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Volcanic activity at Sedankinsky Dol lava field, Sredinny ridge during the
Holocene (Kamchatka, Russia)
Dirksen O.V.1, Bazanova L.I.1, Pletchov P.Yu.2, Portnyagin M.V.3, Bychkov
K.A.2
1Institute of Volcanology and Seismology, Petropavlovsk-Kamchatsky, Russia,
dirksen@kcs.iks.ru, 2Moscow State University, Faculty of Geology, Moscow,
Russia, pavel@cs.ru, 3Dynamics of the ocean floor, IFM-GEOMAR, Kiel,
Germany, mportnyagin@ifm-geomar.de
Kamchatka hosts more than 30 Holocene stratovolcanoes and large number
of monogenetic vents. The recent volcanism is restricted to three main
zones: the Eastern Volcanic Belt and South Kamchatka, the Central Kamchatka
Depression, and the Sredinny Ridge. While the first two zones are
relatively well investigated, only few data is now available on the
Sredinny Ridge magmatism.
Here we report preliminary results on chronology and composition of
volcanism from the Sedankinsky Dol lava field, which is an area of most
voluminous volcanism in the northern Sredinny Ridge during the Holocene.
This area is situated 100 km NW from Shiveluch, the northernmost active
volcano in Kamchatka and comprises several small shield- and
stratovolcanoes and more than 100 monogenetic cones. The area is situated
to the north of the edge of the subducting Pacifc plate [Gorbatov et al.,
1997, Levin et al., 2002, Park et al., 2003], and origin of magmatism in
the area is of broad scientific interest. The recent magmatism in the
Sredinny Ridge has been assigned (1) to fluids from the subducting Pacific
plate triggering mantle melting, (2) to melting of the Pacific plate edge
and [Avdeiko et al., 2001, Yogodzinski et al., 2001] (3) to mantle plume
activity [Portnyagin et al., 2003].
Detailed geological and tephrochronological investigations revealed
three main stages of the volcanic activity within the Sedankinsky Dol: (1)
Late Pleistocene, (2) Early Holocene and (3) Late Holocene. Most of shield-
and stratovolcanoes appeared during the II stage of Late Pleistocene
glaciation and erupted about 4-5 km3 of basaltic, basaltic andesite magmas.
The Early and Late Holocene stages are marked by abundant monogenic
volcanism and several eruptions of Titila volcano, which is probably the
only known potentially active Iceland-type shield volcano in Kamchatka. The
total volume of erupted products of the 2nd and 3rd stages is about 0.5
km3.
All the erupted lavas are predominantly Ol-basalts. Total amount of
phenocrysts, Ol (Fo78-85) and Pl (An65-82) ranges from 8 to 20%. Determined
sequence of crystalization (Ol85-83->Ol80-83->Pl71-73->Ol-Mt-Pl->Cpx-Pl)are
consistent with fractionation at upper crust level. Complex studying of
magmatic paragenesis and melt inclusions in Ol allow to recognized the
parent melts composition (SiO2- 47.46, TiO2- 1.44, Al2O3- 18.18, FeO- 9.73,
MnO- 0.18, MgO-8.21, CaO-9.91, Na2O-3.44, K2O- 0.67) wich extisted at T~
12100C, P~1.5 Kbar, and H2O~ 0.3 %. Oxigen fugasity, determined according
to [Ballhause et al., 1991], corresponds to NNO buffer. Close resemblance
of melts composition and similar condition of fractionation of these melts
suggest the common mechanism of formation of areal basalts for this area.
Geochemical results indicated that Sedanka basalts have larger amount
of K2O, Na2O, TiO2 and P2O5, compared with basalts of Eastern volcanic
belt, that possibly indicates some admixture with intraplate basalts.
Investigation of melt inclusions in Ol phenocrysts revealed existence of
two types of parent melts in some samples: low-K tholeite and medium-K high-
Ti basalts. Presents of these heterogeneous melts allows to suggest the
mixture of different parent melts during the magma generation.
Our results confirm the existing of the Holocene volcanism in the
Sedanskinsky Dol area, as was previously reported by [Ogorodov et al.,
1972]. Established periods of volcanic activity within northern part of the
Sredinny Ridge correspond well to those in the Central Kamchatka Depression
and in the Eastern Volcanic Belt and South Kamchatka. The observation
implies common trigger mechanism of volcanism in the entire Kamchatka arc.
This research was supported by RFBR grant ? 03-05-64027 and President
grant "Leading Scientific Schools of Russia" ? 1645.2003.5