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951.
In distribution areas of the Pekul’neiveem and Chirynai formations customary distinguishable in the Koryak Upland, complicated tectonostratigraphic units are composed of alternating thrust sheets of different lithologic composition and age, which are juxtaposed because of widespread thrust faulting, as is proved by the radiolarian analysis. Nineteen radiolarian assemblages of different age are first established here in the Lower Jurassic-Hauterivian succession of siliceous-volcanogenic sediments. In the Lower Jurassic interval, the lower and upper Hettangian, lower and upper Sinemurian, and Pliensbachian beds are recognized. Paleontological characterization is also presented for the Aalenian (or Toarcian?-Aalenian), upper Bajocian, lower and upper Bathonian, and Callovian beds of the Middle Jurassic. Within the Upper Jurassic, the Oxfordian-early Kimmeridgian, late Kimmeridgian-early Tithonian, Tithonian, and late Tithonian-early Berriasian radiolarian assemblages are distinguished. The late Berriasian-early Valanginian, middle-late Valanginian, and Hauterivian radiolarian assemblages are first recognized or compositionally revised. Radiolarians and lithofacies data are used to correlate the tectonostratigraphic units and individualize the jasper-alkali basaltic (lower Hettangian), chert-terrigenous (Hettangian-Sinemurian), jasper-cherty (Pliensbachian-Aalenian), jasper (Bajocian-Hauterivian), jasper-basaltic (upper Bajocian-Valanginian), Fe-Ti basaltic (upper Bajocian-Bathonian), tuffitejasper-basaltic (Bathonian-Hauterivian), and terrigenous-volcanogenic (Bajocian-Valanginian) sequences. The correlation results are extrapolated into other continental areas flanking the Pacific, i.e., to the western Kamchatka, northern and northwestern coastal areas of the Sea of Okhotsk, where the analogous radiolarian assemblages are characteristic of comparable allochthonous units of terrigenous-siliceous-volcanogenic sediments. 相似文献
952.
T. N. Palechek E. P. Terekhov A. V. Mozherovskii 《Stratigraphy and Geological Correlation》2008,16(6):650-663
The results of radiolarian analysis confirm the Campanian-Maastrichtian age of the Malokuril’skaya Formation in the Shikotan Island. The Campanian-Maastrichtian age of the formation is implied simultaneously by radiolarians and inoceramids. The studied Campanian and Campanian-Maastrichtian radiolarian assemblages include abundant specimens representing genus Prunobrachium, characteristic of which was bipolar distribution in cold-water to temperate basins. The new occurrence site of prunobrachids is established at the latitude of 43°N, the Far East of Russia. 相似文献
953.
V. A. Lebedev S. N. Bubnov O. Z. Dudauri G. T. Vashakidze 《Stratigraphy and Geological Correlation》2008,16(2):204-224
Isotopic-geochronological study of the Pliocene magmatic activity in western part of the Dzhavakheti Highland (northwestern region of the Lesser Caucasus) is carried out. The results obtained imply that the Pliocene magmatic activity lasted in this part of the highland approximately 2 million years from 3.75 to 1.75–1.55 Ma. As is established, the studied volcanic rocks correspond in composition mostly to K-Na subalkaline and more abundant normal basalts. Time constraints of main phases in development of basic volcanism within the study region are figured out. We assume that individual pulses of silicic to moderately silicic volcanism presumably took place in the Dzhavakheti Highland about 3.2 and 2.5 Ma ago. 相似文献
954.
