Table 1: Potassium-argon dates on whole rock lavas from Mt. Giluwe

A series of K-Ar dates from Mt Giluwe volcano is reported and its relevance to the Quaternary history of the volcano is discussed. The period between about 380 000 and 220 000 years BP seems to have been one of major volcanic activity. During the volcanic activity there were periods of ice cover probably of short duration. The oldest evidence of glacial action predates a lava flow dated at between 340 000 and 380 000 years. At about 290 000 years an ice cap of a thickness of at least 100 m covered the summit area and one or a series of subglacial eruption(s) led to the formation of palagonitic breccia. This event was probably associated with a complete melting of the ice since it was followed almost immediately by the eruption of a thick sequence of normal lava flows which range in age from about 289 000 years to about 220 000 years. Subsequent volcanic activity was less significant and no dates are available on this.

(Table 1) K-Ar age of alkaline igneous rocks from the Jan Mayen fracture zone

Bottom morphology of the Jan Mayen transform fracture zone and rock chemistry data show that petrological and chemical specific features of igneous rocks can result from higher permeability of the transform fracture zone and deeper penetration of ocean water into the lithosphere in comparison with rift zones of the Kolbeinsey and Mohn's mid-ocean ridges. Age of alkaline magmatism of the Jan Mayen fracture zone is similar to that of rift zones due to palingenesis of metamorphosed and hydrated mantle and crustal rocks.

Geochemistry and radionuclide content of sediment and water samples obtained from the Ob and Irtysh river, Russia

This paper reports the results of the investigations of 2006-2007 on the distribution and migration forms of artificial radionuclides and chemical elements in the Ob-Irtysh water system. Three regions were studied. One of them is a local segment of the Ob River upstream from the confluence with the Irtysh River; its investigation allowed us to estimate the general radioecological state of the aquatic environment affected by the activity of the Tomsk 7 plant. The second region is a local segment of the Irtysh River upstream from its confluence with the Ob River, where the influence of emissions from the NPO Mayak could be estimated. The third region is the water area of the Ob River after its confluence with the Irtysh River. It characterizes the real level of radioactive and chemical contamination of the middle reaches of the Ob River. In order to explain horizontal variations in the distribution of radionuclides in the upper layer of bottom sediments collected at various sites, the results of sorption-kinetic experiments with radioactive tracers in the precipitate-solution system were used. The investigation of the migration forms of trace elements and radionuclides occurring in river water was based on the method of tangential-flow membrane filtration. Chemical element contents were determined in 400-ml water samples. A set of Millipore polysulfone membranes with pore sizes of 8, 1.2, 0.45, 0.1, and 0.025 µm was employed. Taking into account the ultralow specific concentrations of radionuclides in the water, they were analyzed in 300-500 litre samples using Millipore polysulfone membranes with pore sizes of 0.45 µm and 15 kDa. This allowed us to estimate the percentages of cesium-137 and plutonium-239, 240 in the suspended particulate fraction, colloids, and dissolved species.

Composition and age of rocks from the King's Trough and Palmer Ridge

This paper presents results of studies of rocks sampled during Cruise 19 of R/V Akademik Mstislav Keldysh with the Mir submersibles in the Atlantic Ocean (slopes of the King's Trough and Palmer Ridge). Based on these materials and published data two stages of magmatism and evolution in the region are distinguished: 1) formation of a mid-ocean ridge in the rift zone (68-32 Ma); 2) development of intraplate volcanism during movement of the plate over a "hot spot" (32-0 Ma).

Age determinations of rocks from Vestfjella and Ahlmannryggen in Antarctica

The Proterozoic country rock at Ahlmannryggen consists of flat lying basaltic lo andesitic lava flows and sedimentary rocks intruded by dioritic sills (Borgmassivet Intrusives). The suites display a typical platform cover. K-Ar age determinations gave maximum ages of about 1200 Ma on the magmatic rocks. All these suites were intruded bv Proterozoic dikes dated also at about 1200 Ma. Localiy the Proterozoic rocks have a slaty cleavage grading into mylonitic texture which strike parallel to the Jutul Penck graben. Such tectonic structures were dated at 525 Ma using syntectonic white micas. Evidence of the break-up of Gondwana during the Early Jurassic/Triassic is given by dikes at Ahlmannryggen and lava flows, dikes and sills at Vestfjella. At Ahlmannryggen the initial rift phase is documented by the development of the Jutul Penck graben and the intrusion of the 200-250 Ma continental-tholeiitic dikes striking parallel to the graben axis. The lava flows, dikes and sills at Vestfjella represent a later stage of the Gondwana break-up at about 180 Ma that probably reflects the initial stage of the opening of the Weddell Sea.