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The Okhotsk-Chukotka volcanic belt is part of an extensive late Early to Late Cretaceous Andean-style magmatic arc that spans the entire eastern margin of the Asian continent. The belt itself stretches 3000 km from the Chukotka Peninsula to the Uda River and comprises ∼1.2 x 10 6 km 3 of volcanic rock over a 500,000 km 2 area. Despite its size and regional tectonic significance, the time span of magmatic activity is poorly constrained and the subject of significant debate, mostly in the Russian literature. In this paper, we provide new geochronologic control on the timing of inception and cessation of magmatism for the Arman and Maltan-Ola volcanic fields. These field localities were chosen because they are well studied, relatively accessible, and contain floral assemblages that have been used to correlate volcanic sequences at the regional scale. The majority of the volcanic sequence was emplaced between 85.5 ′ 1.3 Ma and 74.0 ′ 1.2 Ma, as shown by 17 new 4 0 Ar/ 3 9 Ar ages. The Coniacian-Santonian to Campanian age range indicated is 15 m.y. younger than the Albian to early Cenomanian age range given by a synthesis of floral stratigraphic, K-Ar, and Rb-Sr geochronologic data. The calc-alkaline part of the volcanic section spans an apparent age range of 85.5 ′ 1.3 Ma to 80.7 ′ 0.8 Ma. Capping basalts were emplaced between 77.5 ′ 1.1 Ma and 74.0 ′ 1.2 Ma and exhibit a within-plate geochemical signature, which we attribute to a temporally and geochemically distinct, possibly extension-related, phase of magmatism. The apparent northwestward migration of the arc front from the interior (seaward) zone (Taigonos Peninsula, Magadan batholith) in Albian-Cenomanian time to the Arman and Maltan-Ola volcanic fields in Coniacian-Santonian to Campanian time may be explained by shallowing of the subducting paleo-Pacific (Kula?) oceanic plate. The flat-lying nature of these volcanic rocks and the within-plate geochemical affinity of the capping basalt unit are inconsistent with prevailing tectonic models for the cessation of arc magmatism and formation of the Sea of Okhotsk which require the collision of a microcontinental block or oceanic plateau with the northeast Asian margin in the Late Cretaceous.

Translated from Probl. Prochnosti; 5: No. 1, l15-118(Jan 1973). The dynamic resonance method was used to determine the temperature dependence of the modulus of elasticity of W, Mo, NiCr, and ZrO₂ coatings applied by the plasma spraying method. An increase in test temperature was found to cause a monotonic decrease in the modulus of elasticity. The absolute value of the modulus of elasticity for plasma-sprayed materials is lower than the corresponding value for the same materials applied by other methods (electron- beam melting, arc melting, and powder metallurgy methods). For W and Mo this difference, for example, was 15 to 20% which may be attributed to a difference in porosity, which also depends on coatmg thickness for plasma-sprayed material. It has been noted that the temperature dependence of the modulus of elasticity has two sections with different temperature coefficients. Thus, investigation results showed that the static adhesion strength of the combination base metal-- coating obtained by the method of continuous plasma spraying, depends on the test temperature and coating thickness. It was shown that the modulus of elasticity of coating materials decreases during the temperature rise to 1200 deg C by 25 to 60% thereby affecting the cohesion strength ofmore » the combination. (auth)« less

Neogene alkaline intraplate volcanic rocks from the Viliga Volcanic Field (NE-Russia) were studied both to precisely characterize their geochemical composition and to unravel their petrogenetic history. The sampled volcanic rocks crop out within the voluminous calc-alkaline sequences of the Cretaceous Okhostk–Chukokta Volcanic Belt, an Andean-type arc formed during subduction of the Paleo-Pacific Plate beneath modern far-east Asia. The mantle xenolith- and xenocryst-bearing basanites and nephelinites have intraplate ocean island basalt-type geochemical features. Sr and Nd isotopes combined with major and trace element systematics and rare-earth element modeling suggest polybaric melt generation of these alkaline magmatic rocks from a homogeneous garnet peridotite facies source with minor involvement of spinel peridotite facies partial melts. The basanite samples indicate segregation PT conditions around 1500 °C at 33–38 kbar whilst the nephelinites reflect smaller melt fractions segregated at over 40 kbar. During ascent, olivine (up to 7%) was the main fractionating phase in the basanites; whereas in the nephelinites, both olivine and minor clinopyroxene fractionation occurred. Crustal contamination during ascent was insignificant. We argue that the melt generation of these alkaline magmas from the Viliga Volcanic Field was triggered by an extending lithosphere resulting in upwelling asthenosphere and decompression melting, analogous to geodynamic models of the coeval alkaline volcanic rocks along the adjacent North Pacific continental margins, rather than by subduction- or plume-related processes., Research Highlights ►Neogene alkaline intraplate magmatism in northeast Russia. ►Asthenospheric decompression melting in an extensional geodynamic setting. ►Polybaric melt evolution. ►En-route olivine fractionation.

1. The strength with which a coating of chromium-nickel spinel adheres to an OT-4 titanium alloy substrate lies in the range 1.15–1.40 kg/mm2. Preheating the surface to be coated to 450°C increases the adhesion of the coating by 25–30%. 2. The adhesion of a coating to its substrate begins to decrease appreciably after 10 thermal cycles. 3. An 80% Ni-20% Cr alloy undercoat has no effect upon the adhesion of a spinel coating and adversely affects its thermal fatigue resistance. 4. The degree of blackness (coefficient of absorption) of a spinel coating is 0.94–0.95.

Clinopyroxene megacrysts from young melanephelinitic lavas were divided into Cr-rich and Cr-poor suites. Sr, Nd, and Pb isotopic ratios of leached megacrysts and host lava are indistinguishable from each other and indicate a depleted source. Host lavas do not display chemical evidence for significant fractional crystallization, which is required to explain the compositional range of the megacrysts. This rules out a simple cognate genetic relationship between the two, and strictly defines megacrysts as xenocrysts. The well-defined correlations of trace elements with the Mg-numbers in the megacrysts are interpreted as the result of extensive fractional/equilibrium crystallization of magma over a large temperature range at near isobaric condition in the upper mantle. Trace element variations in megacrysts are consistent with fractional crystallization of clinopyroxene alone for the Cr-rich suite, and clinopyroxene + garnet for the Cr-poor suite from at least two bathes of related melts. Megacrysts parent magma might represent mantle melts, which were never erupted in their initial composition.