G. V. Ovchinnikova A. B. Kuznetsov I. M. Vasil’eva I. M. Gorokhov M. T. Krupenin A. V. Maslov T. L. Turchenko 《Stratigraphy and Geological Correlation》2008,16(2):138-142
The mineral composition and U-Pb and Rb-Sr systematics of phosphorites from the Satka Formation of Lower Riphean carbonates, the Burzyan Group of Southern Urals, are studied. Phosphorites occurring as small lenses between stromatolite layers are composed largely of fluorapatite with admixture of detrital quartz, feldspars, illite, and chlorite. Phosphorite samples have been subjected to stepwise dissolution in 1 N (fraction L-1) and 2 N (fraction L-2) HCl. As is established, the maximum apatite content is characteristic of fraction L-1, while fraction L-2 is enriched in products of dolomite and sulfide dissolution and in elements leached from siliciclastic components. The Sr content in the Satka apatites (280–560 ppm) is substantially lower as compared with that in unaltered marine apatite. The 87Sr/86Sr “initial ratio in the phosphorites studied (0.71705–0.72484) and host dolomites from the lower part of the Satka Formation is significantly higher than in the Early Riphean seawater that indicates a reset of the Rb-Sr original systems in sediments. The Pb-Pb age of 1340 ± 30 Ma (MSWD = 6.4) estimated based on 7 data points characterizing fractions L-1 and L-2 is younger than the formation time of overlying Burzyan sediments, being consistent, within the error range, with date of the Mashak rifting event recorded at the Early-Middle Riphean boundary. The comparative U-Pb characteristics of two soluble fractions (L-1 and L-2) and silicate residue of phosphorites show that epigenetic redistribution of Pb and U was characteristic of the phosphorite horizon only. The initial Pb isotope composition and μ (238U/204Pb) estimated according to model by Stacey and Kramers for the early diagenetic fluids in carbonate and phosphate sediments of the Satka Formation suggest that they were in isotopic equilibrium with erosion products of the Taratash crystalline complex. 相似文献
955.
M. P. Chekhovskaya I. A. Basov A. G. Matul T. A. Khusid S. A. Gorbarenko 《Stratigraphy and Geological Correlation》2008,16(3):328-342
Taxonomic composition and distribution of planktonic foraminifers are studied in section of Core GC-11 that penetrated through Upper Quaternary sediments of the Bowers Ridge western slope, the southern Bering Sea. As is shown, structure of foraminiferal assemblage and productivity have varied substantially during the last 32000 calendar years in response to changes in surface water temperatures and water mass circulation in the northern part of the Pacific, the Bering Sea included. The productivity was maximal during deglaciation epoch, being notably lower in the Holocene and minimal at the glaciation time. 相似文献
956.
The described fusulinids of the Moscovian Stage are found in the Asad-Abad section of the Sanandaj-Sirjan tectonic zone of Iran. Five successive fusulinid assemblages are distinguished. Three lower of them belong to the Kashirian Substage, the other two to the Podolskian Substage. The section studied is correlated with most complete sections of the Moscovian Stage in the western Tethys. Two new species Fusulinella (Moellerites) pygmea and Putrella primaris are identified; in addition to nominative taxon, the latter includes new subspecies P. primaris compacta. 相似文献
957.
V. S. Kulikov Ya. V. Bychkova V. V. Kulikova Yu. A. Kostitsyn O. S. Pokrovsky M. V. Vasil’ev 《Petrology》2008,16(6):531-551
The Ruiga differentiated mafic-ultramafic intrusion in the northwestern part of the Vetreny Belt paleorift was described for the first time based on geological, petrological, geochronological, and geochemical data. The massif (20 km2 in exposed area) is a typical example of shallow-facies peridotite-gabbro-komatiite-basalt associations and consists of three zones up to 810 m in total thickness (from bottom to top): melanogab-bronorite, peridotite, and gabbro. In spite of pervasive greenschist metamorphism, the rocks contain locally preserved primary minerals: olivine (Fo 75–86), bronzite, augite of variable composition, labradorite, and Cr-spinels. A mineral Sm-Nd isochron on olivine melanogabbronorite from the Ruiga Massif defines an age of 2.39 ± 0.05 Ga, while komatiitic basalts of the Vetreny Belt Formation were dated at 2.40–2.41 Ga (Puchtel et al., 1997). The rocks of the Ruiga intrusion and lava flows of Mt. Golets have similar major, rare-earth, and trace element composition, which suggests their derivation from a single deep-seated source. Their parent magma was presumably a high-Mg komatiitic basalt. In transitional crustal chambers, its composition was modified by olivine-controlled fractionation and crustal contamination, with the most contaminated first portions of the ejected melt. In terms of geology and geochemistry, the considered magmatic rocks of the Vetreny Belt are comparable with the Raglan Ni-PGE komatiite gabbro-peridotite complex in Canada (Naldrett, 2003). 相似文献
958.
