Magnetic parameters of rocks from the Red Sea rift zone

Results of detailed geomagnetic and geomorphological studies carried out by R/V Akvanavt together with data obtained by a side-scanning sonar and high-frequency profiles from a towed Zvuk-4 vehicle plus results of visual observations of deep-sea manned Pisces submersible have shown that the spreading axis is divided into segments, whose strike (330°) differs from the overall strike (310°) of the axial magnetic anomaly. In the study area segments are about 1 km long and transform displacements are 0.5 km. Calculations on a model have shown that spreading is asymmetric: during the Brunhes epoch accretion rate of the African Plate was 6 mm/yr and that of the Arabian Plate 7 mm/yr. Earlier it had been 9 and 11 mm/yr, respectively.

Ages of rocks and minerals from the Okhotsk-Chukotka volcanic belt

Current geochronological data on the Okhotsk-Chukotka volcanic belt (OCVB) and relevant problems are discussed. The belt evolution is suggested to be modeled based on 40Ar/39Ar and U-Pb dates more useful in several aspects than common K-Ar or Rb-Sr dates and methods of paleobotanical correlation. Based on new40Ar/39Ar and U-Pb dates obtained for volcanic rocks in the OCVB northern part, the younger (Coniacian) age is established for lower stratigraphic units in the Central Chukotka segment of the belt, and eastward migration of volcanic activity is shown for terminal stages of this structure evolution.

Chemical composition of rocks and minerals from the Mid-Atlantic Ridge near 15°20'N

The monograph summarizes results of petrological and geochemical studies of rocks from the ocean floor collected by the authors during expeditions to the Central Atlantic. Detailed work in the Capa Verde transform fault zone gave a large amount of new information about magmatic and hydrothermal systems of the Mid-Atlantic Ridge.

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.

Analysis of rocks from Shackleton Range

Studies were made of the glacial geology and provenance of erratic in the Shackleton Range during the German geological expedition GEISHA in 1987/88, especially in the southern and northwestern parts of the range. Evidence that the entire Shackleton Range was once overrun by ice from a southerly to southeasterly direction was provided by subglacial erosional forms (e.g. striations, crescentic gouges, roches moutonnées) and erratics which probably orriginated in the region of the Whichaway Nunataks and the Pensacola Mountains in the southern part of the range. This probably happened during the last major expansion of the Anarctic polar ice sheet, which, on the basis of evidence from other parts of the continent, occurred towards the end of the Miocene. Till and an area of scattered erratics were mapped in the northwestern part of the range. These were deposited during a period of expansion of the Slessor Glacier in the Weichselian (Wisconsian) glacial stage earlier. This expansion was caused by blockage of the glacier by an expanded Filchner ice shelf which resulted from the sinking of the sea level during the Pleistocene, as demonstrated by geological studies in the Weddell Sea and along the coast of the Ross Sea. Studies of the erratics at the edges of glaciers provided information about rock concealed by the glacier.

Chemical composition of rocks from the Eastern Indian Ocean

The monograph presents results of comprehensive geological and geophysical studies carried out in 1973 and 1976 during Cruises 54 and 58 of R/V "Vityaz" in the Eastern Indian Ocean. On the base of obtained data a description of topography, magnetic and gravity fields, structure of the sedimentary series and deep crustal structure of the East Indian Ridge, Central, West Australian and Cocos Basins, the Sunda Trench has been done. Materials on petrography, petrochemistry and geochemistry of igneous rocks in the region have been summarized. New geological and geophysical information has been compared with with DSDP materials. Tectonics and geological history of the Eastern Indian Ocean are under consideration.

Chemical and isotopic compositions of rocks and minerals from the Ashadze and Logachev hydrothermal fields, Mid-Atlantic Ridge

This study was aimed at reconstructing a sequence of events in the magmatic and metamorphic evolution of peridotites, gabbroids, and trondhjemites from internal oceanic complexes of the Ashadze and Logachev hydrothermal vent fields. Collections of plutonic rocks from Cruises 22 and 26 of R/V "Professor Logachev", Cruise 41 of R/V "Akademik Mstislav Keldysh", and from the Serpentine Russian-French expedition aboard R/V "Pourquoi pas?" were objects of this study. Data reported here suggest that the internal oceanic complexes of the Ashadze and Logachev fields formed via the same scenario in these two regions of the Mid-Atlantic Ridge. On the other hand, an analysis of petrological and geochemical characteristics of the rocks indicated that the internal oceanic complexes of the MAR axial zone between 12°58'N and 14°45'N show pronounced petrological and geochemical heterogeneity manifested in variations in degree of depletion of mantle residues and in Nd isotopic compositions of rocks from the gabbro-peridotite association. Trondhjemites from the Ashadze hydrothermal field can be considered as partial melting products of gabbroids under influence of hydrothermal fluids. It was supposed that presence of trondhjemites in internal oceanic complexes of MAR can be used as a marker for the highest temperature deep-rooted hydrothermal systems. Perhaps, the region of the MAR axial zone, in which petrologically and geochemically contrasting internal oceanic complexes are spatially superimposed, serves as an area for development of large hydrothermal clusters with considerable ore-forming potential.

Chemical composition of rocks and minerals from the Doldrums and Arkhangelsky Fracture Zones

The book deals with results of complex geological and geophysical studies in the Doldrums and Arkhangelsky Fracture Zones of the Central Atlantic. Description of the main features of bottom relief, sediments and crustal structure, geomagnetic field, composition of igneous and sedimentary rocks are given in the book. The authors made conclusions on tectonic delamination of the oceanic crust and existence of specific rock complexes forming non-spreading blocks

Chemical composition of rocks and minerals from the Central Atlantic fracture zones

The monograph summarizes materials on geology and deep structure of the Central Atlantic fracture zones. These materials have been obtained during eight expeditions of R/V ''Akademik Nikolaj Strakhov''. The studies have been based on the integrated geological approach. As a result, many new tectonic, magmatic, metallogenic and historical-geological features of these phenomenal structures of the deep ocean have been revealed.

Grain-size distribution and frictional behaviour of sediment cores from the Nice Slope

The upper shelf of the landslide-prone Ligurian Margin (Western Mediterranean Sea) off Nice well-known for the 1979 Airport Landslide is a natural laboratory to study preconditioning factors and trigger mechanisms for submarine landslides. For this study low-stress ring shear experiments have been carried out on a variety of sediments from >50 gravity cores to characterise the velocity-dependent frictional behaviour. Mean values of the peak coefficient of friction vary from 0.46 for clay-dominated samples (53 % clay, 46 % silt, 1 %) sand up to 0.76 for coarse-grained sediments (26 % clay, 57 % silt, 17 % sand). The majority of the sediments tested show velocity strengthening regardless of the grain size distribution. For clayey sediments the peak and residual cohesive strength increases with increasing normal stress, with values from 1.3 to 10.6 kPa and up to 25 % of all strength supported by cohesive forces in the shallowmost samples. A pseudo-static slope stability analysis reveals that the different lithologies (even clay-rich material with clay content >=50 %) tested are stable up to slope angles <26° under quasi-drained conditions.