinnularia and Eunotia were the most diverse in the studied area. The diatom flora of the studied volcanoes comprises mostly cosmopolitan small-sized taxa with a wide range of ecological plasticity. Our data confirm the high adaptive potential of diatom algae and add new knowledge about the ecology and biogeography of this group of microorganisms.
... At the next step, the obtained damage distribution was subjected to spatial smoothing with the radius that increases for the deeper layers of the model. The heterogeneity function determined using the fault tectonics schemes presented in (Kozhurin et al., 2006;Avdeiko et al., 2007). The corresponding normalized distribution of rock damage is shown in Fig. 5. ...
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Volcanism is one of the main mechanisms transferring mass and energy between the interior of the Earth and the Earth's surface. However, the global mass flux of lava, volcanic ash and explosive pyroclastic deposits is not well constrained. Here we review published estimates of the mass of the erupted products from 1980 to 2019 by a global compilation. We identified 1,064 magmatic eruptions that occurred between 1980 and 2019 from the Smithsonian Global Volcanism Program database. For each eruption, we reported both the total erupted mass and its partitioning into the different volcanic products. Using this data set, we quantified the temporal and spatial evolution of subaerial volcanism and its products from 1980 to 2019 at a global and regional scale. The mass of magma erupted in each analyzed decade ranged from 1.1–4.9 × 10¹³ kg. Lava is the main subaerial erupted product representing ∼57% of the total erupted mass of magma. The products related to the biggest eruptions (Magnitude ≥6), with long recurrence times, can temporarily make explosive products more abundant than lava (e.g., decade 1990–1999). Twenty‐three volcanoes produced ∼72% of the total mass, while two different sets of 15 volcanoes erupted >70% of the total mass of either effusive or explosive products. At a global scale, the 10 and 40‐year average eruptive rates calculated from 1980 to 2019 have the same magnitude as the long‐term average eruptive rates (from thousand to millions of years), because in both cases rates are scaled for times comparable to the recurrence time of the biggest eruptions occurred.
––The Klyuchevskoy group of volcanoes (KGV) located in the central part of Kamchatka is a unique complex that demonstrates exceptional variety and intensity of volcanic manifestations. These features of the eruptive activity of the KGV are determined by a complex system of magmatic sources in the crust and mantle. While the structure of deep anomalies is quite reliably determined by tomography techniques based on body waves, the structure of the upper crust can only be determined using ambient noise tomography. We present the results of processing data from the KISS temporary network. This network consisted of more than 100 seismic stations that were installed from 2015 to 2016 over a large area covering the Klyuchevskoy group of volcanoes and its surroundings. To retrieve Rayleigh surface waves, cross-correlation of continuous seismic noise records from pairs of stations was used. We obtained the dispersion curves of the group velocities of these Rayleigh surface waves using frequency–time analysis (FTAN) of the calculated correlograms. These curves served as input data for performing ambient noise tomography. Tomography was performed in two stages: (1) computation of two-dimensional group velocity maps for different frequencies and (2) calculation of a three-dimensional model of the shear wave velocity to a depth of about 8 km based on the inversion of local dispersion curves obtained from these maps. The resulting models revealed the structural features of individual volcanic systems of the KGV. High velocities were observed at shallow depths beneath the large basaltic edifices of the Ushkovsky and Tolbachik volcanoes. At greater depths, while the velocity structure beneath Ushkovsky remained unchanged, we detected low velocities beneath Tolbachik. This fact illustrates the difference between dormant and active magmatic systems. Velocity anomalies of a complex shape are observed beneath the Klyuchevskoy, Kamen, and Bezymianny volcanoes, varying both laterally and with depth. Absolute velocities in vertical sections show that the edifices of these volcanoes are relatively low-velocity bodies located on a horizontal high-velocity basement. A low-velocity anomaly was discovered under the Bezymianny Volcano at a depth of 6 km, which is presumably associated with a shallow magma reservoir. An intense low-velocity anomaly was found beneath the Udina Volcano. It was interpreted as an image of a magma reservoir experiencing strong seismic unrest that began in December 2017 and continues to this day.
Microplastic (MP) pollution affects almost all ecosystems on Earth. Given the increasing plastic production worldwide and the durability of these polymers, concerns arise about the fate of this material in the environment. A candidate to consider as a depositional final sink of MP is the sea floor and its deepest representatives, hadal trenches, as ultimate sinks. In this study, 13 sediment samples were collected with a multiple-corer at depths between 5740 and 9450 m from the Kuril Kamchatka trench (KKT), in the Northwest (NW) Pacific Ocean. These samples were analysed for MP presence in the upper sediment layer, by slicing the first 5 cm of sediment cores into 1 cm horizontal layers. These were compared against each other and between the sampling areas, in order to achieve a detailed picture of the depositional system of the trench and small-scale perturbations such as bioturbation. The analyses revealed the presence of 215 to 1596 MP particles per kg ⁻¹ sediment (dry weight), with a polymer composition represented by 14 polymer types and the prevalence of particles smaller than 25 μm. A heterogeneous microplastic distribution through the sediment column and different microplastic concentration and polymer types among sampling stations located in different areas of the trench reflects the dynamics of this environment and the numerous forces that drive the deposition processes and the in situ recast of this pollutant at the trench floor.