G. P. Zaraisky A. M. Aksyuk V. N. Devyatova O. V. Udoratina V. Yu. Chevychelov 《Petrology》2008,16(7):710-736
The concept of granitic melt fractionation as the main process in the concentration of rare elements in granites calls for
the development of a reliable method to determine the evolutionary sequences of granite series. We propose to use for this
purpose a zirconium-hafnium indicator, the Zr/Hf weight ratio in granitic rocks (Zaraisky et al., 1999, 2000). By the example
of three classic regions of rare-metal deposits, eastern Transbaikalia, central Kazakhstan, and Erzgebirge (Czech Republic
and Germany), it was empirically shown that the Zr/Hf ratio of granites decreases during the fractional crystallization of
granite magmas in the sequence granodiorite → biotite granite → leucogranite → lithium-fluorine granite. The reason is the
higher affinity of Hf compared with Zr to a granite melt. This implies that the crystallization and settling of accessory
zircon will cause the progressive enrichment of Hf relative to Zr in the residual melt. As a result, the Zr/Hf ratio decreases
regularly in the series of sequential phases of granite intrusion related to a single magma chamber from granodiorite to biotite
granite, leucogranite, and Li-F granite (from 45-30 to 10-2). Our experimental investigations supported the preferential enrichment
of haplogranite melt in Hf and zircon crystals in equilibrium with melt in Zr (T= 800°C and P = 1 kbar). The Zr/Hf indicator was tested by the example of the wellknown Kukulbei rare-metal granite complex of eastern
Transbaikalia (J3), which is unique in the degree of fractionation of initial granite melt with the formation of three phases
of granite emplacement and vein derivatives. An important feature of the complex is its “short” differentiation trend. It
was supposed that the granite magma of the first phase is parental, and the later phases forming small intrusive bodies in
large massifs of biotite granites of the first phase are sequential products of its crystallization differentiation in a magma
chamber. The biotite granites of the first phase are barren. The leucocratic granites of the second phase are accompanied
by tin-tungsten greisen deposits (e.g., Spokoininskoe), and the upper part of cupola-like stocks of Li-F amazonite granites
of the third phase host apogranite-type tantalum deposits (Orlovka, Etyka, and Achikan). In addition to three granite phases,
the Kukulbei complex includes dikes of ongonites, elvans, amazonite granites, and chamber miarolitic pegmatites. All of the
granitic rocks of the complex have similar isotopic ages of 142± 0.6 Ma. The Zr/Hf ratio decreases systematically from phase
1 (40–25), to phase 2 (20–10), and phase 3 (10–2). The ongonites, elvans, and pegmatites have similar Zr/Hf ratios (15-5),
falling between the ranges of leucocratic muscovite granites and Li-F granites. Compared with other granite series, the granitic
rocks of the Kukulbei complex show specific petrographic and geochemical features: they are strongly enriched in Rb, Li, Cs,
Be, Sn, W, Mo, Ta, Nb, Bi, and F but depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From the early
to late intrusion phases, the degree of enrichment and depletion in these element groups increases regularly. This is accompanied
by a significant decrease (from 40 to 2) in Zr/Hf, which can be used as a reliable indicator of genetic relations, degree
of fractionation, and rare-metal potential of granites. Granites with Zr/Hf values lower than 25 are promising for prospecting
for Sn, W, Mo, and Be greisen deposits, whereas the formation of Ta deposits requires Zr/Hf values lower than 10. 相似文献
959.
960.
The paper is devoted to the conditions under which opacite rims developed around hornblende grains in andesite of the catastrophic eruption (March 30, 1956) of Bezymyannyi volcano, Kamchatka. The opacite rims were produced by a bimetasomatic reaction between hornblende and melt with the development of the following zoning: hornblende → Px + Pl + Ti-Mag → Px + Pl → Px → melt. Biometasomatic reaction was accompanied by the active removal of CaO from the rim, addition of SiO2, and more complicated behavior of other components. The hornblende also shows reactions of its volumetric decomposition under near-isochemical conditions. The opacite rims developed under isobaric conditions, at a pressure of approximately 6 kbar. The main reason for the instability of the hornblende was the heating of the magma chamber from 890 to 1005°C due to new hot magma portion injection. The time interval between the injection and the start of eruption was estimated from the thickness of the opacite rims and did not exceed 37 days. Hence, the March 30, 1956, eruption was not related to the volcanic activity in November of 1955 but to the injection of a fresh magma portion in February–March of 1956. 相似文献