Volume 24, 2, 2005
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Volume 24, 2, 2005 |
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N.P. Romanovsky, V.G. Gurovich,
Yu.F. Malyshev, Ye.G. Ivolga
The petromagnetic map of the junction area of the Central-Asian and Pacific
belts
The petromagnetic map of the junction area of the Central-Asian and
Pacific belts has been compiled for the first time at a scale of 1:5,000,000 on
the formalized base with the information conveyed in a continuous integral form.
The compilation of the map involved 378 thousand definitions of magnetic
susceptibility of rocks. The isolines of the values have been drawn at 20, 50,
100, 200, 300, 700 and 1500 x 10-5SI. The map provides recognition of regional
petrophysical regularities in the structure of the Earth’s crust upper mantle at
the expense of generalization of the trends of chemical characteristics of rocks
in their entire age and material ranges, and helps recognize the regularities in
the structure and geodynamic evolution of the Earth’s crust and lithosphere.
S.V. Passkazov, O.A. Melnikov,
A.V. Rybin, V.A. Guryanov, T.A. Yasnygina, I.S. Brandt, S.B. Brandt, Ye.V.
Saranina, M.N. Maslovskaya, N.N. Fefelov, A.E. Zharov
The spatial change of deep sources of Cenozoic volcanic rocks on the
western coast of South Sakhalin
Variations in petrogenic oxides and microelements (ICP MS method) were
studied and the strontium isotope ratios were measured in the volcanic rocks of
the Middle and Late Cenozoic on the western coast of South Sakhalin dated by the
K-Ar method. The Chekhovskaya and Lesogorskaya zones with different compositions
of magmatic sources were distinguished. The volcanic material of the
Chekhovskaya zone contained a subduction component with high K/Nb, Ba/La and low
Nb/U, Nb/La, Ce/Pb ratios. In the interval 31-26 Ma depleted mantle material
with (87Sr/86Sr)0 0,7036-0,7040was supplied, and in the interval 21-17 Ma,
material with a lower value of (87Sr/86Sr)0 0,7030-0,7038. The volcanic rocks of
the Lesogorskaya zone were mantle meltings deprived of any admixture of the
subduction component. The depleted mantle meltings with (87Sr/86Sr)0 0,7040
appeared in the Middle Miocene (~16 Ma), and the most concentrated with
(87Sr/86Sr)0 0,7044-0,7050, at the Middle – Late Miocene boundary (12-11 Ma) and
at the beginning of the Pliocene (5-4 Ma). The Chekhovskaya zone was laid down
on the heterogeneous substratum containing Cretaceous volcanic island arc
complexes; and the Lesogorskaya zone, on the Cretaceous West Sakhalin turbidite
trough where volcanic island arc-type complexes were absent.
F.I.
Rostovsky
Pb isotope ratio of the ore leads of Eastern Asia
Pb is one of the elements whose geochemical history is totally
reflected in its isotopic composition. While Pb, U and Th are in the mantle in a
dispersed state, Pb is constantly enriched in radiogenic isotopes. The
appearance of plums dissociating in the apical parts into series of mid-water
areas of the asthenosphere, results in Pb mineral phases devoid of U and Th that
do not change their isotopic composition. The ratio of isotopes in such leads
indicates the age of formation of paleoasthenospheric areas.
D.P. Savelyev, T.N. Palechek, M.V.
Portnyagin
Campanian oceanic siliceous-volcanogenic deposits in the basement of the
East Kamchatka volcanic belt
We studied siliceous-volcanogenic deposits from the coastal
outcrops of Mokhovaya Bay near the City of Petropavlovsk-Kamchatsky. A
radiolarian assemblage was distinguished in the chert interbeds among pillow
basalts. This assemblage makes it possible to date the enclosing deposits as
Campanian. Such dating was obtained for these deposits for the first time;
earlier the Late Cretaceous age was only presumptive. The inferred age and the
structure of the deposits allows a comparison of the studied deposits with the
Valaginskaya series of East Kamchatka. The petrogeochemical characteristics of
basalts suggest their formation in conditions of an oceanic or backarc setting.
Yu.D. Markov, A.V. Mozherovsky, N.N.
Barinov, A.N. Derkachev, I.V. Utkin, N.A. Sereda
Highly ferruginous laminated silicates of the East Korean
Upland (Sea of Japan
The mineral and chemical composition of highly ferruginous
laminated silicates (HLS) of “glauconite” sands distributed on the East Korean
Upland outside volcanic structures and on a nameless volcano and Chentsov
Volcano has been studied. The use of cluster and discriminant analyses made it
possible to more objectively distinguish groups among HLS, and the application
of factor analysis permitted illustration of correlation relations between
chemical elements in different groups. It has been established that green
assemblages of the East Korean Upland are heterogeneous in terms of morphology,
composition and origin, and their formation is a complex multistage process both
of neoformation and degradation.
V.M. Novikov,
E.L. Shkolnik, Ye.A. Zhegallo
Composition, biota of initial products of weathering, and their
indicator role for climatic zoning of the territory (as exemplified by the
Russian Far East and Vietnam)
For the first time the initial erosion crusts (up to 1cm thick mainly on
basaltoid rocks) have been studied in detail by a set of modern methods,
including electronic microscopy, in limits of meridian areas: from
Nikolaevsk-na-Amure (Khabarovsk Territory) to the southern part of Primorskiy
Krai and also South Vietnam. Mineral complexes and the chemical composition of
these new formations were established, and for the first time the participation
of mineralized microorganisms in their formation was identified. On the basis of
comparison with the scale weathering crusts of the examined territory, the
indicator role of initial crusts is defined for revealing climatic zoning. As
mineral-indicators of various zones, a sequence of montmorillonite, kaolinite (halloysite)
and gibbsite is examined. The behavior of potassium is the indicator of the
degree of hypergenic change of parent rock.
I.V. Buchko, N.M. Kudryashov
Geochemical peculiarities of stratified massifs of the eastern part of the
West-Stanovoy terrane (southern framing of the North Asian craton)
The paper offers a comprehensive petrological and geochemical characteristic of
the Lukinda, Kengurak, Mongoli, and Veselkinsky ultrabasite-basite massifs of
the West Stanovoy terrane in the southern framing of the North Asian craton. The
study massifs have genuine peculiarities expressed in their rock associations,
petrogeochemistry of their rocks, and most likely they belong to different
intrusive complexes. The petrological and geochemical characteristics obtained
for the above massifs allowed us to consider them as peculiar "bench marks" or
models of "petrotypes" within the West Stanovoy terrane. Using the U-Pb method,
the authors have placed the age of the Veselkinsky massif in the range 165±25 Ma.
It is the evidence that some ultrabasite-basite massifs of the West Stanovoy
terrane are rather of Early Mesozoic age than of Precambrian age, and are likely
to be related to the processes of formation of the Mongol-Okhotsk fold belt.