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A quarter of Kamchatka's Late Quaternary (<50 ka) volcanic deposits is erupted in the back-arc along the Sredinny Range (SR). The eruptions are represented by several dozens of polygenetic volcanoes and hundreds of monogenetic volcanoes located along a SW-NE lineament in the western part of the peninsula. Previous studies explained the generation of magma by (1) fluid induced melting of the mantle due to the input of H2O from the presently subducting slab, (2) decompression-induced melting of the mantle caused by upwelling of the asthenosphere, or (3) delamination and melting of the lower crust of the SR. We present new major and trace elements in olivine and major, trace and volatile (H2O, Cl, F and S) data in quenched olivine-hosted melt inclusions (MI) from three Holocene monogenetic volcanoes that are located in the southern, central and northern volcanic zones of the SR. The reconstructed melts range from basalts to basaltic andesites of medium-K affinity and exhibit trace element signatures that are transitional between island arc magmas (IAM) and enriched mid-ocean ridge basalts (E-MORB). They have high H2O concentrations (from ~ 1.5 to 2.5 wt.%) compared to MORB with similar Nb/Y ratios, which suggests that the H2O played an essential role in their origin. The high H2O/Cl (from ~ 50 to ~ 100) and Ba/Rb (from ~ 20 to ~ 50) ratios and low Cl/K2O (from ~ 0.02 to ~ 0.04) and Cl/F (from ~ 0.2 to ~ 0.5) ratios in these melts indicate that the budget of volatile components was controlled by the breakdown of amphibole. The Fe/Mn ratios and Ni contents in olivine from the studied Holocene volcanoes suggest significant contributions of melts derived from a pyroxenitic source. We propose that the parental magmas of these volcanoes were generated by combined partial melting of a range of delaminat-ing lower crustal lithologies with pyroxene and amphibole and the surrounding peridotites. Their melting was facilitated by the influx of H2O that was released from amphibole breakdown at high pressures. The amount of magma that was erupted along the Sredinny Range during the Late Quaternary can be produced by delamination of at least 7 vol.% of its crust. The proposed mechanism of delamination-induced melting may be involved in magma generation in other back-arc settings with a thick crust, such as back-arc regions of the Andean-type convergent margins and some active intra-oceanic back-arcs.
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The paper reports the results of a detailed geological and mineralogical-geochemical study of metamorphic rocks widespread in the sole of the Cape Kamchatskii ophiolite complex in eastern Kamchatka. The metabasites are classified into mineralogical types (ranging from clinopyroxene-garnet- amphibolite rocks, which are metamorphosed to the highest grades, to albite-epidote amphibolites) that correspond to the prograde stage of metamorphism of the relatively high-pressure parental assemblage. The petrochemical characteristics of the rocks place them among the metamorphic derivatives of plutonic rocks of the N-MORB type (supposedly, tholeiitic gabbroids). The genesis of the metamorphic rocks is thought to be related to Late Cretaceous-Paleocene subduction of the oceanic plate, the development of an inverted thermal gradient in the upper part of the subducted slab, and metamorphism of the mafic rocks to the garnet amphibolite facies, their subsequent uplift, and exhumation during the obduction of the suprasubduction ophiolites in the Eocene-Miocene.
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Cretaceous rocks comparable to mid-oceanic ridge and oceanic island basalts were described in ophiolite association of the Cape Kamchatskii, Eastern Kamchatka (Fedorchuk et al, 1989). New data on the composition of these basalts, their spinels, and melt inclusions in them are presented in this paper. Spinel from olivine-plagioclase basalts corresponds in composition to that of mid-oceanic ridge tholeiites (Mg# = 0.57-0.82, Cr# = 0.33-0.55, TiO2 = 0.03-0.85 wt %). High-K alkali basalts include less magnesian and chromian (Mg# = 0.57-0.70, Cr# = 0.23-0.30), but Ti-rich (TiO2 = 0.60-0.86 wt %) spinel. Low Cr# and very low Fe3+ contents of spinel distinguish the studied rocks from island-arc basalts of Eastern Kamchatka. Melt inclusions in spinel from plagioclase-olivine basalts have tholeiitic low-alkali (Na 2O = 0.8-2.5 wt %, K2O = 0.01-0.09 wt %), high-Ca (CaO = 13-15 wt %), and low-Ti (TiO2 = 0.2-1.2 wt %) composition. Chlorine concentrations are extremely low in the melt inclusions (Cl < 0.005 wt %), while S contents are high (S = 0.12 ± 0.03 wt %). Concentrations of incompatible elements in inclusions (La = 0.3-1.2 ppm, Sr = 27-70 ppm, Zr = 13-21 ppm) are systematically lower than in typical oceanic tholeiites. The melts are selectively enriched in K, Sr, and Ba relative to REE in the N-MORB-normalized trace-element spectra. Participation of plume component in the formation of the Late Cretaceous rift-related basalts of the Pacific Ocean, which are incorporated now in ophiolite association of the Cape Kamchatskii, is inferred from indicative rock assemblage and composition of primitive melts and spinel.
The unusual development of three volcanic chains, all parallel to the trend of the subduction trench, is observed in Kamchatka at the northern edge of the Kurile arc. Elsewhere on the Earth volcanic arcs dominantly consist of only two such chains. In the Kurile arc, magmatism in the third volcanic chain, which is farthest from the trench, is also unusual in that lavas show concentrations of incompatible elements intermediate between those of the two trenchward chains. This observation can be explained by relatively shallow segregation of primary magmas and high degrees of partial melting of magmas in the third chain, compared to the conditions of magma separation expected from a simple application of the general acrossarc variation. Initial magmas in such an atypical third chain may be produced by melting of K-amphibolebearing peridotite in the down-dragged layer at the base of the mantle wedge under anomalously hightemperature conditions. Such an unusual melting event may be associated with the particular tectonic setting of the Kamchatka region, i.e. the presence of subductiontransform boundary. Such a mechanism is consistent with the across-arc variation in Rb/K ratios in the Kamchatka lavas: lowest in the third chain rocks and highest in the second chain rocks.
MORB-type and BABB-like fragments have been discovered within two separate terranes of Eastern Kamchatka: the Kamchatsky Mys terrane in Eastern Kamchatka and the Kumroch terrane in the West. These fragments or terranes originated in different tectonic settings, namely in an oceanic setting (the Ophiolite Sequence and the Early Cretaceous assemblage of the Kamchatsky Mys terrane, the Late Cretaceous OIB-like basalts of both the Kamchatsky Mys and Kumroch terranes). The BABB-like rock compositions show no relation with synchronous subduction processes, but may reflect contamination of a MORB-like mantle by within-plate sources. -from Author
A simplified model is used to calculate the convection structure in the mantle beneath the little movable North American Plate in the junction zone between the Aleutian island arc and Kamchatka. The flows northeast of the western flank of the Aleutian arc are found on the assumption that they are induced by mantle convection to the south of the arc. The induced flows are associated with Miocene subduction beneath Kamchatka, north of the crossing point of the Kurile-Kamchatka and Aleutian trenches.
The total volumes of volcanic rocks and average annual productivities of active volcanoes were calculated for all volcanic zones of Kamchatka for the mid-Pleistocene, Late Pleistocene, and Holocene epochs. Average values were computed for heat and mass transfer. A distinct spatial trend of recent volcanism was substantiated: a growth of the intensity and productivity of volcanism in a northward direction. The temporal trend was the growth of activity in the Late Pleistocene and Holocene with a peak during the Holocene.
This paper presents the results of studying the spatial distribution and structural setting of magnesian basalts and andesites in the Northern group of Kamchatkan volcanoes and in the junction zone of the Kuril-Kamchatka and Aleutian island arcs. The morphology and geologic structure of unique Kamchatkan magnesian basalt stratovolcanoes are described: Kharchinsky, Zarechnyi, and the Kharchinsky regional zone of cinder cones. The reported evidence includes the ages and eruptive histories, and productivities of the volcanoes and the volumes and weights of their edifices. The magnesian basalts were erupted 40-50 thousand years ago, for the first time during the Holocene.
The bulk of the Kamchatkan hydrothermal manifestations and all high-temperature hydrothermal systems are located in three volcanic belts: the East Kamchatka, South Kamchatka, and Sredinnyi Ridge volcanic zones. The fact that subduction has terminated beneath the latter is confirmed by geological evidence and also by the fact that the amount of heat transferred by the Sredinnyi Ridge hot springs is an order of magnitude lower than that in East and South Kamchatka. The hydrothermal manifestations have an almost identical geographical distribution pattern in all of the three volcanic belts. With the 90-100-km widths of the volcanic belts and zones of hydrothermal activity, > 95% of the heat transferred by the hot springs are confined to the roughly 45-km wide zones that border the volcanic fronts. The volcanic fronts of the arcs are distinct boundaries, beyond which heat transfer declines abruptly. Heat transfer is restricted to zones with 70-100-km intervals between the peak heat transfer values. The quantitative evaluation of the contributions of potential heat and water sources revealed that the sole realistic heat source could be shallow magma chambers. A model is proposed for a potential heat and mass transfer mechanism responsible for the formation of hydrothermal systems and associated ore deposits.
This study of the lateral chemical variations of amphiboles from phenocrysts in the andesites of submarine volcanoes located on the Sea of Okhotsk slope of Iturup Island, Kuril Island Arc, did not reveal any significant variations in the mineral chemistry that could be related to the spatial location or geochemical trend of the enclosing rocks. A difference between a petrochemical and a mineral (amphibole) zonal pattern is believed to have been caused by differences in the factors that had caused a spatial heterogeneity of the parental andesite magma and particular physicochemical conditions of its evolution in the magma source. Data on the main variation trend of the amphibolite composition suggest that the main controlling factors had been the temperature and oxidation-reduction conditions of the andesite crystallization. The results of this study can be explained by the local evolution of the physicochemical conditions of andesite magma crystallization in an isolated chamber.